 There are eight AMR 3G TRANSMISSION NETWORK PLANNING AND OPTIMISATION E.g., E.g., Vocoder Vocoder RLC-U RLC-U Node B I -CS UP I -CS UP WCDMA WCDMA E.g., E.g., IPv4, IPv6 3G-SGSN IPv4, IPv6 GTP-U GTP-U RLC-U RLC-U Node B LLC/SNAP LLC/SNAP WCDMA WCDMA Layer Layer Figure 8.8 Protocol stack for (a) user-plane CS traffic, (b) user-plane PS traffic codec rates, from AMR-0 to AMR-7, with the rates ranging from 12.2 kbps to 4.75 kbps respectively. Usually dimensioning for voice is done for AMR-0, or 12.2 kbps codec rate. Soft handover (SHO) overhead: As described in earlier chapters, soft handovers (which ensure continuous connectivity for the subscriber) take up more capacity. In some case the capacity requirement may go up to 150%. Protocol overhead: As the signal moves from one layer to another, some bits are added at each of these layers. This includes the RLC, FP and AAL2, etc., layers. The overhead will vary with the type of call (i.e. with the AMR codec). Signalling overhead: For each call, signalling is required. This signalling also needs capacity to associate itself with the data (CS/PS) when a call is being made from one subscriber to another. Hence, this capacity also needs to be added. If a user is making a data (PS) call, then some of the above overheads will change depending on the type of call (i.e. the data rate). Each different type of data rate will have a different type of overhead. For a data call, however, VAF is not considered, as there will be no voice activity. However, overheads for re-transmission (explained in Chapter 6) and buffering are required. The amount of capacity required for buffering the user data is usually similar to that required for transmission. DIMENSIONING Signalling on Transmission Interfaces We have seen the general protocol structure of UTRAN in Chapter 7. Based on it, the following types of signalling are required at the various interfaces. ATM adaptation layer 2 signalling: AAL2 signalling is required for establishing, main- taining and terminating the AAL2 connections. 