Traffic Engineering

Traffic Engineering, as it applies to traditional voice networks, is determining the number of trunks necessary to carry a required amount of voice calls during a period of time. There are two different types of connections to be aware of: lines and trunks. Companies use switches to act as concentrators because the number of telephone sets required are usually greater than the number of simultaneous calls that need to be made.
Traffic engineering a voice over X network is a five step process.
This information typically records calls that are offered, but does not provide information on calls that were blocked because all trunks were busy.
Start by separating the traffic into inbound and outbound directions. It’s important to break the traffic by distance because most tariffs are distance sensitive.
The holding time of a call (T) must account for the average time trunk is occupied and must factor in variables other than the length of a conversation. Hold times based on call billing records might have to be adjusted based on the increment of billing. Billing records based on the minute increments overstate calls by 30 seconds on average. In order to provide a “decent level of service, “base traffic engineering on a GoS during the peak or busy hour. Regardless of which method is used, the intent is to use a number that is sufficiently large in order to provide a GoS for busy conditions and not the average hour traffic. The equations traditionally used in telephone engineering are based on the Poisson arrival pattern which is an approximate exponential distribution.
Traffic arrival Characteristics:
Poisson distribution is commonly used for infinite traffic sources. In the three graphs below, the vertical axis shows the probability distribution and the horizontal axis shows the calls, once you have determined the amount of traffic in erlangs that occurs during the busy hour, the next step is to determine the number of trunks required to meet a particular GoS. The number of trunks required will differ depending on the traffic probability assumptions.
Potential Sources
The first assumption is the number of potential sources. There can be a major difference between planning for an infinite versus a small number of sources. The table below compares the amount of traffic the system needs to carry in erlangs to the amount of potential sources offering traffic, assuming that the number of trunks holds constant at 10 for a GoS of 01. The LCC option assumes that once a call is placed and the server is busy or not available, the call disappears from the system. In essence, you give up and do something different.
The LCH option assumes that a call will be in the system for the duration of the hold time, regardless of whether or not the call was placed. In essence, you continue to redial for as long as the hold time before giving up.
The LCD option means that once a call is placed, it remains in a queue until a server is ready to handle it. Then is uses the server for the full holding time. This assumption is most commonly used for automatic call distribution (ACD) systems. Assuming that the lost calls will clear the system tends to understate the number of trunks required: on the other hand, LCH overstates the number.
How the switch handless trunk allocation
As mentioned earlier, the purpose of the third step is to calculate the number of physical trunks required. We have determined the amount of offered traffic during the busy hour. We have talked to the customer so we know the GoS the customer is requesting. Finally, we are comfortable with the basic four assumptions. The only thing left to do is to calculate the number of trunks required by using formulas or tables.