iable bit-rate coding are discussed as assemble/disassemble the payload of a transmission system. are a layered approach to video coding for service integration and Cell delineation and Header Error Control are required at the the impact of the ATM network on video coding. The recommenda- end points. tion concludes that layered coding combined with variable bit-rate 2. Digital Section: extends between network elements which as- coding has advantages for video service integration and for utilisa- semble/disassemble a continuous bit or byte stream. tion of ATM network capabilities and therefore recommends that 3. Regenerator Section: a portion of a digital section. studies should be concentrated on these methods. Figures 1,2,3 and 4 of I.311 represent: 41.4.5 I.311: B-ISDN general network aspects 1. The relationship between VC, VP and Transmission Path (Fig- Describes a number of separate network related aspects of B-ISDN: ure 41.11). networking techniques, signalling principles and traffic control and 2. The hierarchy of the ATM transport network (Figure 41.11). 3. The hierarchical layer to layer relationship (Figure 41.12). resource management. 4. VC and VP switching (Figures 41.13 and 41.14). 41.4.5.1 Networking techniques This deals with the layering principles used in defining the B-ISDN TRANSMISSION PATH and the hierarchical relationship between the physical layer, the ATM layer and the layers above. It defines an ATM transport network as being structured in two layers: ATM layer and Physical Layer. The ATM layer has two sub-layers, the Virtual Path (VP) sub-layer and the Virtual Channel Higher layers (VC) sub-layer. The physical layer transport functions are sub- divided into three levels: transmission path, digital section and Virtual channel level regenerator section levels. ATM layer I.311 takes further the VC and VP concepts introduced in I.150: Virtual path level Transmission path level 1. Virtual Channel (VC): a generic term to describe a unidirec- tional communication capability for ATM cells. Physica