It has been a traumatic year or two for 3Com Corp with the company’s decision to abandon its network operating software and concentrate on its networking hardware – suggesting that the cobbler really should stick to his last, Novell Inc went in the reverse direction a year or so ahead of 3Com – but the company is back with a bang with very challenging new Ethernet adaptors using a chip that the company designed itself. Chris Rose has been looking into it.
3Com Corp has made an aggressive bid to regain its Ethernet market share with a new family of adaptors, the Etherlink III. The range is the first to use 3Com’s single-chip Ethernet controller chip, manufactured for the Santa Clara, California company by AT&T Microelectronics Inc – which has been saying it wants to get out of the semiconductor foundry business. The first member of the family is an AT board that marshals a number of techniques to squeeze the last drop of bandwidth from the network. Moreover, the single chip controller has enabled the company to offer the high-performance boards at UKP165 each, UKP150 each when you buy a five-pack. 3Com has bolstered its performance claims by commissioning bench tests from LanQuest Inc in the US and London-based GCO Communications Ltd. However, John Eliott, GCO’s manging director, says that the initial test results should be treated with some caution pending the arrival of NetWare server drivers, which will give a better idea of the speeds that the boards can deliver. Nonetheless, in a 25MHz 80386SX personal computer with no other devices attached to the network, GCO recorded a maximum throughput of 1,111K-bits per second, compared to Ethernet’s theoretical maximum of 1,250K-bits per second.
Parallel Tasking
3Com credits the speeds to what it calls its ‘Parallel Tasking Architecture’, a collection of techniques designed to get data on and off the computer bus as quickly as possible. Instead of treating receive and send operations as a set of discrete steps, the new adaptors can have part of a frame in main memory, while part of it is passing through the adaptor and the rest is out on the cable. The trouble with this approach is that timing is crucial between the board and the bus, and the two devices must be strictly synchronised. Key to speed of data reception is 3Com’s use of ‘predictive interrupts’. Conventionally, an adaptor board will wait until the whole packet arrives before sending an interrupt requesting that the CPU services the data. However, with the new board, the interrupt is sent as soon as the first few bytes of data are received, in the expectation that by the time that the processor gets around to answering, the rest of the data will have arrived. The problem for the adaptor and 3Com is working out how long the processor takes to respond to the interrupt – if it’s misjudged, the computer will either be ready to receive before the data has arrived, or alternatively, too late. Over and above the raw silicon, there is a fair amount of software embedded in the board which is self-tuned by probing the system environment to discover such things as whether the processor is 16-bit or 32-bit, the machine’s interrupt latency, and the effective throughput of its bus, and the same data is used to drive transmission of data at the top speed. On top of that, the company has included an Simple Network Management Protocol management agent in hardware. It can be imagined that second-guessing the machine in this way could lead to problems, and in particular, GCO’s Elliot points out that using an Etherlink III machine to host an asynchronous communications server or high speed modem could lead to data loss. But he says that 3Com pre-empts the problem at install time by asking the user to indicate the maximum speed of the modem. As for the much-vaunted speeds, LanQuest suggests that by using NetWare 3.11 drivers and Novell Inc’s Perform 3 bench test, the Etherlink III can produce throughputs 29% faster than the company’s existing Etherlink 16, 36% faster than Intel Corp’s EtherExpress/16, 25% faster than the Standard Mic
rosystems Corp Elite 16T, and 31% faster than Eagle Technology Inc’s NE2000T. Using LAN Manager drivers, the Intel board is only 21% slower, but the Standard Micro and Eagle ratings slump. Elliot is frankly surprised by the results and points out that Perform 3 is a configurable test, which can produce a variety of results.
Gut feeling
GCO has yet to carry out proper comparative tests, but Elliot says his initial gut feeling is that the 3Com boards are about 7% to 10% faster than the opposition. The new boards represent a strong bid by 3Com to halt the slippage in its Ethernet adaptor market share. Its pricing policy on the new boards means that it has broken the rules of being the market leader, where a company traditionally holds a price umbrella over competitors, and has relinquished its ‘good but pricey’ image. It also says that it is actively pursuing OEM agreements with major personal computer vendors and will license its parallel tasking design for adaptor-motherboard integration. The company says that an Etherlink III 32-bit EISA bus board will be ready for the fourth quarter of this year with a Micro Channel adaptor following on during the first half of 1993.
