Information Technology Reference
In-Depth Information
Summary of WLAN Standards
Ta ble 5 - 2 summarizes WLAN standards, frequencies, and data rates.
Ta b l e 5 - 2
WLAN Standards Summary
IEEE
Protocol
Standard Release
Date
Frequency
Typical Data
Rate
Maximum Data
Rate
Legacy
1997
ISM
1 Mbps
2 Mbps
802.11a
1999
UNII
25 Mbps
54 Mbps
802.11b
1999
ISM
6.5 Mbps
11 Mbps
802.11g
2003
ISM
25 Mbps
54 Mbps
802.11n
2009
ISM or
UNII
200 Mbps
600 Mbps
Service Set Identifier
WLANs use a service set identifier (SSID) to identify the WLAN's “network name.” The
SSID can be 2 to 32 characters long. All devices in the WLAN must have the same config-
ured SSID to communicate. It is similar to a VLAN identifier in a wired network. The diffi-
culty in large networks is configuring the SSID, frequency, and power settings for
hundreds of remotely located access points. Cisco addresses this problem with the Cisco
Wireless Control System (WCS). WCS is covered in more detail in the “Cisco UWN Ar-
chitecture” section.
WLAN Layer 2 Access Method
The IEEE 802.11 Media Access Control (MAC) layer implements carrier sense multiple ac-
cess collision avoidance (CSMA/CA) as an access method. With CSMA/CA, each WLAN
station listens to see whether a station is transmitting. If no activity is occurring, the sta-
tion transmits. If activity is occurring, the station uses a random countdown timer. When
the timer expires, the station transmits. The difference from wired networks is that in
wired networks collisions are detected on the physical wire; hence CSMA/CD (collision
detection) is used.
WLAN Security
WLANs provide an effective solution for hard-to-reach locations and enable mobility to a
level that was previously unattainable. However, the reach of wireless beyond physical
connections and boundaries presents additional security concerns. Several standards have
been developed to address these security concerns. The Wired Equivalent Privacy (WEP)
security protocol, used in the IEEE 802.11b standard, is considered faulty and vulnerable
to numerous attacks. The 802.11b protocol is the most commonly deployed wireless proto-
col, and although WEP's flawed handling of the encryption key left it vulnerable to attack.
