Local-Area Networks

The connection from a three-dimensional graphics workstation to high-speed WANs is most likely to come from a LAN. (Table 10-1 presents LAN capabilities.) Most LANs use Ethernet (10 Mbit/s), which is inadequate for the high-performance demands of VE and multimedia. Several companies have endorsed the proposal of standards for 100 Mbit/s Ethernet. In addition, through the use of switching hubs (which are collapsed backbones with gigabit-speed backplanes), a workstation can use all the bandwidth available on an Ethernet segment.

FDDI (Fiber Distributed Data Interface—100 Mbit/s) is used extensively in supercomputer centers. However, most host interfaces operate in the 20-50 Mbit/s range. A new standard for FDDI over unshielded twisted pair wiring should make FDDI more affordable for general computing. Unfortunately, both FDDI and Ethernet technologies are not ideal for isochronous data because there is no guaranteed data rate or prioritizing in the protocols. The American National Standards Institute (ANSI) has developed FDDI-II to address this problem by dynamically allocating bandwidth to isochronous applications. ANSI is working on FDDI Follow-On with plans for completion to be finished in the middle of the decade. FDDI Follow-On is likely to be designed for speeds up to 1.25 Gbit/s. In addition IEEE has established a working group that issued a final draft of a standard, the Integrated Services LAN Interface, which defines a LAN that carries voice, data, and video traffic over unshielded twisted pair wires.

The high-performance parallel interface (HPPI) is an ANSI standard supporting 32 and 64 bit interfaces that run at rates of 800 and 1,600 Mbit/s, respectively. It is a switched architecture and operates over a distance of 25 m on copper cables connecting supercomputers and their peripheral devices. A serial version of HPPI for fiber optic cables has been proposed to extend the range to 10 km. The NREN Casa test bed researchers from

TABLE 10-1 Local Area Network (LAN) Capabilities

LAN Technology

Capacity Mbit/s

Year of Final Standard

Status

Ethernet

10

1985

In use

FDDI

100

1989

In use

HPPI

800/1600

1992

In use

Fiber Channel

132.8 - 1064.2

1993

Some products available

ATM

45-622

1993

Some products available

FDDI-FO

1250

Approx. 1995

Not available



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