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Chap05 gtp 03_kh

Nov 22, 2014

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  • 1. Chapter 5 GTP the tunnel Contents: 5.1 GTP interfaces 1. Protocols for Combined Procedures 2. GTP interfaces 3. Control and User plane 4. Tunnel Endpoint Identifier 5. GTP and UDP 5.2 Message formats 1. The GTPv1 frame 2. Optional fields in the Header 3. GTP header for the G-PDU Example 5.3 GTP message groups 1. Message groups 2. Path Management Messages 3. Tunnel Management Messages 4. Location Management Messages 5. Mobility Management Messages 5.4 GTP messages
  • 2. Chapter 5 GTP the tunnel 5.1 GTP interfaces 1. Protocols for Combined Procedures 2. GTP interfaces 3. Control and User plane 4. Tunnel Endpoint Identifier 5. GTP and UDP
  • 3. GTP interfacesIn the 2nd generation mobile communication network GSM/GPRS, the GPRS Tunnelling Protocol (GTP) is usedbetween the GPRS Support Nodes (GSN) and for 3 rd generation networks as well between SGSN and RNC (notcovered here):Gn-interface: The Gn interface is in use between SGSN and GGSN within one operators network infrastructureand between SGSNs. The Gn-interface between SGSNs is required to support service continuation in case ofinter-SGSN cell reselection.Gp-interface: The SGSN is located in the visited network, where a roaming subscriber is currently registered, butthe GGSN is located in a foreign network (normally, in the subscribers home network).(Ga-interface: This interface is used between the GSNs and the Charging Gateway Function (CGF). A derivateof the GTP is used, denoted GTP. Both CGF and GTP are optional. The CGF may located in a stand-alonedevice, often called Charging Gateway. Alternatively, it may be implemented in the GSN units. The GTP wasdesigned to carry charging related information. GSM 12.15). GTP version 0 GTP version 1 versions of GTP: GSM 09.60 3GPP TS 29.060 GTP GTP GTP GTP There are important changes from GTP Release 98 to GTP Release UDP / UDP / UDP / UDP / 99. The main reason is that GTP shall also be used in the backbone of TCP TCP TCP TCP UMTS networks(Gn, Gp and Iu interfaces). To meet this requirement IP IP IP IP some additional messages for SGSN Relocation procedure have been defined. L2 L2 L2 L2 Furthermore some Information Elements have changed in Release 99. L1 L1 L1 L1 The most significant change in IEs is that a so-called Tunnel Endpoint Gn Gn Gp Identifier (TEID) substitutes the Tunnel ID (TID) and the Flow Labels. SGSN SGSN GGSN SGSN Anonymous PDP Contexts in Release 98 are not specified any longer in Release 99 Another PLMN
  • 4. Control and User plane GTP-PDU: A GTP Protocol Data Unit is either a control plane (GTP-C) Tunnel control message or a user plane (GTP-U) message. Management protocol The control plane messages (GTP-C) are used to transfer GSN capability information between GSN pairs, to create, update and delete GTP tunnels and for path management. The tunnels for GTP-U protocol entities make a transport service for oneTunnelling mechanism PDP context. The user plane messages are used to carry user data for transfer of user packets and signalling messages for path management and error packet data indication. G-PDU: A G-PDU carries a user data message. It consists of a T-PDU (Original user packet data, for example an IP datagram) plus a GTP header. Note: All GSNs supporting GTPv1 must support a fallback to GTPv0. GSN UDP/IP is the only path protocol defined to transfer GTP messages in the GTP-C GTPv1 1 of GTP. A User version Datagram GTPv1 GTP-U Protocol (UDP) compliant with RFC 768 shall be used. UDP UDP IPvX In Rel 99 IPvX only L2 L2 UDP L1 L1 GSN Gn/Gp
  • 5. Tunnel Endpoint IdentifierA GTP tunnel in the GTP-U plane is defined for each PDP Context or each MBMS (MultiMediaBroadcast/Multicast Service) in the GSNs. It is necessary to forward packets between an external packet datanetwork and an MS user.A GTP tunnel in the GTP-C plane is defined for all PDP Contexts with the same PDP address and APN (forTunnel Management messages) or for each MS (for messages not related to Tunnel Management).A GTP tunnel is identified in each node with a TEID, an IP address and a UDP port number.The Tunnel Endpoint Identifier (TEID) unambiguously identifies a tunnel endpoint in the receiving GTP-U orGTP-C protocol entity. The receiving end side of a GTP tunnel locally assigns the TEID value the transmittingside has to use. The TEID values are exchanged between tunnel endpoints using GTP-C (or RANAP, over theIu) messages. If the TEID 0, then one PDP Context is addressed. TEID = 0 holds messages not associatedwith one PDP context. PDP GTP-C PDP PDP TEIDGSN,control PDP PDP PDP PDP PDP GTP TEIDGSN,user GTP individual UDP PDP Contexts: UDP GTP-U PDP IP IP
  • 6. GTP and UDPUser data and GTP signalling and control information have to be exchanged between GSNs. The path between twonetwork nodes is described by an IP address and the UDP port number. For GTP-C request messages, the UDPdestination port number is always 2123, while the UDP source port number can be allocated locally. For GTP-Urequest messages, the UDP destination port number is always 2152, and the UDP source port number is allocatedlocally. In the response message, the destination port number is the source GSNs source port number, while thesource port number is the source GSNs UDP destination port number. User data packets (so-called T-PDU) aretransmitted in the same way as GTP-U request messages. The combination of UDP port number and IP address isoften called UDP/IP path.UDP/IP Path: connection-less unidirectional or bidirectional path defined by two end-pointsAn IP address and a UDP port number define an end-point. A UDP/IP path carries GTP messages between GSNnodes, and between GSN and RNC nodes related to one or more GTP tunnels. There is one GTP-entity for eachused IP address. GSN GTP-C GSN TEIDGSN,control Source Port Dest. Port PDP Request ? 2123 PDP PDP PDP PDP Response 2123 ? PDP PDP TEIDGSN,user PDP GTP GTP GTP-U Source Port Dest. Port individual UDP Request ? 2152 PDP Contexts:
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