Ethernet vs. ATM coming down to the wire.

The formula was supposed to be different, but both LANs and WANs have found a less expensive alternative to answer the demand for speed.

By now, asynchronous transfer mode (ATM) was supposed to have been corporate America's high-speed service of choice for both local and wide area networks, providing a seamless enterprise network from desktop to desktop.

However, the simplicity and cost-effectiveness of Fast Ethernet has deferred widespread implementation of ATM for LANs, and the emergence of Gigabit Ethernet could delay it even more.

As for wide area networks, the unexpected success of frame relay service has forestalled ATM from its anticipated dominance of corporate backbones. Given the recently announced upgrade of frame relay service to speeds well beyond T1, ATM's pre-eminence may have to wait until the new millennium.

SUCCESS STORY

When frame relay debuted in the early 1990s as a souped-up version of the X.25 packet-switched service, few could have foreseen its phenomenal success. During the last two years, in particular, frame relay has taken off as a less-expensive alternative to leased-line, point-to-point networks.

In 1995, carrier revenues from frame relay service exceeded $500 million, according to Forrester Research of Cambridge, Mass. Forrester expects revenues to grow by 1,000% by the year 2000.

One reason for the success is the widespread availability of frame relay service. When a frame relay point of presence (POP) is close to a corporate site, it cuts down the cost of the leased circuit needed for the connection. Today, most areas of the United States are served by frame relay POPs.

Service interoperability is not an issue because vendors and service providers have cooperated in an unprecedented manner to establish a complete set of frame relay standards.

Also, the cost of the frame relay access devices (FRADs) has dropped dramatically as the market has grown. The once costly units, which are needed to connect devices and networks into the frame relay service, are now available for less than $1,000, making frame relay networks feasible for smaller companies and those with several branch offices.

Frame relay service can cut the cost of private line networks by 50% or more. It also allows managers to optimize their network topologies by utilizing the carrier service to aggregate and route circuits between various locations. Instead of dedicating a leased line to a distant site for each application, for example, you can share multiple applications on a single access line and have the frame relay service route several virtual circuits to numerous distant locations.

Service providers require you to specify both an average or minimum bandwidth, known as the committed information rate (CIR), and a maximum port speed into the frame relay network. The service provider guarantees the CIR, but allows you to burst to the maximum port speed when needed. However, the carrier makes no guarantee that traffic beyond the CIR will be delivered. If the frame relay network is congested, it may drop the extra traffic. (For more on CIR and frame relay, see "Their masters' voices (over frame relay)" in January's CN, or at www .comnews. com.)

Frame relay service used to top out at T1I speeds of 1.544 Mb/s. LDDS World-Com first broke the barrier, offering service at 6, IO, and 19.8 Mb/s. MCI recently rolled out service with speeds to 12 Mb/s, and Sprint says it will offer speeds to 45 Mb/s by mid-year. Ameritech, US West, and Pacific Bell are also launching 45-Mb/s frame relay service.

MCI's service is available from nearly 500 access points in the continental U.S., priced from $2,268 a month for a 2.688-Mb/s port to $5,268 for 12.288-Mb/s access. Circuit and CIR charges run from $240 to $1,400 for a T1 rate, and from $750 to $2,100 for the service's top CIR rate of 10.752 Mb/s.

SNA GROWTH FACTOR

AT&T's position on frame relay is a little more difficult, given its huge income from private lines. However, it recently took the plunge, pushing up private line prices between 3% and 10% while trimming frame relay rates by about 7%.

AT&T went one step further by announcing two managed services to help users move their SNA traffic from private lines to frame relay. The services are based on AT&T-installed FRADs, which assemble packets from legacy SNA and bisynchronous traffic into data frames tailored for frame relay transport.

Under one option, users can ship legacy traffic to an AT&T POP, where the carrier performs the required conversions. Alternatively, the carrier will install FRADs on the customer premises to consolidate legacy SNA and LAN-to-LAN traffic onto the frame relay network.

Other carriers are also making aggressive moves to lure AT&T private line customers who want to migrate their SNA applications to frame relay. Sprint already offers a managed FRAD service, and MCI was close behind AT&T in unveiling its own Enterprise WAN Managed Frame Relay Service. With this service, MCI will set up and manage the frame relay network. It will also provide and manage the FRADs at customer sites.

SNA traffic is expected to account for a large part of frame relay's future growth. Frame relay has already been able to capture the bulk of inter-LAN traffic because of the efficient way it handles the bursty characteristics of LAN applications. Until now, though, network managers have been hesitant to feed SNA traffic over frame relay for fear of compromising mission-critical business applications.

It's estimated that less than 5 % of SNA traffic currently flows over frame relay networks. Those that use frame relay, however, are realizing such savings that the vast majority of companies are expected to support both SNA and LAN traffic over frame relay within the next couple of years.

Besides the savings in line costs, frame relay can bring significant performance gains for SNA users. That's because frame relay eliminates the shared multidrop lines and associated polling that occurs over the wide area network. With frame relay, polling still occurs, but it is handled by on-premises FRADs, which fool the local devices into thinking they are being polled by a remote host.

SNA over frame relay does require more administration and the FRADs are more expensive, running from $1,500 to $4,000 at the remote site and $20,000 or more at the central site. However, the line savings are such that they can pay for the equipment in less than a year.

VOICE TRAVELS FREE

Some organizations are achieving additional savings by carrying voice traffic over frame relay along with the data. The technology is fairly new but, true to form, the standards-setting body for frame relay, the Frame Relay Forum in Foster City, Calif., has been working on a standard for years. It is expected to approve a quality-of-service (QOS) specification soon that will enable carriers to transport delay-sensitive voice traffic smoothly over frame relay. Sprint plans to include the QOS feature in its frame relay service later this year.

To prepare for the future, the Frame Relay Forum has also been working with the ATM Forum to ratify a set of inter-networking standards for the two high-speed services. Most major switch vendors already support the standards, or plan to, so users can rest comfortably knowing that they can protect their investment in frame relay and migrate easily to ATM when the need arises.

Data communications consultant Morris Edwards is program chairman of the Network Computing Solutions Conference and exposition, or NetCom, to be held March 26-27 in Ft. Lauderdale, April 2-3 in Chicago, and April 16-17 in Atlanta.