Imagine typing in your company's Web address and discovering that your site is down. Or what if your entire company lost access to the Internet for even just a few hours. Or perhaps your internal network has crashed, and you can't access important documents on the network.

While you can't prevent these things from happening, you can address these potential blows to your workday by clarifying your expectations in your service level agreement (SLA).

For small businesses in particular, which probably can't afford expensive tools or a large staff to monitor their network, keeping a constant watch on the level of service you're being provided is not always feasible.

A thorough service level agreement defines the performance levels you expect from your ISP, Web site host, VPN host, ASP, or any other service provider. It measures the quality of the service you get and identifies the corrective steps to be taken when your expectations are not met.

Unfortunately, ensuring that the terms in the SLA are being followed may still hinge upon your own vigilance - but at least the contract gives you some grounds for negotiating a solution with your provider.

At the very least, your SLA should guarantee the degree to which the network or the application is working and available - this is also called "uptime." Most service providers will probably guarantee 99.5 percent uptime - very few promise 100 percent.

Some providers, however, define availability in terms of consecutive hours. So as long as service is restored within two hours, for example, even if it fails for a similar period at another time, it's still considered 99.5 percent available.

Some service providers, particularly ASPs, may have cobbled together their service from different elements - like a network provider, an infrastructure provider, and an application management provider, each with its own SLA. Even if each component is guaranteed, the overall service provided to you, the customer, may not be available if each component fails at different times.

Find out what components of the total solution are covered under your SLA. Also ask about any guarantee against dropped connections and the time it takes you to log on to the service. Some SLAs offer a money-back guarantee for the time that your connection is down.

For instance, in the case of a Web hosting service, ask about glitches during data transmittal. Information on a network is divided into "packets" before it is transmitted one packet at a time. Some service providers measure the rate of network traffic based on the packets that go in and out - but they don't mention how many packets of information are inadvertently dropped along the way. Work out a guarantee on packet loss in your SLA.

If the provider with isn't willing to give you these kinds of guarantees, you should look for a replacement.

You should remember, though, that guaranteed service is not the lowest priced option. While most businesses would agree that defining, negotiating, and measuring a good SLA is difficult, you have to be prepared to pay - and follow up - if you want meaningful guarantees.

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