Instead of setting up trunk groups with a single routing destination, it is now expedient to set up trunk groups with many routing possibilities.
Several types of circuit trunk groups can be considered in today's competitive vendor environment: point-to-point private lines, measured-use network services, and private lines interfaced to a measured-use network service at a gateway.
This optimization is performed by a design cycle that consists of three basic steps: selection of vendors, of vendor combinations and of user-defined subnetworks (this involves selection of the traffic destination groups and of the CFTGs), evaluation of the cost and grade of service of the circuit facility trunk groups at a PBX, and optimization (use of mathematical programming techniques to modify the routing and to adjust the trunk-group sizes).
* Step 1--A certain constant, fraction f, is applied to the daily, first-offered traffic of every trunk group to produce representative hourly traffic.
Each trunk group is a stage, and the number of trunks in each stage is a decision variable.
The cost of the overflow traffic is taken from the cost-function table for the succeeding trunk group, which has already been developed.
The cost-function table of the first trunk group has only one entry, which corresponds to the group's first-offered traffic.
This theory takes advantage of the formulas for the mean and the variance of the overflow traffic when a random traffic of "a" Erlangs is offered to a trunk group of size c: Mean, m=aE(c,a) Variance, v=m(1-m+a/(c+m-a)) where m=the mean of the overflow traffic, a=the mean of the original random traffic; c=the trunk group size; E(c,a)=the probability of overflow using Erlang B formula; and v=the variance of the overflow traffic.
This can be demonstrated in a comparison of total overflow traffic calculation for one trunk group using different approximation methods (Figure 6).
In doing so the tool helps eliminate the time, cost and complications that can arise in the planning and maintenance of Trunks, Trunk Groups
, DIDs and DID Groups as well as off-network telephone numbers.
"Rather than have members subjected to busies or long waits in queue, we simply monitor the levels of activity in the trunk groups
and determine whether more or less are needed.
System flexibility allows configuration to meet individual tenant needs for trunk groups
, attendant consoles and call-detail information, plus call-processing, routing and queuing options.