NEC NEAX 2000 IPS Reference Manual page 61

Traffic Capacity In Erlang (For TDM Circuits)
STA
C.O.
Total system traffic capacity (T-erl) is obtainable by the following formula.
T (erl) = I (erl) + E (erl)
In the 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.
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
50.6 erl and ratio of external traffic as shown below:
T (erl) = E (erl) ÷
= 50.6
= 72.3 erl
Traffic capacity per station line
= 72.3erl
= 0.19 erl/L
NEAX2000 IPS Request For Proposal (RFP) Reference Guide
NDA-24349 Issue 4
Calculation Procedure
LC
LC
LC
COT
:
(Ratio of external traffic)
7__
÷
7 ÷ 3
384 lines
÷
TDSW
T(erl) = E(erl)+ 0.5
Chapter 3 System Highlights
Internal Traffic
(I-erl)
External Traffic
(E-erl)
Page 3-9