Tips and tales from the frame relay trenches

Paul Robideux didn't think frame relay could blow up his SNA controllers, but one day it did. Bruce Thatcher didn't know frame relay could make a company's 800 budget soar, but he discovered it can. Robert Nebiker didn't believe he could justify a frame relay connection at a small branch office, but he learned how to do just that.

So it goes in frame relay, in which soaring demand along with a shortage of high-capacity circuits and the shifting economics of local access are changing the game for carriers and users. As a result, some users are making crucial network design mistakes, while others are learning new new ways to help them get the most from frame relay.

Many users who have been told for years they can save money by minimizing the committed information rate (CIR) on their permanent virtual circuits (PVC) - because they can always burst traffic up to the port speed - now find they now have to reverse field.

For example, Robideux, information services manager for Miami-based distributor Southeast Frozen Foods, Inc., wanted branch offices to be able to download a 20M-byte map file showing street routes throughout the Southeast. Because the map file sits on a server attached to an IBM AS/400, the branches use a Pearl communications controller and a frame relay access device to pull the files down.

When one of the branches recently launched the download via a 32K bit/sec virtual circuit terminating at a 56K bit/sec AT&T frame relay switch port, the network burst directly to the port speed and "just knocked the controller down," Robideux said.

"The whole idea of frame relay is that I should be able to burst up to that port speed," protested Robideux. Well, maybe not - or at least not any more, according to experts.

Many users fail to acknowledge the congestion messages that carrier frame nets send back to routers and frame relay access devices, said Tom Jenkins, a broadband consultant at TeleChoice, Inc. of Verona, N.J. As a result, users routinely set their own buffers at the maximum port speed rather than taking care to start throttling back traffic at the CIR level.

Users, especially those with delay-sensitive traffic, should consider raising their presubscribed CIR levels, agreed Rick Malone, president of Vertical Systems Group, a market research firm in Dedham, Mass. Although carriers have recently been increasing their frame relay port prices, they have been reducing overall PVC prices and the increments to add extra CIR to each PVC. As a result, "CIR is very inexpensive," Malone said.

AT&T users should take special care, analysts warned. That is partly because AT&T is getting a disproportionate share of the current frame relay boom.

With all that new traffic, AT&T's method of regulating bursting through its StrataCom BPX switches from Cisco Systems, Inc. comes more and more into play. On AT&T's network, users with higher CIR not only get more of their traffic guaranteed transit through the cloud but also get higher priority over competing users with lower CIR when both have exceeded their CIR.

Lower CIR users can suffer a problem on the large number of AT&T frame relay switch ports that are oversubscribed, said an official with one vendor involved with WAN performance measurement. Those are ports where the aggregate capacity of the PVCs emanating from the port exceeds the actual speed of the port. Reports on some AT&T PVCs are showing a "flattop effect," in which attempts at data bursts repeatedly rise up to the same throughput level - often right to the CIR, or just above - before falling back, he said.

"Unless it's attributable to a regular business cycle, a flattop effect indicates a bottleneck somewhere in the network," said the official, who asked not to be identified.

Thatcher, president of TelCon Associates, Inc., a telecom bill-auditing firm in Overland Park, Kan., noted a danger when companies use 800 service into a remote access server from branch offices thought too small to put on a frame relay network.

One client doing this saw 800 usage soar from 100,000 minutes in November 1996 to 287,000 minutes in March 1997. "People were staying on all day," Thatcher said.

Not only do a lot of employees think of 800 calls as "free," Thatcher explained, but nonusage-sensitive Internet access services have conditioned people to think of remote access to all data networks as free. Yet that is where Nebiker, director of network services for Telxon Corp. in Akron, Ohio, came up with a new solution.

Telxon's branch office in Irvine, Calif., was using switched access to AT&T's Software Defined Network voice service and dial-up data access to headquarters instead of a direct frame relay connection. In order to justify the cost of a T-1 line to the AT&T central office, he needed to demonstrate aggregate cost savings on voice and data networks.

Then AT&T suggested that Nebiker use the carrier's Digital Link service, which reroutes outbound local calls over a T-1 line to AT&T. That enabled him to rip out several hundred dollars a month worth of trunk charges to Pacific Bell, justifying a new 128K frame relay port and ending dial-up tolls.