HP Survivable Branch Communication zl Module powered by Microsoft Lync Planning and Design Guide 2011-02

2-8
Design Considerations
Planning Call Capacity
Figure 2-1. Example Spreadsheet for Estimating Concurrent Calls
In either case, remember to also consider whether you need FXS interfaces
to support devices such as fax machines.
Once you have an estimate of the number of channels and FXS interfaces
required, you can select a card from Table 2-3 on page 2-6.
Estimate Concurrent Calls from Usage
If you cannot obtain accurate records for the site’s current usage, you can
estimate the required number of channels. Microsoft recommends these
guidelines in its planning guides:
■ For light usage (about one PSTN call an hour per user), plan one channel
per 15 users.
■ For medium usage (about two PSTN calls an hour per user), plan one
channel per 10 users.
■ For heavy usage (about three PSTN calls an hour per user), plan one
channel per 5 users.