runks routing) interface to connect between different types of communi- effectively achieves Cell Relay functionality for data traffic. There cations networks because the link layers of these networks are are also proprietary ATM multiplexers available which handle voice already similar. The potential impact on corporate networking is and data traffic, although standard ATM platforms are evolving (See significant, because the approach is relatively straightforward to Section 55.3 and Chapter 41). For the benefit of the following implement compared to a layer 3 approach, and existing hardware discussion, such platforms will be regarded as 'Frame Relay Swit- can be utilised. ches' This idea is by no means a new one. It was suggested back in 1975 Instead of transferring bits between fixed locations like a circuit, during the formative stages of the CCITT X.25 recommendation for a Frame Relay network acts like a wide area LAN. A sending device the packet switch network interface, that a simpler protocol would places an addressed frame into the network and it arrives quickly at have many attractions. However the suggestion was rejected be- its destination. cause of the proliferation of error-prone analogue transmission To achieve these objectives, the network simply 'relays' the facilities still in existence at the time, requiring added complexity packet, or frame, to a destination indicated by the layer 2 address for error recovery. Digital transmission facilities are now wide- field of the packet. The Frame Relay switch performs the core layer spread enough for a simplified protocol with error detection only, to 2 functions, of frame separation with flags, zero bit insertion, frame be a viable option. multiplexing via the address field, and CRC error detection to enable frames with errors to be discarded. The switch does not 55.2.1 Frame Relay Networks acknowledge or request re-transmission. This and all other protocol functions (layer 3 and up) are implemented end-to-end through the network, rather than by it. Fram