Frame relay development could mean improved voice over IP

A new development that promises to transport frame relay packets more efficiently could result in big improvements in the use of voice over IP across corporate networks.

Announced last month by the Frame Relay Forum, FRF.20 is an implementation agreement that reduces the size of voice packets, thereby allowing more VoIP calls to run across a network at the same time. The reduction is achieved by eliminating bytes within a packet's header that are similar to each other. With this redundancy out of the way, headers can shrink from a typical size of 40 bytes to counts as low as two bytes.

These micro alterations could ultimately have the macro result of allowing an ordinary 64K link to handle five uncompressed concurrent calls instead of two.

"When it comes down to it, that header…does not change very much from packet to packet," said Frame Relay Forum President Mike Walsh. "In fact, probably about 80 to 90 per cent of that header stays the same. So we're using the [agreement] in order to identify how to compress that header so that the stuff that's going to be the same from call to call will simply have a reference to (it),…and it will only pass the information that changes."

Steven Taylor, a consultant and Frame Relay Forum member who has written articles about the protocol for Network World (U.S.), said the development is a significant one, especially for the improvement of VoIP. Highly-compressed voice, which demands short packets, has traditionally not been a good fit with IP, which Taylor pointed out is an extremely overhead-intensive protocol.

"You end up with it being a rather inefficient way to do voice because a typical voice packet of voice over IP could rather easily be half-overhead. So anything you can do to minimize the impact of that overhead would be rather important."

With VoIP attracting more attention from IT departments every week, Taylor added that the development comes at an important time. He added, however, that if those IT departments are looking at moving voice throughout a point-to-point internal virtual trunk line, they would be wiser to do voice directly over frame relay rather than VoIP over frame relay, as it would offer better reliability. Due to the current "trendiness" of VoIP, however, Taylor doesn't see too many shops going this route.

"Even though IP is not an ideal transport mechanism for voice, there is so much momentum behind the all-IP network that VoIP is just quite frankly gaining a lot of popularity," he said. "What this (implementation agreement) does is minimize some of the negative impacts of doing VoIP over frame to give it some of the efficiencies of doing voice over frame."

Despite this growing popularity, users must still confront a number of unsavoury issues when using VoIP. One of the biggest, according to Walsh, is quality of service (QoS) - the level of assurance that packets will get where they're going intact and on time. Multiprotocol Label Switching (MPLS) is a concept that promises to bring the fast-switching capabilities of ATM and frame relay to IP networks, but it has yet to be implemented to any great extent, Walsh said. One solution many users are adopting is combining IP with protocols that offer better QoS.

"People are really worried about getting the QoS they need. So a lot of them are saying 'Alright, I'm going to cover my tracks. I'll do voice over IP but then I'll put VoIP over a QoS protocol like frame relay. So I'll do VoIP over frame relay,' and that works pretty well."

However, Giga Group analyst Jim Slaby points out that the price factor often plays a bigger role than QoS in the decision of what protocol to adopt. Although IPSec connections, for example, don't offer the same QoS guarantees that frame relay does, compelling cost savings are enticing cash-strapped IT departments to veer toward them.

"This is a situation where IT managers have to look at (IPSec) VPN connections and say, 'Hmm, response time isn't as good as frame relay, availability is worse, packet loss is worse, but it's a lot cheaper. And particularly in the wake of the (economic) downturn where there is pressure on IT budgets [and no] commensurate dampening of end-user bandwidth demand.…It doesn't know that there is a downturn going on," Slaby said.

He added that savings from IPSec versus frame relay on overseas voice traffic, for example, can be anywhere between 20 and 90 per cent, and that the average is in the 50 to 60 per cent range.

The price factor is also playing a role in the development, or lack thereof, of VoIP, said Slaby. Giga has "not seen many very compelling economic cases for VoIP," he said. "If you're a large enterprise, you can probably negotiate pretty cheap long-distance voice minutes from your primary carrier, and with the kind of competition in that space,…you really have to come up with a very strong business case before you move forward with VoIP."