Specifications
MBG Engineering Guidelines, Release 8.0
12 Sizing Your Installation
MBG installations come in many sizes, from a handful of remote workers, to large call centers with recording
requirements, to service providers with hundreds of SIP trunks routed to customer vMCDs. This section provides
guidelines for selecting appropriate hardware and network capacity for any size of installation.
For site with fewer than 500 users and 100 simultaneous streams, skip to section 12.2 Determine Call
Equivalents.
Note: The calculations in this section assume that no other applications besides MBG will be running on the MSL
server.
12.1Determining Line Size for Large Sites
Step One: Determine Call Rate
The first step is to estimate how busy the site will be. Ideally, this figure will come from observations of actual
usage, but it can be estimated. The services provided by the MBG server affect how much load it needs to
handle.
Consider a typical teleworker scenario: 20 users working in a remote office. Assume that these users are on the
phone about 10 minutes of each hour, or 6 CCS. If the users make two calls per hour, each call is 300s (5
minutes) long.
Multiply the average CPH rate by the total number of users to get the Erlang-B lambda value:
λ = 2 CPH * 20 users = 40 CPH
A call center might have usage of 20 CCS per agent. Assume an average call time of 600s (10 minutes). If the
agent is busy 2000 call-seconds (20 CCS) and each call is 600s, the agent is handling 3⅓ calls per hour. For a
busy call center with 1000 agents, lambda is:
λ = 3.3333 CPH * 1000 users = 3333.3 CPH
Step Two: Determine Service Rate
The service rate, represented by μ, is the mean number of calls the MBG can handle successfully per unit of
time, without blocking. If it takes 20 minutes to service one call, then three calls can be serviced per hour, and
the service rate is 3 CPH.
In the teleworker example above, the call duration is 300s, so MBG is processing 12 calls per hour:
μ = 12
In the call center example, the call duration is 600s, so the MBG is processing 6 calls per hour:
μ = 6
Step Three: Determine Grade of Service
The grade of service, represented by P(b), is the percentage of calls that are turned away (blocked) because of
insufficient capacity. The nominal and recommended P(b) is 1%, or 0.01.
40