Traffic Calculator Tool
The InfoPlus Online Traffic Calculator is a time-saving tool for calulating the number of trunks required for various target grades of service. Incorporating standard telecommunications traffic algorithms, it gives you the ability to perform standard traffic calculations, or 'what if' scenarios, without having to struggle with complex calculations.
Instructions for Use:
- Enter the usage for the trunk group, in 100 Call Seconds, or CCS's, in the field labeled "Usage in CCS:" This must be a positive integer.
- OPTIONAL - Enter a number of trunks in the field labeled "Equipped Trunks"
- Select an engineering method from the pop-up menu. The default is Erlang B. (See below for a description of the commonly used engineering methods)
- Hit the 'Calculate' button.
- You must hit the 'Calculate' button after each change of the parameters.
- Note: to use this tool, you must have a Java-enabled browser. If you don't have this capability, you'll see the words 'Java Not Enabled'.
Understanding the Output:
There are actually 4 pieces of information provided, 3 if you didn't enter a number of equipped trunks.
Current GOS - If you entered a number of trunks in the "Equipped Trunks" field, you will have a value under the heading "Current GOS". This is the Grade of Service that would be achieved for a trunk group with the entered number of trunks receiving the entered amount of usage. (See Grades of Service below) In the example above, the current grade of service is P.013. Below the grade of service is the number of trunks you entered, 45 in the example.
Target Grades of Service - Whether you entered a number of trunks or not, you will be presented with the number of trunks required for three target grades of service, namely P.01, P.02, and P.05, given the entered usage. (See Grades of Service below) Under each heading is the minimum number of trunks required for that grade of service. In the example, we see that 40 trunks are required for a P.05 grade of service, 44 trunks are required for a P.02 grade of service, and 46 trunks are required for a P.01 grade of service.
Grades of Service explained
A Grade of Service (GOS) is a statistical probability of receiving a busy signal for a given volume of traffic, presented to a given number of trunks. We represent GOS as a capital P (for probability) followed by a number between 0 and 1. The number is the probability of receiving a busy signal for a call attempt on the trunk group. For example, a P.02 grade of service would indicate a sufficient number of trunks such that no more than 2 busies out of a theoretical 100 call attempts would be incurred during a given hour.
Engineering Methods explained
Three engineering methods are commonly used in telephone traffic engineering. By-in-large, the differences between them are very subtle. The default method on the Traffic Analyzer is the Erlang B.
- Erlang B - Also called the Lost Calls Cleared Method. A mathematical model of telephone traffic in which blocked calls are not queued. For example, incoming DID calls which exceed the number of DID Trunks are returned as busy by the central office and the call hangs up.
- Erlang C - Also called the Lost Calls Delayed Method. In this case, however, blocked calls do not disappear, but are queued. Many outgoing COT trunk groups, and particularly ACD Queues, employ queuing.
- Poisson - Called the Lost Calls Held Method. In this case, blocked calls are held for their normal holding times, even though unserviced. This method is commonly used for internal system resources, such as requests for internal dial tone, busy tones, etc.
