Service-Level Agreements
Test the connection
Ethernet monitoring ensures adherence to service-level agreements.
by Fred Ellefson
Ethernet was originally conceived to provide an inexpensive, simple means of linking a wide variety of devices (e.g., computers, printers and servers) within an organization. Enterprises eventually looked to Ethernet to provide a foundation for interoffice connectivity for IP-based networking.
The primary reason is cost. Enterprises have sought Ethernet as a wide-area network protocol primarily because it costs about one-sixth of private-line services on a per-bit basis.
Ethernet is a relatively simple protocol to work with and widely familiar. Enterprise IT staffs are comfortable with Ethernet, and all enterprise client/server systems, personal computers and upper-layer protocol stacks (TCP/IP, IPX and NetBEUI) are compatible with Ethernet. Consequently, it provides a scalable, flexible option for extending networks as necessitated by globalization, mergers/acquisitions and increased dependence on electronic commerce.
Yet, for a period of time, enterprise adoption of Ethernet-based services remained limited. It was not a problem of scepticism about the market opportunity. Rather, it was the inadequacy of performance- and service-level agreement (SLA)-monitoring capabilities that discouraged carriers from rolling out SLA-backed Ethernet offerings. Savvy enterprises would not commit their mission-critical traffic to any service–no matter how affordable or familiar–without SLAs.
Ethernet carriers were initially unwilling to offer SLAs along with their early offerings, because they could not measure or monitor Ethernet SLAs for services that went across different connection media and other network operators' infrastructure. Without the performance guarantees found in SLAs, enterprise customers were reluctant to move mission-critical applications to Ethernet services—even though they may have cost a lot less.
The arrival of key standards and equipment for Ethernet service monitoring and testing has triggered a chain reaction in the marketplace:
- New Ethernet standards such as 802.1ag and Y.1731 have enabled performance monitoring and stress testing to see how a service will perform under worst-case traffic conditions.
- The new standards-based capabilities have allowed carriers to offer Ethernet SLAs.
- With the emergence of SLAs, enterprise customers are adopting intelligent Ethernet services, such as voice-over-Internet protocol, dedicated Internet access, remote-site connectivity and virtual private networks.
Standards-based stress testing–readying an Ethernet service under the various conditions that an enterprise might subject it to–has provided another important breakthrough. New demarcation test-head tools can stress a service at its maximum bit rate, while cycling through different Ethernet frame sizes, before it is handed off to the enterprise customer. The key standard here is RFC 2544, "Benchmarking Methodology for Network Interconnect Devices."
The tests in the RFC 2544 suite, designed to verify the switches, routers and other Ethernet equipment used in local area networks, also measure intelligent Ethernet service end-to-end against six key parameters.
- Throughput measures how much bandwidth a service can deliver.
- Latencyto calculate how long (in fractions of a millisecond) it takes for packets to traverse the network.
- Frame loss determines how many frames are dropped as traffic moves from one end of the network to the other.
- Back-to-back measures how many frames can be sent and received with minimum interframe gap using this burst test.
- Resetreveals how long, after devices along the network are reset, service takes to resume performing as intended.
- System recovery determines how quickly a system recovers from an overloaded condition.
RFC 2544 reveals the entire delivery chain for Ethernet service to assure the enterprise of optimum performance under all conditions. Testing can be performed across the full range of frame sizes supported by Ethernet. When performed at the point of demarcation between carrier and enterprise networks, the tests most closely emulate actual performance of the Ethernet service in relation to the SLA.
End-to-end RFC 2544 testing over actual data path.
Fred Ellefson is vice president, business development, with ADVA Optical Networking, Mahwah, N.J.
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