Analysis of Mixtures of Wide- and Narrow-Band Traffic

The traffic aspects of two communications systems are considered. The first case uses a single wide-band facility to simultaneously carry traffic of different bandwidths (for example, a super group to carry single trunk calls and calls requiring a channel group). Both types of callers have full access to the facility, but in order to equalize their grades-of-service the wide-band traffic may be given the advantage of queuing when it cannot gain access. The economy which results from this combined operation must be balanced with the cost of the queuing facility. The second case, facility or group switching, employs the switching of trunk groups to meet individual traffic requests. In this model there are two types of single trunk callers, one which is served on available single trunks and another whose requests are met by establishing temporary exclusive groups to meet subsequent demands of this second type of caller. The blocking probabilities, operating efficiencies, and traffic consequences are discussed, with the conclusion that facility switching must yield switching savings greater than the increased trunk costs (more trunks to meet operational inefficiencies) in order to produce net savings in a system to provide an equivalent grade-of-service. Of particular importance in both cases is the oscillatory form of the blocking probability curves, a characteristic that is endemic to these systems.