Computer Switiching

Network operations center

2011-05-06T18:30:00.000-07:00

A network operations center (or NOC, pronounced like the word "knock") is one or more locations from which control is exercised over a computer, television broadcast , or telecommunications network.

Large organizations may operate more than one NOC, either to manage different networks or to provide geographic redundancy in the event of one site being unavailable or offline.

NOCs are responsible for monitoring the telecommunication network for alarms or certain conditions that may require special attention to avoid impact on the network's performance. For example, in a telecommunications environment, NOCs are responsible for monitoring for power failures, communication line alarms (such as bit errors, framing errors, line coding errors, and circuits down) and other performance issues that may affect the network. NOCs analyse problems, perform troubleshooting, communicate with site technicians and other NOCs, and track problems through resolution. If necessary, NOCs escalate problems to the appropriate personnel. For severe conditions that are impossible to anticipate – such as a power failure or optical fiber cable cut – NOCs have procedures in place to immediately contact technicians to remedy the problem.

NOCs are frequently laid out with several rows of desks, all facing a video wall, which typically shows details of highly significant alarms, ongoing incidents and general network performance; a corner of the wall is sometimes used for showing a news or weather TV channel, as this can keep the NOC technicians aware of current events which may have an impact on the network or systems they are responsible for.

The back wall of the NOC is sometimes glazed; there may be a room attached to this wall which is used by members of the team responsible for dealing with serious incidents to meet while still able to watch events unfolding within the NOC.

Individual desks are generally assigned to a specific network, technology or area. A technician may have several computer monitors on their desk, with the extra monitors used for monitoring the systems or networks covered from that desk.

NOCs often escalate issues in a hierarchic manner, so if an issue is not resolved in a specific time frame, the next level is informed to speed up problem remediation. Many NOCs have multiple "tiers", which define how experienced/skilled a NOC technician is. A newly-hired NOC technician might be considered a "tier 1", whereas a technician that has been there for several years may be considered a "tier 3" or "tier 4". As such, some problems are escalated within a NOC before a site technician or other network engineer is contacted.

Additionally, the NOC staff may perform extra duties; a network with equipment in public areas (such as a mobile network Base Transceiver Station) may be required to have a telephone number attached to the equipment for emergencies; as the NOC may be the only continuously staffed part of the business, these calls will often be answered there.

The term NOC is normally used when referring to telecommunications providers, although a growing number of other organizations such as public utilities (e.g., SCADA) and private companies also have such centers, both to manage their internal networks and to provide monitoring services.

The location housing a NOC may also contain many or all of the primary servers and other equipments essential to running the network, although it is not uncommon for a single NOC to monitor and control a number of geographically dispersed sites.

BlackBerry

2011-04-30T23:23:00.000-07:00

BlackBerry is a line of mobile e-mail and smartphone devices developed and designed by Canadian company Research In Motion (RIM) since 1999.

BlackBerry phones function as a personal digital assistants and portal media player. BlackBerry phones are primarily known for their ability to send and receive (push). Internet e-mail wherever mobile network service coverage is present, or through Wi-Fi connectivity. BlackBerry phones support a large array of instant messaging features, including BlackBerry Messanger.

BlackBerry commands a 14.8% share of worldwide smartphone sales, making it the fifth most popular device manufacturer after Nokia,Samsung,LG and Apple. The consumer BlackBerry Internet Service is available in 91 countries worldwide on over 500 mobile service operators using various mobile technologies.

Modern GSM-based BlackBerry handhelds incorporate an ARM 7, 9 or ARM 11 processor, while older BlackBerry 950 and 957 handhelds used Mudit 80386 processors. The latest GSM BlackBerry models (9100, 9300 and 9700 series) have an Intel PXA930 624 MHz processor, 256 MB (or 4 GB in the Torch 9800) flash memory and 265 MB SDRAM. CDMA BlackBerry smartphones are based on Qualcomm MSM6x00 chipsets which also include the ARM 9-based processor and GSM 900/1800 roaming (as the case with the 8830 and 9500) and include up to 256MB flash memory. The CDMA Bold 9650 is the first to have 512MB flash memory for applications. All BlackBerrys being made as of 2011 support up to 32 GB microSD cards.

The first BlackBerry device, the 850, was introduced in 1999 as a two-way pager in Munich, Germany. In 2002, the more commonly known smartphone BlackBerry was released, which supports push e-mail, mobile telephone, text messaging, Internet faxing, Web browsing and other wireless information services. It is an example of a convergent device. The original BlackBerry devices, the RIM 850 and 857, used the DataTac network.

BlackBerry first made headway in the marketplace by concentrating on e-mail. RIM currently offers BlackBerry e-mail service to non-BlackBerry devices, such as the Palm treo, through its BlackBerry Connect software.

The original BlackBerry device had a monochrome display, but all current models have color displays. All models except for the Storm, series had a built-in QWERTY keyboard, optimized for "thumbling", the use of only the thumbs to type. The Storm 1 and Storm 2 include a SURE TYPE keypad for typing. Originally, system navigation was achieved with the use of a scroll wheel mounted on the right side of phones prior to the 8700. The trackwheel was replaced by the trackball with the introduction of the Pearl series which allowed for 4 way scrolling. The trackball was replaced by the optical trackpad with the introduction of the Curve 8500 series. Models made to use iDEN networks such as NEXTEL and Mike also incorporate a push-to-talk (PTT) feature, similar to a two-way-radio.

Operating System

The operating system used by BlackBerry devices is a proprietary multitasking environment developed by RIM. The operating system is designed for use of input devices such as the track wheel, track ball, and track pad. The OS provides support for Java MIDP 1.0 and WAP 1.2. Previous versions allowed wireless synchronization with Microsoft Exchange Server e-mail and calendar, as well as with Lotus Domino e-mail. The current OS 5.0 provides a subset of MIDP 2.0, and allows complete wireless activation and synchronization with Exchange e-mail, calendar, tasks, notes and contacts.,

Third-party developers can write software using these APIs, and proprietary BlackBerry APIs as well. Any application that makes use of certain restricted functionality must be digitally signed so that it can be associated to a developer account at RIM. This signing procedure guarantees the authorship of an application but does not guarantee the quality or security of the code. RIM provides tools for developing applications and themes for BlackBerry. Applications and themes can be loaded onto BlackBerry devices through BlackBerry App World, Over The Air (OTA) through the BlackBerry mobile browser, or through BlackBerry Desktop Manager.

CPU

Early BlackBerry devices used Intel 80386-based processors. BlackBerry 8000 series smartphones, such as the 8700 and the Pearl, are based on the 312 MHz ARM XScale ARMv5TE PXA900. An exception to this is the BlackBerry 8707 which is based on the 80 MHz Qualcomm 3250 chipset; this was due to the PXA900 chipset not supporting 3G networks. The 80 MHz processor in the BlackBerry 8707 meant the device was often slower to download and render web pages over 3G than the 8700 was over EDGE networks. In May 2008 RIM introduced the BlackBerry 9000 series which are equipped with XScale 624 MHz processors. The BlackBerry Curve 8520 features a 512 MHz processor, while the Bold 9700 features a newer version of the Bold 9000's processor, but is clocked at the same speed

Design and implementation of the Virtual LAN

2011-04-21T18:52:00.000-07:00

Virtual LANs (VLANs) are used to break up broadcast domains in a Layer 2 switched internetwork. As VLANs promote efficient use of network resources, it is wise to beef up your knowledge of this technology. In this Daily Drill Down, I will explain how to implement the VLAN technology using Cisco routers and Layer 2 switches.

The collapsed-backbone network
A common LAN network design implemented in the last 10 years or so is called a collapsed backbone. Basically, it connected all floors or rooms in a building to a network where the company's shared servers were located. The typical collapsed-backbone network would look something like Figure A.

Fiber Distributed Data Interface (FDDI) works great as a backbone.

Here you can see that all floors of the building use a fast transport called Fiber Distributed Data Interface (FDDI) as a backbone. FDDI has been around for many years and it works great. The bad news with FDDI comes in the form of expense. In this network, FDDI was connected to the server room on the first floor and created connection points to each floor in the building. Since FDDI is a physical-ring topology, the fiber must connect from the first floor to each consecutive floor and then finally back to the first floor again. A second ring provides redundancy, if warranted.

Each floor has a 10BaseT hub connecting via a twisted-pair cable to the desktop. All this was just peachy and worked beautifully until users started using their desktop PCs for more then just a simple print job or small (<1 MB) file transfers. In the mid 1990s, this design began to result in ghastly network bottlenecks because not only is this network a huge broadcast domain, it's one enormous collision domain as well. That's because FDDI is only a physical-layer topology; it doesn't break up collision or broadcast domains.

The popular solution to this dilemma was the practice of installing bridges on each floor. The new design looked like Figure B.

When each floor has a separate collision domain, network traffic will improve significantly.

Each floor is now a separate collision domain, which really helped—for a while. But look again—this network is still one immense broadcast domain. As networks grew and more and more network services became available to users, this design became saturated, resulting in lame response time for the users. But by the mid 1990s, Cisco routers became more cost-effective. (Prior to that, they were cost prohibitive for smaller companies, even though they had been available since the late 1980s.)

With the advent of router affordability, the solution to the monstrous broadcast domain issue was to use a Cisco router to break up both collision and broadcast domains. The new and cool network now looked like the one shown in Figure C. The fiber was not discarded but used in point-to-point connections from each floor to the router.

A single router has replaced all the bridges.

In this network, a single router has replaced the bridges. For many years, I would still find bridges installed at my clients’ locations because the administrators didn't understand the purpose of installing a router—that the router breaks up collision and broadcast domains and that this replaces bridges; it doesn't just add to their functionality. In fact, the bridge, if left in the network, only slowed the network down (created latency issues).

A single router connecting all the floors really worked. As long as users kept their data on the local network 80 percent of the time and only crossed the router 20 percent of the time or less, response time truly soared. This type of network design was implemented worldwide, and Ethernet became the de facto standard that ran to each desktop. But for this design to work properly, that 80/20 rule had to be observed. If the network traffic crossing the router exceeded 20 percent, network response issues would rear their ugly heads once again.

This type of network has been discussed, worked, and reworked. Most of the problems that typically surface have to do with physical location. In other words, for the network to work as designed, you create physical networks and assign subnets to these physical networks. Users are then placed in a physical location by job function. As long as everyone on the same floor performed the same job and shared the same network resources, the network sang. But flies land in the ointment en masse when users with disparate functions and needs are placed on the same floor. The problems created by this scenario can include:

Users with different job functions sharing the same broadcast domain.
Anomaly users (those with needs and/or functions not common to a given broadcast domain) required that all their data (packets) cross a Layer 3 device to communicate with the network resources they needed.
Bandwidth usage quickly became an issue because too many users were placed in the same broadcast/collision domain.

