CALL CENTERS (CENTRES) - Faculty of Industrial Engineering and ...

with, the telephone network. It is shown that both network performance and customer behavior
affect the call dispositions and the total call setup time; however, customer-dependent failures
to complete account for 85 percent of all failures, and customer-determined components of the
call setup time make up 71 percent of the total setup time. It is found that traffic composition
in terms of the relative mix of business and residential originations exerts a strong influence
on call dispositions. Network performance affects the probability of equipment blockages and
failures and the interval from end of dialing to receipt of a network response. These are both
found to depend on calling distance, while the latter is also affected by the types of originating
and terminating local switching.
4. Roberts, J.W. Recent observations of subscriber behavior. 9th International Tele-traffic Conference
(ITC-9), Torremolinos, 1979.
Abstract. This paper presents an analysis of experimental observations of subscriber repeated
attempts and subscriber patience in relation to the post-dialing delay. The analysis includes, in
particular, an investigation of the influence of the interval between successive attempts and we
derive estimates of the probability distributions of the subscribers’ patience. The results concern
local, trunk and international calls made by certain subscribers on a Paris exchange.
(Appears also in Section II.)
5. Cohen, H.S. Measuring and modeling user satisfaction with telephone switching and transmission
performance. Proceedings of the 9th International Symposium on Human Factors in Telecommunications,
Red Bank, NJ, 1980, 237–242.
6. Isobe, S., S. Sato and M. Hoshi. Opinion test on dial tone delay and post-dialing delay by PABX
customers. Proceedings of the 9th International Symposium on Human Factors in Telecommunications,
Red Bank, NJ, 1980, 243–250.
7. Liu, K.S. Direct distance dialing: Call completion and customer retrial behavior, Bell System
Technical Journal, 59 (3), 1980, 295–311.
Abstract. Most customers placing a direct-distance-dialing (DDD) call in the United States
are able to complete the call on the first attempt. However, it is reasonable to expect that
the probability of an initial completion will be less than 1. When an initial attempt fails to
complete, a customer may decide to abandon his desired telephone connection or to make one
or more retrials. In general, a sequence of one or more attempts may be initiated by a customer
in an effort to establish the desired connection. A study of DDD call completion and retrials is
important to provide an overall characterization of network performance and customer behavior
in setting up customers’ desired telephone connections. A survey adopting a two-stage stratified
sampling plan was undertaken to obtain DDD retrial statistics. Data associated with sampled
DDD calls that were originated from one of 890 switching entities in the Bell System network
were collected for a period of one week. The basic DDD retrial results reported here are initial
attempt disposition probabilities, retrial probabilities, number of additional attempts, ultimate
success probabilities, and distribution functions for retrial intervals following different types of
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