CNI offers some assistance. It has prepared a highly granular breakout for downtime losses, but its mean figure of $5.35 per hour of messaging downtime across all professions, industries and industry values provides a solid, general starting point for examining this critical component of any TCO analysis.

CNI puts average client/server loss at $229 per user per year, which equates to about three-and-a-half hours of downtime per month and an annual loss of $687,000 for a system serving 3,000 employees. CNI estimates that any given downtime incident affects about 21 percent of client/server system users. CNI suggests that the typical client/server desktop user spends about a third of the day using the mail/collaboration system, compared to 5 percent for a typical laptop user. Each sends about 10 to 15 messages daily and receives about 17.

Among our telephone survey respondents, median downtime for a typical Notes/Domino user was 10 minutes per week, compared to five minutes for Exchange, GroupWise and Internet mail. (Notes tends to be deployed on larger networks, so it's difficult to determine whether Notes' reliability or larger network size accounts for this finding. Networks with more than 5,000 clients reported median downtime of six-and-a-half minutes).

With 32 percent of those surveyed reporting that the typical user's weekly downtime is less than one minute, many businesses may find they can cost-justify migration to a next-generation mail system simply based on downtime.

Another infrequently assessed metric is the actual value of downtime according to system. CNI president Nina Burn says her impression is that downtime is more frequent with Exchange than other systems but that it's costliest with Notes--primarily because so many business-critical applications run on it. One business that has taken this factor into account is Hewitt Associates, a large human resources, consulting and analysis company. Hewitt limits the maximum server load for Notes to 900, primarily because it doesn't want more people than that to be affected should an outage occur.

The flip side of downtime loss metrics is measuring productivity gains inherent in messaging products. CNI estimates a productivity gain of $2,277.39 annually with messaging based on a system that saves each employee (with a fully burdened labor cost of $33.78) 20 minutes daily. Of course, the cost of downtime will vary dramatically by industry.

Certainly, downtime and productivity metrics need to be assessed against two important messaging deployment decisions--the user (client) load borne by individual mail servers, and the pros and cons of deploying much more reliable clustered server configurations. Most businesses keep Windows NT server loads at a 1,000-user maximum or less, even in large headquarters locations; Unix-based Internet servers tend to carry much higher loads. Companies pushing that envelope--to save money in hardware and administration--sometimes find that these larger NT servers crash more often and take longer to re-establish service. The critical question then becomes whether the hardware and administrative savings for these fully loaded servers outweighs the cost of lost work time and revenue.

The value of network downtime also can be weighed against additional hardware and administrative investments in clustered mail servers. One publishing company, for example, was willing to pay $200,000 to create clustered servers for its 1,850 clients, even though the expense accounted for 25 percent of the overall cost of a new Notes/Domino system. Yet if industry time-loss averages were applied to this company, it would be looking at lost time and productivity worth more than $400,000 per year.

CNI suggests that businesses putting a high value on messaging could actually save money by paying a $50-per-user annual premium for a service agreement that guarantees 99.5 percent availability (one hour of downtime per month), instead of 99 percent availability (two hours of downtime per month). Over the course of a year, the additional hour of monthly downtime would tally about $64 in lost revenue and productivity per user, or $14 more per user than the service premium. Some Notes users indicate that because downtime losses can be so devastating, they choose to deploy Notes on highly reliable, if more expensive, platforms, such as the AS/400. This is not a consideration with Exchange, since it runs exclusively on NT.