Abstract

Are PC LANs Ready for ATM?

This September 1994 Data Communications lab test, conducted by Kevin Tolly of The Tolly Group and David Newman of Data Communications, examined whether PC-based LAN environments were ready to take advantage of Asynchronous Transfer Mode (ATM) at the desktop. The article focused on a key question of the period: even if ATM switches could deliver very high throughput and low latency, could mainstream PC operating systems, network clients, and adapters make practical use of ATM connections in real workgroup environments?

The lab evaluated Fore Systems’ ASX-200 ATM switch and ForeRunner ESA-200PC adapter cards. The publication invited 10 vendors to participate: Allied Telesis, Chipcom, Digital Equipment Corp., Fore Systems, Galcom, Hughes LAN Systems, Newbridge Network, Network Systems, SynOptics Communications, and Xyplex. At the time of testing, however, only Fore Systems could supply both an ATM switch and PC adapter cards for the evaluation. The test environment included Fore’s ASX-200 switch, ESA-200PC EISA adapters, Windows NT-based PCs, and Hewlett-Packard ATM analysis equipment.

The results showed that ATM switch performance itself was not the limiting factor. The Fore ASX-200 delivered extremely low latency, adding approximately 9 microseconds on a 100Mbit/s Taxi interface and approximately 6 microseconds on a 140Mbit/s Taxi interface. In a multisegment configuration designed to emulate traffic crossing four ATM switches, aggregate delay remained only about 36 microseconds. Cell jitter was also minimal. The article noted that the ASX-200 could operate at wire speed on its Taxi interfaces and that raw throughput was not the principal concern for most PC LAN applications of the time.

The primary obstacle was software maturity at the end station. Windows NT was the only PC operating system in the test that supported Fore’s adapter, and even then the available client drivers and beta software limited broader application testing. NetWare access depended on additional software rather than native ATM support, and common desktop operating environments such as DOS/Windows lacked practical ATM driver support. The lab found that ordinary LAN applications could communicate across the ATM network when LAN emulation was used, but the benefits were constrained by operating-system support, adapter drivers, and application behavior.

Overall, the article concluded that ATM switching technology was technically impressive and ready to deliver very low-latency backbone and campus-network services, but PC LANs were not yet fully ready for ATM at the desktop. The limiting factors were not the ATM switch fabric or link speeds, but immature client software, limited operating-system support, and the complexity of integrating ATM into existing NetWare, IP, IPX, NetBIOS, and SNA-oriented LAN environments.