Ethernet Evolution

In September, geeks worldwide patched into a teleconference conducted from Berlin during which the Metro Ethernet Forum — less than six months after creating a procedure to certify Ethernet equipment as offering “carrier-grade” service — announced its first batch of certifications. Though the awarding of 39 certificates to 16 equipment vendors was an early step in a long process, it marked an important milestone in the evolution of Ethernet to the foundation of future telecom services.

Now in its fourth year, the MEF is netting together some crucial webbing between the work of existing standards bodies such as the Institute of Electrical and Electronic Engineers and the Internet Engineering Task Force. Those groups have forged many of the important technology decisions regarding Ethernet in carrier networks while leaving room for plenty of inconsistencies in service from the customer's point of view.

“The reason the MEF exists is neither the IETF or IEEE or ATM Forum or ITU — no one took on the task of defining Ethernet ‘services,’” said Bob Mandeville, president of Iometrix, the firm that performed the first certification tests for the MEF. “That's the domain where MEF is justified, necessary and also contained.”

Taking the end customer's view on services, the group is blazing a trail toward finally making Ethernet truly carrier-class, robust and consistent as it travels across the globe and changes hands from carrier to carrier. To manage this, the MEF has instituted iron-girded requirements for Ethernet services.

At its most simple, carrier Ethernet must be scalable and reliable, with “hard” quality-of-service (QOS) capabilities, fast and easy service management and support for legacy time-division traffic. And it will prove these attributes through conformance to 22 standards: nine ratified by the MEF, 10 still being developed by the MEF, and three standards from outside the MEF: 802.1 and 802.1 ITU from the IEEE and the IETF's MPLS fast re-route specification.

To earn the first certifications, equipment vendors had to pass a battery of tests spelled out by MEF 9, a user network interface testing spec within the group's “scalability” rubric. Iometrix tested such features as the Layer 2 control protocols, so that, for example, if customers use Ethernet's common spanning tree protocols, errant Layer 2 frames don't wander out into the service provider's network and create loops.

One of the most challenging areas proved to be the management of virtual local area network (VLAN) tags, which number and identify as many as thousands of possible Ethernet links in a given network. Things would be easier, perhaps, if no single Ethernet frame ever left the confines of its corporate walls without being outfitted with the standard-issue uniform of a VLAN tag. That way, all Ethernet traffic could be identified and managed through a single, common and consistent code.

The real world doesn't work that way, of course. Some Ethernet frames wear VLAN tags that afford them various ranks of importance; some frames wear no tags at all.

Also common is the situation in which corporate clients want to connect several sites, new and old, some of which already have VLANs, and the customer wants to keep those old tag numbers while adding the new ones, which may or may not be possible.