Last week we wrote generally about tunneling protocols. This week we will write about a very specific tunneling protocol to give readers a better sense of how such protocols are developed and used.
GTP is used exclusively in mobile networks and is maintained by the same entity (3GPP) that defines all mobile standards. It came to life during the 2.5G days in the late 90s when a technology known as General Packet Radio Services or GPRS was defined for data communication over a mobile network. The standard has evolved and is used in both 4G LTE and emerging 5G networks.
GTP is an IP-in-IP tunneling protocol in the sense that an original IP packet created by a mobile device such as a phone or tablet – for example, to access www.google.com – is sent into a mobile network core. This original IP packet must be delivered unadulterated to the Internet, however there are various interactions within the mobile network core itself that are required to successfully deliver the packet. These interactions include procedures such as cell handover, QoS, billing, network routing and more. In order to seamlessly accomplish these actions, the mobile network embeds or tunnels the original IP packet inside another IP (using UDP) packet that uses local addressing and a well-defined tunnel endpoint identifier (TEID) to track the specific phone or tablet that originated the message.
There are many tunneling protocols in existence today, but GTP is very prominent amongst them because it is used in the heart of the mobile networks that we all take advantage of on a daily basis.