B227 Lecture Overheads - Topic 4: Bridges

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High Speed LANs

Uses fiber optics or highly parallel copper wires

For faster transfer and longer distances

Fiber Distributed Data Interface (FDDI)

Used as a LAN, or as backbone for connecting bridges

Figure 4-44 p319

Token ring network at 100Mbps, up to 200km, up to 1000 stations.

There are multiple channels on a single fiber lines

Due to the large distances (200km) – too long to wait for token to circle the ring

Multiple tokens for the multiple channels

FDDI protocol is based on IEEE 802.5 (Token Ring), so the frame format is similar

Nomal channels are asynchronous (they transmit whenever they want, without worrying about the other channels).

Synchronous transmission also defined in FDDI– in case it needs to be used over PCM or ISDN lines.

Fast Ethernet

FDDI did not catch on as LAN, only as inter-LAN backbones.

IEEE extended the original 802.3 so that it can support data rates faster than the original 10Mbps.

New standard called 802.3u, or more commonly called Fast Ethernet.

Basic operation the same as 802.3, but has a faster bit time.

Remember that 802.3 uses Manchester encoding, which means to transmit one bit, we have a high voltage followed by a low voltage (or vice-versa). In 802.3, it is defined that this H-L change happens in 100nsec. In 803.3u, it is defined to happen in 10nsec. So in effect, we transmit the one bit 10 times faster.

Needs very reliable cables to support this faster bit time – category 5 twisted pairs or fibers.

Fast Ethernet support data rates of 100Mbps

High Performance Parallel Interface (HIPPI)

Figure 4-48 p 326

Originally designed as a data channel (how to move data from one master component to a slave component along dedicated wires with no switching – an example is between main memory and cache on a computer motherboard) rather than a LAN.

Uses a lot of twisted pair running in parallel to achieve high-throughput – can achieve 1600 Mbps.

Used mainly for interconnecting supercomputers.

Fibre Channel

HIPPI redesigned to use single fibers rather than 50-100 twisted pairs

Contains a very complex protocol structure (see Figure 4-49 p 327).

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