Why GTP-U used instead IP

[praveen44com]

HI,

I am little bit confused, Why GTP-U used instead of using IP directly?

[Techguru01]

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 they have active plus, possibly separate tunnels for specific connections with different quality of service requirements. So its used instead of IP.