sentences:  As the TXE2 call-set-up time was some 50 milliseconds, this design requirement was just met, but even so, the overall capacity of the system was determined by the probability of an incoming call being delayed too long in its initial connection to a register.The grade of service in a TXE2 was dependent on the number of customers in an A-switch group, with access to just 25 A-B trunks.The normal standard on the earlier exchanges was 125 customers per A-switch group.