Amit Bhargava

Performance comparison of error control schemes in high-speed computer communication networks

The authors examine the performance of two different approaches for handling the loss and/or corruption of messages as they are transmitted between two end users in a high-speed network. In the link-by-link approach, two adjacent nodes in an end-to-end path locally detect and recover from message loss or corruption along their joining link. In the end-to-end approach, recovery is done solely on the basis of a single end-to-end protocol. The authors develop analytic performance models, validated with simulation, for comparing the performance of these two approaches. The authors find that for the range of network parameters of practical interest, an end-to-end approach towards error control is superior to a link-by-link approach, even under assumptions that would overly favor the link-by-link approach, while at the same time requiring fewer network resources (e.g. buffers, computation time) than the link-by-link approach. The performance differences arise primarily from the increased buffer requirements of the link-by-link approach. >

Ballot theorems applied to the transient analysis of nD/D/1 queues

The problem of transporting constant-bit-rate (CBR) traffic through a packet network is analyzed. In the system considered, CBR traffic is packetized and packets from several similar sources are multiplexed on a transmission link. The bit streams are recreated at the receiving end by demultiplexing the packets and then playing out the packets of each CBR stream. Traffic fluctuations may cause gaps to appear in the playout process. Their frequency can be reduced by adding a smoothing delay to each stream. The queueing system analyzed has periodic arrivals and deterministic service times. A method of analysis, based on the ballot theorems of Takacs (1967), is presented to provide steady-state delay distributions as well as a transient analysis of the system to predict the statistics of the time for a gap to develop in the CBR stream as a function of the smoothing delay. >

Queueing analysis of continuous bit-stream transport in packet networks

The problem of transporting continuous bit-stream oriented (CBO) traffic through an all-packet network is examined. In the system considered, CBO traffic is packetized by collecting bits generated by a source during a fixed interval of time (packetization time) and packets from K such sources are multiplexed on a transmission link. The bit-streams are recreated at the receiving end by demultiplexing the packets and then playing out the packets of each bit-stream in sequence. The queuing system analyzed is a single-server queue with periodic arrivals and deterministic service times; the steady-state distributions of the queue length and delay are derived. The method of analysis is based on the ballot theorems and has a computational complexity of O(K), as compared to other proposed methods with complexities of O(K/sup 3/) or greater. It is shown that the delay, measured in units of the packetization time, decreases as the link bandwidth increases. Therefore, for the large capacity links, the contribution of the queuing delay to the total network delay is small compared to the packetization time.<<ETX>>

A hybrid media access protocol for high-speed ring networks (fibre optic LAN)

A hybrid protocol is proposed for high bandwidth rings in which the roundtrip propagation delay is much larger than the packet transmission time. Features of random-access protocols and conflict-free protocols such as token passing are combined to achieve superior performance. The scheme permits simultaneous use of the channel by many packets, is fair to all stations, and is completely distributed. Performance results show that the system remains stable for throughputs up to a maximum of 1 and that the delay characteristics are better than those of related access protocols. The protocol additionally provides for reservation of bandwidth on demand and bounded delays for real-time applications. >

Frame loss due to buffer overflows in fast packet networks

An analytical method is derived to estimate the protocol data unit (PDU) frame loss probability as a function of buffer size when identical sources are multiplexed on a fast packet link. The generation of PDUs from each source is governed by an on-off source model, and upper and lower bounds on the frame loss probability are derived. The analysis takes into account the correlated nature of fast packet losses within a PDU due to buffer overflows. The required buffer size for a given frame loss probability is directly proportional to the expected PDU frame length, and the loss probability decreases exponentially with increasing buffer size.<<ETX>>

A hybrid media access protocol for a fiber optic ring network

A hybrid protocol is proposed for high-bandwidth rings in which the round-trip propagation delay is much larger than the packet transmission time. Features of random-access protocols and conflict-free protocols such as token passing are combined to achieve superior performance. The scheme permits simultaneous use of the channel by many packets, is fair to all stations, and is completely distributed. The performance results presented indicate that the system remains stable for throughputs up to a maximum of 1, and that the delay characteristics are better than those of other related access protocols.<<ETX>>