A recent MEF session offered Ethernet Operations Administrations & Maintenance (OAM) Lessons Learned from the trenches at Verizon’s Interoperability Forum (VIF). The VIF is where multiple vendors’ Ethernet gear gets connected together and stressed out by some of the most talented network engineers on a mission – to test how well today’s implementations of OAM work together, where there are gaps in the standards, misunderstandings, shortcoming and otherwise disconnection in this important step in Ethernet’s road to adulthood.
The OAM standards are designed to bring simplicity in management, fault notification and performance monitoring to Ethernet, making it more like TDM – reliable, resilient, carrier-grade. This is no small feat considering the various topologies, technologies, equipment capabilities and the number of non-deterministic factors that affect packets as they attempt to cross the Ether. In addition to connectivity fault management (CFM) specified in IEEE 802.1ag & ITU-T Y.1731, the latter also specifies measurements for performance monitoring (PM) including frame loss ratio, frame delay, delay variation (jitter), throughput and (soon) availability.
The theory has it that once these capabilities are implemented on all Ethernet-able elements, providers will easily be able to detect, isolate, troubleshoot and correct any common fault in an Ethernet Virtual Circuit (EVC), even if the route spans multiple vendors’ equipment and multi-operator networks. A hierarchy of alarms ensures operators have the information they need to fix an issue, while providers using these peered networks for transport or last mile access are notified of the issue – allowing them to reroute traffic over alternative routes. In theory.
The Scorecard
So how are we doing as a vendor community? Conclusions from the first phase of VIF testing (EVPL) offer mixed reviews. With nine vendors in the mix, “Most vendors still have issues but some level of interoperability was achieved” when the basic loopback, link trace and continuity check message functionality was put to the test.
Various failure scenarios revealed difficulty configuring unlike equipment and issues with protocol priorities. A general need for management systems to automate OAM provisioning was a central issue, as was problematic auto-discovery resulting in elements being added to the wrong maintenance association (a logical management group of links between elements). Not surprisingly the 802.1ag and Y.1731 standards for CFM and link trace functions don’t interoperate properly due to slight protocol differences. Perhaps most concerning, most vendors don’t support continuity check messages at sub-second frequency, key to delivering 99.999% reliability.
So how big a mess is this? Not enough to call it quits. The same level of interoperability issues plagues any new technology – a similar multi-year pain-period occurred when GFP, LCAS and VCAT emerged to efficiently transport Ethernet over TDM. It may be that the standards will have to be adjusted, and the basic software approach that vendors have taken to enable OAM in their elements will need to be enhanced, upgraded, or replaced by dedicated hardware to provide a useful level of performance.
So nothing unexpected, but certainly disappointing to service providers who are counting on OAM to simplify and open up the Ethernet wholesale market. For providers looking to get a standards-based head-start into the market, Accedian Networks offers solutions that work today and that are evolving with the standards, while also providing integrated performance monitoring at layer 3. You can learn all about Ethernet OAM, its strengths and shortcomings in the video overview available at www.Accedian.com/oam.
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