d only one, LA, meaning that an RA cannot span more than one LA. An RA is served by only one SGSN. An optimal RA is balanced between the PCH load and RA updates. If the RA size is too large, paging channels and capacity will be saturated due to a limited LAPD (Link Access Procedure on the D channel) Abis or radio interface CCCH paging capacity. On the other hand, with a small RA there will be a larger number of RA updates performed. Based on traffic behaviour of subscribers and the performance of the network (in terms of paging success), it is possible to derive guidelines regarding the maximum number of subscribers per LA/RA. The routing area dimensioning approach assumes the same rule sets as applied to dimensioning the LA of the existing GSM service. This approach is devised by balancing paging traffic from subscribers and the paging capacity offered by a given paging channel configuration. An example of the paging capacity of a combined channel configuration with three pages per block is shown in Figure 2.40. Parameter Planning CAPACITY of PAGING CHANNEL Paging Capacity in Air Interface Combined BCCH [yes/no] Blocks for Access Grant [0-2] Number of Pages/Block [2-4] Max. Capacity: pages / sec 91915 Pages per Hour Figure 2.40 Capacity of the paging channel The number of pages that are sent by the BTS within an LA/RA indicates the number of Mobile Terminating Calls (MTC) that are being sent to subscribers in the LA/RA. This paging demand is a function of three factors: number of MTC; number of subscribers in the LA/RA; the paging parameters within the SGSN defined by the Operator, RA Paging Repetition (RPR), RA Paging Area (RPA), SGSN Paging Area (SPA). The higher the number of MT sessions for subscribers in the RA, the higher the number of pages that have to be sent by the BTS in the RA. The number of subscribers also has a strong influence on the number of pages being sent, since with an increased number of subscribers the number of MT sessions will inevitably rise. The success of paging, i.e. the number of t