Common channel priority acknowledgement schemes for carrier sense cable systems

Abstract

Two techniques that prioritize the common channel acknowledgment traffic are proposed and analyzed in this paper for packet-switched cable systems that employ carrier sense multiple access (CSMA) protocols. Closed-form expression for the packet interdeparture time moment generating function of both priority acknowledgment schemes are obtained, under a Poisson arrival model, to facilitate the performance comparisons with respect to channel throughput and output variation coefficient. A generic p-persistent carrier sense protocol is utilized to unify the treatments of the non-persistent and 1-persistent CSMA protocols. A statistical test procedure is also introduced to evaluate the appropriateness of the Poisson anival model. Both slotted and non-slotted operations are treated along with the use of collision detection (CD). IntroductionThe effects of employing a common channel acknowledgment (CCA) scheme[l] on the information packet output process were examined in a previous study [2] for non-slotted non-persistent and 1-persistent CSMA protocols. On the account of resolving the conflicts between the information and the acknowledgment traffic we have found that, with l-persistent operation, it is imperative to prioritize the latter by means of a pre-transmission deferment (PD). The implementation of PD, however, imposes an extraneous delay on all users that are trying to access the channel. We have also found that, with non-persistent operation, the absence of PD does not severely degrade the channel throughput and a CCA scheme without such pre-deferment is still of value due to its ease of implementation. Therefore, it is of interest to devise a CCA scheme that will prioritize the acknowledgment traffic without incurring the PD. This is the primary objective of this paper. One such scheme will be proposed, and its output process analyzed, for packet-switched cable systems employing a generic p-persistent CSMA protocol[3] which, as described below, includes the usual non-persistent and 1-persistent protocols as special cases. The reason for confining ourself to a cable system is that the post-jamming (PJ) ability required in this new CCA scheme comes naturally with the collision consensus mechanism that is readily available in most operating cable systems. A dual cable broadband topology[4] is also required for implementing such a scheme. Due to the last constraint on the new scheme, the results in [2] will also be extended in this paper to the generic p-persistent protocol with O<p<l. This will provide an altemative CCA scheme and serve as the secondary objective of this paper. We shall refer to it below as the PD scheme. We shall derive the moment generating function D'(s) of the information packet interdeparture time D for both priority acknowledgment schemes. Explicit expressions for the first two moments of D