A good solution to this dilemma really didn't exist. There are a few solutions (workarounds) typically configured on the network:

Adding another broadcast domain by configuring another router port with another hub connected to the floor: This keeps the new users off the existing broadcast domain, but all these new users must still cross a Layer 3 device to get to the network services they use.
Running a cable from the workstations to the correct broadcast domain: This one actually works pretty well (as long as you don't exceed the distance constraints), but there are dollars involved in running the cables.
Moving the whole group to another part of the building that has enough room for everyone: Believe it or not, this was the most common solution.

Enter Layer 2 switching and VLANs
Bridges were the precursor to Layer 2 LAN switching. Switches were basically designed to perform the same function as a bridge but with more ports. A typical bridge only had two ports, although you could buy bridges that had up to 16. A LAN switch can have hundreds of ports, and LAN switches are more intelligent.

LAN switches filter the network by hardware address, break up collision domains, provide port security, and can create VLANs. This has changed network design 100 percent from the world of collapsed backbones. Instead of having to worry about creating networks by physical location, VLANs turned the network-design world on its ear by providing options and flexibility like never before to fit any business model. The only design constraint in this type of network is the network administrator's lack of imagination.

Let's take a look at our previous network design and use VLANs instead of routers to break up our networks. Two VLANs were created for this example (see Figure D)

This network is easy to maintain and create security on, and best of all, the physical location of a user is completely irrelevant. Regardless of where users are located, they can be placed in any broadcast domain (VLAN).

Let's take a look at a network design from a client of mine in the San Francisco Bay area. Figure E shows the network design that was in place when I arrived. Hubs were used to connect all the rooms. A fiber connection was used to connect the basement and the 15th floor

Here, 500 users were in the same broadcast domain and collision domain.

The problem with this design is that 500 users were not only in the same broadcast domain but in the same collision domain as well. When they ran out of IP addresses in the network, the administrator just added a secondary network to the router interface. Unfortunately, this is a solution that too many administrators use, and it's a nasty one. Why? Because instead of breaking up collision and broadcast domains, adding a secondary IP subnet to the same broadcast domain just puts more users on the same physical network, making it run like a sleeping mule. Here's the output of the router's interface that had two subnets assigned to the same network:
interface FastEthernet0/0
ip address 10.1.1.1 255.255.255.0 secondary
ip address 10.1.0.1 255.255.255.0

This customer has an ADSL T1 connection to the Internet, but the connection speed acted more like a 33.6-Kbps dial-up line. This wasn't only because of that secondary network, it was also because of the utter lack of physical network segmentation.

After studying the customer's business requirements by talking with both users and management, I was able to come up with a very cool network that took only a few hours to implement. Figure F shows the new network.

Naming conventions for VLANs often use names of rooms or departments.

In Figure F, MA through ML are the names of the rooms in the building; I named the VLANs after the rooms. This allowed the administrators to easily identify and locate the VLANs. Also, the IP subnet scheme was designed after the floor and room numbers, since the rooms were also numbered. 151 would be floor 15, room 1. I called the basement floor 1 and created the VLANs as 11, 12, 13, etc. VLAN 1 is the Administrative and Sales VLAN.

The IP network I used was 10.1.x.0/24. The third octet in this design is the subnet number. By looking at an IP address on a machine, the network administrator could tell which floor, room, and VLAN this device was a member of. Cool, huh?

The customer already owned two Cisco 24-port 2900 switches that were bought from a salesman who also sold this customer a dozen or so Cisco FastHubs. Although the Cisco FastHubs are a great product, they're expensive little numbers, and, well, a hub is a hub, folks. I used the hubs in each room to connect all the users and then connected each hub into the switch. I assigned each port to a specific VLAN.

I put one 2900 switch in the basement and configured it as the Virtual Trunk Protocol (VTP) Server. I placed the other 2900 on the 15th floor and put it to work as a VTP Client. That way, the 15th floor 2900 would learn about VLANs from the VTP server. (VTP is a protocol that sends VLAN information between switches.) Doing this really streamlined implementation because it meant I only had to create my VLANs on the basement 2900, which would then broadcast the information to the 15th-floor switch.

Creating VLANs by location more than quadrupled the customer's response time. (This makes you very popular.) Plus, since they already had the switches, this network cost my client very little, was elegantly easy to implement, and was designed to make it very simple for the administrators to add new users. (This makes you extremely popular.) Need selling points for this type of design? It can help:

Solve your client's problem efficiently.
Give your client better-than-expected results.
Save time and money.
Create something the client can readily understand, control, and scale for growth (making him/her feel competent and confident).

If you do these things, you can't lose. An important thing to understand in this example is that all users need to get to VLAN 1 because of a shared database. (By the way, I found out this information by asking the users questions about their day-to-day activities before I changed the network.) This means that the users must leave their broadcast domain (VLAN) and get information from the NT Server hosting the database. To do this, I had to configure a router. Luckily, my client already had some good switches and routers. I used the 2600 router to provide Inter-Switch Link (ISL) routing. (ISL routing is a proprietary Cisco method of allowing hosts on different VLANs to communicate through one router interface. Cisco calls this “router on a stick.”) Though this can create a bottleneck for the network, if it becomes a problem, the design allows for an easy upgrade of the router to make the network run even faster.

Here's the output from a 2621 router that shows the ISL configuration:
[output cut]
interface FastEthernet0/0
ip address 10.1.1.1 255.255.255.0
!
interface FastEthernet0/0.11
encapsulation isl 11
ip address 10.1.11.1 255.255.255.0
!
interface FastEthernet0/0.12
encapsulation isl 12
ip address 10.1.12.1 255.255.255.0
!
interface FastEthernet0/0.13
encapsulation isl 13
ip address 10.1.13.1 255.255.255.0
[output cut]

In this configuration, subinterfaces were used to allow all VLANs to be connected to one router interface. In this example, the interface used is FastEthernet 0/0. I made the subinterfaces the same number as the VLAN number for easy identification. The first command under the subinterface is the encapsulation command, which is used to direct the router to the VLAN number of the subinterface and to use ISL inter-VLAN routing.

After the encapsulation command was used to define the VLAN and inter-VLAN routing type (ISL), I added the IP address assigned to the subinterface. The hosts in each VLAN would use the IP address assigned to this interface as their default gateway. For example, users in VLAN 12 would be configured to use 10.1.12.1 as their default gateway. This allowed the users to get out of their own VLAN and to access company shared services, as well as the Internet.

Conclusion
I hope the real-world example I gave you in this Daily Drill Down helped you to understand how valuable using VLAN technology in an internetwork can be and that you now have a clearer picture of how to create them. Even though the largest benefit of creating VLANs in an internetwork is that you are no longer confined to a physical location, this real-life example involved creating VLANs by physical location because that was what was best for the customer.

I can't say enough about how important it is to be fully aware of an individual client's business requirements before you implement any network. Even though I thoroughly discussed the project with every person I could in the company before I performed the upgrade, I still ran into unforeseen problems because the client just forgot to mention a certain application. You can only prepare so much; after that, you must rely on your troubleshooting skills. Hone them well!

Wi-Fi Technology

2011-03-06T03:41:00.000-08:00

CURRENT WIRELESS TECHNOLOGY

In the smallest range, we have a Bluetooth [2] example. It is a wireless network technology that has its own development direction other than the 802.11 family. Bluetooth supports a very short range in the region of 10 meters and relatively low bandwidth roughly around 1-3 Mbps. It is designed for low-power network devices like portable or handheld gadgets. Nowadays it is a normal feature for handheld devices which include notebook to have a built-in Bluetooth support.

In the medium range, the popularity of the wireless Fidelity (Wi-Fi) has developed the market for unregulated band or unlicensed client-access radios in a wide variety of applications. This technology is one of the last-mile wireless broadband and narrowband services. However, the current main type of the last-mile deployment is the large-area coverage normally called hot-spots. Wireless last-mile coverage is based on IEEE 802.11 standard [1] which uses the high-gain antennas, while hot spots use the modified version of the IEEE 802.11 apparatus which is called a mesh operation. Wi-Fi resembles the wireless local area network.

In 2005, for a wider range, the Worldwide Interoperability for Microwave Access (WiMAX) certified the IEEE 802.16-2004 standard [3] for fixed-position radios. WiMAX will provide the point-to-multi-point and point-to-point wireless broadband devices in both the regulated and unregulated bands. Then, the IEEE 802.16e standard [4] for portable devices has been approved in 2006, regulating the client radio frequencies in licensed and unlicensed bands. This promising technology will provide service providers an additional layer of services benefits.

WiMAX actually resembles a wireless metropolitan-area network segment which provides broadband wireless connectivity to portable, fixed and roaming users. Its designed target is for long-range networking as opposed to local area wireless networking and the research in this field still continues. It is developed independently from Wi-Fi, providing additional distance up to 50 kilometers with total data rates can be up to 75 Mbps, providing sufficient bandwidth to support hundreds concurrent users using a single radio base station. WiMAX has been said to provide many wireless access advantageous to the remote and isolated area.

WIRELESS DEPLOYMENTS

The current trends show that the price of the wireless gadgets keep decreasing with the every advent of new technologies. The affordability makes wireless as a popular and practical alternative. Wireless deployment can be as simple as connecting two adjacent computers wirelessly. More complicated deployment will have hundreds or thousands of devices with centralized servers and distributed APs. Basically, wireless network can be structured into two different modes, based on the coverage size needed. These two modes are

Ad-hoc mode: This mode is a temporary, as is basis type. There is no AP in this mode and the devices are directly sharing their resources when in the range. The shared resources available as long as the devices are running. Bluetooth is one of the examples.
Infrastructure: This mode resembles the wired network. In this mode the AP is used for the wireless devices to communicate each other and it is dominant mode that can be found in residential, corporate building, university campus and plants. The wireless devices can keep connecting as long as they are directly connected to and within the wireless network coverage. Wireless security elements could be enforced on all the wireless devices and users such as through policies, authentication, encryption and many more.

Currently the wireless deployment still dominated in the last mile coverage. This is because of the unregulated frequency availability which lowered the cost of deployment and maintenance. Furthermore, the mass introduction of the cheaper consumer wireless devices makes it an attractive offer. Other than providing an alternative mode of communication medium, the main reason of the adoption is based on the mobility nature of the devices. However, in term of deployments, we can categorize them into four main segments of utilization as listed below.

1. The Wireless Personal area networks (WPAN – 802.16).

2. The Wireless Local area networks (WLAN).

3. The Wireless Metropolitan area networks (WMAN).

4. The Wireless Wide area networks (WWAN).

WIRELESS PERSONAL AREA NETWORK

WPAN can cover a range up to 30 feet or around 10m. Although this seems absurdly small, but this range allows wireless devices to be connected wirelessly to other nearby wireless devices [6]. WPAN provides a very short distant and for small group or community that can share resources wirelessly. Bluetooth which based on the IEEE 802.15.1 standard [7] for example, is mostly used for short range computing and communication peripherals, such as a PDA to a computer or a hand phones. It is normal that the new Bluetooth version can provide data rate performance up to 1Mbps. Another example is the ultra-wide band (UWB) which is designed for multimedia services transmission. The related standard for UWB is IEEE 802.15.3 which can support a data rate up to 400Mbps which equivalent to the DVD video quality standard. In this case the WPAN becomes a high-speed personnel area network. Other usage includes the ad-hoc network where a local area network in which computers and network devices are in close proximity to others in similar subnet. These devices are connected temporarily and as is basis. The receiver and transmitter used are built-in type devices.

