NEC 2000 IPS manual Traffic Capacity In Erlang For TDM Circuits, Calculation Procedure

Chapter 3 System Highlights

Traffic Capacity In Erlang (For TDM Circuits)

Calculation Procedure

TDSW

LC	Internal Traffic
LC	(I-erl)
STA
LC
	External Traffic
COT	(E-erl)
C.O.

Total system traffic capacity (T-erl) is obtainable by the following formula.

T (erl) = I (erl) + E (erl)

In the UNIVERGE NEAX 2000 IPS, external traffic capacity is obtained from the Central Office Trunk (COT) quantity by employing the “Erlang B Table”. There is no limitation for the internal traffic capacity. The time slot is assigned for individual station and the connection between stations can be made without limitation through TDSW (Time Division Switch). Consequently, when describing the traffic capacity in Erlang, it is meaningless unless specifying the ratio of the internal and external traffic. From the above idea, total system traffic capacity (T-erl) is actually obtained by the following formula:

T (erl) = Internal Traffic (I-erl) + External Traffic (E-erl) = E (erl) ‚ (Ratio of external traffic)

When assuming the external and internal traffic is even.

T (erl) = E (erl) + 0.5

For example:

System configuration:

•384 Lines

•64 C. O. Trunks

•External traffic: Internal traffic: = 7:4

In this system, external traffic capacity is obtained from “Erlang B” table. That is, 64 C. O. Trunks at grade of service of 0.01 can carry 50.6 erl. Total traffic capacity of this system is obtained from above

50.6erl and ratio of external traffic as shown below: T (erl) = E (erl) ÷ (Ratio of external traffic)

= 50.6	÷	7__
= 72.3 erl		7 ÷ 3

Traffic capacity per station line

= 72.3erl ÷ 384 lines = 0.19 erl/L

UNIVERGE NEAX 2000 IPS Request For Proposal (RFP) Reference Guide	Page 3-9
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