Section: 4.1 GTP Tunnel
Content: GTP tunnels are used between two nodes communicating over a GTP based interface, to separate traffic into different communication flows. A GTP tunnel is identified in each node with a TEID, an IP address and a UDP port number. The receiving end side of a GTP tunnel locally assigns the TEID value the transmitting side has to use. The TEID value shall be assigned in a non-predictable manner for PGW S5/S8/S2a/S2b interfaces (see 3GPP TS 33.250[ Security assurance specification for the PGW network product class ]  [85]). The TEID values are exchanged between tunnel endpoints using GTP-C or S1-MME or Iu-PS messages. The GTPv2 entity communicates to the peer GTPv2 entity the TEID value at which it expects to receive all subsequent control plane messages related to that GTP tunnel via the: - "Sender F-TEID for Control Plane" IE, - "PGW S5/S8/S2a/S2b F-TEID for PMIP based interface or for GTP based Control Plane interface" IE, - "MSC Server Sv TEID for Control Plane" IE, - "S3/S16/S10 Address and TEID for Control Plane" IE, or - "MME/SGSN Sv TEID for Control Plane" IE. The criteria defining when the same or different GTP tunnels shall be used between the two nodes differs between the control and the user plane, and also between interfaces. For the control plane, for each end-point of a GTP-C tunnel: - The TEID-C shall be unique per PDN-Connection on GTP based S2a, S2b, S5 and S8 interfaces. The same tunnel shall be shared for the control messages related to all bearers associated to the PDN-Connection. A TEID-C on the S2a/S2b/S5/S8 interface shall be released after all its associated EPS bearers are deleted. - There shall be only one pair of TEID-Cs per UE on each of the S3, S10, S16 and N26 interfaces. The same tunnel shall be shared for the control messages related to the same UE operation. A TEID-C on the S3/S10/S16/N26 interface shall be released after its associated UE context is removed or the UE is detached. For the S3 interface, when ISR is active for the UE, during I-RAT handover between the ISR associated nodes, the existing S3 TEID-C may be re-used or new S3 TEID-C may be allocated. During this scenario, if the node decides to allocate new S3 TEID-C, it shall release its own old S3 TEID-C. - There shall be only one pair of TEID-C per UE over the S11 and the S4 interfaces. The same tunnel shall be shared for the control messages related to the same UE operation. A TEID-C on the S11/S4 interface shall be released after all its associated EPS bearers are deleted. - There shall be only one pair of TEID-C per MBMS Bearer Service (i.e. per TMGI and MBMS Flow Identifier, if the MBMS Flow Identifier is provided; or per TMGI, if the MBMS Flow Identifier is not provided) over the Sm and Sn interfaces respectively. The same tunnel shall be shared for the control messages related to the same MBMS Bearer Service. A TEID-C on the Sm/Sn interface shall be released after the MBMS Bearer Session is stopped. For GTP-U, a TEID-U is used according to 3GPP TS 29.281[ General Packet Radio System (GPRS) Tunnelling Protocol User Plane (GTPv1-U) ]  [13]. NOTE: GTP-U is based on GTP version 1 (GTPv1).