Industry readies for optical, IP convergence

By Jim Duffy, Network World |  Networking

In routed networks, MPLS adds a "label" to an IP packet or flow to steer that traffic through the network. MPLS can be used for explicit routing, fast rerouting, "hard" quality-of-service constraints, and for routing with nonunique addresses, such as in setting up private user groups in VPNs, says Yakov Rekhter, a Cisco Fellow engineer and one of the architects of MPLS.

Rekhter presented a conference session at Interop on MPLS and MP Lambda S.

Similarly, optical wavelengths -- or different colors of light -- can be used as the "labels" for steering traffic through optical networks. As a control plane protocol for optical cross connects, MP Lambda S can be used to provision optical channels, facilitate dynamic, reconfigurable networks, and as an integration point for optical cross connects, wavelenngth division multiplexers and routers, Rekhter says.

Indeed, the same signaling mechanisms that are used in routed MPLS -- the Resource Reservation Protocol and Constraint Routing-Label Distribution Protocol -- can be used to set up and tear down paths in optical networks, he says.

"Label-switched paths can span both routers and optical cross connects if they share the same control plane," Rekhter says. "[MP Lambda S] trivializes control coordination problems among network elements [and] simplifies hybrid administration" between routers and optical cross connects, he says.

Corvis' Jha says it's premature to usher in MP Lambda S.

"You should have one control plane in the optical network, one in the routed network, and they should interoperate," he says. "MP Lambda S will happen but perhaps not in its current form."

Corvis has demonstrated interoperability between its optical gear and routers from Cisco, Juniper and Avici. The demonstration showed how the Corvis optical network can steer routed traffic -- from up to 160 routers on one fiber, Jha claims -- to a destination.

Control plan issues aside, conversion issues - optical to electrical, and optical to electrical to optical (OEO) -- are also generating discussion in the IP/optical realm. Converting electrical impulses to light, and light to electrons, can introduce performance delays in the network and make equipment and services more expensive to procure and provision.

VIPswitch, a maker of terabit-capable Ethernet switches for metropolitan-area networks (MAN), says the OEO issue is one for long-haul networks.

"In the MAN, it's a different issue -- cost," says Yves Hupe, director of product marketing for the Montreal switch maker. "What is the cost point between going electrical vs. going optical? Up to 10 terabit/sec, electrical is efficient. Beyond that point, optical has a definite advantage."

Others are anxious to turn up the light on the metro and access infrastructure.

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