Content Overview Compared to wired
LANs, wireless LANs (WLANs) have unique characteristics. First,
the physical characteristics of a wireless LAN introduce range
limitations and unreliable media, dynamic topologies where
stations move about, interference from outside sources, and the
inability for every device to ‘hear’ every other device within
the WLAN. From the point of view of WLAN scalability, this
module covers two key considerations concerning the scalability
of wireless networks: QoS and security. In the past, WLANs
handled the transport of low-bandwidth, data application
traffic. Today, with the expansion of WLANs into enterprise and
vertical (retail, finance, education) markets, WLANs are now
used to transport high-bandwidth, intensive data applications
in conjunction with time-sensitive multimedia applications.
This requirement has led to the necessity for wireless QoS.
This module begins by describing how Cisco has met the
challenges of QoS deployment in WLANs. With increased reliance
on WLANs, businesses are becoming more concerned about network
security. Network managers need to provide end users with
freedom and mobility without offering intruders access to the
WLAN or the information sent and received on the wireless
network. The rest of this module describes wireless security
standards and the importance of wireless LAN (WLAN) security.
It also defines and describes the 802.1x standard and various
authentication processes. The module concludes with a
description of basic WLAN management and configuration tasks
using the Cisco Wireless Control System (WCS). Web
Links Is Your WLAN Ready for Voice?
http://www.cisco.com/en/US/netsol/ns340/ns394/
ns348/networking_solutions_white_paper0900ae
cd80472e80.shtml Design Principles for Voice Over
WLAN
http://www.cisco.com/en/US/netsol/ns340/ns394/
ns348/networking_solutions_white_paper0900ae
cd804f1a46.shtml The Benefits of Centralization in Wireless
LANs
http://www.cisco.com/en/US/products/ps6108/
products_white_paper0900aecd8040f7b2.shtml Understanding the
Lightweight Access Point Protocol (LWAPP)
http://www.cisco.com/en/US/netsol/ns340/ns394/
ns348/ns337/networking_solutions_white_paper09
00aecd802c18ee.shtml The Benefits of Centralization in
Wireless LANs
http://www.cisco.com/en/US/products/ps6108/
products_white_paper0900aecd8040f7b2.shtml Addressing
Wireless Threats with Integrated Wireless IDS and IPS
http://www.cisco.com/en/US/products/hw/modules/
ps2706/products_white_paper0900aecd804f155b.shtml Five Steps
to Securing Your Wireless LAN and Preventing Wireless
Threats
http://www.cisco.com/en/US/netsol/ns340/ns394
/ns348/ns386/networking_solutions_white_paper09
00aecd8042e23b.shtml Wireless LAN Security White
Paper
http://www.cisco.com/en/US/netsol/ns340/ns394
/ns348/ns386/networking_solutions_white_paper09
186a00800b469f.shtml Security of the WEP algorithm
http://www.isaac.cs.berkeley.edu/isaac/wep-faq.html Cisco
Wireless Control System (WCS)
http://www.cisco.com/en/US/products/ps6305/
products_data_sheet0900aecd802570d0.html User Guide for the
CiscoWorks WLSE and WLSE Express 2.13
http://www.cisco.com/en/US/products/sw/
cscowork/ps3915/products_user_guide_book
09186a008061ab4f.html Cisco Wireless Control System
Configuration Guide, Release 4.0
http://www.cisco.com/en/US/products/ps6305/
products_configuration_guide_book09186a008
06b57ec.html
Content 6.1
Implementing WLAN QoS 6.1.1 A Standard for
WLAN QoS WLANs, whether they are overlays to or substitutes
for traditional wired LANs, are based on standard 802.11. The
802.11 standard extends 802.3 to the wireless domain, though
with some complications. Figure depicts a typical WLAN
extension to a wired LAN and highlights areas that require
special consideration: - Both WLANs and wired LANs
define the physical and data link layers and use MAC
addresses.
- LANs and WLANS use many of the same
protocols and applications. Examples of such protocols are the
IP and IPsec protocols for VPNs. Examples of applications are
web, FTP, and Simple Network Management Protocol (SNMP).
- WLANs use carrier sense multiple access with collision
avoidance (CSMA/CA) technology instead of the carrier sense
multiple access with collision detection (CSMA/CD) technology
that Ethernet LANs use. Collision detection is not possible in
wireless applications because a sending station cannot receive
at the same time that the station is transmitting and,
therefore, cannot detect a collision. Wireless 802.11 LANs try
to avoid collisions instead of dealing with them after the
fact, as is the case in 802.3. Wireless 802.11 uses a
Distributed Coordination Function (DCF) to avoid collisions
with the use of radio frequency (RF) carrier sense, interframe
spacing, and random wait timers to avoid collisions.
-
LANs commonly use Layer 3 differentiated services code point
(DSCP) or Layer 2 802.1p to ensure priority and provide quality
of service (QoS). WLANs can use 802.11e. The original 802.11
standards aimed to provide best effort data communication
without QoS support. The new 802.11e standard is an extension
of 802.11 that provides more consistent, quality RF
transmission for voice and video.
- 802.11 devices
operate either in a peer-to-peer fashion or integrated with an
existing wired LAN.
- 802.11 devices often operate
within overlapping 802.11 WLANs.
- The mobility
requirements of 802.11 devices must be met if operation from
moving vehicles is to be considered.
- 802.11 must