INTERTOLL TRUNK NET LOSS MAINTENANCE 959 



Here again the alternate routing follows a definite plan.^ As shown in 

 iMg. 2, a call from toll center, TC, to toll center, TC", will follow the 

 direct route, if it is available and not busy. A second choice will be via a 

 higher ranking office in the chain from TC" to the regional center, RC". 

 A third choice may be available to a still higher ranking office. Thus, if 

 the originating office cannot use its direct route, the call will be advanced 

 over the alternate routes according to a predetermined pattern. If all 

 other alternatives fail, the call will follow the heavy solid line 7-link route 

 shown on Fig. 2, or, in special cases, the 8-link route via RC". 



These attempts involve many operations but the automatic equipment 

 completes them cjuickly. This makes it feasible to provide small, high 

 usage, direct trunk groups between two points, with the realization that 

 in busy periods alternate routes can handle the overflow^ traffic with neg- 

 ligible time delay. Thus over a good part of the day, the direct trunks 

 or first choice trunks will handle the traffic. In the busy periods, use of 

 alternate routes with a mnnber of links in tandem vdW be a frequent 

 occurrence. Therefore, it is important to have losses on alternate routes 

 not greatly different from those on direct routes so customers will not 

 experience noticeable contrasts. 



Operators will seldom talk to each other over the complete connection, 

 and even less over the individual trunks. Only on person-to-person or col- 

 lect calls will they talk even to the called party. On station-to-station 

 calls they merely dial or key up the desired number and rely on super- 

 visory signals to disclose the progress of the call. 



On operator dialed calls, the operator may sometimes pick up the in- 

 tertoU trunk in her switchboard multiple, but in many cases she will 

 reach it over a tandem trunk. In the former case she can identify the in- 

 tertoll trunk forming the first link in the connection but assistance would 

 be needed at intermediate testboards to identify succeeding trunks. In 

 the latter case, testman assistance would be required at the originating 

 office in order to identify even the first trunk of the connection. In either 

 case the need for holding the customer's line during identification, to 

 avoid breaking down the connections makes such means of identifica- 

 tion impracticable Avith presently available techniques. 



On direct distance dialed calls there are no operators involved and pres- 

 ent means of identification of trunks in trouble after the connection has 

 ])een established are even more impracticable. This is because the calling 

 party must release the connection before he can report a trouble, thus 

 destroying any possibility of trunk identification. 



6 R. I. Wilkinson, Theory for Toll Traffic Engineering in the U. S. A., B.S.T.J., 

 March, 1956. 



