An Ontology for Network Services

Most of the network service specifications are implemented using relational databases or XML schemas. However, those specifications are not flexible and expressive enough to be extended with new service classes, different corporate policies, network configurations and deployment strategies; thus, most of the QoS management operations are implemented as hard-coded software components. This paper presents a novel approach in the specification of IP network services, using F-logic knowledge representation framework, aiming to include, in the same specification, the high-level service requirements, the network model and the necessary operations for the deployment of multiple network services

Circuit Emulation over IP Networks

Recent developments in transmission and switching technology has made available low-cost gigabit network capacity forpacket-based WANs (e.g., IP over WDM), that will not require the intermediate SONET/SDH multiplexing layer. For competitive operators that want to minimize their investment by deploying native IP over WDM networks, Circuit Emulation over IP gives support to the important class of legacy circuit-based equipment (e.g., T1/E1 multiplexers), which otherwise will require the deployment of an expensive telecommunication infrastructure, including SONET/SDH equipment. At the user interface, Circuit Emulation is required to maintain the same service of a circuit-based network, including synchronization and structured data delivery. In this paper we design the algorithm and the protocol that provide these two features. First, we identify the protocols and mechanisms used in the Internet and their ability tobe used for Circuit Emulation. Second, we address the problem of synchronization and we propose an algorithm for efficient source clock recovery and handling of delay variations. Finally, we show through simulations that Circuit Emulation over IP provides the needed service performance at the user interface

Circuit Emulation over IP Networks

The best-effort service offered by the Internet is not suitable for a large variety ofmultimedia 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 is a session parameter and can be adjusted by exchanging RTCP messages. The dimensioning of the receiver buffer is the rst 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