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Figure 1. RFC 2544 throughput test results
To ensure a service is going to work under any and all conditions, a provider must stress test a service to the boundaries of an SLA before it is handed over to a customer. Fortunately, such a capability is now available.
By Fred Ellefson
ADVA Optical Networking
Mass-market adoption of intelligent Ethernet services is underway thanks to the introduction of service-level agreements (SLAs) similar to those associated with Frame Relay, ATM, and other legacy data services. In-service performance monitoring using new Ethernet standards 802.1ag and Y.1731 is now an important enabler of this trend; these standards and the demarcation equipment that utilize them help a service provider ensure delivery of an Ethernet service that meets an SLA's strict performance guarantees.
Stress testing via emerging demarcation test head tools gives service providers an even greater level of confidence that their services will deliver what their enterprise customers are expecting under all conditions. Based on the existing Internet Engineering Task Force (IETF) RFC 2544 standard and also part of Y.1731, embedded Ethernet test tools allow a provider to stress a service at its maximum bit rate, while simultaneously cycling through different Ethernet frame sizes. This is a great addition to the SLA monitoring that the new performance monitoring standards offer and it's an effective service commissioning and turn-up test.
Comprehensive, standards-oriented Ethernet service monitoring and testing are of growing interest across the wholesale and retail Ethernet markets. Some early adopter service providers are already relying on capabilities such as RFC 2544-based testing to differentiate their offerings against their competitors' and strengthen relationships with customers committing mission-critical traffic to intelligent Ethernet services.
Beyond mere monitoring
Service providers have long understood that per-bit cost and familiarity would make Ethernet an intriguing WAN transport foundation for wholesale and retail customers.
But until recently the inadequacy of performance- and SLA-monitoring capabilities discouraged service providers from more aggressively rolling out managed or intelligent Ethernet offerings. The ability to offer a consistent Ethernet SLA, regardless of last-mile technology, including use of existing legacy assets and leased infrastructure, was a prerequisite to breaking this logjam. Intense work in the standards and vendor communities helped eradicate these hesitancies.
Ethernet operations, administration, and maintenance (OAM) standards have emerged from the International Telecommunication Union (ITU), Metro Ethernet Forum (MEF), Institute of Electrical & Electronics Engineers (IEEE), IETF, and others. Monitoring standards such as 802.1ag and Y.1731 have proven especially crucial, enabling a provider to see that frame delay and frame delay variation (jitter) on a service do not exceed SLA limits once a service has been handed over to a customer.
Furthermore, Ethernet demarcation devices were developed, providing a definable separation between the service provider's and customer's networks. The devices employ two key components: a user network interface (UNI) enabling service definitions through rate limiting and classification and a network interface device (NID) performing remote OAM for rapid isolation and elimination of service issues. Ethernet demarcation devices offer providers the ability to perform the standards-based SLA monitoring necessary for them to roll out (and enterprises to adopt) intelligent Ethernet services.
But how can a provider go further, to proactively ensure that an Ethernet service is going to consistently behave as the SLA states, even under the heaviest traffic loads? To ensure a service is going to work under any and all conditions, a provider must stress test a service to the boundaries of an SLA before it is handed over to a customer. An IETF specification, RFC 2544, "Benchmarking Methodology for Network Interconnect Devices," offers providers of wholesale and retail Ethernet services an established, proven battery of tests that together convey such assurance. This standard is the basis of new Ethernet test tools that are being deployed in demarcation devices by Ethernet service providers.
RFC 2544
The IETF RFC 2544 standard brings together a suite of tests that were each originally designed to verify Ethernet switches, routers, and other Ethernet equipment being used in intra-office LANs. The test suite addresses five key parameters:
- throughput -- the amount of bandwidth that can get through a service (5 Mbits/sec, 7 Mbits/sec, etc.)
- latency -- the time it takes for packets to travel from one end of the network to the other (measured in fractions of a millisecond)
- frame loss -- the number of frames that are dropped as traffic moves across the network (X out of 100, for example)
- back-to-back -- a "burst" test which determines the largest number of frames successfully sent and received with minimum inter-frame gap
- reset -- the time it takes for a service to resume operation after devices along the network are reset.
Running an RFC 2544 test on an end-to-end basis shows a provider whether every element in the whole chain of delivery for a service -- across intermediate switches, even over leased capacity -- is set up properly. It is not unusual for 5, 10, or 20 different elements to be part of a provider's service delivery chain. And it is also not unusual for one or more of those elements to be configured incorrectly or to be dysfunctional.
