Short-Packet Transfer Performance in Local Area Rings

The performance of various access control protocols for high-speed, bit-serial, computer communication rings is studied. Local Area Computer Network (LACN) applications in which message packets are of fixed length and shorter than the total inherent propagation delay around the ring are the focus of attention. Token, slotted, and static and dynamic insertion rings are included in the study. In all cases, the transmitting station is responsible for removing its transmitted packet from the ring. Under this type of removal rule, it is possible for the stations to execute their access control algorithms with only a short, fixed, inline delay in each station. The insertion rings dynamically switch longer delays (insertion registers) into the ring when they are transmitting a packet. The transmitter-remove rule operates in such a way that hogging of the ring transmission facility by a subset of stations cannot occur. Expressions that approximate average transfer time as a function of utilization are derived for all ring types and are checked by simulation. For the assumed short-packet environment, it is found that token rings exhibit the slowest transfer times, while dynamic insertion rings are fastest.