scope:

SCOPE AND PURPOSE

Availability is a key measure in Service Level Agreements (SLA) between service providers and theircustomers as well as their vendors and suppliers. Metrics for estimating IP packet layer availability [Y.1540] and service level availability [ANSI-Avail] have received considerable attention in various standards bodies.

At the same time, service providers need to constantly evaluate network element reliability and hence, availability metric estimation for network elements plays a critical role in SLA interactions with equipment vendors and suppliers. IP-based networks and related evolving technologies such as Multi- Protocol Label Switching (MPLS) are expected to form the basis for Next Generation Networks (NGN) and Services. The specifics of SLA interactions between service providers and IP equipment vendors are driven by the following:

• Degree of reliability and availability of individual network elements (e.g., Line Cards, Routers, etc.)

• Degree of redundancy built into the network design (e.g., redundant line cards)

Hence, the development of an appropriate availability metric, and subsequent techniques for metric estimation, can be very beneficial to service providers. A Committee T1 Technical Report proposed a metric for assessing the access availability of routers in IP-based networks [T1.TR.78-2003] by characterizing fractional availability of access routers in terms of lost ports that can be further weighted by some factor (e.g., port bandwidth).

This Technical Report proposes a methodology for estimating the availability of IP-based access routers in terms of customer facing router line card availability. This is based on what a customer experiences during network failure occurrences. If such failures result in downtime for the customer facing Line Card, then the Line Card is considered to be unavailable regardless of the actual failure. The purpose is to stimulate interactions between service providers and equipment vendors and suppliers in the development of appropriate reliability/availability SLA's.

It should be noted that this methodology can also be applied to other types of packet network technologies. For example, it can be utilized to assess the access availability of line cards in Frame Relay switches.