Raffaele Noro

Circuit Emulation Over IP Networks

The best-effort service offered by the Internet is not suitable for a large variety of multimedia applications, which require strict guarantees on losses and end-to-end delay. We design functionalities and mechanisms for RTP in order to provide a transport service with the properties of circuit switched networks and with the possibility of transporting both constant and variable rate streams. We consider a source that generates structured data units, which are collected in RTP packets. These packets are forwarded to an IP network and reach the receiver with a stochastic delay. An extra delay is computed (on a per-packet basis) and added at the receiver to have delay equalization. The data units in the packet are then delivered to the application at a rate specified in the RTP header. The total delay Delta is a session parameter and can be adjusted by exchanging RTCP messages. The dimensioning of the receiver buffer is the first problem to be solved. The buffer space results in a function of the network delay bounds and the maximum RTP packet size. This information can be conveyed from the source to the receiver through RTCP messages. The timing of the data delivery process and the source clock recovery are also required functionalities. They are both implemented by means of an extension to the RTP header. We developed a method for source clock recovery that removes the network induced jitter by processing the clock indications contained in some RTP header. The recovered clock is then used in combination with other information contained in the packets to control the delivery process. Simulations prove that the circuit emulation service can be implemented on top of the RTP with satisfactory performance.

Clock synchronization of MPEG-2 services over packet networks

We address the problem of time-base synchronization for MPEG services in the presence of network jitter. The conventional methods to obtain a stable clock indication are based on Phase Locked Loops (PLLs). They have the disadvantage of a long startup phase and thus are unsuitable for services that require simultaneous accuracy and rapidity. We develop a new time-base synchronization technique based on a Least-square Linear Regression algorithm (LLR). We show that LLR is able to perform time-base synchronization with the same accuracy as of a PLL and with a substantial gain of rapidity. Finally, we discuss the implementation of the LLR technique as an intermediate time-base synchronization level between the network and a generic multimedia application.

Real-time telediagnosis of radiological images through an asynchronous transfer mode network: The ARTeMeD project

The ARTeMeD project aims to solve problems of interactivity and real-time in teleradiology. It integrates personal multimedia facilities and patient data access in a common platform that allows radiologists to collaborate from remote sites through a suitable communication support. ARTeMeD is based on asynchronous transfer mode (ATM) network technology and an optimized manipulation of medical image material. The ARTeMeD system opens interesting perspectives in the area of collaborative teleradiology.

Improving Clock Synchronization for MPEG-2 Services over ATMM Networks

A stable clock indication is needed for the processing and playout of MPEG-2 streams. ATM networks can support the transfer of such streams but contribute significantly (as well as other system operations) to delay and delay variation. The MPEG-2 standard specifies strong temporal constraints for processing and presentation. MPEG-2 is also based on the assumption of a common time base shared among sender and receiver. Clock synchronization covers this requirement and is traditionally performed using PLLs. Unfortunately, their linear nature cannot simultaneously guarantee rapidity and good clock reconstruction. The non-linear technique we propose in this paper is able to offer such guarantees and also can handle higher amounts of delay variations. Such technique is not restricted to the scope of MPEG-2 clock synchronization and can also succeed in the reconstruction of time bases for generic distributed applications. It does not require any specific device, like very precise oscillators or filters.