However there is no independent pre-existing network for WPAN. All the devices in WPAN communicate based on the ad-hoc network, can be connected when within the range and disconnected when out of range. Better built-in devices can be designed in the future to provide non ad-hoc network. Other similar scenario can be found when using the Infrared (IR) to exchange data between laptops. The nature of wireless devices discovering each other and in many situation it is automatic, is a very big issue in wireless security field.

2.2.2 WIRELESS LOCAL AREA NETWORK

Similar to its counterpart, LAN in fixed line, WLANs can provide coverage larger than WPAN but still limited. Typical coverage areas can be found in a campus, a corporate building, a hospital, or a manufacturing plant [8]. Take note that, the traditional wired LAN can be expanded using wireless through the wireless Access Points (APs) for example, creating a heterogeneous network. The standards-based WLAN typically serve more users and applications compared to WPAN and can serve a distance up to 10 meters or more although this depend on the physical environment such as walls and frequency reflectors. The legacy and new wireless standards that have been released associated with WLAN are included the following three major revisions.

802.11n - bandwidth speeds up to 600 Mbps (2009).
802.11g - bandwidth speeds up to 54 Mbps.
802.11b - bandwidth speeds up to 11 Mbps.
802.11a - bandwidth speeds up to 54 Mbps.

On the service provider part which normally called Wireless Internet Service Providers (WISPs) usually use the existing Wi-Fi mesh topologies or the directional antennas for better signal and larger coverage. For example those deployments can increase the performance beyond the 54Mbps with 10 kilometers in range while still obeying the 802.11 standard. The increased range creates the WLAN and WMAN segments as shown in Figure 1. However there are many more variables such as the APs to user’s distance, the number of users and topologies which actually define the WLAN and WWAN.

Figure 1: Wireless technologies target segments

METROPOLITAN AREA NETWORK AND WIRELESS WIDE AREA NETWORK

The WMAN is the third usage segment shown in Figure 2. The WLANs collection makes the WMAN and the range can be up to 50 km. The implementation examples in this segment include the WiMAX, DSL/ADSL and DOCSIS legacy coppered wired technologies.

Figure 2: Wireless networks categories

The fourth usage segment shown in Figure 2 is the WWAN. WWAN aggregates WMANs and the range can cover the area up to 50 km. Compared to the previous wireless technology, this is a large area coverage which makes the backhaul or core network possible. In order to cater for the big amount of traffic, WWAN still utilizes various type of existing technology such as fiber optic links and terrestrial microwaves as a complement which normally acts as the backhaul for inter-WWAN connections. Depending on the type of traffic (data, voice or video), the performance can goes up to 10Gbps.

There must be very compelling reasons for deploying wireless communication in all the segment usage because the traditional wired communication already existed long time ago. In the WPAN and WLAN, the main reason of deployment is the mobility while in the WMAN and WWAN it is more on the cost per user, for example, deployment in remote area with less user population. In this case there should be no landline and Radio Base Station (RBS). However the real requirements for each segment are based on a variety of variables as listed below:

The distance and power of the signal.
The topology including the user location.
The bandwidth needs.
The services offered.
The security features.

Figure 1 also shows the wireless standards, standards bodies and their features such as distance and bandwidth which mapped to the four usage segments previously explained. Regarding the standard, there are three main bodies involved in wireless technology as listed below:

European Telecommunications Standards Institute (ETSI) [9]
Institute of Electrical and Electronics Engineers (IEEE) [10]
Third-Generation Partnership Project (3GPP) [11]

The IEEE and ETSI standards are interoperable and concentrate mainly on wireless packet-based networking. However, ESTI is concentrated more on the technology and standard for the European countries. The 3GPP standard focuses on cellular and third-generation mobile systems and very apparent in the mobile sectors.

Wireless Mesh Topology

2011-03-06T01:37:00.000-08:00

A wireless network as described in this document is a network of wireless local area networks (LAN) connected together to form a metropolitan network (MAN), usually located in one geographical area, such as a city or small town. Several wireless interface standards currently exist, some operate within licensed and others within unlicensed spectrum, some point to point, others point to multi-point, and yet others more flexible. The most common readily available standard at the moment is the 802.11 family (802.11, 802.11a, 802.11b and 802.11g]). This is consumer equipment that operates on an unlicensed radio frequency. Each wireless network is composed of various nodes connected together. A node is a collection of various PCs or other equipment connected together directly using the IP network and within direct radio range. A node consists of at least one router and one of more clients. The clients normally require little configuration and talk only to the router, whilst the router will route it’s own data and that of its clients to the rest of the network. It will also participate in exchange routing information with other nodes to ensure it always knows how to reach the rest of the network. The nodes can be connected together by radio links or by other means. The term node can loosely be associated with the router/host which manages each node’s own local network. Due to the limited range of the radio signals a large number of nodes will be required to provide coverage to a whole town, thus requiring a complex mesh of connections between the nodes to provide a robust network.
The network’s clients, the people who connect to the nodes from their home or office, make up the complete network. The nodes without clients form each group’s network infrastructure.

Wireless Mesh Topology

A wireless mesh network is made up of three or more wireless access points, working in harmony with each other while sharing each other routing protocols, in a collection of cross-connect links to create an interconnected electronic pathway for the transmission between two or more computers. When a wireless mesh is form it creates a single name identifier for access and the signals between wireless access points are used with each other to clearly distinguishable from another network. The organization of sharing access points working in harmony is known as the mesh topology. The defined mesh topology of a given area defined by the access points is known as mesh cloud. Access to this mesh cloud is dependent on the network created by the access points.

There are three types of mesh networks:

	Fixed wireless installations that connect multiple locations using Ad-hoc mode,
	Mobile, peer-to-peer, ad-hoc networks that have variable availability and a potentially ever changing set of nodes and finally
	Node-to-node infrastructure network that connect multiple locations and combine with mobile giving the best of the both world.

Fixed mesh networks are generally built with the expectation that many nodes have no direct backhaul, network, or Internet access. In fact, if each location had some kind of enterprise or Internet access, distributing service by wireless would be almost unnecessary.

In a fixed installation, locations for nodes are chosen with an eye for providing the right overall level of bandwidth with the fewest points. Fixed mesh networks also can effectively offer non-line-of-sight service by ringing an obstacle -- a tall building, a hill, a cluster of trees, an area of known interference -- with enough nodes to bypass it. These fixed networks are typically directional enough over each link to avoid major security risks.

In contrast, peer-to-peer mobile mesh networks -- which are a long way from actual deployment -- rely on individual devices connecting to each other through devices within radio range. Scalability can be an issue because each device has to manage known optimal paths, which can change from millisecond to millisecond. When an uplink of some kind is added via cell, satellite, or wire, the network becomes dynamically aware and can handle queued interactions.

Node-to-node network utilizes a fixed mesh network with mobile mesh network in an infrastructure mode. Node-to-node connects each node using infrastructure mode and it provides a network cloud that none-nodes or clients using 802.11b or g can roam in the network. It is has the benefits of both mobile mesh and fixed installations. Clients have the ability to roam the network similar to roaming a cellular network.

Roaming in Node-to-node

There are two methods of roaming in a node-to-node configuration: Patchwork roaming and Mobile Mesh roaming.

Nodes in a mobile mesh by their very nature roam in and out of coverage and between networks.

With Patchwork roaming, wireless connection between client’s hardware and mesh network, a wireless data networks, public Wi-Fi hotspots, and enterprise WLAN’s, are difficult to operate at best. The clients using Ipv4 that do not automatically change the IP address when moving between mesh nodes and wireless nodes. Manual intervention may be required. With Patchwork seamless roaming can be achieve; however, it requires DHCP to set every few seconds. The solution will be wait until Ipv6.

Mobile meshes implements self-contained dynamic addressing and rendezvous technologies to simplify address management and enable true nomadic operation without reliance on external clients hardware. Mobile devices can join and leave a mobile mesh and/or connect to public or private fixed infrastructure, all while retaining connectivity to critical services.

Wireless Mesh topology every node has a connection to every other node in the network realm. There is two types of mesh topologies: full mesh and partial mesh.

Full wireless mesh topology occurs when every node in a realm is connected to every other node in a network. Full mesh is yields the greatest amount of redundancy, so in the event that one of those nodes fails, network traffic can be directed to any of the other nodes. Full wireless mesh is difficult to achieve on a large scale using MeshAP; however, small-scale area like offices or small campus may be ideal. One should note that it is difficult to deploy a full mesh topology.

Partial mesh topology yields less redundancy than full mesh topology. With partial mesh, some nodes are organized in a full mesh scheme but others are only connected to one or more nodes in the network realm. Partial mesh topology is commonly found in either small or large networks or fulfilling the last mile connection to a full meshed backbone.

There are 4 main types of partial wireless mesh nodes topologies:

Point-to-point

Point-to-multipoint or Multipoint-to-point, and

Multipoint-to-multipoint,

Metropolitan

Point-to-point and point-to-multipoint networks have long been the standard for fixed wireless deployments and some 802.11 based networks. In testing of mesh networks have proven to be most versatile, overcoming a number of disadvantages in traditional wireless topologies. This section will detail the fundamentals of MeshAP and its inherent advantages.

Point-to-Point nodes topology

A point-to-point network is the simplest form of wireless network, composed of two radio and two high gain antennas in direct communication with each other. Point to point links are often used to provide high-performance, dedicated connections or high-speed interconnect links. These links are quick to deploy individually, but do not easily scale to create a large network. Client used these nodes in a site-to-site configuration.

Point to Multipoint nodes topology

A point-to multipoint or a Multipoint to point nodes share link between an uplink node with omni directional antenna and repeater nodes or downlink nodes with high gain directional antennas. This type of network is easier to deploy than Point to point network because adding a new subscriber only requires equipment deployment at the subscriber site, not at the uplink node; however, each remote site must be within range and clear line of sight of the base station. Trees, hills and other line of sight obstruction make point to multipoint nods impractical for residential and home office coverage. A Point to Multipoint network is suited for either backhaul operations or customers that need reliable, high-speed connections, but are not willing to pay for dedicated capacity that may go unused. The nodes performed as a bridge to the uplink network and are generally in wired configuration for the clients. The problem with point to Multipoint node topology is that they are not design to mesh with other nodes due to the directional antenna.

Multipoint nodes topology

Multipoint to multipoint networks creates a routed mesh topology that mirrors the structure of a wired Internet. To build a mesh network, indoor or outdoor Internet access is first established with the deployment of an access switch connected to a wired ISP. Additional access routers are then deployed throughout the coverage area until a maximum density is achieved. Each access router not only provides access for attached users, but also become part of the network infrastructure by routing traffic through the network over multiple hops. This allows any client to join the network at any point of the mesh, even if the clients are not using a node. Client can access the entire mesh wireless or wired making this the best choice to deploy for areas that require larger coverage MeshAP.

