Previous Table of Contents Next


LAN Standards and Standards Bodies

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:

  802.1: Architecture and Internetworking (High-Level Interface). Defines architecture layers and rules for interconnection of disparate LAN protocols. Includes data formatting, network management and internetworking.
  802.2: Defines equivalent of Logical Link Control services, including protocol for data transfer.
  802.3: Defines CSMA/CD Access Method and Physical Layer specifications.
  802.4: Token-Passing Bus Access Method and Physical Layer specifications.
  802.5: Token-Passing Ring Access Method and Physical Layer specifications.
  802.6: Metropolitan Area Network (MAN) Access Method and Physical Layer specifications. DQDB (Distributed Queue Dual Bus) is defined.
  802.7: Broadband Technical Advisory Group. Standards for definition of a broadband cable plant design. Established guidelines for LAN construction within a physical facility such as a building.
  802.8: Fiber Optic Technical Advisory Group. Established to assess impact of fiber optics and to recommend standards. Note that this standard is distinct from that of ANSI’s FDDI.
  802.9: Integrated Voice and Data Networks (Isochronous Traffic)
  802.10: Internetwork Security.
  802.11: Wireless.
  802.12: High-Speed LANs (e.g., 100VG-AnyLAN).

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:

  X.3T9-3: HPPI (High Performance Parallel Interface).
  X.3T9-5: FDDI (Fiber Data Distributed Interface).
Table 9.1 Dimensions of popular LAN 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

Life in the Fast LAN: The Need for Speed

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 technologies—especially voice and videoconferencing. Also users have became increasingly impatient, demanding faster response times. In general, LAN users mirror the times in which we live—more is better, bigger is better, and faster is better yet. Bandwidth of 10 Mbps, 16 Mbps and even 20 Mbps just doesn’t cut the mustard anymore! In response to this requirement, Fast LANs have been developed, offering bandwidth of 100 Mbps—soon to be 1 Gpbs. Fast LAN options currently include 100Base-T, or Fast Ethernet, and 100VG-AnyLAN.

100Base-T, or Fast Ethernet

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 Dell’Oro 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].


Previous Table of Contents Next