Wireless Networking

Table of Contents

1. About the IEEE 802.11 Standards
2. When to Use 802.11 Wireless
2.1. Mobile or Roaming Networks
2.2. LAN-Size Networks
2.3. Directional Links
2.4. Backup Links
3. When Not to Use 802.11 Wireless
3.1. Reliability
3.2. Security
4. Interference and Absorption
4.1. Interference Robustness
4.2. RTS/CTS
5. Configuring Access Points
5.1. Resetting Access Points to a Factory Defaults
5.2. IP Settings
5.3. ESSID / SSID
5.4. Channel
5.5. WEP Settings
5.6. WPA
5.7. Bridging or NAT
5.8. Port forwarding for NAT
5.9. Offer Addresses Using DHCP
5.10. Access Control
5.11. Less Common and Non-Standard Features
5.12. SNMP Authentication Traps
5.13. Syslog
5.14. Broadband Router/Wireless Combos
5.15. Multicast Rate
6. Locating Access Points
7. Assessment

Note

You are supposed to read the lab sheets before starting this lab. If you have done so, jump directly to Section 5, “Configuring Access Points” to start configuring a wireless access point. By the way, VirtualBox is not used for this lab.

What we are aiming for in this lab is to give you some experience configuring and using wireless networking, and give you an understanding of its benefits and limitations. This should be useful to you in developing or understanding a wireless network solution. You should be able to directly use the knowledge gained in this lab to set up a simple home wireless network.

1. About the IEEE 802.11 Standards

There are multiple varieties of 802.11 standards. Here are the most common standards you will need to know about, in the order they were released to the market. The letter indicates the time order in which the design of the particular standard began.

802.11b

At a theoretical maximum of 11Mbps, the 11b standard is the one that started to capture the market, due largely to the success of Apple’s Airport.

802.11a

The first of the 54Mbps standards, the 11a series uses a much higher frequency, in the 5GHz ISM (Industry, Scientific & Medical) band. There are three unlicenced bands. 2.4Ghz is the most common.

This means there is less interference with other consumer devices, giving better performance, since most other consumer devices use the 2.4GHz frequency. However, because of its shorter wavelength, it is affected by obstacles to a greater degree, and uses more battery power when transmitting. Also, because of the different frequency, different antennas must be used, which is a major pitfall of 802.11a, due to the upgrade cost from 802.11b.

Shortly after 11a was released, 11g was released, which is now the de facto 54Mbps standard. Most cards you buy new are B and G compatible. Some cards are tri-mode (dual-band), which means that can do all of B, A and G, but are more expensive.

802.11g

The defacto 54Mbps standard, this runs at 2.4GHz, and, like its 11a cousin, runs at a theoretical maximum of 54Mbps, though is not quite as high-performance. Because it runs in the 2.4GHz ISB band it, like 802.11b, is susceptible to interference from devices such as Bluetooth devices, various cordless phones (not cell-phones) and microwave ovens. In order to support 11b clients, 11g access points can slow the network down to 11Mbps when an 11b client is present. To avoid this, a network can be made exclusive, meaning only 11g clients can connect.

802.11n

802.11n is an enabling technology for wireless multimedia, particularly for HD (High Definition) video. Some of the associated WiFi standards such as WiFi MultiMedia (WMM), which provides performance guarantees for multimedia, and the up-and-coming WiFi Voice-Personal, which can be seen as a refinement of WMM for very low-jitter traffic for WiFi handsets, signal the readyness and acceptance of the use of WiFi for real multimedia delivery, and the performance levels associated with that.

802.11n introduces numerous innovations to achieve performance roughly five times that of 802.11g. Consistent numbers for throughput of the standard are hard to find and not particularly meaningful, because some of these innovations may not be suitable or applicable in particular deployments.

The first innovation that 802.11n brings is that it can use both the 2.4GHz and 5GHz frequency bands. To co-operate with other WiFi deployments, typically for transition periods, a 802.11n access-point may be configured not to use a particular band.

Related to this is the second technique, which standardises a practice already seen from some vendors[20] such as D-Link’s Turbo range of products, whereby twice as many channels are used. So 802.11n can use 40MHz channels in the 5GHz band instead of the 20MHz channels that have been used previously and will still be used in the 2.4GHz band. This feature is commonly called Channel Bonding

You will find many 802.11n devices easy to recognise because they will typically (not always) have perhaps three antennas; this is used for something called MIMO (Multiple Input Multiple Output). MIMO takes advantage of spatial multiplexing to send two different frames at the same time, thus doubling the throughput. Previously, signals experienced interference by reflections off things like metal furniture; this was called multi-path inteference: 802.11n turns this liability into an asset and manages to actually use multi-path to its advantage. We can therefore expect better performance indoors compared to outdoors; opposite to what we would expect with previous WiFi technologies.

All of these added features come with a cost of extra power draw, which can cause problems in enterprise environments where the access-point is powered using IEEE 802.3af Power over Ethernet (POE). Enterprises will have some other considerations to make as well. 802.11n: Enterprise Deployment Considerations from the Burton Group gives a good overview of the issues that an Enterprise should consider when moving to 802.11n. The same report is also the source for the following comparison. Remember though, that 802.11n performance depends on a number of factors; some of the numbers will depend very much on equipment and environment, and these 802.11 numbers are “theoretical maximums”.

Table 1. Comparison of Different Wi-Fi Protocols

 802.11b802.11g802.11a802.11n
Maximum signaling rate11Mbps54Mbps54Mbps300Mbps[a] ; up to 600Mbps[b]
Operating frequency band2.4GHz2.4Ghz5GHz2.4GHz & 5GHz
Range100 m100 m100 m150 m[c]
Non-overlapping channels (varies by country)33233 (2.4GHz), 23 (5GHz)
Interference sourcesBluetooth, microwave ovens, baby monitors etc.Same as 802.11bCordless phonesSame as 802.11b/g at 2.4GHz. Same as 802.11a at 5GHz.
Standard approvedYesYesYesYes
WiFi CERTIFIED™YesYesYesYes

[a] Assumes 40MHz channel and 2×2 MIMO

[b] Assumes 40MHz channel and 4×4 MIMO

[c] Assumes 50% range improvement over 802.11g/a


For further authoritative information of what makes 802.11n different, I strongly encourage you to read a whitepapeg (registration required) released by the Wi-Fi Alliance on Wi-Fi CERTIFIED™ 802.11n Draft 2.0: Longer-Range, Faster-Throughput, Multimedia-Grade Wi-Fi® Networks



[20] It is useful to realise that standards are simply a means of codifying existing practice.