On various modifications of the PARS random access scheme

Variations of a multiple-access scheme, preassigned retransmission slots (PARS), are introduced for different applications. PARS was studied through simulation runs for the variable-packet-length case, showing the superiority of PARS over time-division multiple-access (TDMA), especially in cases where the network structure/architecture allows no idle slot insertion to report end of the packet, or in cases where traffic is not uniform. A nonslotted version of PARS, suitable for networks in which no slot synchronization is desired, is reported. This variation is introduced for both fixed and variable message lengths. A double-channel version of PARS, PARS/DC, is also introduced. It has the basic capabilities of PARS but uses two channels for transmission. The channels can be physically separate or they can be separated by frequency- or time-division multiplexing. Besides reliability, this version offers the property that a packet at the head of the transmission queue will not suffer more than N-1 (N is the number of stations in the network) slots of access delay, even in the worst case. The definite upper bound on the access delay can be helpful in some delay-variance-sensitive applications