This is the reason why the Frame Relay interface does not include an underlying sublayer assigned with error and flow control tasks such as LAP-B in X.25. Subsequently, Frame Relay is suitable for existing private and public networks based on digital TDM transmission systems. This paper is divided into 4 chapters. This is an introductory chapter. Next chapter is dedicated to a review of the literature on the technology. Then comes the methodology part and finally the conclusion.
ISDN represents another ideal carrier for frame relay traffic able to support a number of frame mode bearer services (FMBS). This plurality of frame mode bearer services was considered necessary by the CCITT because Frame Relay may have to be supported over segments of analog technology, at least during the early stages of ISDN.
There are two types of Frame Relay connections: permanent virtual connections (PVCs) and switched virtual connections (SVCs). The establishment, maintenance, and release of PVCs are subject to local management operations. On the other hand, signalling is required to manage SVCs. Of course, dynamically allocated SVCs are much more attractive compared to PVCs which function much like dedicated private lines. At present, the Frame Relay implementations are only PVC-based. This is due to both the complexity of the required signalling  and it s unavailability on the local loop. However, PVCs provide a good immediate solution because LAN-to-LAN interconnectivity is the main Frame Relay application. But the need for products supporting SVCs is growing and a lot of work is being done in this area.
Review of the Research Literature
Frame Relay Interface
Work on the definition of the Frame Relay interface has been carried out by several organizations during the past years. CCITT has produced a series of standards covering the support of Frame Relay over ISDN, the provision of several Frame Mode Bearer Services (FMBS) and the involved signalling. Working in parallel, the T1 committee of ANSI is developing consistent standards. Also, a number of working papers on this topic have been produced by the Frame Relay Implementer's Forum.
Here, the Frame Relay interface is described as outlined by the CCITT because of its international significance. This description is mainly concerned with the support of Frame Relay in ISDN because of its extensive standardization by the CCITT. We also try to clarify the opinions of the PTTs and the private vendor community with regard to the Frame Relay interface. This should help the reader to get a more complete picture of how the Frame Relay interface is viewed by various communities.
As far as the underlying physical layer is concerned, Frame Relay can b supported at a maximum rate of 1 .544Mbit/s and 2.048 Mbit/s over a primary rate ISDN interface. The same applies to all current Frame Relay implementations in n the private sector but here Frame Relay at DS3 (44 .736 Mbitls) rates is expected to become available soon. As shown in Figure 1, the Frame Relay interface is based on the core functions of the LAP-F protocol O. This protocol is defined in the CCITT Rec. Q.922 and it is also sometimes referred to as