Two ISPs Show How IP Challenges ATM

Consider one of the major bandwidth-hungry Internet service providers (ISPs), Media One. It's gambling that it won't have to use any ATM in its national backbone. Media One's decision is ample evidence that even in the WAN, once-unchallenged assumptions of ATM's superiority are under attack.

Instead of ATM, Media One will use "packet over SONET," a way of transporting IP packets over the Layer 1 Synchronous Optical Network, an ANSI standard for high-speed, high-quality digital optical transmission, which many ATM networks rely on. Media O ne plans to offer all the snazzy new services that ATM promised to deliver, such as voice and video, all using IP over SONET.

There are various flavors of packet over SONET. Cisco Systems, whose routers built the Internet, announced in February that it is moving forward with PPP over SONET. Four months later, Cisco bought Skystone Systems, which makes chip sets to allow Ethernet/PPP and frame relay protocols to run over SONET fiber, and announced that it would incorporate Skystone technology into "next-generation Cisco products." Cisco's OC3 PPP over SONET is working its way through the Internet Engineering Task Force (IETF) as RFC 1163. Cisco is already planning its own OC12 (622-Mbps) version.

Another ISP, Best Internet, has already ditched ATM on its redundant SONET DS3 lines and instead went to Border Gateway Protocol (BGP), a TCP/IP routing protocol for interdomain routing in large networks. "Most people use ATM because it's cheap, but it's not as useful as a direct point-to-point link," says Richard White, Best Internet's chief technical officer. "We don't do backbone routing -- we let the national servi ce providers do our backbone for us."

But the move to replace ATM with IP is risky. Few experts predict that IP alone can become the standard transport for WANs. "There has to be an underlying packet technology under IP to build scalable IP networks," says Chuck Davin, chief technical officer of PSINet, a leading ISP. "We know from experience that the most critical factor that determines Internet application performance is not so much bandwidth as it is packet loss." These packets are often lost by congested Internet routers, Davin says.