Metropolitan nodes topology

Metropolitan node topology uses the two mesh type networks. They are Backhaul and Last Mile.

Backhaul are either a Point-to-Point or Point-to-Multipoint topology. It design is to provide a backbone to the uplink nodes (see MeshAP configuration.) The nodes use dual antennas one being directional to the uplink the other providing connection to the last mile. The last mile antenna tends to be omni directional. Backhaul Wiana configuration uses two different realms, channels, and ESSID. Clients do not use the backhaul as an access point. The prime mission is to bring bandwidth to different part of the last mile. The uplink nodes in backhaul provide multi redundant connections to the wired Internet and have more capacity than 11 MBPS. Depending on the size of the area cover numerous backhaul points maybe required to cover a large city.

Last Mile is a Multipoint-to-Multipoint topology is nodes that have single radio cards with omni antennas and are linked to the backhauls omni antenna. The difference between Last Mile and Multipoint-to-Multipoint topology is that Internet connection does not come from a wired router but through the backhaul mesh via a central point.

These are just a few examples of the type of topology that a LocustWorld MeshAP can configure. The complexity increases when adding a second wireless radio card to a node and adding different types of antennas.

Mixed node topology

A mixed node network is the complex form of wireless network, composed of two radio and two high gain antennas in direct communication with each other and a third party wireless bridge/repeater. Mixed Nodes are often used to provide high-performance, dedicated connections or high-speed interconnect links. These links are quick to deploy individually, but do not easily scale to create a large network. Client used these bridge/repeater nodes in an indoor environment. The main benefit is that the indoor unit is a low cost commercial product.

Mixed Node Indoor topology

Similar to a mixed node network is the complex form of wireless network, composed of two radio and two high gain antennas in direct communication with each other and a series of third party wireless bridge/repeater. Mixed Nodes are often used to provide high-performance, dedicated connections or high-speed interconnect links. These links are quick to deploy individually, although they do not easily scale to create a large outdoor network they do scale to become a large indoor network. Client used these bridge/repeater nodes in an indoor environment. The main benefit is that the indoor unit is a low cost commercial product.

Mesh Structure

Rectangular Mesh Structure

The rectangular mesh structure, is the original topology proposed for a digital wave guide mesh. The main problem with this structure is the direction-dependent dispersion, which increases with frequency.

Triangle Mesh

Alternative sampling lattices have been studied to obtain more uniform wave propagation characteristics in all directions. When the sampling of the surface is hexagonal, the triangular digital wave guide mesh is obtained. This structure has better dispersion characteristics than the rectangular mesh. The same dispersion analysis as presented for the rectangular mesh is valid for the triangular mesh.

Network Topologies

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Some of the most common topologies in use today include:

Bus - Each node is daisy-chained (connected one right after the other) along the same backbone, similar to Christmas lights. Information sent from a node travels along the backbone until it reaches its destination node. Each end of a bus network must be terminated with a resistor to keep the signal that is sent by a node across the network from bouncing back when it reaches the end of the cable.

Bus network topology

Ring - Like a bus network, rings have the nodes daisy-chained. The difference is that the end of the network comes back around to the first node, creating a complete circuit. In a ring network, each node takes a turn sending and receiving information through the use of a token. The token, along with any data, is sent from the first node to the second node, which extracts the data addressed to it and adds any data it wishes to send. Then, the second node passes the token and data to the third node, and so on until it comes back around to the first node again. Only the node with the token is allowed to send data. All other nodes must wait for the token to come to them.

Ring network topology

Star - In a star network, each node is connected to a central device called a hub. The hub takes a signal that comes from any node and passes it along to all the other nodes in the network. A hub does not perform any type of filtering or routing of the data. It is simply a junction that joins all the different nodes together.

Star network topology

Star bus - Probably the most common network topology in use today, star bus combines elements of the star and bus topologies to create a versatile network environment. Nodes in particular areas are connected to hubs (creating stars), and the hubs are connected together along the network backbone (like a bus network). Quite often, stars are nested within stars, as seen in the example below:

A typical star bus network

LAN Switch

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How LAN Switches Work

If you have read other HowStuffWorks articles on networking or the internet, then you know that a typical network consists of:

nodes (computers)
a connecting medium (wired or wireless)
specialized network equipment like routers or hubs.

In the case of the Internet, all of these pieces work together to allow your computer to send information to another computer that could be on the other side of the world!

Switches are another fundamental part of many networks because they speed things up. Switches allow different nodes (a network connection point, typically a computer) of a network to communicate directly with one another in a smooth and efficient manner.

There are many different types of switches and networks. Switches that provide a separate connection for each node in a company's internal network are called LAN switches. Essentially, a LAN switch creates a series of instant networks that contain only the two devices communicating with each other at that particular moment. In this article, we will focus on Ethernet networks that use LAN switches. You will learn what a LAN switch is and how transparent bridging works, as well as about VLANs, trunking and spanning trees.

Networking Basics

Here are some of the fundamental parts of a network:

Network - A network is a group of computers connected together in a way that allows information to be exchanged between the computers.
Node - A node is anything that is connected to the network. While a node is typically a computer, it can also be something like a printer or CD-ROM tower.
Segment - A segment is any portion of a network that is separated, by a switch, bridge or router, from other parts of the network.
Backbone - The backbone is the main cabling of a network that all of the segments connect to. Typically, the backbone is capable of carrying more information than the individual segments. For example, each segment may have a transfer rate of 10 Mbps (megabits per second), while the backbone may operate at 100 Mbps.
Topology - Topology is the way that each node is physically connected to the network (more on this in the next section).
Local Area Network (LAN) - A LAN is a network of computers that are in the same general physical location, usually within a building or a campus. If the computers are far apart (such as across town or in different cities), then a Wide Area Network (WAN) is typically used.
Media Access Control (MAC) address - This is the physical address of any device -- such as the NIC in a computer -- on the network. The MAC address, which is made up of two equal parts, is 6 bytes long. The first 3 bytes identify the company that made the NIC. The second 3 bytes are the serial number of the NIC itself.
Unicast - A unicast is a transmission from one node addressed specifically to another node.
Multicast - In a multicast, a node sends a packet addressed to a special group address. Devices that are interested in this group register to receive packets addressed to the group. An example might be a Cisco router sending out an update to all of the other Cisco routers.
Broadcast - In a broadcast, a node sends out a packet that is intended for transmission to all other nodes on the network.

Bluetooth Technology Contd..

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Bluetooth is an open wireless technology standard for exchanging data over short distances (using short length radio waves) from fixed and mobile devices, creating personal area networks (PANs) with high levels of security. Created by telecoms vendor Ericsson in 1994, it was originally conceived as a wireless alternative to RS-232 data cables. It can connect several devices, overcoming problems of synchronization

Implementation

Bluetooth uses a radio technology called frequency hopping spread spectrum, which chops up the data being sent and transmits chunks of it on up to 79 bands of 1 MHz width in the range 2402-2480 MHz. This is in the globally unlicensed Industrial, Scientific and Medical (ISM) 2.4 GHz short-range radio frequency band.

Bluetooth is a packet-based protocol with a master-slave structure. One master may communicate with up to 7 slaves in a piconet, all devices share the master's clock. Packet exchange is based on the basic clock, defined by the master, which ticks at 312.5 µs intervals. Two clock ticks make up a slot of 625 µs; two slots make up a slot pair of 1250 µs. In the simple case of single-slot packets the master transmits in even slots and receives in odd slots; the slave, conversely, receives in even slots and transmits in odd slots. Packets may be 1, 3 or 5 slots long but in all cases the master transmit will begin in even slots and the slave transmit in odd slots.

Bluetooth provides a secure way to connect and exchange information between devices such as faxes, mobile phones, telephones, laptops, personal computers, printers, Global Positioning System (GPS) receivers.

The Bluetooth specifications are developed and licensed by the Bluetooth Special Interest Group (SIG). The Bluetooth SIG consists of more than 13,000 companies in the areas of telecommunication, computing, networking, and consumer electronics.

To be marketed as a Bluetooth device, it must be qualified to standards defined by the SIG.

Communication and connection

A master Bluetooth device can communicate with up to seven devices in a Wireless User Group. This network group of up to eight devices is called a piconet. The devices can switch roles, by agreement, and the slave can become the master at any time.

At any given time, data can be transferred between the master and one other device.

The master switches rapidly from one device to another in a round-robin fashion. Simultaneous transmission from the master to multiple other devices is possible via broadcast mode, but not used much.

The Bluetooth Core Specification allows connecting two or more piconets together to form a scatternet, with some devices acting as a bridge by simultaneously playing the master role in one piconet and the slave role in another.

Many USB Bluetooth adapters or "dongles" are available, some of which also include an IrDA adapter. Older (pre-2003) Bluetooth dongles, however, have limited services, offering only the Bluetooth Enumerator and a less-powerful Bluetooth Radio incarnation. Such devices can link computers with Bluetooth, but they do not offer much in the way of services that modern adapters do.

List of applications

Wireless control of and communication between a mobile phone and a hands free headset This was one of the earliest applications to become popular.
Wireless networking between PCs in a confined space and where little bandwidth is required.
Wireless communication with PC input and output devices, the most common being the mouse,keyboard and printer.
Transfer of files, contact details, calendar appointments, and reminders between devices with OBEX.
Replacement of traditional wired serial communications in test equipment, GPS receivers, medical equipment, bar code scanners, and traffic control devices.
For controls where infrared was traditionally used.
For low bandwidth applications where higher USB bandwidth is not required and cable-free connection desired.
Sending small advertisements from Bluetooth-enabled advertising hoardings to other, discoverable, Bluetooth devices.
Wireless bridge between two Industrial Ethernet networks.
Dial-up internet access on personal computers or PDAs using a data-capable mobile phone as a wireless modem like NOVATEL mifi,
Short range transmission of health sensor data from medical devices to mobile phones, set top box or dedicated telehealth devices.

Computer requirements

A personal computer that does not have embedded Bluetooth can be used with a Bluetooth adapter or "dongle" that will enable the PC to communicate with other Bluetooth devices (such as mobile phones,mice and keyboards). While some desktop computers and most recent laptops come with a built-in Bluetooth radio, others will require an external one in the form of a dongle.

Unlike its predecessor, IrDA, which requires a separate adapter for each device, Bluetooth allows multiple devices to communicate with a computer over a single adapter.

Operating system support

For Microsoft platforms, Windows XP Service Pack 2 and SP3 releases have native support for Bluetooth 1.1, 2.0 and 2.0+EDR.Previous versions required users to install their Bluetooth adapter's own drivers, which were not directly supported by Microsoft. Microsoft's own Bluetooth dongles (packaged with their Bluetooth computer devices) have no external drivers and thus require at least Windows XP Service Pack 2. Windows Vista RTM/SP1 with the Feature Pack for Wireless or Windows Vista SP2 support Bluetooth 2.1+EDR. Windows 7 supports Bluetooth 2.1+EDR and Extended Inquiry Response (EIR).

