THROWDOWN MACHINE FOR TRAFFIC STUDIES 301 



tion of markers, registers or the particular number group link frames 

 required. Busy condition of lines or trunks may result in rerouting the 

 call. In general, the grade of service is measured by the delay in con- 

 necting a subscriber to a register (dial tone delay) and the probability 

 of not finding an idle trunk or channel. 



Intraoffice Trunks 



The intraoffice trunks, used on locally originated and completed sub- 

 scriber connections, include the supervisory, charging and ringing func- 

 tions. The trunk is held on a connection for the duration of the call in 

 distinction to markers and registers which have short holding times. 



Outgoing Trunks and Senders 



Calls to other offices are completed via outgoing trunks which incor- 

 porate the supervisory and charging functions. In order to transmit 

 information to the distant office, an outgoing sender is connected to the 

 trunk for a short period of time by means of an outgoing sender link. 

 In establishing the call, the marker first connects itself to the sender via 

 the sender connector in order to register in the sender the called number, 

 and then sets up the trunk-sender linkage. When the sender, which may 

 be one of several varieties depending upon the type of signaling required 

 by the distant office, has transmitted the number to the distant office, it 

 drops off the connection. 



Incoming Trunks and Registers 



Calls from a distant office are completed through an incoming trunk, 

 which includes supervisory and ringing functions. In order to receive 

 signals from the distant office, the trunk connects itself to an incoming 

 register by means of an incoming register link. When the register, which 

 again may be one of several varieties, has received the called number, 

 it obtains a marker through the marker connector for setting up the 

 connection. When its functions have been accomplished, the register 

 disconnects. 



Tone Trunks 



This group of trunks includes those to which calls are routed when 

 line busy or all trunk or channel busy conditions are met. Subscriber 

 error or excessive delay in diaUng also result in routing to these trunks. 

 The tone trunks return distinctive tone signals to the subscriber. If 



