OAM to the carrier-class Ethernet rescue

Evolution of Ethernet
Robert Metcalfe was a member of the research staff for Xerox at its Palo Alto Research Center (PARC) when he was asked to build a networking system for PARC's computers so that all of the computers could access a printer, which happened to be the first laser printer in the world.

Robert Metcalfe had two challenges: the network performance had to be fast enough to drive the very fast new laser printer; and it had to connect many computers within the same building. History records that the birthday of Ethernet was May 22, 1973, when Metcalfe wrote a memo to his boss stating the possibilities of Ethernet's potential thereby starting the Ethernet revolution.

Over 35 years since its inception, Ethernet has already evolved into a highly reliable technology and has been embraced by the industry, than to build bigger, better and cheaper networks. An Infonetics study¹ involving 25 service providers worldwide with an average $9B annual revenue revealed that the providers are planning to a multitude of network-based services over Ethernet, for Ethernet Services, Voice, Video and Storage, indicating that Ethernet is becoming the access and transport technology of the next generation metro networks.

The broadband revolution is changing the foundation of network planning and this is likely to accelerate. Although Ethernet's ability to support residential applications is one of the factors in Ethernet migration and convergence, the Ethernet-based business services market is the dominant factor in the migration. While the growing need for solutions for managing legacy technologies shifts the focus to Ethernet as these older technologies are phased out, green field rollouts are also growing, thanks to Ethernet's simplicity and lower CAPEX and OPEX promise.

While the residential customer applications demand more bandwidth, business customers will continue to demand stringent requirements for differentiated service offerings, such as predictable throughput, latency, resilience; performance monitoring and fault diagnostics as well as security and management at a lower cost per bit parity than legacy technologies. ROI is a critical factor and a carrier must watch its capital spending while accurately predicting operational expenses, since these recurring costs will ultimately define profitability.

Since, more and more carriers are now competing for the same customers the financial models for lower OPEX and CAPEX are much different than in bygone days of old monopolies. Therefore, carriers are also under pressure to offer differentiated services to retain and attract customers.

Carrier-class Ethernet
On top of the already existing challenges, adding and managing quality and class of service attributes will continue to pose operational challenges, however; service differentiation is a key attribute for the competitive edge and the potential revenue is significant. Better metrics will draw premium customers or at least help retain existing ones.

For the differentiated services, carriers are seeking service level agreements (SLA) verification capabilities, while migrating from traditional services running on legacy technologies to Ethernet. For a majority of carriers, SLA metrics monitoring and verification, such as frame delay, frame delay variation (jitter), and frame loss will be important in ensuring that the end users are delivered the quality services, for which they are paying. Adding quality of service (QoS) and class of service (CoS) to SLAs will pose operational challenges and added cost to the carriers. Therefore, for some customers, a traffic pipe with best-effort services and a simple hand-off method will be sufficient, especially if the customers have in-house expertise and resources to manage their own services. However, for a majority of customers, SLAs with QoS and CoS will enable service differentiation, help retain and attract premium customers and bring in higher revenues. It is all easier said than done, since new and advanced technical capabilities bring the need for interoperability and manageability requirements. There are many selections to choose from and many networks are running on equipment from multiple suppliers.

Although it seems like the challenges are overwhelming, Carrier-class Ethernet is already offering powerful standards-based solutions to carriers. Among the key reasons for the rapid growth of the Ethernet are the recent standards activities, which are bringing additional dimensions in Traffic Management, Quality and Class of Service, Resiliency, and Manageability to Ethernet.

The IEEE 802.1Q standard defined architecture for Virtual Bridged LANs, the services provided in Virtual Bridged LANs and the protocols and algorithms involved in the provision of those services. No Quality of Service mechanisms were defined in this standard, but an important requirement for providing QoS is included in this standard, e.g. the ability to regenerate user priority of received frames using priority information contained in the frame. The IEEE 802.1D MAC Bridges standard covers all parts of the Traffic Class Expediting and Dynamic Multicast Filtering described in the IEEE 802.1p standard. All parts of the IEEE 802.1p standard are merged with IEEE 802.1D standard. All QoS issues have been discussed in IEEE 802.1p. Building upon these advances, provider networks with a mesh interconnecting several Ethernet switch based devices known as Provider Bridge concept has been introduced, which is defined in the IEEE 802.1ad Provider Bridges (PB) standard.

IEEE 802.1ad Provider Bridging is the first Ethernet bridging project expressly created for provider networks. PB standardizes the use of multiple Virtual Local Area Network (VLAN) tags in the same frame. In 802.1ad Provider Bridge frame the existing fields of the customer frame are preserved. This allows a customer's full 4K VLAN range to be transported seamlessly across a PB network to each of its other locations. Using the 802.1ad PB, multiple L2VPNs are enabled and complete customer separation is achieved. Both customers have complete freedom to use internal, customer VLANs (C-VLANs) as they choose. The provider configures up to 4K Service VLANs (S-VLANs) supporting up to 4K separate customers.

While topology and address scaling are critical issues, an additional feature that the IEEE 802.1ad PB has introduced is drop eligibility and packet marking capabilities. Rather than a fixed interpretation of the 3-bit priority of the legacy IEEE 802.1Q VLAN standard, PB allows a variety of priority code point (PCP) encoding, which enables distinct priority/drop eligible interpretations.

In addition to the quality of service, resiliency and manageability attributes, another important consideration for the migration towards Ethernet is the reduced overhead offered by Ethernet. Through the use of VLAN tagging and Q-in-Q double tagging standards, service and customer separation can be introduced into Ethernet traffic without burdening bandwidth, whereas MPLS draft Martini encapsulation requires additional bytes.

With Ethernet the protocol conversions are eliminated, the network designs are simplified and the familiarity of Ethernet enables the carriers with ease and fewer complications, collectively reducing the capital and operational expenses.

Despite lower CAPEX and OPEX, one other key issue that limits frame relay is that it lacks the intelligent flow control capabilities that are a necessity when transporting much of application-based traffic. Frame relay simply lacks the capability to identify specific application traffic, such as voice and video, and to selectively prioritize its delivery over other traffic in the network. This ability, which Ethernet can offer is the key for these types of applications due to their sensitivity to network latency and jitter.

Complementary technologies
Up until a few years ago, trends hinted that MPLS would extend all the way to the edge. However, in 2007, Ethernet revenues surpassed MPLS and it is forecasted that Ethernet will gain more ground.