The Wireless Challenge
What is WiFi?
WiFi, or Wireless Fidelity, is a term used to describe products that follow the 802.11 standards developed by the Institute of Electrical and Electronic Engineers (IEEE). However, today WiFi is used more broadly to refer to wireless local area networks (WLANs). WiFi products based on the 802.11 standard are primarily used to transfer data using radio frequencies (RF) in the 2.4 GHz and 5 GHz bands, thus eliminating the need for wires or cables. Wireless technology allows people to connect to the Internet and share data from any location, both inside or out, as long as they are within range of a base station (also known as Access Point).
WiFi includes technologies that adhere to the 802.11b, 802.11a and 802.11g standards. Products and technologies that operate at 2.4 GHz band, also known as 802.11b, can transfer data at 11 megabits per second. The 5 GHz band, also known as 802.11a, can transfers data up to 54 Mbps. Additionally, the new 802.11g standard is compatible with 802.11b and operates in the same 2.4 GHz band, but can transfer up to 54 Mbps like 802.11a.
Products displaying the WiFi logo have been certified by the WiFi Alliance as interoperable with a wide variety of other manufacturer's WiFi certified products www.weca.net. WiFi has become the commonly accepted global standard for wireless LANs.
WiFi is a wireless technology that allows for connections to the Internet from anywhere without wires, such as the couch at home, a bed in a hotel room or a conference room at work.
WiFi enabled computers send and receive data indoors and out; anywhere within the range of an Access Point. Best of all, WiFi is fast - several times faster than the fastest cable modem connection.
WiFi networks use radio technologies called IEEE 802.11b or 802.11a to provide secure, reliable, fast wireless connectivity. A WiFi network can be used to connect computers to each other, to the Internet, and to wired networks.
WiFi networks operate in the unlicensed 2.4 and 5 GHz radio bands, with an 11 Mbps (802.11b) or 54 Mbps (802.11a) data rate or with products that contain both bands (dual band), so they can provide real-world performance similar to the basic wired Ethernet networks used in many offices.
Large corporations and campuses use WiFi to extend standard wired Ethernet networks to public areas like meeting rooms, training classrooms and large auditoriums. Many corporations also provide wireless networks to their off-site and telecommuting workers to use at home or in remote offices.
Service providers and wireless ISPs use WiFi to distribute Internet connectivity within individual homes and businesses as well as apartments and commercial complexes. WiFi networks are also found in coffee shops, hotels, airport lounges and other locations where large crowds gather.
For more information about WiFi, visit the WiFi Alliance at www.WiFi.org.
Various kinds of radio-based networks
Single Radio Mesh
In a single radio mesh, each mesh node acts as an Access Point that supports local clients and also forwards traffic wirelessly to other mesh nodes. The same radio is used for access and wireless backhaul.
This approach requires that almost every packet generated by local clients must be repeated on the same channel in order to send it to at least one neighboring node in the mesh. The packet is then forwarded to another node in the mesh and ultimately to a node that is connected to a wired network.
This packet forwarding generates a lot of traffic. As you add more mesh APs, a higher percentage of the wireless traffic in any cell is dedicated to forwarding. Very little of the channel capacity is actually available to support users.
Also, in a single radio mesh architecture all clients and mesh nodes must operate on the same channel. As a result, the entire mesh ends up acting like a single, giant Access Point—all of the mesh nodes and all of the clients must contend for a single channel.
For this reason, single radio wireless mesh architectures don’t deliver enough capacity for broadband service and can’t scale. As you add more mesh nodes, the system capacity gets worse.
Single radio mesh networks are fine for free community networks where service expectations are low and ad-hoc networks where the emphasis is on basic connectivity. But they are not ideal for large broadband deployments.
Dual Radio Mesh
Infrastructure wireless mesh networks designed for large deployments should use mesh nodes built with multiple radios. The most basic multi-radio approach is the dual-radio mesh.
In a dual-radio mesh, the nodes have two radios operating on different frequencies. One radio is used for client access and the other radio provides wireless backhaul. The radios operate in different frequency bands so they can run in parallel with no interference.
In a dual radio wireless mesh the scaling problem encountered in single radio mesh designs is solved with mesh forwarding.
Since the mesh interconnection is done with a separate radio operating on a different channel, local wireless access capacity is not affected by traffic forwarding. However, there is still a scaling issue that limits capacity as the network grows. But in this design, the scaling problem is with the wireless backhaul.
In a dual-radio design, the wireless backhaul mesh is a shared network. With only one radio dedicated to backhaul at each node, all of the mesh nodes must use the same channel fairly in order to get backhaul connectivity and participate in the mesh. Parallel operation is not possible and most of the mesh APs hear multiple APs.
The APs must contend for the channel and they generate interference for each other. The result is reduced system capacity as the network grows.
Like a dual-radio wireless mesh, a multi-radio wireless mesh also separates access and backhaul, but it goes a step further in order to provide increased capacity, reliability and scalability.
Additional radios in each mesh node are dedicated to the wireless backhaul. The backhaul mesh is no longer a shared network. It is built from multiple point-to-point wireless links and each of the backhaul links operates on different independent channels.
When used as a backhaul in this fashion, the performance of a multi-radio mesh is similar to switched wired connections between the mesh nodes.
The mesh radios operate independently on different channels so latency is very low. There are only two nodes per link, so contention is very low. In fact, it is possible to run a customized protocol on the backhaul links that optimizes throughput in this simple contention free environment.
Performance in a multi-radio mesh is much better than the dual radio or single radio mesh approaches.
The mesh delivers more capacity and scales up as the size of the network is increased—as more nodes are added to the system, overall system capacity increases.
The purpose of a wireless mesh is to support WiFi clients and applications.
A multi-radio wireless mesh architecture is the only one capable of providing multiple, high-capacity networks that can be custom-configured to meet public and private service and application needs.
For example, in a metro multi-radio mesh deployment, one network can be dedicated to provide public high-speed Internet access. At the same time, other secure networks can support essential service communications for police, fire, and ambulance.
And a multi-radio mesh is the only one capable of delivering the network bandwidth to handle multiple simultaneous connections for high capacity data, voice and video services.
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