Wi-Fi Technology

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

1. 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.

2. 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.

1. 802.11n - bandwidth speeds up to 600 Mbps (2009).

2. 802.11g - bandwidth speeds up to 54 Mbps.

3. 802.11b - bandwidth speeds up to 11 Mbps.

4. 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:

1. The distance and power of the signal.

2. The topology including the user location.

3. The bandwidth needs.

4. The services offered.

5. 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:

1. European Telecommunications Standards Institute (ETSI) [9]

2. Institute of Electrical and Electronics Engineers (IEEE) [10]

3. 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

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:

1. Point-to-point
2. Point-to-multipoint or Multipoint-to-point, and
3. Multipoint-to-multipoint,
4. 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

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

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.