5.6 User and Control Planes
23.0603GPPGeneral Packet Radio Service (GPRS)Release 17Service descriptionStage 2TS
5.6.1 User Plane (A/Gb mode)
5.6.1.1 MS – P‑GW/GGSN
The user 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 user plane independence of the Network Subsystem (NSS) platform from the underlying radio interface is preserved via the Gb interface. The following user plane is used in A/Gb mode.
Figure 4: User Plane for A/Gb mode and for Gn/Gp
Figure 4a: User Plane for A/Gb mode and for GTP-based S5/S8
NOTE: Refer to TS 23.402 [90] for the S‑GW ‑ P‑GW protocol stack with the PMIP-based S5/S8.
Legend:
– GPRS Tunnelling Protocol for the user plane (GTP‑U): This protocol tunnels user data between core network nodes in the backbone network. The GPRS Tunnelling Protocol shall encapsulate all PDP PDUs. GTP is specified in TS 29.060 [26], or TS 29.274 [92].
– UDP carries GTP PDUs for protocols that do not need a reliable data link (e.g. IP), and provides protection against corrupted GTP PDUs. UDP is defined in RFC 768 [39].
– IP: This is the backbone network protocol used for routeing user data and control signalling. The backbone network may initially be based on the IPv4. Ultimately, IPv6 shall be used. When IPv6 is used in the backbone, then IPv4 shall also be supported. IPv4 is defined in RFC 791 [40] and IPv6 is defined in RFC 2460 [48].
– Subnetwork Dependent Convergence Protocol (SNDCP): This transmission functionality maps network-level characteristics onto the characteristics of the underlying network. SNDCP is specified in TS 44.065 [16].
– 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 TS 44.064 [15].
– Relay: In the BSS, this function relays LLC PDUs between the Um and Gb interfaces. In the SGSN, this function relays PDP PDUs either between the Gb and Gn interfaces or between the Gb and S4 interfaces.
– Base Station System GPRS Protocol (BSSGP): This layer conveys routeing- and QoS-related information between the BSS and the SGSN. BSSGP does not perform error correction. BSSGP is specified in TS 48.018 [78].
– Network Service (NS): This layer transports BSSGP PDUs. NS is specified in TS 48.016 [20].
– 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 TS 44.060 [77].
– GSM RF: As defined in the TS 45.xxx series of specifications.
5.6.1.2 Core Network Node – Core Network Node
Figure 5: User Plane for GTP-based Interfaces between Core Network Nodes
NOTE: Refer to TS 23.402 [90] for the protocol stack with the PMIP-based S5 or S8.
Legend:
– GPRS Tunnelling Protocol for the user plane (GTP‑U): This protocol tunnels user data between SGSNs and GGSNs (Gn or Gp), between SGSNs and S‑GWs (S4), between S‑GWs and P‑GWs (S5 or S8) and between SGSNs in the backbone network (Gn or S16).
– User Datagram Protocol (UDP): This protocol transfers user data between GSNs. UDP is defined in RFC 768.
5.6.2 User Plane (Iu mode)
5.6.2.1 MS – GGSN user plane with GERAN in Iu mode
NOTE 1: The user plane for GERAN in Iu mode is described in TS 43.051 [74].
NOTE 2: The user plane for a HNB Subsystem in Iu mode is described in TS 25.467 [103].
5.6.2.2 MS – P‑GW/GGSN user plane with UTRAN
Figure 6a: User Plane with UTRAN for Gn/Gp
Figure 6b: User Plane with UTRAN for Gn/Gp and Direct Tunnel
Figure 6c: User Plane with UTRAN for GTP-based S5/S8
NOTE: Refer to TS 23.402 [90] for the S‑GW ‑ P‑GW protocol stack with the PMIP‑based S5/S8.
Figure 6d: User Plane with UTRAN for GTP-based S5/S8 and Direct Tunnel
NOTE: Refer to TS 23.402 [90] for the S‑GW ‑ P‑GW protocol stack with the PMIP-based S5/S8.
Legend:
– Packet Data Convergence Protocol (PDCP): This transmission functionality maps higher-level characteristics onto the characteristics of the underlying radio-interface protocols. PDCP provides protocol transparency for higher-layer protocols. PDCP supports e.g. IPv4, PPP and IPv6. Introduction of new higher-layer protocols shall be possible without any changes to the radio-interface protocols. PDCP provides protocol control information compression. PDCP is specified in TS 25.323 [57].
