 which is SGSN in UMTS. Backbone bearer services between the core network main gateways, i.e. SGSN and GGSN. 5.2 QoS in 3G Broadband Mobile Networks 3G mobile network External IP networks UTRAN Core network (CN) NodeB Remote peer node End-to-end service bearer UMTS bearer External bearer Core network Radio access bearer (RAB) bearer Backbone Radio bearer lu bearer bearer GGSN - Gateway GPRS support node SGSN - Serving GPRS support node UMTS - Universal mobile telecommunication system Figure 5.6 Bearer architecture for QoS support in UMTS. All three bearers in UMTS form the UMTS bearer service (Figure 5.6), which should be mapped on the external bearer (between the mobile core network and external net- works with which the core network is interconnected). To have end-to-end QoS requires appropriate QoS mapping between each adjacent pair of bearers. For example, in the backbone network they may use Carrier (i.e. Metro) Ethernet, which requires map- ping of UMTS bearers to available CoS. MPLS, meanwhile, requires different bearers to be mapped with different labels. The main bearer services in UTRAN and in the core network are established by using tunneling protocols, which gives the possibility of aggregation of the same type or the same class of traffic, thus providing the possibility for QoS class differentiation (not differentiation per flow). The standard for tunneling in 3GPP mobile networks (GPRS, UMTS, LTE/LTE-Advanced) is GTP (General Packet Radio Service Tunneling Protocol), which is standardized by 3GPP [5] and not by the IETF (although there are also IP tunneling standards established by the IETF, such as IP-in-IP tunneling [6]). GTP is used in PS parts of GSM/GPRS (2.5G) and UMTS (3G), as well as in LTE/LTE-Advanced/LTE-Advanced-Pro mobile networks. There are three main GTP types: GTP-C (General Packet Radio Service Tunneling Protocol-Control plane) for transfer of signaling traffic, such as bearer activation, modification; GTP-U (General Packet Radio Service Tunneling Protocol-User plane) for carrying 