Crafting an SLA - important facts to consider

Why even worry about network uptime and redundancy when using a public-switched service? After all, any frame relay carrier worth their salt offer standard service-level agreements (SLA) for network availability and other metrics as part of their basic services, and it is up to the carrier to figure out how to architect their networks to deliver on those promises.

Well, first of all, at the end of the day, an SLA can be worth little more than the paper it is written on, depending on how mission-critical your network is. Yes, an SLA means that, contractually, a carrier will have to reimburse you to some extent for downtime, if an outage renders your network unavailable for longer than your SLA specifies. But if you are an online transaction business standing to lose several hundred thousand dollars in a mere minute of downtime (not to mention credibility with your customers, which is probably a more serious result in the long run), such reimbursements really won't make up for what you have lost. (For network diversity options, see our past three newsletters.)

However, in addition to standard SLAs, most carriers will allow you to negotiate custom SLAs, and there is nothing wrong with getting the tightest SLA you can afford. To do so, you must understand exactly what your carrier is promising in terms of network performance. For example, make certain you understand exactly how "network uptime" or "network availability" is defined. Does the percentage associated with it include the access link? If not, you probably want to buy some extra diversity insurance there.

Other considerations:

* What period of time does the promised percentage of availability apply to - 99.9% per day, per week, per month or per year? The shorter the time period (for example, 99.9% uptime guaranteed per day rather than per year), the shorter any particular outage is allowed to be. For example, under a per-year SLA, in a very large network, one segment might experience a weeklong outage - but the overall network could still be within the limits of the SLA.

* What set or subset of network elements does the promised percentage of availability apply to - 99.9% per PVC and 99.9% per port? Or does the 99.9% pertain collectively to all network segments? Again, the more granular the definition (per port, per PVC), the better off your are.

The tradeoff, of course, is cost. You generally have to pay more for bigger promises. But at least being sure about the details of your SLA puts you in a better position to negotiate tighter service level guarantees if you decide you need them and can afford them.

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Steven Taylor, consultant and broadband packet evangelist, and Joanie Wexler, an independent networking technology editor and writer, team up to bring you this analysis and commentary. Taylor specializes in education and market analysis, and Wexler adds incisive reporting and research. For more detailed information on most of the topics discussed in this newsletter, connect to www.webtorials.com, the first Web site dedicated exclusively to market studies and technology tutorials in the Broadband Packet areas of Frame Relay, ATM, and IP. Feedback and additional topic ideas are welcome. Please contact taylor@webtorials.com or joanie_wexler@mindspring.com>

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