JITTER ANALYSIS IN ATM NETWORKS

Wassim A.J. MATRAGI

Unlike traditional data networks, future broadband ‑ISDN (BISDN) wide‑area net­works based on Asynchronous Transfer Mode Technology (ATM) are being proposed to provide a single integrated access to a variety of services and applications such as data, voice, video and image. Statistical multiplexing of fixed size cells generated from diverse traffic sources, introduces considerable flexibility in the allocation of network resources, but may have severe impact on the Quality of Service (QOS) requirements (delay and loss ) of individual streams.

Most of the work done so far determines the performance of the aggregated network traffic, in a single node environment. The main focus of this thesis is to characterize the performance (QOS) requirements on an‑individual, per‑session basis, in a multiple node environment. In particular, in this thesis, we consider Constant Bit Rate (CBR) sources, which are expected to represent a considerable portion of the traffic in ATM networks. An important performance measure for CBR sources, in addition to the aforementioned measures‑ delay, and loss‑ is jitter, which describes the deterioration of the periodic nature of CBR traffic.

 We first investigate the jitter in a single node. The queueing model consists of the superposition of two streams: the renewal stream (stream under consideration) and a background traffic (which models the traffic interfering with the tagged stream). We obtain very simple results for the jitter expression in the heavy and light traffic mode. We then extend the analysis to a networking environment.

Our results indicate that for any number of nodes, the jitter variance is (almost) proportional to the variance of the background traffic competing for resources with the tagged stream. We also find that in general, as the number of nodes increases, the jitter distribution tends to a limit. In the heavy traffic, we provide the functional equation satisfying this limit which readily gives all the moments of the jitter in closed form for large number of nodes in the network.

Our results also show, that as a result of multiplexing, the packets belonging to the periodic stream tend to cluster resulting in an increase of the bandwidth requirement of the CBR stream as it proceeds through the network. A remedy for that would be traffic shaping at the intermediate multiplexers.