PBT and T-MPLS:

More Hype or The Future of Transport

By Daniel Joseph Barry, TPACK

Meriton Networks and TPACK have embarked on an exciting collaboration on PBT (or PBB-TE to be more correct) and T-MPLS. But are these technologies a case of more hype or are they a glimpse of the future of packet transport?

“Hype” is defined as a figure of speech in which statements are exaggerated or extravagant. Considering that PBB-TE and T-.MPLS are new and, thus-far unproven technologies, one could be forgiven for treating them as hype. However, the key to understanding the impact of PBB-TE and T-MPLS is in the motivation for their development: the desire for a packet network that looks and feels like SONET/SDH.

Connection-less networking based on Ethernet and IP/MPLS has been around for some time. Indeed there are many carriers who have not only implemented these technologies, but have even used them to completely replace their legacy network. So, why are we even discussing connection-oriented packet networking?

While it is generally accepted that a fully packet based network with services based on IP is the future, migrating the existing telecom network is a major undertaking not only technically, but also organisationally.

Managing a connection-less transport network can be a challenge. Fault isolation, in particular, can prove to be a lengthy process. New solutions are constantly being developed to improve these issues, but it is difficult to provide the same determinism and control inherent in connection-oriented networks.

The resources, work practices and processes developed over decades in support of connection-oriented networks, such as PDH and SONET/SDH cannot easily be applied to connection-less networks. Extensive re-training and process re-engineering is required with all the inherent costs and risks that such projects entail.

For carriers with a considerable investment in SONET/SDH networks, this can be a large risk to take. Especially since much of its existing revenue is probably based on legacy services, such as voice and leased lines. The challenge is to support a packet based future without disrupting current business.

Both PBB-TE and T-MPLS can meet this challenge. Both provide the ability to:

• Engineer end-to-end, bi-directional packet tunnels
• Protect and monitor the tunnels on an end-to-end basis using OAM
• Protection switch within 50msec
• Configure, provision and control the network using network management

T-MPLS builds on the maturity of MPLS technology and standards to provide a transport-focused solution. Features, which interfere with the integrity of OAM packets on an end-to-end basis, have been removed. These include Penultimate Hop Popping, Equal Cost Multiple Path and LSP Merge functionality. LSPs are configured and provisioned using network management.

PBB-TE provides a simplified version of IEEE 802.1ah Provider Backbone Bridging (PBB). The frame format of PBB is retained, which allows 802.1ad (QinQ) switches to be used in the core of a PBB-TE network, as well as providing address and service scalability. However, the major difference between PBB and PBB-TE is the removal of Spanning Tree Protocol and broadcasting of unknown MAC addresses. Network management is used to populate forwarding tables providing determinism and control. This also allows OAM support on an end-to-end basis with protection switching.

Clearly, PBB-TE and T-MPLS provide connection-oriented approaches that resemble SONET/SDH. By using PBB-TE or T-MPLS, it is possible to smoothly migrate from the existing SONET/SDH network while relying on the same resources, work practices and processes that are already established.

So, are PBB-TE and T-MPLS the future? It is probably too early to say, but it’s clear that connection-oriented packet transport provides both technical and organisational advantages that are difficult to overlook.