The Effect of Frame Load and Balance on Dial-Tone Delay in No. 5 Crossbar

Vol. 54, N o . 10, December 1975 Printed, in U.S.A. The Effect of Frame Load and Balance on Dial-Tone Delay in No. 5 Crossbar By H. A. GUESS (Manuscript received May 22, 1975) Recently obtained field data and theoretical studies show that, for a fixed subscriber calling rate, dial-tone delay in No. 5 crossbar can be appreciably increased by high average line-link frame loads and also by poor load balance. The increased delay is caused by waste dial-tone-marker usage generated by a small number of calls that encounter horizontal group blocking in obtaining a dialing connection. This paper discusses an analytical model to predict the time from receiver off-hook to receipt of dial tone under various service conditions in No. 5 crossbar. I. INTRODUCTION 1.1 Description of the dial-tone connection process In a No. 5 crossbar switching machine, dial tone is provided to a subscriber line, terminating on a line-link frame (LLF), by an originating register (OR), terminating on a trunk-link frame (TLF), via a series of three network links: line links, junctors, and trunk links. The dialing connections are set up by dial-tone markers (DTMS), which are common control devices. Each line-link frame contains a number of crossbar switches that are used to establish connections between subscriber lines and trunks, or between subscriber lines and service circuits, such as originating registers. The crossbar switches that form line concentrators on which groups of subscriber lines terminate are called horizontal groups.