application. In this process, the packet core network takes a secondary role, since the most restrictive subsystem is the radio access network. However, there is a need to consider the process from an end-to-end perspective; otherwise there is a substantial risk of missing a link in the complex chain. It can be argued that the QoS is either an essential optimisation process or a powerful optimisation tool, but it seems clear that the QoS is an end-to-end matter and can significantly contribute to increasing the network and end user performance in given situations. Role of the Packet Core Network in the QoS Process Normally, the main packet core network nodes, SGSN and GGSN, provide different treatments for the different traffic classes defined by 3GPP by means of implementing in those nodes some of the known functions in this area, such as queuing and shaping. The complexity is mostly in the network node design in order to deal with the expected traffic flows. Normally, there are few possibilities of tuning network node QoS parameters in order to increase the performance. Configuration of queues is one possibility, tuning the relative sizes of the queues for the different traffic classes according to the current traffic mix in terms of traffic classes. An other possibility is to tune or redefine the marking of the packets in the differentiated services code point (DSCP) field of the IP header in order to optimise the IP routing within a large and complex packet core backbone, perhaps also having multiprotocol techniques in use such as the MPLS for a more efficient handling of backbone traffic. However, it is difficult to provide concrete advice on this matter, since it is very dependent on the concrete network node implementation characteristics (some of which may not leave a margin for optimisation) and the concrete backbone design (which in some cases may not be subjected to optimisation). Role of the HLR in the QoS Process There is another network node that is not usually considered under the scope of a mobile