NOTE: Unlike in A/Gb mode, user data compression is not supported in Iu mode, because the data compression efficiency depends on the type of user data, and because many applications compress data before transmission. It is difficult to check the type of data in the PDCP layer, and compressing all user data requires too much processing.
– GPRS Tunnelling Protocol for the user plane (GTP‑U): This protocol tunnels user data between UTRAN and the 3G‑SGSN, and between the GSN CN nodes in the backbone network. GTP shall encapsulate all PDP PDUs. GTP is specified in TS 29.060 [26].
– SGSN controls the user plane tunnel establishment and may establish a Direct Tunnel between UTRAN and GGSN as shown in Figure 6b or a Direct Tunnel between UTRAN and S‑GW as shown in Figure 6d.
– UDP/IP: These are the backbone network protocols used for routeing user data and control signalling.
– Radio Link Control (RLC): The RLC protocol provides logical link control over the radio interface. There may be several simultaneous RLC links per MS. Each link is identified by a Bearer Id. RLC is defined in TS 25.322 [55].
– Medium Access Control (MAC): The MAC protocol controls the access signalling (request and grant) procedures for the radio channel. MAC is specified in TS 25.321 [60].
5.6.2.3 Core Network Node – Core Network Node
This user plane is the same as for A/Gb mode, see clause "Core Network Node – Core Network Node" above.
5.6.3 Control Plane
The control plane consists of protocols for control and support of the user plane functions:
– controlling the GPRS network access connections, such as attaching to and detaching from GPRS;
– 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 control planes are used in both A/Gb mode and Iu mode unless specifically indicated.
5.6.3.1 MS – SGSN (A/Gb mode)
Figure 7: Control Plane MS – SGSN in A/Gb mode
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 clauses "Mobility Management Functionality" and "PDP Context Activation, Modification, Deactivation, and Preservation Functions".
5.6.3.2 MS – SGSN (Iu mode)
NOTE 1: The control plane for GERAN in Iu mode is described in TS 43.051 [74].
NOTE 2: The control plane for a HNB Subsystem in Iu mode is described in TS 25.467 [103].
Figure 8: Control Plane MS – SGSN in Iu mode
Legend:
– Iu mode Mobility Management and Session Management (GMM/SM): GMM supports mobility management functionality such as attach, detach, security, and routeing area update, as described in clause "Mobility Management Functionality". SM supports PDP context activation and PDP context deactivation, as described in clause "PDP Context Activation, Modification, Deactivation, and Preservation Functions".
– SMS supports the mobile-originated and mobile-terminated short message service described in TS 23.040 [8].
– Radio Access Network Application Protocol (RANAP): This protocol encapsulates and carries higher-layer signalling, handles signalling between the 3G‑SGSN and Iu mode RAN, and manages the GTP connections on the Iu interface. RANAP is specified in TS 25.413 [56b]. The layers below RANAP are defined in TS 25.412 [56] and TS 25.414 [64].
– Radio Link Control (RLC): The RLC protocol offers logical link control over the radio interface for the transmission of higher layer-signalling messages and SMS. RLC is defined in TS 25.322 [55].
5.6.3.3 Gn/Gp-SGSN – HLR
Figure 9: Control Plane Gn/Gp-SGSN ‑ HLR
Legend:
– Mobile Application Part (MAP): This protocol supports signalling exchange with the HLR, as defined in TS 29.002 [23].
– TCAP and SCCP are the same protocols as used to support MAP in CS PLMNs.
– The Signalling Bearer is one of the signalling bearers specified in TS 29.202 [72].
5.6.3.4 SGSN – MSC/VLR
Figure 10: Control 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 clause "Mobility Management Functionality" and in TS 29.018 [25]. The requirements for the lower layers are specified in TS 29.016 [24].
5.6.3.5 SGSN – EIR
Figure 11: Control Plane SGSN ‑ EIR
Legend:
– Mobile Application Part (MAP): This protocol supports signalling between the SGSN and the EIR, as described in clause "Identity Check Procedures".
5.6.3.5a S4-SGSN – EIR
Legend:
– Diameter: This protocol supports MS identity check procedure between S4-SGSN and EIR (S13′), as described in clause "Identity Check Procedures". Diameter is defined in RFC 3588 [96].
– Stream Control Transmission Protocol (SCTP): This protocol transfers signalling messages. SCTP is defined in RFC 4960 [35].
Figure 11A: Control Plane S4-SGSN – EIR
5.6.3.6 SGSN – SMS-GMSC or SMS-IWMSC
Figure 12: Control Plane SGSN ‑ SMS‑GMSC and SGSN ‑ SMS‑IWMSC (MAP based)
Legend:
– Mobile Application Part (MAP): This protocol supports signalling between the SGSN and SMS‑GMSC or SMS‑IWMSC over the Gd interface, as described in clause 16.1.
