Nota

VoLTE: Using TCP parameters in packet analysis The TCP is used to transfer a continuous stream of octets in each direction between users by packaging some number of octets into segments for transmission through the internet system[RFC793]. In SIP realm, the TCP is one of the most commonly used protocol along with UDP to transfer user data. The above diagram shows an example of the protocol map for LTE user plane. The backhaul is placed between eNB and the EPC in the operator's network in general. The IPv4 packet sent by the UE over the air is wrapped by the eNB using GTP and IPv6 headers. The eNB sends the IPv6 packet through the GTP tunnel and the PGW at the end of GTP tunnel unwraps the IPv6 and GTP headers. The retrieved IPv4 packet at PGW is forwarded to the P-CSCF over SGi interface. I. TCP header The following shows the TCP headers and parameter descriptions as specified in RFC793 Sequence Number(32bits): The sequence number of the first data octet in th...

VoLTE: Understanding of GTP TEID to use in LTE trouble shooting The GTP(GPRS Tunneling Protocol) is a communication protocol used by the LTE to deliver IP packets within the EPC. The GTP-C is used to deliver the controlling signals over S11 and S5, whereas the GTP-U is used to deliver application payload over S1 and S5.  I. TEID exchanges The TEID(Tunnel Endpoint IDentifier) is generated by each node during the initial attach procedure. The Create Session Request includes the S11 MME DL TEID and the S5 SGW DL TEID, which are generated and included by MME and Serving GW respectively. The Create Session Response includes the S5 PGW UL TEID and the S11 SGW UL TEID, which are generated and included by PGW and Serving GW respectively. The following diagram shows the actual call flow and depicts how the TEID is exchanged between NEs. Upon receiving the Create Session Request, the Serving GW establishes the downlink GTP-C tunnel towards the MME using the received S11 ...