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Abstract -- TCP/IP on Gigabit Networks Network and Application Engineering Track
N5: High Speed Networking

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TCP/IP on Gigabit Networks

Wilson, Anne ( awilson@chernikeeff.co.uk)


The volume of traffic being offered to the Internet continues to increase. Many of the other presentations at this conference describe applications which will add to this volume. (Include pointers to other sessions, especially if there is one which gives statistics on traffic growth trends).

Currently the fastest communications in general widespread use are FDDI for the local area (100 Mbps) and T3 (45 Mbps) for the wide area. There is a great deal of marketing promotion and limited actual experience of the use of ATM at 155 Mbps for both local and wide area connections. My purpose is to discuss technologies which can be used to carry TCP/IP at 1 Gbps - as one possible view of the technologies in widespread use before the year 2000. Using combinations of fibre optic cable, amplification and electronic switching, gigabit speeds are achievable in local, campus and world wide networks. Technologies like HIPPI and fibre channel support 1 Gbps data streams over limited distances. SDH/Sonet is required for long distance multicarrier connections. By "gigabit networks", I mean sending data at approximately 1,000 Mbits/s (ie 10 times FDDI, or 1000 times conventional Ethernet speeds).


HIPPI is currently in widespread use as a connection method for supercom puters, normally at 800 Mbps. There are also HIPPI interfaces available for HP, DEC Alpha, SGI Indigo 2, RS 6000, and Sun workstations, and even a HIPPI card to fit into a PCI bus. There is a specification for HIPPI at 1600 Mbps, though this is rarely used. RFC 1374 specifies IP and ARP over HIPPI. The European Centre for Medium Range Weather Forecasting has documented 57 Mbytes/s (456 Mbps) transfer rates using a ver sion of ttcp between two Cray Research machines connected using an IP router over HIPPI. There are other connections to an IBM 3090, a Silicon Graphics Challenge, and RS6000 workstations. (This installation can be described to whatever level of detail required - network diagrams, packet formats, packet sequences, etc). Sample pricing for host interface cards and IP routers at June 95 can be provided.

HIPPI advantages

Technology has been in use for several years There is an established standard Excellent for transferring large volumes of data Maximum packet size is 64K bytes


One connection excludes any other traffic until first transfer complete Inefficient for small packet sizes On copper, maximum distance 25 meters. Connectors fragile. Serial HIPPI runs at much longer distances over fibre.

Fibre channel

Fibre channel is ANSI standard X3T11 for the physical and signalling interface. Also refer to the Internet Draft "IP and ARP on fibre channel" It is much more complex than HIPPI, having a connectionless, a connection oriented and a `mixed' mode. It can be used in `direct channel' mode, to support TCP/IP, or for peripheral connection, in a switched configuration, in a routed environment, or in a loop. `Quarter speed' fibre channel products are in use (at 266 Mbps) and 1 Gbps fibre channel host interface cards and switches will be available by June 95. One customer running TCP/IP between two RS6000s connected via a fibre channel switch at quarter speed measured a transfer rate of more than 125 Mbps using TCP/IP, at which point the bottleneck in the file transfer was the disk access speed of the RS6000s, not the network transfer rate. (By June I expect to have implemetation experience with fibre channel at 1 Gbps, both host interface cards and switches). Sample pricing valid at that date can be provided, and compared to HIPPI prices.


SDH and Sonet are similar but significantly different systems used for modern trunk digital communictions network infrastructures by long distance carriers. They offer substantial improvements over the PDH for sustainable service, given adequate network design, both because to the fundamental architecture (dual rings) and the SS7 signalling. In the UK the new carriers (Mercury Communications, Energis, Scottish Power, United Artists, Videotron) have installed it as they have built their infrastructures. BT are retrofitting it to their existing network. Certain customers have been already been able to have SDH connections at 155 Mbps installed on their premises. RFC 1619 specifies PPP encapsulation for IP over SDH/Sonet. If router manufacturers were to implement this, then it would be possible to use existing and developing IP routing and mulitcasting protocols (BGP4, DVMRP, PIM, and mobile IP) directly on the SDH framing. ATM then becomes just one of the many protocols which can be carried in IP. The SDH hierarchy starts at 155 Mbps, and goes up through 622 Mbps, to 2.4 Gbps.

ATM Equipment is available but very little of it is in actuall service use. Much of the necessary standardisation work has not been completed. Customers are beginning to realise that ATM is in a similar state to ISDN five years ago. ATM is specified at a range of speeds, the highest of which is 620 Mbps. Operated at this speed, there is a very substantial throughput loss due to overhead, giving an effective rate of approximately 450 Mbps - a long way short of 1 Gbps.

Conclusion : This has been a brief discussion of possible technologies for running IP at speeds higher that the currently widely available fast ethernet or 155 Mbps ATM speeds.