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Standards developed by the IEEE (Institute of Electrical and Electronics Engineers) have largely governed the world of LANs since the formation of Project 802 in February 1980. Project 802, working within the scope of the OSI reference model, was chartered to deal with the two bottom layers. Notably Layer 2, the data link layer, was divided into two subgroups, Media Access Control (MAC) and Logical Link Control (LLC) [9-2]. The initial focus was on Ethernet, with the first recommendation being finalized in December 1982. That first release of the three standards were accepted by the IEEE membership, the U.S. National Bureau of Standards and the ECMA (European Computer Manufacturers Association). Correlating international standards were issued by the ISO (International Standards Organization). The ISO standards are known as 8802 LAN Standards.
Since that time, the IEEE has continued to develop a broad range of LAN and MAN standards. IEEE standards include the following:
In addition to the IEEE, other standards bodies are involved in the establishment and promotion of certain LAN and computer networking standards. ANSI (American National Standards Institute), for example, developed the following standards:
ETHERNET | IBM TOKEN RING | FDDI | |
---|---|---|---|
Standard | IEEE 802.3 | IEEE 802.5 | ANSI X3T9-5 |
Logical Topology | Bus | Ring | Ring |
Physical Topology | Bus, Star | Ring, Star | Dual Ring, |
Dual Bus | |||
Media | Coax, UTP, STP | Coax, UTP, STP | Fiber |
Transmission Mode | Baseband | Baseband | Baseband |
Bandwidth | 10 Mbps | 4, 16, 20 Mbps | 100 Mbps |
Media Access Control | Non-Deterministic: | Deterministic: | Deterministic: |
CSMA/CD, CSMA/CA | Token-Passing | Token-Passing | |
Traffic Type | Data | Data | Data, Video, Voice |
During the past few years, traditional LANs have been pushed to their limits. More workstations and more active users have resulted in more LAN traffic. Increased use of graphics and other bandwidth-intensive applications have increased LAN traffic. Collaborative computing increased the demands on existing LAN technologiesespecially voice and videoconferencing. Also users have became increasingly impatient, demanding faster response times. In general, LAN users mirror the times in which we livemore is better, bigger is better, and faster is better yet. Bandwidth of 10 Mbps, 16 Mbps and even 20 Mbps just doesnt cut the mustard anymore! In response to this requirement, Fast LANs have been developed, offering bandwidth of 100 Mbpssoon to be 1 Gpbs. Fast LAN options currently include 100Base-T, or Fast Ethernet, and 100VG-AnyLAN.
A variation of 10Base-T, and standardized as IEEE 802.3u (June 14, 1995), 100Base-T is a high-speed LAN standard, that uses CSMA/CD and operates at 100 Mbps through an Ethernet switching hub. Multiple 10 Mbps connections are supported through multiple ports on the switch. Cat 3, 4, or 5 UTP can be used in 4-pair configuration; Cat 5 UTP is generally used for a maximum LAN diameter of 500 meters. Three pairs are used for transmission, with the fourth pair used for signaling and control (CSMA/CD) in half-duplex mode [9-28]. Connections to nodes, servers and other switching hubs are provided at 100 Mbps, supporting 10 10-Mbps channels. The 100 Mbps media include fiber (up to 30 miles or 50 Km without repeaters) and Cat 5 UTP at 100 meters. Full duplex transmission is supported by some manufacturers, yielding a theoretical total bandwidth of 200 Mbps [9-29]. Ethernet, however, is collision-prone; 100 Mbps of theoretical bandwidth may yield only 58 Mbps throughput. 100Base-T seems destined for greatness, given the huge installed Ethernet base. Additionally, the cost per port for 10Base-T and 100Base-T hubs has decreased over the past year from an average of $632 in October 1995 to $428, according to the DellOro Group [9-30]. Fast Ethernet workstation adapters are now priced as low as $150, compared to approximately $75 for conventional 10-Mbps adapters [9-31].
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