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

4-5
Example Solutions
Solution
Figure 4-2. Example Network Topology
Purchase Telephony Cards
In the example, the large branch at Dallas has about 900 users. It is estimated
that each user will make no more than two local public switched telephone
network (PSTN) calls an hour. This includes calls that might be routed from
other sites out this site according to least-cost routes. (Note that branch users
might make additional calls to other Lync users, as well as PSTN calls that are
routed out other gateways according to least-cost routes. However, these calls
only affect the number of PSTN lines required during failover situations.)
Using the basic Microsoft guidelines, you can estimate that the branch office
will need 90 voice channels. A Four-Port T1/E1 Telephony Card provides an
adequate number of channels (96 channels with T1). This site also has several
fax machines, so the company purchases a Four-Port FXS Telephony Card.