TRANSMISSION DATA FOR RATING TELEPHONE CIRCUITS 337 



terminals. The normal adjustment is that for which the working 

 reference system has an 18 db volume equivalent. The effective 

 equivalent of any other complete telephone circuit is also equal to 

 18 db if it provides the same grade of service as the normal adjustment 

 of the working reference system. 



Ratings for Circuit Elements 



The division of the effective equivalent of a complete circuit into 

 its various parts, which are called effective losses, could be done in 

 any one of several ways. The procedure described below appears to 

 be the most suitable considering convenience, significance of the losses 

 assigned to each element, and consistency with the form of previous 

 transmission data. 



The individual effective losses which in general make up the effective 

 equivalent of a complete circuit include the following: 



1. Transmitting loop loss. 



2. Receiving loop loss. 



3. Trunk loss. 



4. Terminal junction loss. 



5. Central office loss. 



6. Intermediate junction loss. 



7. Circuit noise loss. 



8. Room noise loss. 



The apportionment of the total normal rating of 18 db among the 

 parts of the reference system can be done in any way which is con- 

 venient. The performance significance of the numerical values as- 

 signed by the volume loss method of rating has been retained by 

 making the effective ratings of the working reference trunk and trans- 

 mitting and receiving loops equal to those obtained from the previous 

 volume loss data. 



The loop losses are ratings of a subscriber station, subscriber loop, 

 and a basic central office circuit. They are determined by comparison 

 with the corresponding element of the working reference system, in 

 each case using the remaining elements of the working reference system 

 to complete the circuit and using the same electrical circuit noise and 

 the same room noise as specified for the reference system. For ex- 

 ample, any transmitting loop, which is substituted for the reference 

 transmitting loop and which gives the same grade of service, also has 

 an effective loss equal to the loss of the reference loop. Any loop 

 which gives service effectively X db better has an effective loss equal 

 to the assigned loss of the reference loop minus X db, and any loop 



