Standards bodies vow to resolve MPLS flap

The Internet’s leading standards bodies have agreed to work together to ensure that a new transport protocol being developed for Multiprotocol Label Switching (MPLS) networks is compatible with the billions of dollars worth of MPLS equipment that carriers have installed in recent years.

The International Telecommunication Union (ITU) and the Internet Engineering Task Force (IETF) have agreed to work "in close collaboration" on Transport-MPLS, according to a report from a recent meeting attended by representatives of both groups. The meeting was held in Stuttgart, Germany, from Sept. 10 to 14.

"The agreement so far is to form this joint working team of experts to ensure that problems can be avoided going forward, but many of the details are still to be worked out," says Stephen Trowbridge, chairman of the ITU’s Telecommunication Standardization Sector (ITU-T) Working Party 3 of Study Group 15, which is developing T-MPLS.

The final decision on how the two groups will work together on T-MPLS will be considered at a February 2008 meeting of the ITU-T’s Study Group 15.

"Whilst productive discussions took place and a proposal was drafted, it is my understanding that a number of other ITU-T groups have to consider the matter," explained Stewart Bryant, IETF liaison to the ITU-T on MPLS issues and a technical leader at Cisco. "It is also my understanding that the ITU process then requires the recommendation of [four related study groups] to be ratified at a plenary before they can be considered definitive output for consideration by ITU-T management."

The IETF leadership and its sister organization, the Internet Architecture Board, also need to review the proposal for the joint T-MPLS working group, Bryant added.

The joint meeting "was a good first step" in resolving the IETF’s concerns about T-MPLS, Bryant says.

"The scope and authority of this particular meeting was limited, and we still need to see broad acceptance and ratification in both the IETF and the ITU of its recommendation in order to know if we truly made progress," Bryant added.

T-MPLS is a controversial transport network architecture that the ITU-T is developing to allow MPLS traffic to run over an Ethernet backbone.

The crux of the problem between the ITU-T and the IETF is that T-MPLS uses the same EtherType as MPLS. An EtherType is a field in the Ethernet networking standard that indicates which protocol is being transported.

The IETF, which developed the original MPLS specifications, said T-MPLS as currently envisioned by the ITU-T would cause massive interoperability issues for carriers that had already installed MPLS routers and switches.

The ITU-T says the situation is fine because MPLS and T-MPLS will be used on networks that don’t connect to each other.

Nonetheless, the ITU-T has agreed to begin cooperative work with the IETF on T-MPLS "as soon as possible," the report says.

"The IETF and ITU-T will work in close collaboration on T-MPLS toward solutions that ensure MPLS/T-MPLS compatibility, consistency, and coherence, recognizing that the sole design authority for MPLS resides in the IETF, and the domain of expertise for Transport Network Infrastructure resides in ITU-T [Study Group] 15," the report says.