Is TEID chosen by GGSN unique for all SGSN nodes ?

Hi all,

This question is related to the behaviour of GGSN (Gateway GPRS Support
Node) when supporting GTP(GPRS Tunneling Protocol).

Does the GGSN assign unique Tunnel Endpoint Identifier for all SGSN
nodes ? To put the question in another way "Is the TEID assigned by a
GGSN unique for all the SGSN it talks to ?"

The GTP v1 specification doesn't clearly talk about this behaviour of
GGSN and is left to the design of GGSN. The GGSN may choose to reuse
the same TEID for different SGSN nodes i.e have < SGSN, TEID> unique or
assign unique TEID and have <TEID> unique. To me the latter options
looks good as it would involve faster retrieval of PDP Contexts,
however it will limit the maximum number of Tunnels to 2^32 as against
Number_of_SGSN_supported * 2^32 for the former approach.

Thanks,
Elan