 operation of the telephone instrument 30.10 References and appropriate values of SLR and RLR. 2. Power loading. Codecs have a limited dynamic range as defined in G.711 for 8 bit PCM systems. SLR values in line CCITT(1989a) General aspects of quality of service and network with the CCITT recommended ranges should adequately limit performance in digital networks, including ISDN, CCITT Rec- ommendation 1.350. Blue Book Fascicle 111-8. Geneva. the speech power to prevent codec overload. If digital attenua- tors are used then care needs to be taken to prevent codec CCITT (1989b) Telephone Transmission Quality, CCITT Series P overload. Recommendations. Blue Book Fascicle V. Geneva. 3. Synchronisation. Covered in 30.6.11. An inadequate synchroni- sation scheme will lead to slips in the digital circuits resulting CCITT (1989c) General Characteristics of International Telephone in additional noise at the analogue output. Connections and Circuits, CCITT Series G.100. Recommenda- tions Blue Book fascicle 111-1. Geneva. Future network trends CCITT (1989d) Digital Networks, Transmission Systems and Multi- plexing Equipment, CCITT Series G.700-G.956 Recommenda- tions Fascicle 111-3. Geneva. The example case considered above covered an all-digital switching network with analogue 2-wire access to customers. The major CCITT (1989e) Digital Local, Transit, Combined and International difficulty in the transmission plan exercise was finding an accept- Exchanges in Integrated Digital Networks and Mixed Anal- able compromise between loss and echo performance for the propa- ogue-Digital Networks, CCITT Series Q.500 - Q.554. Recom- gation delays in question. This problem will increase in the future, mendations Fascicle V1.5. Geneva. even for this network configuration, as the majority of customers will still be served by analogue copper access for many years. ITU (1976) Transmission Planning of Switched Telephone Net- Meanwhile there will be pressure for the switched network to works, International Telecommunication Union. Geneva Annex