Avaya 11-300244 Manuel D’Utilisation
Avaya Modular Messaging Concepts and Planning Guide
12-22
November 2004
Avaya Modular Messaging Concepts and
Planning Guide
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Number of calls generated during busy hour = 120
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Average duration of each call = 30 seconds
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Busy hour traffic = (120 x 30) / 3600 = 1 Erlang
!
1 Erlang of busy hour traffic = 3,600 call seconds, or 60 call
minutes, or 36 CCS of busy hour traffic.
minutes, or 36 CCS of busy hour traffic.
Note: 1 CCS = 100 call seconds. There are 3,600 seconds in 1 hour.
3,600 call seconds(/60) = 60 call minutes(/60) = 1 call hour or
Erlang = 36 CCS.
Erlang = 36 CCS.
Busy hour offered
traffic
traffic
Busy hour offered traffic is the total traffic offered to a group of ports
during the busy hour, including calls that are delayed or blocked. Offered
traffic is usually expressed in minutes, Erlangs, or CCS.
during the busy hour, including calls that are delayed or blocked. Offered
traffic is usually expressed in minutes, Erlangs, or CCS.
Grade of service
Grade of service (GOS) is the probability that an incoming call is
significantly delayed or blocked because all ports are in use.
significantly delayed or blocked because all ports are in use.
With switches that support queueing, calls are queued up on the switch
and the caller hears multiple rings because all ports are in use. The call is
eventually answered if the caller does not hang up.
and the caller hears multiple rings because all ports are in use. The call is
eventually answered if the caller does not hang up.
With switches that do not support queuing, calls are blocked when all
ports are in use and the callers hear a busy tone.
ports are in use and the callers hear a busy tone.
GOS is expressed as a percentage of callers who call during the busy
hour. For example, if the number of ports is sized so that no more than 2
of 100 calls are likely to be delayed or blocked during the busy hour, the
system is said to provide a P.02 GOS. If no more than 5 of 100 calls are
likely to be delayed or blocked, the system provides a P.05 GOS. P.01 is a
better GOS than P.05 and, therefore, requires more ports.
hour. For example, if the number of ports is sized so that no more than 2
of 100 calls are likely to be delayed or blocked during the busy hour, the
system is said to provide a P.02 GOS. If no more than 5 of 100 calls are
likely to be delayed or blocked, the system provides a P.05 GOS. P.01 is a
better GOS than P.05 and, therefore, requires more ports.
Common industry GOS for messaging servers is P.01, P.02, P.03, and
P.05.
P.05.
There is a trade-off between cost and GOS. The choice is a business
decision based on a number of factors, including an assessment of how
critical the application is to the business, and an assessment of the cost of
ports required to provide the required GOS.
decision based on a number of factors, including an assessment of how
critical the application is to the business, and an assessment of the cost of
ports required to provide the required GOS.
The tables in
show the maximum amount
of busy hour traffic supported by a number of ports for each GOS.
Estimating port requirements
Planners must make an accurate estimate of ports needed to provide an
acceptable level of service to subscribers.
acceptable level of service to subscribers.