Page 240 - DCAP311_DCAP607_WIRELESS_NETWORKS

Wireless Networks

Notes provided an evolving, cooperative, scalable and interoperable networking standard. With line
speeds ranging from 10mbps to 1000mbps, Ethernet has attempted with fairly good success to
keep pace with the public demand for higher bandwidth. Twelve years ago the IEEE established
the 802.11 Working Group to create a wireless local area network (WLAN) standard. The
standard specified an operating frequency in the 2.4GHz band, which lay the groundwork for
this technology. In 1997 the group approved IEEE 802.11 as the first WLAN standard. Data rates
for 802.11 at that time were a mere 1 and 2 Mbps. Due to the disparity between the 1 to 2 mbps
WLAN and the current wired LAN with speeds of 10-100mbps, the committee quickly agreed
that more work needed to be done in this area, that is, a technology that was more scalable and
faster. The group began work on another 802.11 extension that would satisfy these future needs.
In 1999, the group approved two new extensions to 802.11 which were designed to work with
the existing 802.11 MAC layer, one being the IEEE 802.11a - 5GHz, and the other IEEE 802.11b
- 2.4GHz.
Wireless LANs, because of their broadcast nature, require the addition of:

z z User authentication to prevent unauthorized access to network resources
z z Data privacy to protect the integrity and privacy of transmitted data
The 802.11 specification stipulates two mechanisms for authenticating wireless LAN clients: open
authentication and shared key authentication. Two other mechanisms—the Service Set Identifier
(SSID) and authentication by client Media Access Control (MAC) address—are also commonly
used. This section explains each approach and its weaknesses. The use ofWired Equivalent Privacy
(WEP) keys can function as a type of access control because a client that lacks the correct WEP key
cannot send data to or receive data from an access point. WEP, the encryption scheme adopted by
the IEEE 802.11 committee, provides encryption with 40 bits or 104 bits of key strength.
Authentication in the 802.11 specification is based on authenticating a wireless station or device
instead of authenticating a user. The specification provides for two modes of authentication:
open authentication and shared key authentication. The 802.11 client authentication process
consists of the following transactions (Figure 1):
1. Client broadcasts a probe request frame on every channel
2. Access points within range respond with a probe response frame

3. The client decides which access point (AP) is the best for access and sends an authentication
request
4. The access point will send an authentication reply
5. Upon successful authentication, the client will send an association request frame to the
access point
6. The access point will reply with an association response
7. The client is now able to pass traffic to the access point

Figure 14.7: 802.11 Client Authentication Process

Source: http://www.cisco.com/warp/public/cc/pd/witc/ao1200ap/prodlit/wswpf_wp.pdf

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