The individual tests that compose the RFC 2544 suite are not new. Test set vendors have for years offered instruments that performed the test suites. But only recently, with the maturation of the demarcation device market and the Y.1731 standard, has the test head function and RFC-2544 started to show up at the service hand-off points, to allow the whole range of tests to be run in an automated fashion and present the results in useful, graphical representations (Figure 1).
Test strategies
Providers need demarcation-device-based test tools that subject their services to conditions that anticipate extreme traffic scenarios end to end across the actual data paths used by a given wholesale or retail customer.
Today's leading demarcation test tools can perform RFC 2544 tests across the full range of frame sizes that Ethernet supports: 64, 128, 256, 512, 768, 1,024, 1,280, and 1,536 bytes. Problems most frequently reveal themselves at either end of this range. Sometimes in the case of small frames, a service might run more sluggishly because a great deal of frame processing must be carried out. Other equipment in the network, however, might struggle more with larger frames.
Verifying the three key MEF-recommended SLA parameters (throughput, latency, and frame loss ratio) at all frame sizes covers everything a provider's customer might be doing with its services. In fact, each individual customer will run multiple frame sizes, so the key is for the service provider to at least test frame sizes at the extremes of the frame size spectrum.
Some test tools enable the provider to select the frame sizes that are used in the RFC 2544 suite (the high and low extremes, as well as a mid-range size, perhaps). This flexibility is valuable especially when time to service turn-up is of the essence, as the entire process can be shortened from multiple minutes per service to less than a minute.
Some test tools are designed to perform the RFC 2544 tests from the service provider's central office. While this central-network perspective can be valuable in terms of helping narrow down where in the network a potential problem might exist once it is identified, it does not provide the most accurate representation of how a service will perform from the customer's perspective. Instead, the ability to originate tests from the customer premises enables the service provider to most closely emulate actual service performance in relation to the terms of the SLA (Figure 2).
A friend in need
The issues that RFC 2544 stress testing might uncover would not necessarily creep up immediately upon service activation for a new customer. Instead, they might not show themselves until weeks later, during a high-bandwidth, mission-critical file transfer -- the type of crucible moment that will make or break a service provider's reputation with a given customer. These are the moments when a service provider must show itself to be worthy of an enterprise customer's trust with its lifeblood traffic, for example, and a failure might irrevocably damage that relationship. This is the primary reason why deployment of demarcation-based test tools that carry out the RFC 2544 tests is intensifying among providers of both wholesale and retail Ethernet services.
In the wholesale arena, RFC 2544 compliance is looming as a more and more important differentiator, especially when selling Ethernet access for business services, as well as for backhaul for wireless service providers, whose bandwidth needs are soaring.
And while the consumer Ethernet market is still dominated by best-effort offerings, there is plenty of interest in RFC 2544 verification among providers who sell retail services to business customers. In the business-services market, the service provider might not address the standard by name in competing for customers -- but enterprise IT managers are increasingly interested in factoring their candidate providers' stress-testing practices when making buying decisions.
Multi-service operators (MSOs) are among the first to roll out Ethernet services and RFC 2544. They seek to capitalize on the commercial business opportunity of offering competitive, carrier-class, Ethernet-based business services such as voice over Internet Protocol, dedicated Internet access, remote-site connectivity, and virtual private networks to lucrative multi-site enterprise customers. Stress testing via RFC 2544-based test suites has proven valuable in helping some MSOs overcome "Cable Guy" scepticism and convince the enterprise marketplace to contract with them for mission-critical services.
Conclusion
Ethernet has matured beyond its "cheap, dumb pipe" adolescence. Today, providers of both wholesale and retail services are offering SLAs for Ethernet-based services that are every bit as exacting as those associated with traditional private-line offerings. The emergence of integrated RFC 2544-based test tools is a key reason that providers of intelligent Ethernet services can confidently offer such strict SLAs. By cost-efficiently stress testing its entire service delivery chain for the toughest traffic conditions that its customers might offer, a service provider poises itself for success in building trusting, long-term relationships with its most lucrative customers.
Fred Ellefson is vice president, business development, with ADVA Optical Networking. He is an active member of the Metro Ethernet Forum and speaks around the world on intelligent Ethernet, Ethernet demarcation, and Ethernet OAM issues such as RFC 2544 and.802.1ag/Y.1731.
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Figure 2: End-to-end RFC 2544 testing over an actual data path
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