R. Radhakrishna Pillai

Effect of TCP/LLC protocol interaction in GPRS networks

The interference between retransmissions at the Logical Link Control (LLC) protocol and the Transmission Control Protocol (TCP) in a General Packet Radio Services (GPRS) network is studied in this paper by means of simulations. The factors that contribute to the TCP/LLC protocol interference are discussed. The results show that in the presence of wireless link errors, LLC protocol does not cause severe interference with TCP but will enhance the network performance when the LLC parameters are set properly.

Call performance studies on the ATM forum UNI signalling implementations

Asynchronous Transfer Mode (ATM) is widely accepted as the transfer mode for Broadband Integrated Services Digital Networks (B-ISDN). As ATM networks provide connection-oriented services, signalling is an essential component of these networks. The performance of the signalling system is crucial in determining the scalability of the network. Call performance measurements on two different ATM switches were carried out using a broadband network analyser. Calls are generated according to a deterministic/Poisson distribution and various components of the call set up delay are analysed. The probability distribution of the delays is obtained and the correlation between the set up delay and its different constituents is established. It is observed that the delays at the calling and the called user entities of the UNI form a major component of the call set up delay. The average call set up delay is found to be 21 and 27ms, respectively, when a single switch is involved in call set up and 50ms when two switches are involved in call set up. With simultaneous call arrivals, though with higher delays, both the switches are found to establish calls at the rate of 100calls/s.

Impact of ATM cell delay on multimedia applications

The impact of ATM cell delays on multimedia application performance is studied through measurements using a broadband network analyser. A method is developed to measure the ATM cell delays of an application using the analyser. It is found that the cell delay distribution becomes continuous as the traffic load on a connection becomes lighter. The effect of background traffic on cell delay for a reference connection is studied. Though the cell delay of the reference connection is unaffected by the presence of background traffic, the cell-delay auto-correlation is found to decrease. A gamma distribution is used to approximate the cell delay distribution. The measurement results closely match the delay prediction using the approximation. In a network with multiple ATM switches, the gamma distribution only slightly overestimates the delay. The frame level statistics and the cell delay performance of a video conferencing application based on motion JPEG are measured. Using the gamma cell delay distribution, the frame loss of an MPEG-I video source is predicted and compared against the measured values based on MPEG-I traces.

Improving fault detection and reliability in FDDI networks

FDDI (Fibre Distributed Data Interface) is a 100 Mbit/s token ring network with two counter rotating optical rings. In this paper various possible faults (like lost token, link failures, etc.) are considered, and fault detection and the ring recovery process in case of a failure and the reliability mechanisms provided are studied. We suggest a new method to improve the fault detection and ring recovery process. The performance improvement in terms of station queue length and the average delay is compared with the performance of the existing fault detection and ring recovery process through simulation. We also suggest a modification for the physical configuration of the FDDI networks within the guidelines set by the standard to make the network more reliable. It is shown that, unlike the existing FDDI network, full connectivity is maintained among the stations even when multiple single link failures occur. A distributed algorithm is proposed for link reconfiguration of the modified FDDI network when many successive as well as simultaneous link failures occur. The performance of the modified FDDI network under link failures is studied through simulation and compared with that of the existing FDDI network.

Research: A method to improve the robustness of MPEG video applications over wireless networks

It is important that applications deployed in wireless networks be robust enough to accommodate different kinds of data losses due to link errors, connection re-routing, and network congestion. A scheme to improve the robustness of MPEG based video applications is proposed. Under this scheme, the packet size at the sender is optimized to the MPEG system layer unit size to enable fast recovery of the time stamps. The receiver buffers the data packets for re-playing during packet losses, preserves useful time stamps for synchronisation, and re-synchronises the decoder when packet loss occurs. This involves no feedback and results in faster recovery of critical timing information for video decoding. The proposed method has been implemented on a video application based on MPEG-I over an Asynchronous Transfer Mode (ATM) network. The experiments show that the proposed technique is very effective when there is deterministic/random packet losses with burst size less than 21. The method is equally applicable to video applications based on MPEG-II program stream and, to wireless Internet.

Distributed control of wireless ATM networks using CORBA

This paper reports the design, implementation, and performance evaluation of a CORBA based distributed control architecture for signalling and mobility management in the Wireless ATM Research project (WARP). The distributed control architecture makes use of open signalling to manipulate the various network resources to realise network services such as call control, multicast, and mobility management. Open signalling provides the flexibility and ease in creating new network services as opposed to standard signalling approaches such as the ATM Forum signalling. The network control architecture provides inter-working with the ATM Forum UNI signalling. The open signalling is found to be more flexible compared to the UNI-PNNI based signalling and yields comparable delay performance.

Throughput performance of distributed applications in switched networks in presence of endźsystem bottlenecks

The steady state throughput performance of distributed applications deployed in switched networks in presence of end‐system bottlenecks is studied in this paper. The effect of various limitations at an end‐system is modelled as an equivalent transmission capacity limitation. A class of distributed applications is characterised by a static traffic distribution matrix that determines the communication between various components of the application. It is found that uniqueness of steady state throughputs depends only on the traffic distribution matrix and that some applications (e.g., broadcast applications) can yield non‐unique values for the steady state component throughputs. For a given switch capacity, with traffic distribution that yield fair unique throughputs, the trade‐off between the end‐system capacity and the number of application components is brought out. With a proposed distributed rate control, it has been illustrated that it is possible to have unique solution for certain traffic distributions which is otherwise impossible. Also, by proper selection of rate control parameters, various throughput performance objectives can be realised.

A Modified Distributed Queueing Access Protocol for Dual Unidirectional Bus Networks

The protocol is described. Packet access delay is the sum of request bus access delay and data bus access delay. An upper bound on data bus access delay is obtained that is equal to twice the propagation delay from the node to the most upstream node. The expected request bus access delay for Poisson offered traffic is the expected waiting time in a slotted M/D/1 non-preemptive priority queue, for which an expression is obtained. The upper bound on data bus access delay is smaller and the expected request bus access delay is larger at a more upstream node. A bandwidth balanced version of the protocol is also described, for which the upper bound continues to hold

Distributed Queue Dual Bus Metropolitan Area Network: A Review of Performance Analysis of the Medium Access Control Protocol

Standardization, prototyping and application of unidirectional bus networks are introduced followed by a detailed description of Distributed Queue Dual Bus Medium Access Control (DQDB MAC) protocol. A review or throughput analysis and delay performance of the MAC protocol along with a survey of related literature is presented (42 refs.)

Distributed Bandwidth Management in FDDI Networks with Multiple Isochronous Services

The Fiber Distributed Data Interface (FDDI) is a proposed American National Standard for a 100 Mbps token ring using an optical fiber medium. The timed token protocol used in FDDI allows the integration of digital voice, video, interactive data communications and large file transfers over the same network. The performance of the protocol has been studied in the past for asynchronous class of service with a single isochronous service.In this paper, we focus on the performance of the protocol when multiple class of isochronous services are to be provided along with the asynchronous class of service. It is found that the performance of the protocol is affected by the different delay requirements of different isochronous services. The performance of the protocol is studied through simulation with two classes of isochronous services viz video and voice. We also propose two distributed algorithms to improve the performance of the protocol under multiple isochronous services.