GTP stands for "General Packet Radio Service Tunneling Protocol". This protocol supports tunneling concepts that are used for IP packets flow from UE to external world and vice a versa. There is no need of connection oriented protocol for flow of IP packets, therefore UDP is used at transport level. Some application/protocol is required to support and differentiate millions of sessions, that application protocol is known as GTP protocol.
GTP deals with control as well as data plane, that is the reason of having two variants i.e. GTP-C and GTP-U.
Since UDP is a connection less protocol, GTP provides echo request/response messages to check the availability of peer.
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