GTP User Data Tunneling
GTP-U is, in effect a relatively simple IP based tunneling protocol which permits many tunnels between each set of end points. When used in the UMTS, each subscriber will have one or more tunnel, one for each PDP context that they have active, as well as possibly having separate tunnels for specific connections with different quality of service requirements.
The separate tunnels are identified by a TEID (Tunnel Endpoint Identifier) in the GTP-U messages, which should be a dynamically allocated random number. If this random number is of cryptographic quality, then it will provide a measure of security against certain attacks. Even so, the requirement of the 3GPP standard is that all GTP traffic, including user data should be sent within secure private networks, not directly connected to the Internet. This happens on UDP port 2152.
The GTPv1-U protocol is used to exchange user data over GTP tunnels across the Sx interfaces. An IP packet for a UE is encapsulated in an GTPv1-U packet and tunneled between the P-GW and the eNodeB for transmission with respect to a UE over S1-U and S5/S8 interfaces.
Read more about this topic: GPRS Tunnelling Protocol, GTP-U
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