Owner: ieee80211b URL:http://www.ieee80211b.blogspot.com Join Date: Fri, 07 Mar 2008 13:43:02 -0600 Rating:0 Site Description: IEEE 802.11b Wireless LANs Site statistics:Click here
What’s New in Wireless LANs: The IEEE 2008-03-05 10:33:00 A wireless LAN (WLAN) is a data transmission system designed to provide location-independent network access between computing devices by using radio waves rather than a cable infrastructure. In the corporate enterprise, wireless LANs are usually implemented as the final link between the existing wired network and a group of client computers, giving these users wireless access to the full resources and services of the corporate network across a building or campus setting. WLANs are on the verge of becoming a mainstream connectivity solution for a broad range of business customers. The wireless market is expanding rapidly as businesses discover the productivity benefits of going wire-free. According to Frost and Sullivan, the wirelessLAN industry exceeded $300 million in 1998 and will grow t Read more:Wireless
The 802.11 Physical Layer 2008-03-05 10:16:00 The three physical layers originally defined in 802.11 included two spread-spectrum radiotechniques and a diffuse infrared specification. The radio-based standards operate within the2.4 GHz ISM band. These frequency bands are recognized by international regulatory agencies, such as the FCC (USA), ETSI (Europe), and the MKK (Japan) for unlicensed radio operations. As such, 802.11-based products do not require user licensing or special training. Spread-spectrum techniques, in addition to satisfying regulatory requirements, increase reliability, boost throughput, and allow many unrelated products to share the spectrum without explicit cooperation and with minimal interference. Figure 2. Infrastructure ModeThe original 802.11 wireless standard defines data rates of 1 Mbps and 2 Mbps via radio Read more:Layer
The 802.11 Data Link Layer 2008-03-05 09:54:00 The data link layer within 802.11 consists of two sublayers: Logical Link Control (LLC) and Media Access Control (MAC). 802.11 uses the same 802.2 LLC and 48-bit addressing as other 802 LANs, allowing for very simple bridging from wireless to IEEE wired networks, but the MAC is unique to WLANs.The 802.11 MAC is very similar in concept to 802.3, in that it is designed to supportmultiple users on a shared medium by having the sender sense the medium before accessing it. For 802.3 Ethernet LANs, the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol regulates how Ethernet stations establish access to the wire and how they detect and handle collisions that occur when two or more devices try to simultaneously communicate over the LAN. In an 802.11 WLAN, collision detectio Read more:Layer
Support for Time-Bounded Data 2008-03-05 09:36:00 Time-bounded data such as voice and video issupported in the 802.11 MAC specificationthrough the Point Coordination Function (PCF).As opposed to the DCF, where control is distributedto all stations, in PCF mode a singleaccess point controls access to the media. If aBSS is set up with PCF enabled, time isspliced between the system being in PCF mode and in DCF (CSMA/CA) mode. Duringthe periods when the system is in PCF mode, the access point will poll each station for data, and after a given time move on to the next station. No station is allowed to transmit unless it is polled, and stations receive data from the access point only when they are polled. Since PCF gives every station a turn to transmit in a predetermined fashion, a maximum latency is guaranteed. A downside to PCF is that it is Read more:Support
Mobility 2008-03-05 08:16:00 While 802.11b defines how a station associates with APs, it does not define how APs Figure 6. Mobile IPtrack users as they roam about, either at Layer2 between two APs on the same subnet, or atLayer 3 when the user crosses a router boundarybetween subnets.The first issue is handled by vendor-specificinter-AP protocols, which vary in performance.If the protocol is not efficient, there is a chance of packets being lost as the user roams from access point to access point. Eventually WECA and the IEEE are likely to create standards in this area.The second issue is handled by Layer 3 roaming mechanisms. The most popular of these is Mobile IP (Figure 6), which is currently known as RFC 2002 in the InternetEngineering Task Force (IETF). Mobile IP works by having an access point assigned asthe “ Read more:Mobility
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