All other messages not arriving on a protected port

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All other messages not arriving on a protected port shall be rejected or silently discarded by the UE. Data related to the use of UDP encapsulated tunnel mode - Tunnel endpoint addresses and header construction for tunnel mode: In case UDP encapsulated tunnel mode is selected, an "outer" IP header is added to protected packets exchanged between UE and P-CSCF, following the rules of tunnel mode processing according to RFC 4301 53 []. While the IP addresses of the inner IP header are as specified above in the section about "Selectors", the IP addresses of the outer IP header shall be selected as follows: - P-CSCF: For the outbound SA at the P-CSCF the source address shall be the IP address of the P-CSCF, the destination address shall be the public IP address of the UE. For the inbound SA only the destination address of the outer IP header is used to identify the SA at the P-CSCF, together with the SPI. This address is the IP address of the P- CSCF. 3GPP 3GPP TS 33.203 V12.67.0 (2014-0609) 64 Release 12
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- UE: For the outbound SA at the UE the source address shall be the local IP address of the UE, the destination address shall be the address of the P-CSCF as in the destination address of the IP header of the initial unprotected REGISTER message. For the inbound SA only the destination address of the outer IP header is used to identify the SA at the UE. This address is the local IP address of the UE. Other data of the outer IP header (apart from IP addresses) shall be constructed as specified in RFC 4301 [53]. - Ports used in the encapsulating UDP header: In case UDP encapsulated tunnel mode is selected, an encapsulating UDP header is inserted after the outer IP header. With respect to the ports used in the UDP header, the following rules shall be applied in accordance with standard IETF RFC 3948 [28]: - UE: Each protected and UDP encapsulated packet shall use port 4500 as source and destination port in the encapsulating UDP header. - P-CSCF: When the UE sends an UDP encapsulated packet towards the P-CSCF with the ports as described in the previous paragraph, the NAT will change the source port to a port different from 4500. This port is called port_Uenc. When the P-CSCF receives the first protected and UDP encapsulated message from the UE it shall store port_Uenc (cf. Section 7.2). From then on, all protected UDP encapsulated messages from the P-CSCF to the UE shall use port 4500 as source port and port_Uenc as destination port in the encapsulating UDP header. The following rules apply: 1. For each unidirectional SA which has been established and has not expired, the SIP application at the P-CSCF stores at least the following data: (UE_IP_address, UE_protected_port, P-CSCF_protected_port, SPI, IMPI, IMPU1, ... , IMPUn, lifetime, mode) in an "SA_table". The pair (UE_protected_port, P-CSCF_protected_port) equals either ( port_uc , port_ps ) or ( port_us , port_pc ).
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