he delay between those messages is observed in the signalling links with the HLR for the Gd/Gf/Gr interfaces, the topology and proper dimensioning of those signalling links should also be verified and corrected. Another possible scenario could be the case where only visiting roaming subscribers experience this perceived low performance, which may lead to a verification of the service provisioning policies and roaming agreements and its correct implementation in SGSNs and HLR nodes. This type of optimisation activity built around packet switch procedures can also be used for the PDP context activation procedure, which normally leads to backbone issues, GTP tunnelling issues or GGSN issues, especially with the newer generation of GGSNs with increased intelligence for handling PDP context requests for different services, and the extensive use in the field of new generation release 4 mobile phones with multiple PDP context capabilities. Another type of procedure that can be the subject of procedure optimisation is the routing area update (RAU) procedure. There could be several reasons for needing an RAU procedure, but normally the OSS counters provide the lead for low performance in this aspect, presenting lower than normal success rate values. If the values can be clearly identified with a given geographical area, this could well be a system optimisation scenario, where the definition of the routing areas at the BSS side might be redesigned Core Network Planning and Optimisation order to improve the success rate of the basic mobility management procedure. Another possibility can be built around tuning the timers that control this procedure. This may be a BSS only procedure (intra-PCU RAU) or a BSS and core network procedure (inter-PCU/intra-SGSN RAU and inter-PCU/inter-SGSN RAU, the later involving also the packet core backbone and the Gn interface). This categorisation will help to identify the trouble, as it can be found only in one of the types of procedure described, and to find the correct timer values for tuni