The Windows XP and Windows Vista/Windows 7 Bluetooth stacks support the following Bluetooth profiles natively: PAN, SPP, DUN, HID, HCRP. The Windows XP stack can be replaced by a third party stack which may support more profiles or newer versions of Bluetooth. The Windows Vista/Windows 7 Bluetooth stack supports vendor-supplied additional profiles without requiring the Microsoft stack to be replaced.

Linux has two popular Bluetooth stacks, BlueZ and Affix. The BlueZ stack is included with most Linux kernels and was originally developed by Qualcomm. The Affix stack was developed by Nokia. FreeBSD features Bluetooth support since its 5.0 release. NetBSD features Bluetooth support since its 4.0 release. Its Bluetooth stack has been ported to OpenBSD as well.

Mobile phone requirements

A Bluetooth-enabled mobile phone is able to pair with many devices. To ensure the broadest support of feature functionality together with legacy device support, the Open Mobile Terminal Platform (OMTP) forum has published a recommendations paper, entitled "Bluetooth Local Connectivity" The Bluetooth SIG Web site offers additional information about use cases for Bluetooth-enabled mobile phones.

Specifications and features

The Bluetooth specification was developed in 1994 by Jaap Haartsen and Sven Mattisson, who were working for Ericsson in Lund, Sweden. The specification is based on frequency-hopping spread spectrum technology.

The specifications were formalized by the Bluetooth Special Interest Group (SIG) . The SIG was formally announced on May 20, 1998. Today it has a membership of over 13,000 companies worldwide. It was established by Ericsson, IBM, Intel, Toshiba, and Nokia , and later joined by many other companies.

Introduction To Bluetooth Technology

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What is Bluetooth ?

Bluetooth is a high-speed, low-power microwave wireless link technology, designed to connect phones, laptops, PDAs and other portable equipment together with little or no work by the user.

Bluetooth is the name for a short-range radio frequency (RF) technology that operates at 2.4 GHz and is capable of transmitting voice and data. The effective range of Bluetooth devices is 32 feet (10 meters). Bluetooth transfers data at the rate of 1 Mbps, which is from three to eight times the average speed of parallel and serial ports, respectively. It is also known as the IEEE 802.15 standards. It was invented to get rid of wires. Bluetooth is more suited for connecting two point-to-point devices, whereas Wi-Fi is an IEEE standard intended for networking.

Why is the technology called Bluetooth

The heart of the Bluetooth brand identity is the name, which refers to the Danish king Harald "Bluetooth" Blaatand who unified Denmark and Norway. In the beginning of the Bluetooth wireless technology era, Bluetooth was aimed at unifying the telecom and computing industries.

Bluetooth can be used to wirelessly synchronize and transfer data among devices. Bluetooth can be thought of as a cable replacement technology. Typical uses include automatically synchronizing contact and calendar information among desktop, notebook and palmtop computers without connecting cables. Bluetooth can also be used to access a network or the Internet with a notebook computer by connecting wirelessly to a cellular phone.

Types of Bluetooth Devices

Bluetooth Dongle

Bluetooth Dongle : Installing a Bluetooth dongle is easy; simply insert the CD that came with it, follow the on screen prompts and then plug the dongle into a free USB port. If you had a Bluetooth compatible laptop you could just plug the dongle into an internet enabled personal computer and check your e-mail, download Windows updates, or transfer files. On the same lines you could also synchronize your PDA with your personal computer and download the latest appointments, e-mails or send text messages.

Bluetooth Headset

Bluetooth Headset : Bluetooth headsets are mainly used with compatible cell phones, place the headset on your ear and roam freely while talking to colleagues, friends and family. You could also connect to a dongle on a personal computer and use it for voice conferencing for example. A number of products exist on the market today, which all offer good sound quality and have a similar variety of features. Prices vary depending on manufacturer but usually you can get a decent one for around $75 to $150.

Other Examples

It comprises of a base band processor, a radio and an antenna. The base-band processor converts the data into signals, which radios can decipher. The antenna of another blue tooth device, within at least 30 feet distance, receives a transmitted signal in the air. The signals are processed in the reverse order.

Bluetooth technology provides a 10-meter personal bubble that supports simultaneous transmission of both voice and data for multiple devices. Up to 8 data devices can be connected in a piconet, and up to 10 piconets can exist within the 10-meter bubble. Each piconet supports up to3 simultaneous full duplex voice devices (CVSD).The gross data rate is 1Mb/s, but the actual data rates are 432Kbps for full duplex transmission, 721/56Kbps for asymmetric transmission, and 384 Kbps for TMS2000 transmission. A Time-Division Duplex scheme is used for full-duplex transmission.

Blue tooth specification is a de facto standard, which contains the information needed to ensure that the devices supporting the Blue tooth wireless technology can communicate with each other worldwide. It uses a frequency hopping spread spectrum technique (FHSS) - which is one of two basic modulation techniques used in spread spectrum signal transmission. Frequencies are switched repeatedly during radio transmission to help reduce unlawful access or other means of telecommunications to cross paths and cause interruption. It also makes Bluetooth communication more robust and secure. Interference from other devices will not cause the transmission to stop, but the speed to be reduced.

Ethernet Switch

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An Ethernet Switch is a LAN interconnection device which operates at the data link layer (layer 2) of the OSI refrence model. A switch is fundamentally similar to a bridge, but usually supports a larger number of connected LAN segments and has a richer management capability.

Modern LANs have increasingly replaced the shared media with a switched media, by installing Ethernet switches and bridges in place of hubs and repeaters. These logically partition the traffic to travel only over the network segments on the path between the source and the destination. This reduces the wastage of bandwidth which results from sending the packet to parts of the network which do not need to receive the data. There are also benefits from improved security (users are less able to tap-in into other user's data), better management (the ability to control who receives what information (i.e. Virtual LANs) and to limit the impact of network problems), and the ability to operate some links in full duplex (rather than half duplex required for shared access).

Architecture

At the centre of a Switch is a type of switching element which controls the ports to which each frame is forwarded. Three types of switching element have been used, each has some merits in terms of cost/performance:

Matrix Switches
Shared bus
Shared Memory

In addition, many switches include processing capability beyond that required for forwarding. This may be used to implement additional features.

Switches and Multicast Traffic

Many Ethernet switches handle multicast traffic as if were broadcast traffic. When a multicast packet reaches such a bridge/switch, it forwards the packet to all active interfaces, effectively flooding the network. This ensures all clients receive the multicast data, but has the drawback that every LAN segment carries all the multicast traffic, even when the directly connected clients do not require the data. This mitigates most of the advantages of switching when considering multicast traffic.

Multicast Traffic from F is delivered to all output interfaces (ports)

A bridge/switch may be designed to provides multicast support by implementing filters at the output ports of the device which remove the packets for which the clients attached to the ports have no registered interest. This operation resembles the processing for Virtual LANs (VLANs) and may be performed using the same/similar processing engine. Three approaches are possible when configuring this style of operation:

Manual table configuration The network manager determines which clients should receive which multicast packets, in the same manner that VLAN membership is configured. Many multicast applications however select their multicast groups dynamically as the application executes.
"Snooping" the multicast "Join" and "Leave"messages sent by clients. Clients use a protocol called the Internet Group Management Protocol (IGMP) to register the address groups in which they have an interest with their local multicast router. Some switches (e.g. FORE, 3COM) are able to monitor/emulate these packets and use the information to configure the switch filters dynamically
Down-loading a switch filter table from the local multicast router. Each IP multicast network must have at least one multicast. The router must track the multicast membership of each client, and may utilise this information to inform the switch which clients require which packets. In practice, this may be as simple as down-loading a multicast address filter table to all attached switches. Most CISCO equipment support the CISCO Group Management Protocol (CGMP) to provide this function.

With multicast Filtering. The multicast traffic form F is only forwarded to those interfaces which have equipment connected that wishes to receive the multicast packets. In this case, only E and H.

Some level of multicast filtering is highly desirable within a bridge/switch handling multicast traffic. These procedures allow a the device to selectively forward multicast packets only to hosts which register an interest in the corresponding multicast group address. Without the addition of such procedures, Level 2 bridges/switches are forced to broadcast multicast packets to all connected LANs. While manual configuration may suffice for applications such as multicast file transfer, or multicast distribution to network news/web cache clients. For the majority of multicast applications, one of the two dynamic schemes is recommended.

Network Switching

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What is a Switch?

Switches occupy the same place in the network as hubs. Unlike hubs, switches examine each packet and process it accordingly rather than simply repeating the signal to all ports. Switches map the Ethernet addresses of the nodes residing on each network segment and then allow only the necessary traffic to pass through the switch. When a packet is received by the switch, the switch examines the destination and source hardware addresses and compares them to a table of network segments and addresses. If the segments are the same, the packet is dropped ("filtered"); if the segments are different, then the packet is "forwarded" to the proper segment. Additionally, switches prevent bad or misaligned packets from spreading by not forwarding them.

Filtering of packets, and the regeneration of forwarded packets enables switching technology to split a network into separate collision domains. Regeneration of packets allows for greater distances and more nodes to be used in the total network design, and dramatically lowers the overall collision rates. In switched networks, each segment is an independent collision domain. In shared networks all nodes reside in one, big shared collision domain.

Easy to install, most switches are self learning. They determine the Ethernet addresses in use on each segment, building a table as packets are passed through the switch. This "plug and play" element makes switches an attractive alternative to hubs.

Switches can connect different networks types (such as Ethernet and Fast Ethernet) or networks of the same type. Many switches today offer high-speed links, like Fast Ethernet or FDDI, that can be used to link the switches together or to give added bandwidth to important servers that get a lot of traffic. A network composed of a number of switches linked together via these fast uplinks is called a "collapsed backbone" network.

Dedicating ports on switches to individual nodes is another way to speed access for critical computers. Servers and power users can take advantage of a full segment for one node, so some networks connect high traffic nodes to a dedicated switch port.

Full duplex is another method to increase bandwidth to dedicated workstations or servers. To use full duplex, both network interface cards used in the server or workstation, and the switch must support full duplex operation. Full duplex doubles the potential bandwidth on that link, providing 20 Mbps for Ethernet and 200 Mbps for Fast Ethernet.

Network Congestion

As more users are added to a shared network or as applications requiring more data are added, performance deteriorates. This is because all users on a shared network are competitors for the Ethernet bus. A moderately loaded 10 Mbps Ethernet network is able to sustain utilization of 35% and throughput in the neighborhood of 2.5 Mbps after accounting for packet overhead, interpacket gaps and collisions. A moderately loaded Fast Ethernet shares 25 Mbps of real data in the same circumstances. With shared Ethernet and Fast Ethernet, the likelihood of collisions increases as more nodes and/or more traffic is added to the shared collision domain.

