5.6 Transmission and Signalling Planes

03.603GPPGeneral Packet Radio Service (GPRS)Release 1998Service descriptionStage 2TS

5.6.1 Transmission Plane

The transmission plane consists of a layered protocol structure providing user information transfer, along with associated information transfer control procedures (e.g., flow control, error detection, error correction and error recovery). The transmission plane independence of the Network Subsystem (NSS) platform from the underlying radio interface is preserved via the Gb interface. The following transmission plane is used in GPRS:

Figure 4: Transmission Plane

Legend:

– GPRS Tunnelling Protocol (GTP): This protocol tunnels user data and signalling between GPRS Support Nodes in the GPRS backbone network. All PDP PDUs shall be encapsulated by the GPRS Tunnelling Protocol. GTP is specified in GSM 09.60 [25].

– TCP carries GTP PDUs in the GPRS backbone network for protocols that need a reliable data link (e.g., X.25), and UDP carries GTP PDUs for protocols that do not need a reliable data link (e.g., IP). TCP provides flow control and protection against lost and corrupted GTP PDUs. UDP provides protection against corrupted GTP PDUs. TCP is defined in RFC 793 [42]. UDP is defined in RFC 768 [39].

– IP: This is the GPRS backbone network protocol used for routeing user data and control signalling. The GPRS backbone network may initially be based on the IP version 4 protocol. Ultimately, IP version 6 shall be used. IP version 4 is defined in RFC 791.

– Subnetwork Dependent Convergence Protocol (SNDCP): This transmission functionality maps network-level characteristics onto the characteristics of the underlying network. SNDCP is specified in GSM 04.65 [14].

– Logical Link Control (LLC): This layer provides a highly reliable ciphered logical link. LLC shall be independent of the underlying radio interface protocols in order to allow introduction of alternative GPRS radio solutions with minimum changes to the NSS. LLC is specified in GSM 04.64.

– Relay: In the BSS, this function relays LLC PDUs between the Um and Gb interfaces. In the SGSN, this function relays PDP PDUs between the Gb and Gn interfaces.

– Base Station System GPRS Protocol (BSSGP): This layer conveys routeing- and QoS-related information between BSS and SGSN. BSSGP does not perform error correction. BSSGP is specified in GSM 08.18 [20].

– Network Service (NS): This layer transports BSSGP PDUs. NS is based on the Frame Relay connection between BSS and SGSN, and may be multi-hop and traverse a network of Frame Relay switching nodes. NS is specified in GSM 08.16 [19].

– RLC/MAC: This layer contains two functions: The Radio Link Control function provides a radio-solution-dependent reliable link. The Medium Access Control function controls the access signalling (request and grant) procedures for the radio channel, and the mapping of LLC frames onto the GSM physical channel. RLC/MAC is defined in GSM 04.60 [12].

– GSM RF: As defined in GSM 05 series.

5.6.2 Signalling Plane

The signalling plane consists of protocols for control and support of the transmission plane functions:

– controlling the GPRS network access connections, such as attaching to and detaching from the GPRS network;

– controlling the attributes of an established network access connection, such as activation of a PDP address;

– controlling the routeing path of an established network connection in order to support user mobility; and

– controlling the assignment of network resources to meet changing user demands.

The following signalling planes are used in GPRS:

5.6.2.1 MS ‑ SGSN

Figure 5: Signalling Plane MS ‑ SGSN

Legend:

– GPRS Mobility Management and Session Management (GMM/SM): This protocol supports mobility management functionality such as GPRS attach, GPRS detach, security, routeing area update, location update, PDP context activation, and PDP context deactivation, as described in subclauses "Mobility Management Functionality" and "PDP Context Activation, Modification, and Deactivation Functions".

5.6.2.2 SGSN ‑ HLR

Figure 6: Signalling Plane SGSN ‑ HLR

Legend:

– Mobile Application Part (MAP): This protocol supports signalling exchange with the HLR, as defined in GSM 09.02 [22], with enhancements for GPRS as described in the present document.

– TCAP, SCCP, MTP3, and MTP2 are the same protocols as used to support MAP in non-GPRS GSM PLMNs.

5.6.2.3 SGSN ‑ MSC/VLR

Figure 7: Signalling Plane SGSN ‑ MSC/VLR

Legend:

– Base Station System Application Part + (BSSAP+): A subset of BSSAP procedures supports signalling between the SGSN and MSC/VLR, as described in subclause "Mobility Management Functionality" and in GSM 09.18 [24]. The requirements for the lower layers are specified in GSM 09.16 [23].

5.6.2.4 SGSN ‑ EIR

Figure 8: Signalling Plane SGSN ‑ EIR

Legend:

– Mobile Application Part (MAP): This protocol supports signalling between the SGSN and the EIR, as described in subclause "Identity Check Procedures".

5.6.2.5 SGSN ‑ SMS-GMSC or SMS-IWMSC

Figure 9: Signalling Plane SGSN ‑ SMS-GMSC and SGSN ‑ SMS-IWMSC

Legend:

– Mobile Application Part (MAP): This protocol supports signalling between the SGSN and SMS-GMSC or SMS-IWMSC, as described in subclause "Point-to-point Short Message Service".

5.6.2.6 GSN ‑ GSN

Figure 10: Signalling Plane GSN ‑ GSN

Legend:

– GPRS Tunnelling Protocol (GTP): This protocol tunnels user data and signalling messages between SGSNs and GGSNs, and between SGSNs, in the GPRS backbone network.

– User Datagram Protocol (UDP): This protocol transfers signalling messages between GSNs. UDP is defined in RFC 768.

5.6.2.7 GGSN ‑ HLR

This optional signalling path allows a GGSN to exchange signalling information with an HLR. There are two alternative ways to implement this signalling path:

– If a SS7 interface is installed in the GGSN, the MAP protocol can be used between the GGSN and an HLR.

– If a SS7 interface is not installed in the GGSN, any GSN with a SS7 interface installed in the same PLMN as the GGSN can be used as a GTP-to-MAP protocol converter to allow signalling between the GGSN and an HLR.

5.6.2.7.1 MAP-based GGSN ‑ HLR Signalling

Figure 11: Signalling Plane GGSN ‑ HLR Using MAP

Legend:

– Mobile Application Part (MAP): This protocol supports signalling exchange with the HLR, as described in subclause "Network-Requested PDP Context Activation Procedure".

5.6.2.7.2 GTP and MAP-based GGSN ‑ HLR Signalling

Figure 12: Signalling Plane GGSN ‑ HLR Using GTP and MAP

Legend:

– GPRS Tunnelling Protocol (GTP): This protocol tunnels signalling messages between the GGSN and the protocol-converting GSN in the GPRS backbone network.

– Interworking: This function provides interworking between GTP and MAP for GGSN ‑ HLR signalling.