LTE: What does mean by fully qualified tunnel id (FTEID) in GTP control messages ?

Question

I have seen GTP control messages and found that F-TEID consists of an IP address and 32 bit long Tunnel Id. For example: Create Session Response message contains control plane F-TEID and user plane F-TEIDs. I have a question here, why not only TEIDs are included in Create Session Response message when IP address would be common ? or Does it mean control and user plane both F-TEIDs may have different IP address ?

Answer 1

In GTP endpoints were uniquely identified by F-TEIID(IP Address + teid). Each F-TEID pair was treated as a logical tunnel.
GTP will create different tunnel ID's for control and user plane. So, in create session response one F-TEID is for control plane and another is for user plane.
For example, on S5/S8 interface create session response carries PGW control plane F-TEID(PGWC IP Adress + PGW control plane TEID) and PGW user plane F-TEID(PGWU IP Adress + PGW user plane TEID). Here PGWC and PGWU may or may not be the same.

Tunnel-ID's should be created as follows.
- On S11-C interface, control plane tunnel-Id's is per UE.
- On S5/S8-C interface, control plane tunnel-id's per APN/PDN.
- On S5/S8-U interface, user plane tunnel-id'd per bearer.
- On S1-U interface, user plane tunnel-id'd per bearer.