Ethernet itself is a shared media, so there are rules for sending packets to avoid conflicts and protect data integrity. Nodes on an Ethernet network send packets when they determine the network is not in use. It is possible that two nodes at different locations could try to send data at the same time. When both PCs are transferring a packet to the network at the same time, a collision will result. Both packets are retransmitted, adding to the traffic problem. Minimizing collisions is a crucial element in the design and operation of networks. Increased collisions are often the result of too many users or too much traffic on the network, which results in a lot of contention for network bandwidth. This can slow the performance of the network from the users point of view. Segmenting, where a network is divided into different pieces joined together logically with switches or routers, reduces congestion in an overcrowded network.

Collision rates measure the percentage of packets that are collisions. Some collisions are inevitable, with less than 10% common in well running networks.

The Factors Affecting
Network Efficiency

- Amount of traffic
- Number of nodes
- Size of packets
- Network diameter

Measuring Network Efficiency

- Average to peak load devition
- Collision Rate
- Utilization Rate

Utilization rate is another widely accessible statistic about the health of a network. This statistic is available in Novell's Console monitor and WindowsNT performance monitor as well as any optional LAN analysis software. Utilization in an average network above 35% indicates potential problems. This 35% utilization is near optimum, but some networks experience higher or lower utilization optimums due to factors such as packet size and peak load deviation.

A switch is said to work at "wire speed" if it has enough processing power to handle full ethernet speed at minimum packet sizes. Most switches on the market are well ahead of network traffic capabilities supporting full "wire speed" of ethernet, 14,480 pps (packets per second).

Routers

Routers work in a manner similar to switches and bridges in that they filter out network traffic. Rather than doing so by packet addresses they filter by specific protocol. Routers were born out of the necessity for dividing networks logically instead of physically. An IP router can divide a network into various subnets so that only traffic destined for particular IP addresses can pass between segments. Routers recalculate the checksum, and rewrite the MAC header of every packet. The price paid for this type of intelligent forwarding and filtering is usually calculated in terms of latency, or the delay that a packet experiences inside the router. Such filtering takes more time than that exercised in a switch or bridge which only looks at the Ethernet address but in more complex networks network efficiency is improved. An additional benefit of routers is their automatic filtering of broadcasts, but overall they are complicated to setup.

Switch Benefits

- Isolates traffic, relieving congestion
- Separates collision domains, reducing collisions
- Segments, restarting distance and repeater rules

Switch Costs

- Price: currently 3 to 5 times the price of a hub
- Packet processing time is longer than in a hub
- Monitoring the network is more complicated

General Benefits of Switching

Switches replace hubs in networking designs, and they are more expensive. So why is the desktop switching market doubling ever year with huge numbers sold? The price of switches is declining precipitously, while hubs are a mature technology with small price declines. This means that there is far less difference between switch costs and hub costs than there used to be, and the gap is narrowing.

Since switches are self learning, they are as easy to install as a hub. Just plug them in and go. And they operate on the same hardware layer as a hub, so there are no protocol issues.

There are two reasons for switches being included in network designs. First, a switch breaks one network into many small networks so the distance and repeater limitations are restarted. Second, this same segmentation isolates traffic and reduces collisions relieving network congestion. It is very easy to identify the need for distance and repeater extension, and to understand this benefit of switching. But the second benefit, relieving network congestion, is hard to identify and harder to understand the degree by which switches will help performance. Since all switches add small latency delays to packet processing, deploying switches unnecessarily can actually slow down network performance. So the next section pertains to the factors affecting the impact of switching to congested networks.

Switching in Your Network

The benefits of switching vary from network to network. Adding a switch for the first time has different implications than increasing the number of switched ports already installed. Understanding traffic patterns is very important to switching - the goal being to eliminate (or filter) as much traffic as possible. A switch installed in a location where it forwards almost all the traffic it receives will help much less than one that filters most of the traffic.

Networks that are not congested can actually be negatively impacted by adding switches. Packet processing delays, switch buffer limitations, and the retransmissions that can result sometimes slows performance compared with the hub based alternative. If your network is not congested, don't replace hubs with switches. How can you tell if performance problems are the result of network congestion? Measure utilization factors and collision rates.

Good Candidates for
Performance Boosts from Switching

- Utilization more than 35%
- Collision rates more than 10%

Utilization load is the amount of total traffic as a percent of the theoretical maximum for the network type, 10 Mbps in Ethernet, 100 Mbps in Fast Ethernet. The collision rate is the number of packets with collisions as a percentage of total packages

Network response times (the user-visible part of network performance) suffers as the load on the network increases, and under heavy loads small increases in user traffic often results in significant decreases in performance. This is similar to automobile freeway dynamics, in that increasing loads results in increasing throughput up to a point, then further increases in demand results in rapid deterioration of true throughput. In Ethernet, collisions increase as the network is loaded, and this causes retransmissions and increases in load which cause even more collisions. The resulting network overload slows traffic considerably.

Switching To A New Computer?

2009-07-16T00:10:00.000-07:00

Switching to a new computer? Make a virtual machine to hold the old one.

If you've ever needed to move from one computer to another, you may know the pain of losing all the work of setting up the old one. Don't wish you could just magically keep the old one around to refer to when needed? And I mean really run it, not just look at backup files. Well, here's a solution you may not have considered: make a virtual machine out of the old computer. Then while you work on the new one, you can always go back to the VM to either see how things were before, or remind yourself of apps or settings you had, etc. You can do it for free (both create the VM and then use it) on Windows, and there are options for Linux and Mac as well. Here's how.

Background, and less satisfactory approaches

What am I getting at? Well, I've had to trade up laptops a couple times in recent years, and each time I've lamented having to lose all the work that went into setting it up.

Now, some will say "take a backup", but that's no good. First, if you mean to restore onto the new machine, if I have an OEM licensed version of Windows that would wipe out the new OS. With some vendors, like Dell, that could be a problem. (If you don't use Windows, again, don't leave yet. I cover Linux and Macs below).

But even if you'd deny the significance of that, the point is that the alternative I'll describe still has many benefits over simply doing a backup/restore (in that you can continue to use both the old and new setup at once, by way of virtual machines).

Some may also point out that there are programs to help move apps to a new computer, and even built-in OS features to move settings. And then there are tools like Ghost. Or at least by taking a backup, I could refer back to the files I had in the old machine.

But again none of these offer the "magic" solution of allowing me to really keep the "old image" of the previous machine available to view and even run with while installing, configuring, and going on to use the new machine.

With the VM approach, you could keep around the old machine's installation for months or years. Just fire it up as a VM whenever you want to recall how things were on the old machine. Sweet! :-)

One Solution: VMWare Converter

So what prompted me to write this? Well, I've known about and occasionally used virtual machine software for years. I last wrote about them several months ago when the two market leaders, VMWare and Microsoft's Virtual PC/Server products.

I figured then that creating a VM would be a solution to my challenge, but I never got around to it because I lacked space to hold the "backup". I've since gotten a larger external hard drive, and so could reconsider this.

Then I read today (in a magazine) of VMWare now having a product called VMWare Converter. Well, it turns out to be just the ticket (at least for Windows users. While VMWare runs on Linux, too, support for the Converter.

And note that beyond using VMWare Converter to create a VM out of any machine, you can also use it to make a VMWare VM out of a Virtual PC VM, or out of a Ghost image, and much more. Very compelling stuff, and again, all for free.

It seems that this is just the ticket for what I was trying to do, so I have installed it and will see how it goes. But I wanted to let folks know about it rather than wait to write of experiences after the fact.

(Even slicker, I noticed when I installed it that a hint popped up saying that if you wanted to create such a clone of a current machine without Converter being in the footprint, you could instead install Converter and create the clone from a bootable CD.)

Another Solution for Mac: Parallels Transporter

For those using Macs, you may already know that the favored tool for using VMs there, Parallels, also offers this feature in a tool called Transproter. It too can create a Parallels VM out of a Windows PC, or out of a VMWare or Virtual PC VM. There's even a youtube video the process.

Circuit Switching vs. Packet Switching

2008-12-04T05:24:00.000-08:00

The old telephone system (PSTN) uses circuit switching to transmit voice data whereas VoIP uses packet-switching to do so. The difference in the way these two types of switching work is the thing that made VoIP so different and successful.

To understand switching, you need to realize that the network in place between two communicating persons is a complex field of devices and machines, especially if the network is the Internet. Consider a person in Mauritius having a phone conversation with another person on the other side of the globe, say in the US. There are a large number of routers, switches and other kinds of devices that take the data transmitted during the communication from one end to the other.

Switching and routing

Switching and routing are technically two different things, but for the sake of simplicity, let us take switches and routers (which are devices that make switching and routing respectively) as devices doing one job: make a link in the connection and forward data from the source to the destination.

Paths or circuits

The important thing to look for in transmitting information over such a complex network is the path or circuit. The devices making up the path are called nodes. For instance, switches, routers and some other network devices, are nodes.

In circuit-switching, this path is decided upon before the data transmission starts. The system decides on which route to follow, based on a resource-optimizing algorithm, and transmission goes according to the path. For the whole length of the communication session between the two communicating bodies, the route is dedicated and exclusive, and released only when the session terminates.

Packets

To be able to understand packet-switching, you need to know what a packet is. The Internet Protocol (IP) , just like many other protocols, breaks data into chunks and wraps the chunks into structures called packets. Each packet contains, along with the data load, information about the IP address of the source and the destination nodes, sequence numbers and some other control information. A packet can also be called a segment or datagram.

Once they reach their destination, the packets are reassembled to make up the original data again. It is therefore obvious that, to transmit data in packets, it has to be digital data.

In packet-switching, the packets are sent towards the destination irrespective of each other. Each packet has to find its own route to the destination. There is no predetermined path; the decision as to which node to hop to in the next step is taken only when a node is reached. Each packet finds its way using the information it carries, such as the source and destination IP addresses.

As you must have figured it out already, traditional PSTN phone system uses circuit switching while VoIP uses packet switching.

Brief comparison

Circuit switching is old and expensive, and it is what PSTN uses. Packet switching is more modern.
When you are making a PSTN call, you are actually renting the lines, with all it implies. See why international calls are expensive? So if you speak for, say 10 minutes, you pay for ten minutes of dedicated line. You normally speak only when your correspondent is silent, and vice versa. Taking also into consideration the amount of time no one speaks, you finally use much less than half of what you are paying for. With VoIP, you actually can use a network or circuit even if there are other people using it at the same time. There is no circuit dedication. The cost is shared.
Circuit-switching is more reliable than packet-switching. When you have a circuit dedicated for a session, you are sure to get all information across. When you use a circuit which is open for other services, then there is a big possibility of congestion (which is for a network what a traffic jam is for the road), and hence the delays or even packet loss. This explains the relatively lower quality of VoIP voice compared to PSTN. But you actually have other protocols giving a helping hand in making packet-switching techniques to make connections more reliable. An example is the TCP protocol. Since voice is to some extent tolerant to some packet loss (unless text - since a comma lost can mean a big difference), packet-switching is finally ideal for VoIP.

Various Switching Techniques

2008-12-04T05:01:00.000-08:00

Circuit switching

In telecommunications, a circuit switching network is one that establishes a fixed bandwidth circuit (or channel) between nodes and terminals before the users may communicate, as if the nodes were physically connected with an electrical circuit.

