Heavy Traffic Characteristics of a Circular Data Network

The concept of a loop network for data transmission has been proposed recently by J. R. Pierce.1 In such a network the stations are connected to a closed loop main line on which one-way traffic is allowed. A message to be delivered from one station to another is arranged, at the sending station, into standard packets each carrying the address of the receiving station. These packets are then delivered onto the main line, one at a time, where they flow around in the allowed traffic direction. The address of each packet is checked at each station on the way until it reaches the receiving station where it is removed from the main line. Traffic on the main line cannot be delayed; therefore, a station can deliver a packet onto the main circular line only when permitted by the existence of a gap in traffic or when receiving a packet from the main line. Principal 2521 2522 T H E BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1971 features of the system may be explained with the aid of the fourstation network shown schematically in Fig. 1. The four-armed structure revolves around the central axis and stops briefly every time the four packet-carrying compartments at the ends of the arms are aligned with the four stations. During such a stop each station is able to check the content of the aligned compartment. If the compartment is empty, the station can load it with a packet. If there is a packet in the compartment, it will not be removed unless it is addressed to the said station, in which case the station is permitted to load the compartment again after unloading it.