Lucent Technologies Octel Unified Messenger Concepts and Planning Guide 101-1620-005 - Manual (Page 32)

Octel Unified Messenger Concepts & Planning Guide
2-6 101-1620-005
To convert this total into call minutes, divide by 60:
67,500/60 = 1,125 call minutes.
To convert this total into Erlangs, divide by 3600:
67,500/3600 = 18.75 Erlangs.
To convert this total into CCS, divide by 100:
67,500/100 = 675 CCS.
To predict busy hour traffic accurately, you must collect reliable traffic
data that reflects the calling patterns specific installation or application. If
busy hour calls are underestimated, the number of ports may not be
sufficient to provide users with an acceptable level of service. If busy hour
calls are overestimated, the additional number of ports increases the cost
of providing the service needlessly. To calculate the number of ports
accurately, it is necessary to understand the concept of “grade of service”,
see below.
Grade of service Grade of service (GOS) is the probability that an incoming call is blocked
and therefore the caller hears a busy signal because all ports are in use.
This 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 out of
100 calls are likely to be blocked during the busy hour, the system is said
to provide a P.02 GOS. If no more than 5 out of 100 calls are likely to be
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 are P.01, P.02, P.03, and
P.05.
There is an obvious trade-off between cost and grade of service. The
choice is a business decision based on a number of factors, including how
critical the application is to the business, and the cost of ports and other
physical resources that are required to provide the desired GOS.
The tables in Appendix B “Grade of Service” show the maximum amount
of busy hour traffic supported by a number of ports for each GOS.