The bit delay is constant during a connection, as opposed to packet switching, where packet queues may cause varying delay. Each circuit cannot be used by other callers until the circuit is released and a new connection is set up. Even if no actual communication is taking place in a dedicated circuit that channel remains unavailable to other users. Channels that are available for new calls to be set up are said to be idle.

Virtual Circuit Switching is a packet switching technology that may emulate circuit switching, in the sense that the connection is established before any packets are transferred, and that packets are delivered in order.

There is a common misunderstanding that circuit switching is used only for connecting voice circuits (analog or digital). The concept of a dedicated path persisting between two communicating parties or nodes can be extended to signal content other than voice. Its advantage is that it provides for non-stop transfer without requiring packets and without most of the overhead traffic usually needed, making maximal and optimal use of available bandwidth. The disadvantage of inflexibility tends to reserve it for specialized applications, particularly with the overwhelming proliferation of internet-related technology.

Examples of circuit switched networks

Public Switched Telephone Network(PSTN)
ISDN B-Channel
Circuit Switched Data(CSD) and High Speed Circuit Switched Data in a cellular system such as GSM
X.21

Compared to datagram packet switching

Since the first days of the telegraph it has been possible to mutiplex multiple connections over the same physical conductor, but nonetheless each channel on the multiplexed link was either dedicated to one call at a time, or it was idle between calls.

With circuit switching, and virtual circuit switching, a route is reserved from source to destination. The entire message is sent in order so that it does not have to be reassembled at the destination. Circuit switching can be relatively inefficient because capacity is wasted on connections which are set up but are not in continuous use (however momentarily). On the other hand, the connection is immediately available and capacity is guaranteed until the call is disconnected.

Circuit switching contrasts with packet switching which splits traffic data (for instance, digital representation of sound, or computer data) into chunks, called packets, that are routed over a shared network.

Packet switching is the process of segmenting a message/data to be transmitted into several smaller packets. Each packet is labeled with its destination and the number of the packet, precluding the need for a dedicated path to help the packet find its way to its destination. Each is dispatched and many may go via different routes. At the destination, the original message is reassembled in the correct order, based on the packet number. Datagram packet switching networks do not require a circuit to be established and allow many pairs of nodes to communicate almost simultaneously over the same cha

Packet switching

Packet switching is a network communications method that splits data traffic (digital representations of text, sound, or video data) into chunks, called packets, that are then routed over a shared network. To accomplish this, the original message/data is segmented into several smaller packets. Each packet is then labeled with its destination and the number of the packet. This precludes the need for a dedicated path to help the packet find its way to its destination. Each packet is dispatched and may go via different routes. At the destination, the original message/data is reassembled in the correct order, based on the packet number and other statistically determined factors. In each network node, packets are queued or buffered, resulting in variable delay. This contrasts with the other principal paradigm, circuit switching, which sets up a specific circuit with a limited number of constant bit rate and constant delay connections between nodes for exclusive use during the communication session.

Packet mode or packet-oriented communication may be utilized with or without a packet switch, in the latter case directly between two hosts. Examples of that are point-to-point data links, digital video and audio broadcasting or a shared physical medium, such as a bus network, ring network, or hub network.

Message switching

In telecommunication, message switching was the precursor of packet switching, where messages were routed in their entirety, one hop at a time. It was first introduced by Leonard Kleinrock in 1961. Message switching systems are nowadays mostly implemented over packet-switched or circuit-switched data networks.

Examples

Hop-by-hop Telex forwarding and UUCP are examples of message switching systems. E-mail is another example of a message switching system.

When this form of switching is used, no physical path is established in advance in between sender and receiver. Instead, when the sender has a block of data to be sent, it is stored in the first switching office (i.e. router) then forwarded later at one hop at a time. Each block is received in its entity form, inspected for errors and then forwarded or re-transmitted.

A form of store-and-forward network. Data is transmitted into the network and stored in a switch. The network transfers the data from switch to switch when it is convenient to do so, as such the data is not transferred in real-time. Blocking can not occur, however, long delays can happen. The source and destination terminal need not be compatible, since conversions are done by the message switching networks.

A message switch is “transactional”. It can store data or change its format and bit rate, then convert the data back to their original form or an entirely different form at the receive end. Message switching multiplexes data from different sources onto a common facility.

Store and forward delays

Since message switching stores each message at intermediate nodes in its entirety before forwarding, messages experience an end to end delay which is dependent on the message length, and the number of intermediate nodes. Each additional intermediate node introduces a delay which is at minimum the value of the minimum transmission delay into or out of the node. Note that nodes could have different transmission delays for incoming messages and outgoing messages due to different technology used on the links. The transmission delays are in addition to any propagation delays which will be experienced along the message path.

In a message-switching centre an incoming message is not lost when the required outgoing route is busy. It is stored in a queue with any other messages for the same route and retransmitted when the required circuit becomes free. Message switching is thus an example of a delay system or a queuing system. Message switching is still used for telegraph traffic and a modified form of it, known as packet switching, is used extensively for data communications.

Components Of switching

2008-11-28T05:34:00.000-08:00

The Basics of Switches

If you have ever installed a set of cold cathodes, or other special lighting gadgetry, then you most likely have been presented with an optional switch to install along with it to allow you to turn the device off and on instead of it staying on as long as the PC is on. I'm sure there people new to this sort of installation out there so here is a simple guide for hooking up a few types of switches you may encounter while tricking out your own PC with special electronics and/or lighting/cooling devices.

Why bother installing a switch?

The answer to that is really simple... control. A switch allows you to be in control of the state of activity of a component; whether that means a simple off or on state or something that will let you choose a setting among more than just two choices. For a device as simple as a cold cathode you may think, "Why even both with hooking up a switch when I can just let my lighting bling 24/7?" (or while the PC is on).

There times when the glare of an uber-lit PC next to you is not a desirable thing... like when gaming at a LAN party in tournament? When playing in total darkness for gaming ambiance? How about if you have to sleep in the same room with your PC? Plus, lighting fixtures all have a lifespan of use. When you turn off your lighting occasionally, and/or when you go to sleep at night, you are extending the life of that product's usefulness. That way the bling is there when you want it there and not in the way other times.

Then there is, of course, the matter of safety. I have seen first-hand a cold cathode burst into flames and melt it's housing. A switch allowed me to immediately cut juice to the inverter for that cathode and may have prevented serious damage to my other PC components.

Switch Terminology

Several terms are used to describe a switch and some other "need to know" terms:

- Pole - The number of switch contact spots.
- Throw - The number of conducting positions (single or double).
- Way - The number of conducting positions (three or more).
- Momentary - The switch returns to its original position when released. A PC Reset switch is a momentary switch.
- Open - The "off" position (contacts not conducting).
- Closed - The "on" position (contacts conducting; there may be several on positions).
- (+) Positive - The pole that connects to the live current source (usually via the various 5V [usually red wired] or 12V [usually yellow wired] contacts provided by the PC motherboard and/or PSU). Often marked with a "+" symbol, a small triangle or is labeled as pole #1.
- (-) Negative (Ground) - The pole that is the ground connection. Usually marked with a "-" symbol.
- Source, Trigger, Etc. - The pole that a signal/current is sent to when in a particular position. The pole will be labeled differently on various devices. Check it's documentation when available. When not available, simply eliminate the other poles by finding the ones marked with a + or -. If you only find one or the other, then the pole furthest from it is usually the opposite. The pole in the middle will normally be the trigger.

Example: the most simple on-off switch has one set of contacts (single pole) and one switch position which conducts (single throw); ie. SPST (Single Pole Single Throw). The switch has two positions: open (off) and closed (on); but it is called 'single throw' because only one position conducts.

Typical Types of Switches

We'll use four basic switches which you may cross paths with or find a use for someday. We'll use examples from the Frozen CPU Center for an easy reference point. There are many other forms of switches out there but these are the most commonly used types for a PC application.

Rocker Switch - A simple toggle switch that is used to control when a device receives current. This is what most cold cathode kits come with as an optional install method.

Rocker LED Switch - A rocker switch which includes a small LED that is normally lit when in the "On" position.

Military LED Toggle Switch - Very similar to the Rocker LED switch; just in a different form.

Bulgin LED Switch - SP Push-to-Make Switch that is a nice replacement for standard PC Power and Reset buttons.

Note: There are other components which are used as a type of switch (so to speak) which include devices like Rheostats. These devices are hooked up much the same way as the switches described above, except they allow you to "dial down" the juice that is delivered the devices powered through it. This is a popular setup for a system fans because it gives you the ability to turn up or down the speed of your fans to find the right balance of performance and noise for your needs.

Install

I don't feel that there is much need to show examples of the regular rocker switch installed since you really can't mess it up as long as you install the switch on the (+) positive line going to your device. Enough said. Instead, I will show you a VERY easy method for hooking up a rocker LED switch or a Military Toggle switch (using FrozenCPU's excellent custom leads) to turn off/on a device as well as an easy method for replacing your PC's Power and/or Reset buttons.

First, here is an example of using Frozen CPU's EZ Bulgin Cable for extra easy install of LED lit switches. (These are the same cables I personally use.) In order to make your Bulgin switch install as painless as possible you will need the 2-Pin Power LED or HDD LED Cable and the 2-Pin Power Switch cable. You can create your own cables like these but it can be a fairly tedious task. For the work and supplies involved, FrozenCPU's prices for these cables are very fair. Be sure NOT to confuse the two cables, however. The LED cables have a much needed resistor embedded in the cable to make sure that the LED in your switch doesn't get fried with too much current.

Bulgin Vandal Switch Install

Using FrozenCPU's provided diagram of the Bulgin Vandal Switch you can see that the outer polls are for the (+) and (-) current leads and that the inner poles are for the wire leads to turn on whatever devices you are hooking up (the PC power switch in our case). Start by sliding the Spade connectors for the 2-Pin Power Switch cable over the two inner posts. For this application a specific post is not needed for the switch wires. Next, slide the spade connectors for the 2-Pin Power LED cables on the outer poles; MAKE SURE you pay attention to where you are placing these! The black wire should be slid over the (-) pole and the colored (usually yellow [+12v] or red [+5v]) wire should be slid over the (+) pole. Now all you have to do is connect the 2-Pin ends of the wires to the appropriate motherboard pins; Connect the Power Switch cable to the power switch pins and connect the Power LED cable to the power LED pins on the motherboard. Simple! If you would instead like to use your Bulgin switch as a HDD activity indicator you can connect the LED cable to the HDD LED activity pins on the motherboard instead of the Power LED pins.

Uses: Bulgin Vandal switches are momentary so the switch is only "closed" when held down. This works well for a PC power or reset switch which works the same way. This is not a good choice for a switch to turn on a set of fans or lights since once you release the switch, the power will be cut off from these devices.

