Thomas Curran

Evolutionary trends in intelligent networks

A number of groups are currently developing technologies aimed at evolving and enhancing the capabilities of intelligent networks. In this article we discuss three of these initiatives: PINT, Parlay, and IN/CORBA interworking. The IETF PINT work addresses how Internet applications can request and enrich telecommunications services. The Parlay consortium is specifying an object-oriented service control API that facilitates the access, control, and configuration of IN services by enterprise IT systems. The OMGs IN/CORBA interworking specification enables CORBA-based systems to interwork with existing IN infrastructure, thereby promoting the adoption of CORBA for the realization of IN functional entities. We address how all three of these technologies could be deployed together in order to provide a basis for a more flexible and open IN architecture. We also identify a number of common trends and potential pitfalls highlighted by current work on the evolution of IN.

SCTP congestion control: Initial simulation studies

Abstract This paper uses simulation studies to explore the behaviour of SCTP congestion control. Several possible variants of SCTP congestion control are identified and each is compared with the behaviour of Reno TCP, a well-known TCP variant. We identify three flaws in the current SCTP congestion control mechanisms. 1. Recovery without a timeout after a packet loss is only possible if SCTP generates the optional Gap Ack Blocks in SACK messages. 2. The SCTP fast retransmit procedure is vulnerable to being mistakenly triggered multiple times leading to under-utilization of the network during recovery and duplicate retransmissions of the lost packet. 3. The SCTP fast retransmit procedure must wait for half a window of data to be acknowledged before retransmitting a lost packet yielding a slow response to packet loss. We also provide suggested remedies for these flaws. Finally we demonstrate how SCTP congestion control mechanisms can cause a burst of packets after recovery from a packet loss.

Path allocation in a three-stage broadband switch with intermediate channel grouping

A method for path allocation for use with three-stage ATM switches that feature multiple channels between the switch modules in adjacent stages is described. The method is suited to hardware implementation using parallelism to achieve a very short execution time. This allows path allocation to be performed anew in each time slot. A detailed description of the necessary hardware is presented. This hardware counts the number of cells requesting each output module, allocates a path through the intermediate stage of the switch to each cell, and generates a routing tag for each cell, indicating the path assigned to it.<<ETX>>

Simplified overflow analysis of an optical burst switch with fibre delay lines

We develop an approximate analytic model of an Optical Burst Switch with share-per-node fibre delay lines and tuneable wavelength converters by employing Equivalent Random Theory, an approach from circuit-switching analysis. Our model is formulated in terms of virtual traffic flows within the switch from which we derive expressions for burst blocking probability, fibre delay line occupancy and mean delay, which we then resolve numerically. Emphasis is on simplicity of the model to achieve good numerical efficiency so that the method can be useful for formulating dimensioning problems for large-scale networks. Solution values from the analysis are compared with discrete-event simulation results.

Hierarchical semiautomatic video object segmentation for multimedia applications

In this paper, an efficient tool to extract video objects from video sequences is presented. With this tool, it is possible to segment video content in a user-friendly manner to provide easy manipulation of video content. The tool is comprised of two stages. Firstly, the initial object extraction is performed using the Recursive Shortest Spanning Tree (RSST) algorithm and the Binary Partition Tree (BPT) technique. Secondly, automatic object tracking is performed using a single frame forward region tracking method. In the first stage, an initial partition is created using the RSST algorithm which allows the user to specify the initial number of regions. This process is followed by progressive binary merging of these regions to create the BPT. The purpose of creating the BPT is to allow the user to browse the content of the scene in a hierarchical manner. This merging step creates the binary tree with nearly double the user-specified number of homogenous regions. User interaction then allows grouping particular regions into objects. In the second stage, each subsequent frame is segmented using the RSST and corresponding regions are identified using a forward region tracking method.

Load Balancing for a Distributed CORBA-Based SCP

This paper examines load balancing issues relating to a distributed CORBA-based Service Control Point. Two types of load balancing strategies are explored through simulation studies: (i) A novel ant-based load balancing algorithm, which has been devised specifically for this type of system. This algorithm is compared to more traditional algorithms, (ii) A method for optimal distribution of the computational objects composing the service programs. This is based on mathematically minimising the expected communication flows between network nodes and message-level processing costs. The simulation model has been based on the recently adopted OMG IN/CORBA Interworking specification and the TINA Service Session computational object model.

Cell-level path allocation in a three-stage ATM switch

A method of cell-level path allocation for three-stage ATM switches has previously been proposed by the authors. The performance of ATM switches using this path allocation algorithm has been evaluated by simulation, and is described. Both uniform and non-uniform models of output loading are considered. The algorithm requires knowledge of the number of cells requesting each output module from a given input module. A fast method for counting the number of requests is described.<<ETX>>

A strategy for the resolution of intelligent network (IN) and Signalling System No. 7 (SS7) congestion control conflicts

Signalling System No. 7 (SS7) networks are used to transport call control messages for both traditional telephony and advanced intelligent network (IN) based services. A large number of IN implementations have been successfully deployed, however a key factor in ensuring their ongoing commercial success will be that they continue to meet specified performance targets. Because network congestion may have a serious adverse effect on IN service performance, much research effort has been focused on IN congestion control. However, in general, this research has not taken into account operation of the standardised congestion controls operating at the SS7 plane of the network. This paper outlines an investigation that demonstrates that the interaction between SS7 and IN congestion controls is not always harmonious and can lead to serious performance degradation. A congestion control strategy, which resolves the problems identified, is presented and evaluated.

Signalling System No. 7 as an Agent Platform Message Transport Protocol

FIPA has provided a standardised model for implementing interoperable agent systems that may prove the basis for new solutions to the problem of managing the growing complexity of the telecommunications infrastructure. However, the ability of agents to operate in the telecommunications domain would be greatly enhanced if the FIPA architecture was refined to deal with the standardised Signalling System No. 7 (SS.7) communications protocol suite almost universally used for the control of telecommunications networks. The current FIPA model is TCP/IP centred, thus in order to use the SS.7 infrastructure a mapping from FIPA message transport requirements to SS.7 protocol transport capabilities must be performed. A protocol for the distribution of FIPA ACL messages in SS.7 networks must also be defined. Analysis of the possibilities shows that there are different design choices depending upon the exact deployment model and agent capabilities required. In addition it is necessary to allow the use of SS.7 addresses within the FIPA management protocols. An evaluation of best common practice for CORBA-based FIPA implementations in the SS.7 domain must also be defined. This treatment highlights the failings of the current FIPA model when applied to the real-time, bandwidth-constrained, specialised protocol environment of telecommunications signalling.

Sensitivity properties of SC filters derived from LC ladder prototypes

The sensitivity properties of a class of switched-capacitor LDI ladder filter are investigated. It is shown that, because of the frequency variation of the termination in the equivalent circuit of such filters, the passband sensitivity property of the LC prototype filter is not retained. It is shown how the introduction of an extra switched capacitor at the input can result in lower passband sensitivities to the capacitance ratios. >