Traffic Loading

How to Calculate Your
Traffic Loading Requirements

Determining The Number of Possible Subscribers

To determine the number of possible subscribers a system can handle, the grade of service must be decided upon, and the average call length (ACL) must be determined. The average call length should be calculated in seconds. Typical telephone calls can average 120 to 240 seconds (2-4 minutes).

After the grade of service and call length are known, find the value of the unit call factor (UC) from the following tables. Each table corresponds to a different grade of service. The UC factor is then divided by the average call length to give the total number of subscribers for the system.

Traffic Tables

The numbers shown in the ACL = XX column of "The Traffic Table" (shown below), correspond to the number of subscribers on the system for the ACL level listed in the column heading The Traffic Tables illustrate the advantage of trunking multiple communications channels.

It can be seen from the tables that on small systems, adding even one more channel can double the number of subscribers who may access the system. Every channel that is added to the system can actually increase the number of possible subscribers per channel.

These tables assume that the average user will make one call of ACL length during the busy hour. If an average user makes an ACL call twice during the busy hour, divide the number in the ACL = XX column by 2. If the average user makes a call of ACL length during the busy hour only 50% of the time, multiply the number in the ACL = XX column by 2.

Examples

A typical user makes 3 telephone calls per day over any given 12 hour period, with the average call lasting approximately 2 minutes. From this estimation, the ACL can be computed:

NOTE: 2 x 60 is used to convert the call length to seconds.

The service level required for the system is chosen to be 1 in 200, with 4 radio channels being utilized in a trunking configuration. The number of subscribers is:

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