Service Validation Tests for Carrier Ethernet
Quite a few test procedures for Carrier Etherent – both standard and non-standard – are available to carriers and network operators for monitoring network health and managing service-affecting faults. Ethernet OAM (operation, administration and maintenance) functions as well as other tools can be performed via dedicated probes connected to the carrier’s network equipment at different service sites. Ideally, however, the tests are performed directly by demarcation devices at the service handoff points, provided that these devices are equipped to handle such tests effectively. Below is an overview of the different test tools in use today.
Service Validation Tests
IEEE 802.3-2005 (formerly 802.3ah)
Ethernet Link OAM is part of the IEEE (Institute of Electrical and Electronics Engineers) set of standards. It relates to a single Ethernet link, typically the access connection between the customer premises and the network edge. Specific link monitoring procedures include auto-discovery, heartbeat, and fault notification messages; link statistics; MIB variable retrieval; and remote
loopbacks.
IEEE 802.1ag
Ethernet Service OAM, also termed Connectivity Fault Management (CFM), enables Ethernet service monitoring over any path, whether a single link or end-to-end, allowing the service provider to manage each Ethernet virtual connection (EVC) separately regardless of the underlying transport layer. CFM partitions a network into maintenance domains and hierarchy levels that are allocated between users, service providers and third-party operators. It assigns maintenance end points, or MEPs, to the edges of each domain and maintenance intermediate points, or MIPs, to ports within domains. This helps define the relationships between all entities from a maintenance perspective and permits each entity to monitor the layers under its responsibility to easily localize problems. Service monitoring use several functions including continuity check, link trace and
loopback.
Ethernet Service OAM maintenance domain levels
ITU-T Y.1731
The “OAM Functions and Mechanisms for Ethernet-based Networks” standard by the International Telecommunication Union (ITU) is used for Ethernet service performance monitoring (PM), enabling the service provider to measure frame delay, delay variation and frame loss SLA parameters. It also includes fault management functionalities similar to CFM’s, such as continuity check, loopbacks and link trace, with the addition of alarm indication signal (AIS) and remote defect indication (RDI) messages.
RFC-2544
The Internet Engineering Task Force (IETF) standard RFC-2544, Benchmarking Methodology for Network-Interconnect Devices, defines testing procedures for evaluating the performance of network devices, among which are network throughput measurements. These allow the service provider to baseline service performance and determine the available bandwidth for each EVC, by establishing the maximum transmission rate at which no packets are dropped. In addition to throughput testing, RFC-2544 includes frame loss and frame latency tests.
Diagnostic Loopbacks
Loopback messages between service points are important tools in the process of detecting and repairing connectivity problems. Today operators have a large variety of disruptive (out-of-service) and non-disruptive (in-service) loopback test procedures at their disposal, to help them address faults at various layers.
Table 1 summarizes the various loopback methodologies and their main capabilities.
Ethernet Link, Connectivity and Service layer OAM over different network
segments
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