Wireless Introduction
To Be Wireless
With the introduction of wireless LAN (WLAN), IP networks are now also available for those applications on which wired technologies are not suitable or no wired connectivity is available at all. The following are a few wireless use cases:
- Home ISP connectivity: Consumer products
- Building-to-building connectivity: Point-to-point and multipoint
- “Last mile” ISP connectivity: Rural Internet access
- Mobility applications: Car rental returns and parcel deliveries
- Enterprise network extension: Reduce, move, add, and change/mobile office environment
Although WLAN appears to be “just another LAN type/protocol,” the nature of wireless is to be a shared medium, and shared not only between a certain workgroup but also shared across the walls, across the building, and with your neighbor. On top of normal networking issues, WLAN adds a couple of new challenges, such as Layer 1 (radio frequency [RF]) issues; a set of L2 protocols, such as IEEE 802.11; and the need for agencies to regulate the use of this shared medium.
Layer 1: Radio Frequencies
Radio frequencies are high-frequency, alternating current (AC) signals that are radiated into the air through an antenna, creating radio waves. Radio waves propagate away from the antenna in a straight line in all directions at once, just like light rays from a bulb. More light bulbs spread around the room will provide better overall lighting. This translates into a stronger average signal for mobile clients. When radio waves hit a wall, door, or any obstruction, there is attenuation of the signal, which weakens the signal and can reduce throughput. The signal can also be reflected or refracted.
Industrial, Scientific, and Medical (ISM) Radio Bands
WLAN devices work in a frequency range (wavebands) that belongs to the industrial, scientific, and medical (ISM) radio bands. The ISM band was originally reserved internationally for the use of RF electromagnetic fields for industrial, scientific, and medical purposes other than communications. In general, communications equipment must accept any interference generated by ISM equipment.
- Within the ISM band, WLAN devices use wavebands as follows:
- Bluetooth 2450-MHz band
- HIPERLAN 5800-MHz band
- IEEE 802.11/WiFi 2450-MHz and 5800-MHz bands
Cisco WLAN technologies use the IEEE 802.11 range, which is what this book focuses on.
WLAN Organizations and Regulations
You should be familiar with the following WLAN organizations and regulations:
- FCC (Federal Communications Commission), www.fcc.gov: Regulates the use of wireless devices in the United States.
- ETSI (European Telecommunications Standards Institute), www.etsi.org: Chartered to produce common standards in Europe.
- IEEE (Institute of Electrical and Electronic Engineers), www.ieee.org: Creates and maintains operational standards.
- Wi-Fi Alliance, www.wi-fi.com: Promotes and tests for WLAN interoperability.
- WLANA (WLAN Association), www.wlana.org: Educates and raises consumer awareness regarding WLANs.
- CCX (Cisco Compatible Extensions): The CCX specification is for makers of 802.11 wireless LAN chips to ensure compliance with the Cisco proprietary WLAN protocols. For example, Cisco Lightweight Extensible Authentication Protocol (LEAP) and Extensible Authentication Protocol-Flexible Authentication via Secure Tunneling (EAP-FAST) are part of CCX.
IEEE 802.11 Standards and Protocols
802.11 Alphabet Soup
In June 1997, the IEEE finalized the initial standard for WLANs: IEEE 802.11. Each amendment has been published with a letter in addition to the 802.11. Those letters are often used to name features, data rates, and so on.
Here is a typical example: IEEE 802.11a defined operations in the 5-GHz band. The radio interface operating at 5 GHz is therefore called the “A radio.”
In 2007, the IEEE consolidated all amendments into a new 802.11 standard. Table 1-1 gives a summary of the standards in place at the time of this writing.