LED Rocker Switch Install

The LED Rocker Switch is like the Bulgin switch in that the outer poles are the (+) and (-) contacts; but notice that there is only a single center pole. Also notice that the outer poles are not labeled very clear like the Bulgin switch poles were. In the picture below I have circled where the manufacturer has labeled the poles as "1", "2" and "3". When you first look at the switch poles it can be a little confusing at first since the #3 pole is labeled with both a (+) and (-) symbol. A few things usually stay pretty constant when determining where the actual (+) pole is. The (+) pole will usually be labeled as "1", it will have a "+" symbol next to it, or it will have a tiny triangle pointing to it. If you ever get lost, look for one or more of these tell-tale signs. After you determine where the (+) contact is then the (-) contact should be the furthest one from the (+) contact. The reason for this is because if the live (+) and (-) lines touch one another you are in store for a light and sound show (the bad kind) and risk damaging your hardware.

To install this switch as an on/off switch for components you will need these spade connectors in order to ensure a safe and secure contact with the pole. Install is just what you would predict. Attach the (+) and (-) wires to the appropriate poles and connect the device to be turned on to the center pole.

Uses: Unlike the Bulgin switch, the rocker switch is not momentary which makes it a poor choice for a PC power or reset switch but it is an ideal choice for devices you want to be able to turn off and on like cold cathodes or supplemental cooling.

Military LED Toggle Switch Install

You will notice now that you have a basic knowledge of how to hook up an electrical switch that it gets easier and easier to hook them up. This Military LED toggle Switch is a bit of an exception. Using the tips I gave you earlier, I was unable to determine where the (+) line needed to be connected. After some quick googling for "military LED Toggle switch" I found a company diagram showing how to hook this switch up properly. Notice in the picture below that the power line is connected to the #2 pole which is in the middle of the poles on the underside of the switch. The ground (-) wire is connected to the single pole on the side of the switch. Lastly, the #3 pole is used to connect the devices to for on/off control. Note that the #1 pole is not used at all. The lesson here is to always double and triple check your findings before hooking unknown things up. Protect your gear and yourself; do your research first.

Uses: The uses for this switch are the same as the Rocker switches. Since it is not a momentary switch it is not suited for use as a PC power or reset switch.

Creating your own source of power

In closing, here is a simple idea for making your own source of power for your components. Just in case you have more than one Bulgin switch to power or your motherboard pins are not in a convenient location, etc. Take an old pass-through cable or other molex plug cable you are not using and then remove any extra wires besides the main 4 power wires. Then simply snip off the "male" molex plug and you now have access to solder on your own component wires. I have marked the wire voltages for you for easy reference. Red is normally +5V, Yellow is normally +12V and black is normally ground (-). Once you know what power line you need you can even remove the pins you don't need to keep everything as tidy as possible. FrozenCPU has a great little tool for that.

In Closing

Hopefully, those of you that were a bit intimidated by tinkering with your eletronics setup or installing a new PC power switch are now a little more confident with the terminology, process and reasoning behind switches. If you make heavy use of special lighting in your case I highly recommend putting that lighting on its own switch so you can turn them off when you aren't around to enjoy them. It will greatly extend the life of your lighting setup.

Network switch

2008-11-23T07:36:00.000-08:00

a NEtwork Switch is a broad and imprecise marketing term for a computer networking device that connects network segmants.

The term commonly refers to a network bridge that processes and routes data at the data link layer (layer 2) of the OSI model. Switches that additionally process data at the Network layer (layer 3) (and above) are often referred to as Layer 3 switches or Multilayer switches.

The term Network switch does not generally encompass unintelligent or passive network devices such as hubs and repeaters

Function

As with hubs, ethernet implementations of network switches support either 10/100 Mbit/s or 10/100/1000 Mbit/s ports Ethernet standards. Large switches may have 10 Gbit/s ports. Switches differ from hubs in that they can have ports of different speed.

The network switch, packet switch (or just switch) plays an integral part in most Ethernet Local Area Networks or LANs. Mid-to-large sized LANs contain a number of linked managed switches. Small office,home office(SOHO) applications typically use a single switch, or an all-purpose converged device such as gateway access to small office/home office broadband services such as DSL router or cable, Wi-Fi router. In most of these cases, the end user device contains a router and components that interface to the particular physical broadband technology, as in the Linksys 8-port and 48-port devices. User devices may also include a telephone interface toVOIP.

In simple terms, in the context of a standard 10/100 Ethernet switch, a switch operates at the data-link layer of the OSI model to create a different collision domain per switch port. This basically says that if you have 4 computers A/B/C/D on 4 switch ports, then A and B can transfer data between them as well as C and D at the same time, and they will never interfere with each others' conversations. That is the basic idea. In the case of a "hub" then they would all have to share the bandwidth, run in half-duplex and there would be collisions and retransmissions. Using a switch is called micro-segmentation - it allows you to have dedicated bandwidth on point to point connections with every computer and to therefore run in full duplex with no collisions.

Role of switches in networks

Network switch is a marketing term rather than a technical one. Switches may operate at one or more OSI layers, including physical,data link,network or transport .A device that operates simultaneously at more than one of these layers is called a multilayer switch, although use of the term is diminishing.

In switches intended for commercial use, built-in or modular interfaces make it possible to connect different types of networks, for example ethernet,fibre channel,ATM and 802.11. This connectivity can be at any of the layers mentioned. While Layer 2 functionality is adequate for speed-shifting within one technology, interconnecting technologies such as Ethernet and token ring are easier at Layer 3.

Again, "switch" is principally a marketing term; interconnection of different Layer 3 networks is done by routers. If there are any features that characterize "Layer-3 switches" as opposed to general-purpose routers, it tends to be that they are optimized, in larger switches, for high-density Ethernet connectivity.

In some service provider and other environments where there is a need for much analysis of network performance and security, switches may be connected between WAN routers as places for analytic modules. Some vendors provide firewall network and performance analysis modules that can plug into switch ports. Some of these functions may be on combined modules.

In other cases, the switch is used to create a "mirror" image of data that can go to an external device. Since most switch port mirroring provides only one mirrored stream, network hubs can be useful for fanning out data to several read-only analyzers, such as packet sniffers.

2008-02-20T00:48:00.000-08:00

Switching Elements
Responsible for the transport of data across a network - routing
May support congestion handling or quality of service mechanisms
Examples
routers - IP
switches - ATM or local area networks (e.g., Ethernet-802.3, token ring)
bridges, hubs - local area networks

Protocols
A protocol is a set of conventions that specifies the rules or parameters for communication between two entities (hosts, processes, switching elts, devices, etc).

Protocols specify conventions for:
The type, semantics, and format of information to be conveyed between entities
Establishing/closing connections or sessions
Routing across a network or internetwork
Flow control: speed matching between entities
Reliability: error detection, handling, correction
ABSTRACT
The problem of finding a minimum number of patterns to exercise the logic elements of a combinational switching net is investigated. Throughout, the word “testing” refers to exercising of this kind; or, equivalently, to fault diagnosis where each line of the net can be directly observed. Any set of permanent faults can be selected to test against, examples of which range from “stuck-at” faults (allowing the most economical test) to “any possible fault” (requiring the most complete test). The method used depends upon exact structural analysis rather than upon search algorithms or random pattern generation. The types of results presented appear to be fundamentally new. In particular, the maximum number of patterns required to test any one of an infinite class of nets is frequently found to be finite and extremely small. For example, any nontrivial connected tree of 2-input nand gates can be tested for “any possible fault” by exactly five patterns—no more and no less. The method in brief: Given a set F of switching functions and a set of required inputs for each (collectively denoted T), a “testing” function is defined for each element of F for each positive integer r. If the lines of a net can be mapped to the domain of the testing functions P(T, r) so that the gates perform consistent with these functions, we say the net “accepts” P(T, r)—and then r patterns are sufficient to test the net for T. Only nets in which each logic element is intended to realize the same switching function are discussed here. Trees (nets without fanout) are studied first, and the conditions under which a tree of identical gates “accepts” a partial function on an arbitrary domain is established. Then the common symmetric switching functions are separately investigated to find for each a minimum value of r such that all trees composed solely of the function accept P(T, r) (for various T). In most cases, as in the example given, the number of patterns required to test any such tree is extremely low. The conditions under which all nets (nontrees included) accept a set of partial functions with arbitrary domain are then established. These conditions are rarely met in practice, even where F consists of a single function. However, many subclasses of nets can be identified which require only a few patterns at most (depending on the function and the class of faults selected). These subclasses often contain nets of arbitrary size and complexity, and frequently consist of exactly those nets for which a related graph can be “colored” (i.e., h-node colored for some particular h) in the classical graph-theoretic sense. For example, any net of 2-input nand gates can be tested by five patterns if one of its related graphs is 2-colorable and another one is 3-colorable (!). The detailed results and methods used to obtain them are summarized, and in conclusion coloring problems and test construction are commented upon.
REFERENCES
Note: OCR errors may be found in this Reference List extracted from the full text article. ACM has opted to expose the complete List rather than only correct and linked references.

1
CHANG, H.Y., MANNING, E., AND METZE, G. Fault Diagnosis of Digital Systems Wiley- Interscience, New York, 1970.

2
HARARY, F. Graph Theory Addison-Wesley, Reading, Mass., 1969.

3
HORNBUCKLE, GARY D., AND SPXNN, R.N. Diagnosis of single-gate failuresin combinational circuits. IEEE Trans. EC-18, 3 (Mar. 1969), 216-220.

4
Kenneth E. Iverson, A Programming Language., John Wiley & Sons, 1962

5
KAUTZ, W H. Fault testing and diagnosis in combinational digital circuits. IEEE Trans. EC.17, 4 (Apr. 1968), 352-366.

6
MALING, K., AND ALLEN, E.L. A computer organization and programming system for automated maintenance IEEE Trans. EC-IP, 5 (Dec. 1963), 887-895.

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OaE, O. The Four-Color Graph Problem. Academic Press, New York, 1967.

8
POWELL, T. J A procedure for selecting d~agnostic tests IEEE Trans. EC-18, 2 (Feb. 1969), 168-175.
9
Donald L. Richards, Efficient Exercising of Switching Elements in Combinatorial Nets, Journal of the ACM (JACM), v.20 n.2, p.320-332, April 1973 [doi>10.1145/321752.321763]

10
RICHARDS, DONALD L. Test size and optimum detection in switching nets J. ACM (to appear).

11
ROTH, J.P. Diagnosis of automata failures: A calculus and a method. IBM J. Res. Devel. 10, 4 (July 1966), 278-291.

12
ROTH, J.P., BOURICIUS, W. G, AND SCHNEIDER, P.R. Programmed algorithms to compute tests to detect and distinguish between failures in logical circuits. IEEE Trans. EC-I6, 5 (Oct 1967), 567-580. {In addmon, consult IEEE Trans. EC-20, 11 (Nov. 1971).}
CITED BY

Donald L. Richards, Efficient Exercising of Switching Elements in Combinatorial Nets, Journal of the ACM (JACM), v.20 n.2, p.320-332, April 1973
INDEX TERMS
Primary Classification: G. Mathematics of Computing G.2 DISCRETE MATHEMATICS
Additional Classification: B. Hardware B.8 Performance and Reliability
General Terms: Design, Measurement, Performance, Reliability, Theory, Verification
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