sed services. A TSN may also convert the bearer from one type of packet network to another. The GSN is similar to the TSN since it also handles BICC on both sides. A GSN acts as a gateway between network operators in a full BICC environment. BICC IP Bearer Control Protocol (IPBCP) (ITU Q. 1970) is used for the exchange media stream characteristics, port numbers, and IP addresses of the source and destination of a media stream to establish and allow the modification of IP bearers. The information exchanged with IPBCP is done during BICC call establishment. In addition it may be exchanged after a call has been established. IPBCP uses the Session Description Protocol (SDP) defined in RFC 2327 to encode this information. See Figure 14.13. Section 15.8 describes the similar PDP context. Signalling transport is described in section 14.9.2. 14.6 PACKET MODE DOMAIN The packet mode domain is introduced in GPRS and it is conveyed into UMTS. In the IMS phase the SGSN and GGSN node become the main core nodes. GGSN will then partly be controlled by IMS CSCF. Understanding Changing Telecommunications - Building a Successful Telecom Business 14.6.1 SGSN The SGSN server, which is located in the packet-switched domain, handles control layer functions related to packet-mode communication services at the border between the access network and the core network. The SGSN server may host the following main functions: Session management. This means the establishment, maintenance and release of end- user packet data protocol (PDP) contexts. This includes interworking with the GGSN for IP addresses. Session management also includes functionality for establishing WCDMA radio access bearers for end-user IP data transportation, as well as functionality for end-user QoS negotiation. Mobility management. This means the functionality that supports roaming within and between GSM and UMTS mobile networks. Integrated VLR and subscriber data management. The SGSN server supports the stan- dardized interface to the HLR in order to manage end-user sub