Table 1-1. IEEE 802.11 Standard Overview
|
Name |
Description |
Obsoleted By |
|
802.11 |
Original standard defining 1- and 2-Mbps 2.4-GHz RF and IR. All the following are amendments to this standard. |
802.11-2007 |
|
802.11a |
This standard defines Orthogonal frequency-division multiplexing (OFDM) 54-Mbps operation in the 5-GHz band. |
802.11-99 |
|
802.11b |
Enhancements to 802.11 to support 5.5 Mbps and 11 Mbps in the 2.4-GHz band. |
802.11-99 |
|
802.11c |
Defi nes bridging operations for 802.11. 802.11c has been included as a chapter in the 802.1D standard concerning wireless bridging. |
802.1D |
|
802.11d |
International roaming extensions. Adds a country fi eld in beacons and other frames. Adds countries not defi ned by the original standard. |
802.11-2001 |
|
802.11e |
Quality of service (QoS) features. Wi-Fi Multimedia (WMM) is a subset of 802.11e. |
802.11-2007 |
|
802.11F |
Set of recommendations (optional) defi ning the Inter-Access Point Protocol (IAPP) for exchanging client security context between access points (AP). This amendment was withdrawn in 2006. |
802.11-2003 |
|
802.11g |
Defines effective radiated power - OFDM (ERP-OFDM) modulation in 2.4 GHz, enabling 54 Mbps with backward compatibility with 802.11b. |
802.11-2003 |
|
802.11h |
Amendment for spectrum and transmit power management. It adds Dynamic Frequency Selection (DFS) to avoid radar in the 5-GHZ band as well as Transmit Power Control (TPC) to the 802.11a specifi cation. |
802.11-2007 |
|
802.11i |
Wi-Fi Protected Access (WPA) was an early subset of 802.11i, whereas Wi-Fi Protected Access 2 (WPA2) is the full 802.11i implementation. It defi nes Robust Security Network's (RSN), Advanced Encryption Standard (AES), and Temporal Key Integrity Protocol (TKIP) encryptions. |
802.11-2007 |
|
802.11j (2004) |
Amendment specific for regulation in Japan allowing use in the 4.9-GHz band. |
802.11-2007 |
|
802.11-2007 |
Currently the latest revision of the standard, including amendments for 802.11a through 802.11j (except for .11c and .11F). |
__ |
|
802.11k |
Proposed amendment that defi nes radio management. It will facilitate roaming in an Extended Service Set (ESS) by helping to choose the best access point available (load balancing). |
__ |
|
802.11l |
Reserved and will not be used. |
__ |
|
802.11m |
An ongoing task group charged with the maintenance of the standard. It periodically produces the revisions as well as clarifi cations and modifi cations. |
__ |
|
802.11n |
Amendment unleashing high speeds, Multiple Input Multiple Output (MIMO), 40-MHz channels, and many other features. |
__ |
|
802.11o |
Reserved and will not be used. |
__ |
|
802.11p |
Defines WAVE (Wireless Access for Vehicular Environment) for ambulances and other high-speed vehicles and a roadside infrastructure in the licensed band of 5.9 GHz. |
__ |
|
802.11q |
Not used, to avoid confusion with 802.1q VLAN trunking. |
__ |
|
802.11r |
This amendment is charged with ensuring fast roaming, even for vehicles in motion. It is supposed to reduce the roaming delay between two basic service sets (BSS) to less than 50 ms. |
__ |
|
802.11s |
This amendment will standardize mesh networks. |
__ |
|
802.11T |
This amendment regroups recommended practices to test and measure performance in wireless networks. Also called WPP (Wireless Performance Prediction). |
__ |
|
802.11u |
Proposed amendment to improve internetworking with external non-802.11 networks. The idea is to be able to specify services provided by a BSS, to allow access to the BSS depending on previous authentication with other networks, and to restrict access to the BSS. |
__ |
|
802.11v |
This amendment will enable confi guring clients while they are connected to the network. |
__ |
|
802.11w |
This amendment will bring protected management frames. It is supposed to be an add-on to 802.11i covering management frame security. |
__ |
|
802.11x |
Not used to avoid confusion with 802.1x. |
__ |
|
802.11y |
Allows operation in the 3650- to 3700-MHz band (licensed), allowing higher power and thus longer ranges. |
__ |
|
802.11z |
Direct Link Setup (DLS) allows two stations to communicate directly with each other. |
__ |