Carrier Ethernet-Choices- Present and Future

Ethernet, conceptualized and initiated as a technology to connect nodes within a small, limited area, administered by common policy, in a defined physical space brought with it a distinct advantage, working on Collision Detection. This allowed physical reuse, no waiting period resource wastage and high bandwidth together with highly granular bandwidth control. Then with the opening of the dotcom floodgate with Yahoo!! and Googles of the world, substantiated by newer application like online trading, Instant Messaging etc. made it very common for people to stay connected on the net for the entire of their waking hours, although their talk time stayed limited to six to seven hours for high usage subscribers. This exemplifies the importance that data traffic has gained in the last decade. While the voice volume was more or less not increasing per sub, or at best increasing at very slow pace, the exponential growth of data as a tool of communication, empowerment and entertainment attracted the traditional service providers to stake claim in then tempting market segment. The large behemoths walked in to kill the smaller ISPs, positioning themselves as converged service provider. Immediate access requirments were met with by putting in place a parallel data network, carrying date on the IP devices, while voice continued to move on the physical layer, with a distinct segregation of Circuit switched (Voice) and Packet Switched (Data) traffic. This did impose some demands on the data networks as it came out of the protected LAN environment to the large public space, specifically in terms of High availability, High capacity and scalability. While this did bring in business, it came with its own share of trouble. There was a need to ensure the upkeep and growth of two separate networks, both needing different skill sets. The pre-existing voice carrying network was already on the last legs, with PSTN equipments getting phased out, OEMs pulling out the support and discontinuing the products. Dual cost and worry of the future, pushed operators and vendors alike to look for the means to put in place a single network which could carry diverse kind of traffic. This put additional demand on the existing carrier ethernet network, to ensure voice grade traffic on the network, support for large number of subscribers (identified in IP world by MAC), Mechanism to manage the limitations of MAC addresses and VLAN, technical ability of the network to provide, what is termed as Voice-grade 50ms protection.
The initial struggle between RPR(Resilient Packet Ring, IEEE802.17) and VPLS as a mechanism to provide for 50ms protection finally ended in favor of VPLS (which does the protection based on TE-FRR- Traffic Engineering - Fast Reroute). The key reason for this outcome, apart from industry support, was the traffic engineering benefit that VPLS brought with it. While both VPLS and RPR based solutions used Q-in-Q for the VLAN scalability, with the technology question for the backbone already settled in favor of MPLS long time back, it made sense to extend the same technology to the aggregation and access with VPLS (or Layer 3 MPLS, if need be so). MAC scalability still remained an issue, further the network with Labels being distributed on DoD (Downstream on Demand) was not as deterministic as we would want it to be in order to be able to phase out the SDH based network completely. Physical layer did not give up however, backed by IEEE it came back with technology called PBB (Provider Backbone) to address the MAC scalability based on IEEE 802.1ah. This proposition put forward my ethernet proponents like Nortel, based MAC scaling on the idea similar to QinQ, that is encapsulating customer MAC in Provider MAC. While it used Ethernet OAM to provide for providing reliability, it left the QoS issue unaddressed with only basic ethernet features like IEEE 802.1p and 802.1q (priority and queuing) for QoS. Which was a feeble attempt against strong traffic engineeting offered by MPLS. MPLS forum responded to the MAC challenge with VPLS-PBB integration (Draft-Balus), while IETF got together with ITU-T, leading to the scrapping of earlier ITU-T proposition for Aggregation, T-MPLS, forming a Joint Working team (JWT) in February, 2008, giving way to MPLS- Transport Profile, which unlike its predecessor could interwork with MPLS on the backbone. IEEE on the other hand responded to the QoS challenge by statically provisioning multiple paths with deterministic QoS, based on IEEE 802.1Qay. Both MPLS-TP and IEEE802.1Qay are currently under standardizationa and are likely to be vetted by early 2010. Although industry majors like Alcatel-Lucent, Ericsson, NSN and Huawei have thrown their weight behind MPLS-TP, wholeheartedly since BT abandoned its PBB plans, it is more of wait and watch situation. Both the standards will bring with them the promise of a network with Quality of Service, Capacity and High availability numbers at par with or better than the traditional network that they seek to replace. A converged network would also mean a single network on which entire traffic including mobile traffic will flow, requiring support for features like Synchronous Ethernet and 1588v2 etc. which are leading the standardization work covered in MMBI(MPLS Mobile Backbone Initiative) undertaked by MPLS forum. The latter will be an interesting subject in itself, while the key summary points at the present are:
1. VPLS is technology of choice in the aggregation.
2. VLAN scalilibility is addressed in Metro or Carrier Ethernet scenario by QinQ, and MAC Scalability with IEEE 802.1ah on access or by PBB-VPLS integration on the aggregation.
3. Future choices are split between PBB-TE and MPLS-TP, both being in pre-standard stage.