Figure 12A: Control Plane SGSN SMS GMSC and SGSN SMS IWMSC (Diameter based)
The Gdd interface may be used to support a Diameter based signalling between a SGSN supporting EPS interfaces and the SMS GMSC or SMS IWMSC, as described in clause 16.1.
An Interworking Function may be used for interworking between a SGSN supporting the Gdd interface (Diameter based), and a SMS-GMSC or SMS-IWMSC only supporting the Gd interface (MAP Based).
5.6.3.7 Core Network Node – Core Network Node
Figure 13: Control Plane for GTP-based Interfaces between Core Network Nodes
NOTE: Refer to TS 23.402 [90] for the S‑GW ‑ P‑GW protocol stack with the PMIP‑based S5 or S8.
Legend:
– GPRS Tunnelling Protocol for the control plane (GTP‑C): This protocol tunnels signalling messages between SGSNs and GGSNs (Gn or Gp), between SGSNs and S‑GWs (S4), between S‑GWs and P‑GWs (S5 or S8) and between SGSNs in the backbone network (Gn or S16).
– User Datagram Protocol (UDP): This protocol transfers signalling messages between GSNs. UDP is defined in RFC 768 [39].
5.6.3.8 GGSN – HLR
NOTE: This interface is not supported when UEs are served via S5/S8.
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 an SS7 interface is installed in the GGSN, the MAP protocol can be used between the GGSN and an HLR.
– If an SS7 interface is not installed in the GGSN, any GSN with an 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.
5.6.3.8.1 MAP-based GGSN – HLR Signalling
Figure 14: Control Plane GGSN ‑ HLR Using MAP
Legend:
– Mobile Application Part (MAP): This protocol supports signalling exchange with the HLR, as described in clause "Network-Requested PDP Context Activation Procedure".
5.6.3.8.2 GTP and MAP-based GGSN – HLR Signalling
Figure 15: Control Plane GGSN ‑ HLR Using GTP and MAP
Legend:
– GPRS Tunnelling Protocol for the control plane (GTP‑C): This protocol tunnels signalling messages between the GGSN and the protocol-converting GSN in the backbone network.
– Interworking: This function provides interworking between GTP and MAP for GGSN ‑ HLR signalling.
5.6.3.9 S4-SGSN – HSS
Legend:
– Diameter Base+Apps: Diameter Base Protocol as defined in RFC 3588 [96]. The Apps are various Diameter Applications as necessary for the operation between SGSN and HSS.
– SCTP: This protocol guarantees delivery of upper layer packets between SGSN and the HSS with built-in redundancy scheme. SCTP is defined in RFC 4960 [35].
Figure 15a: Control Plane S4-SGSN ‑ HSS
NOTE: As specified in clause 6.4, between S4-SGSN and HSS, the interface is Diameter based (S6d); however, to assist with SGSN transition the use of MAP based Gr between the S4-SGSN and HSS is not precluded".
5.6.3.10 Gn/Gp-SGSN – CSS
Legend:
– Mobile Application Part (MAP): This protocol supports signalling between Gn/Gp-SGSN and CSS, as defined in clause "Mobility Management Functionality".
Figure 5.6.3.10-1: Control Plane Gn/Gp-SGSN‑CSS
5.6.3.11 S4-SGSN – CSS
Legend:
– Diameter: This protocol supports signalling messages between S4-SGSN and CSS (S7d), as described in clause "Mobility Management Functionality". Diameter is defined in RFC 3588 [96].
– Stream Control Transmission Protocol (SCTP): This protocol transfers signalling messages. SCTP is defined in RFC 4960 [35].
Figure 5.6.3.11-1: Control Plane S4-SGSN‑CSS
5.6.3.12 SGSN – RCAF (Iu mode)
Legend:
– Nq-AP: This application layer protocol supports the APN information retrieval procedure between the RCAF and the SGSN.
– Stream Control Transmission Protocol (SCTP): This protocol transfers signalling messages. SCTP is defined in RFC 4960 [35].
Figure 5.6.3.12-1: Control Plane SGSN RCAF
Editor’s note: The protocol stack will be added once Stage 3 has selected the protocol type to use between S4-SGSN and RCAF. It is up to Stage 3 to decide whether the same or different protocols will be used for the Nq’ interface to the Gn/Gp-SGSN and the S4-SGSN, respectively.