If you believed some predictions, Frame Relay should be dead by now and Asynchronous Transfer Mode (ATM) should have one foot in the grave. But rumours of their death have been greatly exaggerated.

Frame Relay was introduced in 1991 as a replacement for leased lines. At the time, it was widely

expected to be a stopgap technology that would be replaced by higher-capacity ATM. Yet Frame Relay is still around — and that is not because ATM failed to live up to its promise. In fact, the two have turned out to be complementary.

Erin Dunne, an analyst with research firm Vertical Systems Group Inc., in Westwood, Mass., says Frame Relay continues to chalk up growth of around 20 per cent per year, while ATM — thanks in part to a smaller installed base — is growing at about double that rate.

Vertical Systems Group projects worldwide ATM revenues at US$3.3 billion this year, and Frame Relay revenue at US$15.4 billion.

Dunne takes issue with claims that these decade-old technologies are being replaced by new developments such as Internet Protocol Virtual Private Networks (IP-VPNs), Digital Subscriber Line (DSL) and Metropolitan Ethernet. Metropolitan Ethernet simply isn’t widely available, and the attractions of DSL aren’t enough to induce corporate customers to switch, she says. IP-VPNs are the strongest contender to steal ATM’s thunder, Dunne admits, but their present high growth rate is based mostly on installations in new enterprises — the benefits just aren’t compelling enough to induce companies to make the move.

Frame Relay often used within companies

So ATM and Frame Relay remain well entrenched and continue to grow.

The choice between the two depends on the individual customer’s needs.

Joe Kimball, president and chairman of the Frame Relay Forum – a Fremont, Calif.-based advocacy organization for Frame Relay technology – says ATM capacities start at the T1 level, or 1.544 megabits per second, which is more than many customers need. Frame Relay is well suited to situations that require less bandwidth, he says.

Telus Corp., the Burnaby, B.C.-based telephone company, bears that out.

Brian Ting, business development manager at Telus, says the company often uses Frame Relay connections to link customers in smaller centres to its fibre-optic network when installing fibre to the customer premises would not be economical. The core of Telus’ network uses ATM, over which the company can run Digital Subscriber Line (DSL) and Gigabit Ethernet connections.

Kimball also says Frame Relay is widely used for intra-company applications, such as carrying e-mail and data traffic from one site to another. It provides secure, reliable access and can support many application protocols, he says.

Kimball says most communications carriers run Frame Relay over ATM backbones alongside Internet Protocol (IP) and voice traffic. “”Frame Relay is one of the best customers for ATM today,”” says Marlis Humphrey, chairman of the board of the ATM Forum, a Dedham, Mass.-based industry body formed to promote ATM.

Meanwhile enterprises are showing considerable interest in running voice over Frame Relay. Frame today can support up to 45 megabits per second of traffic, which Kimball says is plenty for most customers, though ATM might be used for particularly high-volume links.

Humphrey says Frame Relay still lacks the Quality of Service capability that ATM can provide, and this can be an issue for voice traffic.

MPLs an emerging competitor to ATM

However, she says, Quality of Service capabilities – the ability to give priority to traffic such as voice for which delayed packets are not acceptable – are not as important if there is lots of bandwidth to spare, so that delays rarely occur anyway. If an organization has a Frame Relay network for data with bandwidth to spare, she says, “”then fine, throw bandwidth at the problem and do voice over Frame Relay, because then you’ve got one technology to manage, everything is under frame and your operating expenses are lower.””

Although ATM predominates in network cores today, Humphrey acknowledges it has an emerging competitor in Multi-Protocol Label Switching (MPLS). A move toward using MPLS in the core of networks is under way, Humphrey says. Telus, in fact, is planning to make this switch next year. Humphrey says there may be a transition over time to MPLS at the core of networks, with ATM and Frame Relay at the endpoints. However, she predicts ATM will predominate in the core for five to 10 more years.

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