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ATM's future in the DSL arena

Posted: 18 Nov 2002 ?? ?Print Version ?Bookmark and Share

Keywords:atm networks? dsl? adsl? dslam? mpls?

Though IP is encroaching on the MAN/WAN in the form of MPLS, ATM might still hold on for some time to come. Until then, the future of ATM in the DSL arena may remain hanging in the balance.

Majeed Ahmad is senior technology editor of Electronic Engineering Times Asia.
When ATM technology, once the darling of almost every tenant of communications industry, be it LAN, WAN or multimedia, came down to earth in the late 1990s, it found its home in the nascent xDSL market by providing multiplexing services in the access network.

ADSL was initially conceived of as a technology incumbent telecom operators could use to offer voice, video and data services to the home. But once the Internet came along, the broadband-capable xDSL technologies seemed a natural fit for Internet access services. That was when a debate raged in the ADSL Forum as to whether or not ATM or IP (packet) should be the native format over the loop.

This was driven, in part, by the realization that the "killer application" for xDSL deployment was not video, but Internet access. However, the Baby Bells stepped in at that point, and let it be known that they continued to see DSL technology as more than "just Internet access." They wanted to retain the ability to carry additional voice and video services over xDSL, so ATM became their encapsulation format of choice.

Certainly, in the upstream direction (where ADSL bandwidth is lower), a long data packet must be broken up into fragments or it will create unacceptable latency for voice services. However, with the recently-adopted packet fragmentation standards, you can achieve this with a packet-based architecture. But since the U.S. telecoms were already deploying regional ATM networks, they probably saw no reason not to use a rather mature ATM technology they were familiar with.

ATM is an end-to-end technology, so there is little separation in core and access parts of the network. If a service provider has ATM in the core, then it will choose ATM for the DSLAM. If they have converted to an IP core (very little of this today), then they will buy an IP DSLAM.

One way to avoid this conflict, according to Tom Sun, VP of PMC-Sierra's Asia-Pacific operations, is to be agnostic to the ATM vs. packet debate. So comms chipmakers like PMC-Sierra started rolling out PHYs that support both ATM and packets. Such products buffer schedule and transmit packet-contiguous streams of AAL-5 traffic in order to ensure packet level throughput rather than simply optimizing for ATM cell level traffic.

Though IP has finally started to encroach on the MAN/WAN in the form of MPLS, says Jeremey Donovan, principal analyst at Gartner Dataquest, ATM might still hold on for some time to come. Telecom folks never quite throw out old network infrastructure; the worst that will happen to ATM is it will go into maintenance mode. Still, we are many years away from that.

Until then, the future of ATM in the DSL arena may remain hanging in the balance.

- Majeed Ahmad

EE Times Asia





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