Specifications

1725-86914-000_C.docx
September 2013 21
Chapter 3: Features and Capacity
System Capacity Requirements
There are several relevant capacity metrics that must be determined before determining what
resources are required in the type of system we have tested – the number of users, the number
of simultaneous connections required to the PBX, and the various call configurations that are
used in any particular facility.
The number of users is straightforward – how many simultaneously registered users are
required? Multiple users of a single wireless handset that are never registered at the same time
do not need to be factored in – just the maximum number of simultaneously registered users.
The next relevant metric, the number of simultaneous connections required to the PBX is not so
easily calculated. A dedicated voice channel is not required for every user since all of the users
would likely never be connected to the PBX at the same time in the same way that all the PBX
users would be unlikely to be connected at the same time. Although endpoints registered to a
single Mediant Gateway will not need a PBX channel when calling another endpoint registered
to the same Mediant Gateway, a multiple Mediant Gateway system will require PBX channels to
place calls between phones registered to different Mediant Gateways.
The third measurement to consider is the number of endpoint to endpoint calls to/from handsets
registered to a single Mediant Gateway . We have seen that the Mediant Gateway will directly
connect locally registered Spectralink 84-Series handsets with each other and this type of call
does not require connection through a PBX. In some environments this type of call could be the
most prevalent. In other facilities, we would expect heavier use of a PBX. Every installation is
unique and must be evaluated accordingly.
Capacity Analysis
The Mediant Gateway can support up to 600 handsets on the SIP side of the system. This
means that if all calls were placed only between SIP handsets, 300 simultaneous calls would be
possible. However, the T1 trunk has 23 channels and this is the limiting factor when calls are
routed through the PBX. Each call uses at least one of these channels, and if multiple lines are
deployed, then one handset could potentially utilize as many channels as it has lines. Therefore
any analysis of capacity requirements must study the ratio of the endpoint-to-endpoint usage
against the demands that will placed upon the PBX and the T1 line.
Multiple PRIs installed in the Mediant Gateway solve the capacity issue to some degree. Each
T1 module can support up to four T1 trunks and each Mediant Gateway can support up to four
T1 modules, but the number of PRIs is limited to four therefore the capacity of any single
Mediant Gateway is 92 channels.