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Deploying Carrier Ethernet

Fri, 12/31/2010 - 7:35pm
Brian Santo, Editor-in-Chief

It’s set to get much, much easier.

A new test methodology for activating carrier Ethernet services is sailing toward imminent ratification by the ITU. Once adopted, this methodology – called Y.156sam – will be a means for service providers to deploy carrier Ethernet services for their business customers with the full expectation that when they bring the service up, it will work as guaranteed.

Business customers set specific performance that they expect to get from their service providers in service-level agreements. For providers that are used to best-effort services, SLAs are a different beast.

Ethernet is tremendously flexible and is getting ever-less expensive. Ethernet was originally a best-effort technology, however, and thus an uneasy fit for satisfying SLAs.

But Ethernet’s advantages are strongly attractive, and it is becoming increasingly difficult to not use it. So the industry, through the Metro Ethernet Forum (MEF), developed carrier Ethernet, a set of specifications for carrying Ethernet traffic dependably and reliably enough to satisfy SLAs.

Performance still needs to be tested and verified, however, and that’s where Y.156sam comes in; “sam” is short for service activation methodology, which gives rise to a nickname for Y.156sam – EtherSam.

CIR in Y-156sam

One test standard, RFC2544, predates Y.156sam and is in wide use for bringing up carrier Ethernet services, but as it is largely concerned with device characterization, it is ultimately inadequate for the purpose. Y.156sam, on the other hand, was designed specifically to enable service providers to verify the purchased bandwidth profile configuration and performance to the SLA of a carrier Ethernet service.

Y.156sam is the first test to verify SLA performance according to the bandwidth profile, according to Paul Marshall, CTO of Sunrise Telecom. It is faster, it tests multiple streams (rather than just one), and it tests the whole network rather than any single device.

The test method does not waste time on permutations associated with design verification, Marshall noted, and it skips tests designed to crash the network.

Y.156sam is, again, for configuration testing, which comes in at the front end of the test process. The types of questions that Y.156sam answers, Marshall said, include: Did the right information rate get provisioned? Did the right burst size get provisioned?

Some of these other tests include 802.1ag, which is for handling connectivity fault management. Performance management is covered through Y.1731.

As for speed, network engineers could accomplish a configuration test in as little as 15 minutes using Y.156sam, Marshall claimed, compared with a typical six hours using other test methods.

SYNCHRONOUS ETHERNET
Ethernet is inherently asynchronous. This makes it unsuitable for use in handling synchronous network traffic, a notable example being mobile backhaul. Yet Ethernet’s advantages are too overwhelming to ignore in this arena, as well. LTE and WiMAX actually require Ethernet as backhaul.

There are multiple parts to making Ethernet appropriate in a synchronous environment. For starters, MPLS-TP is an emerging standard for OAM&P (operation, administration, management and provisioning), although Provider Backbone Bridge (PBB, developed by Nortel) is also an option.

Synchronous Ethernet (SyncE), a physical layer synchronization scheme, is being developed. It “smells like SONET, looks like SONET, feels like SONET, but it’s not yet fully implemented in Ethernet,” according to Trilithic’s Pete Moulds, but various chipmakers are in the process of implementing it.

IEEE 1588v2 (aka Precision Time Protocol, or PTP), ratified in 2008, is also emerging as a useful standard. It specifies a protocol for a master clock for timing generation, or a clock that can be tapped into.

They can be used in conjunction with each other, and there are advantages and disadvantages to both. T&M tools and methods may have to be developed to support the verification of either or both.

E-Mail: brian.santo@advantagemedia.com

The archived discussion of SyncE and carrier Ethernet, and how to verify that they are working, is available online at CED's website, in the Webinars section. The CED Webinar was sponsored by Sunrise Telecom and Trilithic.

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