344 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1953 



The route number in some cases is required only for location purposes 

 since many trunk groups are identified by name. It is assigned to a 

 common group of trunks, maximum 100, or 10 per frame. However, in 

 the case of outgoing trunks, the route number is required to identify 

 the specific trunk group desired. The route number for originating reg- 

 isters is the same as the marker connector number for each register and 

 is unusual in that any route number from 0-9 represents the same reg- 

 ister group. 



The register jacks occupy the lower trunk level on the array and are 

 supphed with pegs which are used to originate the second half of out- 

 going and intraoffice calls. During dialing time, the associated line peg 

 occupies the register jack to mark it busy. The next higher level on the 

 array is the group of incoming trunks. These are furnished on a two- 

 jack per trunk basis and are, in effect, multiples of the incoming trunk 

 array at the originating position. The two jacks are required to hold 

 the terminating line peg and the incoming trunk peg. The route number 

 for these trunks is significant only for the function of location since it is 

 not necessary for throwdown purposes to segregate incoming trunks into 

 groups as it is with outgoing trunks. 



The intraoffice trunks are divided into an A- and a B-group since 

 more than 20 trunks per frame are required. The No. 5 marker can only 

 test up to 20 trunks per frame at one time. The machine automatically 

 allots calls between the two groups. Two jacks per trunk are required 

 for originating and terminating line pegs. Unlike the incoming trunk 

 jacks each jack of an intraoffice pair corresponds to a different switch 

 location, although only one switch number is used for identification 

 purposes. 



The outgoing trunk groups are disposed above the intraoffice trunks. 

 For the most part, these trunks will be in small groups, each with its 

 own route number. When a call is set up to an outgoing trunk, it is 

 necessary for the marker operator to inform the assignment operator of 

 the correct route number. Several of these trunk groups can occupy the 

 same horizontal level to conserve space. Only one jack per trunk is 

 required to hold the originating fine peg. 



Tone trunks (busy, overflow, partial dial, no dial trunks) are at the 

 top of the array. Only one jack per trunk is required. 



Within the trunk link frame, the preference order in which a No. 5 

 marker tests trunks and the manner in which the order shifts from call 

 to call is rather complex. In order to reduce the load on the assignment 

 operator in trunk hunting, the actual trunk preference is approximated 

 by reversing the direction of hunting within a frame group from call 



