he following aspects: of the nominally balanced 2-wire parts of the connection. 1. Network structure and routeing rules. 30.6.3 Loss frequency distortion 2. Performance of the individual network systems. 3. System interface requirements. The influences on end to end distortion are similar to those for transmission loss, i.e. the distortion introduced by systems together Successful end to end planning therefore requires an under- with mismatch losses at the interface points. In this case the mis- standing of how these aspects apply to the transmission parameters match losses may be more significant as the values are likely to vary under study. with frequency. 30.6.4 Non linear distortion and quantising 30.6 Key influences on end to end distortion performance Calculation of overall non-linear distortion is generally not under- Section 30.4 identified the major end to end parameters together taken as any calculation requires an exact knowledge of the non-li- with CCITT recommended limits. Section 30.5 illustrated the need near characteristic. to identify the factors contributing to end to end performance for For the specific case of quantising distortion it is possible to each parameter. estimate the total quantising distortion using the quantising distor- This process is outlined below and concludes with a table summa- tion unit approach (qdu) outlined in Section 30.4.4. rising the key dependencies. It has been found that such an approach is reasonably accurate for coding systems with bit rates of 32kbit/s and above. The accuracy for lower rate systems is under study within CCITT. 30.6.1 Transmission loss 30.6.5 Propagation delay Key factors influencing transmission loss are: Calculation of overall propagation delay is straightforward provid- 1. Transmission loss of individual network components. ing the delays contributed by the component parts are known. 2. Mismatch losses introduced at analogue interconnection points. Information on typical planning delays is given in Recommendation G.114. Overall delays for any