protocol termination protocol protocol termination termination termination Gr,Gc Figure 9.8 A generic HSS structure with protocols over the basic interfaces. 9.3.3 Transport Signalling Gateway Function (T-SGW) This component serves as the PSTN/PLMN termination point for a defined network. Terminates, e.g. the call control signalling from GSTN mobile networks (typically ISDN) and maps the information onto IP (SIGTRAN) towards the Media Gateway Con- The UMTS Network and Radio Access Technology trol Function (MGCF). The functionality defined within T-SGW should be consistent with existing/ongoing industry protocols/interfaces that will satisfy the requirements: maps call related signalling from/to PSTN/PLMN on an IP bearer and sends it to/from the MGCF; needs to provide PSTN/PLMN IP transport level address mapping. 9.3.4 Roaming Signalling Gateway Function (R-SGW) The role of the R-SGW concerns only roaming to/from 2G/R99 CS and the GPRS do- main to/from the ROO UMTS teleservices domain and the UMTS GPRS domain and does not involve the multimedia domain. According to Ref. [7] the main functions are: to ensure proper roaming, the R-SGW performs the signalling conversion at trans- port level (conversion: Sigtran SCTP/IP versus SS7 MTP) between the legacy SS7 based transport of signalling and the IP based transport of signalling. The R-SGW does not interpret the MAP/CAP messages but may have to interpret the underlying SCCP layer to ensure proper routing of the signalling. to support 2G/R99 CS terminals: we use R_SGW services to ensure transport inter- working between the SS7 and the IP transport of MAP_E and MAP_G signalling interfaces with a 2G/R99 MSC/VLR. 9.3.5 Media Gateway Control Function (MGCF) The MGCF serves as the PSTN/PLMN termination point for a defined network. Its de- fined functionality will satisfy the standard protocols/interfaces to: control parts of the call state that pertain to connection control for media channels in a MGW; communicate with CSCF; select the CSCF depending on the routing number fo