Senthil Sengodan

Gatekeeper discovery mechanism for H.323 systems

Multimedia communications over packet switched networks - commonly referred to as Internet telephony - has generated immense interest in recent years. The International Telecommunication Union is currently developing the H.323 umbrella of standards for this purpose. In the H-323 standard, a gatekeeper is a control entity that performs functions such as address translation, bandwidth management etc. A H.323 terminal needs to discover a suitable gatekeeper and register with it. When a H.3232 terminal wishes to call another H.323 terminal, communication between the gatekeepers result in the determination of the transport layer address of the destination terminal for sending the connection setup message to. There is thus a need not only for terminals to discover gatekeepers but also for gatekeepers to discover other gatekeepers. In this paper, we propose a mechanism whereby terminals and gatekeepers can discover other gatekeepers. The proposed mechanisms result in efficient use of network bandwidth within the administrative domain. The security issues involved in such communications are discussed, and a proposal is made to establish a shared secret during the discovery process. Such a shared secret may be used for subsequent confidentiality or authentication of messages.

On applying SIP security to networked appliances

The importance of security to Networked Applicances is unarguable. In one of the worst possible scenarios, a successful attacker may gain control of the networked devices in a victim¿s home. Disastrous consequnces are not difficult to imagine. In this work, we provide a general security threats analysis for Networked Appliances and discuss the implications of using Session Initiation Protocol (SIP) for security.

On end-to-end security for Bluetooth/WAP and TCP/IP networks

With the convergence of the Internet protocol (IP) and wireless technologies such as Bluetooth and the wireless application protocol (WAP), a study on end-to-end security issues has become important. Differences in security algorithms and protocols between these technologies needs to be clearly understood in order to understand the impact on end-to-end security. This paper describes some of these aspects in the context of Bluetooth and WAP interfacing with IP networks. Various security services - key generation, authentication and confidentiality - are considered and compared.

A shared buffer architecture for interactive VOD servers

Video-on-demand (VOD) servers need to be efficiently designed in order to support a large number of users viewing the same or different videos at different rates. While considering a disk-array based VOD server, use of a shared buffer at the server end may be more economical than the sole use of dedicated buffers at each users end. In this paper, we propose a simple buffer sharing architecture that may be used when disk-array based video servers are used. Our aim is to support the maximum number of users for a given number of video server disks while employing a simple scheme requiring less buffer space. The number of video segment retrievals that can occur within a certain time (the service round) is maximum when the scan disk scheduling algorithm is used. Consequently, we shall assume use of the scan algorithm for disk retrieval. The VOD server has a buffer manager that directs retrieved segments to appropriate buffer locations depending on their release and deadlines. The release and deadlines of segments are such that buffer requirement at the users set-top box is minimized to two video segments while avoiding video starvation and buffer overflow at the users end. We propose a novel scheme for the operation of the shared buffer that aims at increasing buffer utilization and decreasing cell loss due to buffer overflow. An ATM based broadband network is assumed and all segments are stored in buffers as fixed length ATM cells. We also use a novel scheme for grouping frames into segments and illustrate its advantages over earlier ones.

Impact of different cellular-IP convergence strategies on mobile terminals

The last few years has seen a proliferation of the Internet, making it accessible to several millions of users worldwide. At the same time, the use of mobile devices such as cellular telephones and personal digital assistants (PDA) has been on the rise. Currently, we are beginning to see the convergence of these technologies whereby access to the Internet and other (potentially private) packet switched networks happens via mobile devices. The Internet protocol (IP) and the associated TCP/IP protocol suite - which is used in the Internet - is beginning to find its way into mobile devices as well. However, the cellular-IP convergence strategy and the extent to which the TCP/IP protocol suite is being embraced varies from one cellular standard to another. We compare differences in cellular-IP convergence strategies and discuss the impact that this has on cellular terminals.

An NAI resolution mechanism for GPRS and TETRA PMR networks

Dialup users of data networks that use the point-point protocol (PPP) make use of a network address identifier (NAI) for user identification. NAI is also being used for roaming and tunneling service in data networks. On the other hand, cellular networks make use of an alternative user identification format which is usually the international mobile subscriber identity (IMSI) or the mobile identification number (MIN). Similarly, terrestrial trunked radio (TETRA)-based professional mobile radio (PMR) networks make use of the individual TETRA subscriber identity (ITSI) for user identification. With the impending integration of cellular/PMR networks and data networks, it is desirable to have a one-one mapping between IMSI/MIN/ITSI and NAI. An operational procedure is needed whereby such a mapping occurs within the network and is transparent to the user. The Mobile IP working group within the IETF is currently investigating such a mapping for cellular networks. However, no mechanisms have been described for GPRS or TETRA networks. We outline a mechanism for such a mapping and the associated operational procedures when the cellular network is a general packet radio service (GPRS) network and also when the access network is a TETRA PMR network.

DIVeR: a dynamic interactive video retrieval protocol for disk array based servers

Video-on-demand (VOD) is a very promising multimedia application of the near future. In order for such a service to be commercially viable, efficient storage and retrieval schemes need to be designed. Grouping MPEG frames into segments and retrieving segments instead of individual frames can result in a more efficient use of disk retrieval resources. In conjunction with efficient scheduling protocols for handling multiple users, a large number of users can be supported resulting in a more cost-effective system with good quality of service (QoS). Our contribution in this paper is two-fold: we propose a scheme for grouping MPEG frames into segments wherein no frames are discarded during fast playback (with segment skipping) due to the unavailability of other frames needed for their decoding. The grouping scheme can handle any desired segment size and the fast playback rate can also take on any desired value. We propose the dynamic interactive video retrieval (DIVeR) protocol, a protocol for scheduling the retrieval of multiple users from disk-array servers. DIVeR has a low interactive latency while supporting a large number of users at a high QoS. Two variations, DIVeR-2 and DIVeR-3, are discussed. Numerical results utilizing both schemes are provided using data from an MPEG coded video of Star Wars and a model of the Seagate Barracuda disk.

Wireless and mobility issues in IP telephony

IP telephony has seen a tremendous surge in interest in the last couple of years. Several equipment vendors, application developers and service provides are entering into this emerging market. Regional as well as international standardization organizations have been involved in developing standards in the area, while several other forums have been actively promoting the industry as a whole. However, until recently, mobility and wireless issues have not been considered in detail with the scope of IP telephony, and the focus has been on fixed IP telephony systems. In this paper, we discuss some of the issues that need to be considered when mobility and wireless transport is introduced within IP telephony.

Standardization efforts in IP telephony

The recent interest in IP telephony has led to a tremendous increase of standardization activities in the area. The three main standards bodies in the area of IP telephony are the International Telecommunication Unions (ITU-T) Study Group (SG) 16, the Internet Engineering Task Force (IETF) and the European Telecommunication Standards Institutes (ETSI) TIPHON project. In addition, forums such as the International Multimedia Teleconferencing Consortium (IMTC), the Intelligent Network Forum (INF), the International Softswitch Consortium (ISC), the Electronic Computer Telephony Forum (ECTF), and the MITs Internet Telephony Consortium (ITC) are looking into various other aspects that aim at the growth of this industry. This paper describes the main tasks (completed and in progress) undertaken by these organizations. In describing such work, an overview of the underlying technology is also provided.