Lucent Technologies Release 8.2 manual G3r G3si, Poe =, 57% 65% 52% 60%

D Capacities and Performance

Erlang. The Erlang is a unit of measure of the intensity of telephone traffic. It measures the average utilization of a set of system resources during a given time period. For example, if a server (trunk) is busy for 30 seconds over a measurement period of 2 minutes, the traffic intensity for that measurement period is 0.25 (30sec/120sec) Erlangs. An intensity of one Erlang represents the full utilization of one call server, or an average of 1/nth utilization of n servers, over the measurement time period. Since the Erlang is time divided by time, it is a dimensionless unit.

The maximum capacity of one trunk is one Erlang and the maximum capacity of a group of trunks is equal to the number of trunks in Erlangs. For example, the maximum capacity of a group of 30 trunks is 30 Erlangs. If, during a given hour the utilization of the trunk group was 10 Erlangs, on average 10 trunks were busy. This could have happened for 10 one-hour calls (unlikely) or 600 one-minute calls, or any combination of calls and durations that result in 36,000 call-seconds.

Another measure of traffic intensity is the CCS, or hundred (century) call-seconds per hour. Since one Erlang is equal to 3600 call-seconds per hour, one Erlang is equal to 36 CCS per hour.

Erlang B. The probability distribution used to estimate the number of trunks needed to carry a given amount of traffic for a “loss system.” It assumes that when a call arriving at random finds all trunks busy, it vanishes and doesn’t return (“lost calls cleared”).

Erlang C. The probability distribution used to estimate the number of trunks needed to carry a given amount of traffic for a “delay system.” It assumes that all calls will wait indefinitely to get through.

Processor performance The number of thousands busy-hour calls (KBHC) can be estimated as a function of the processor occupancy estimate (POE) and the time per call (T), in milliseconds, as follows:

KBHC ≤ 36*POE / T

The following table gives the estimated BHC capacity for the G3r and G3si models given various values of POE and T.

	G3r			G3si
T(ms)	POE =	POE =	T(ms)	POE =	POE =
	57%	65%		52%	60%
100	20,500	23,400	200	9,400	10,800
150	13,700	15,600	300	6,200	7,200
200	10,300	11,700	400	4,700	5,400

TDM bus performance The impact of H.323 voice-only calls on the TDM bus is the same as for circuit switch voice calls.

		Administration for Network Connectivity
410	CID: 77730	555-233-504 — Issue 1 — April 2000