What is TFT?Is it an Id or is it derived from the IP header of the packet(i.e. type of service field)?

Question

I was looking into NAS header. First four bits are used for security header type. Few values I understood but one value I could not understand which was 1100 saying "security header for service request message". I could not understand why such thing is defined only for service request message not for the other messages ?

Answer 1

TFTs are Traffic-Flow-Templates and are assigned to the dedicated bearers.
TFTs are used to give differential treatments to different services.
A TFT can have a set of packet filters which is associated for that bearer.

Example:-
If there are 2 dedicated bearers, then there will be 2 TFTs .
TFT 1 -> dedicated bearer for VoIP service
TFT2 -> dedicated bearer for FTP service
Now TFT1 can have 4 packet filters-
Packet Filter (1/2) - For TCP (uplink/downlink)
Packet Filter (3/4) - For UDP (uplink/downlink)
TFT2 can have 2 packet filters.
Packet Filter(1/2) - For FTP (uplink/downlink)