LTE: Why MME ask for multiple authentication vectors from HSS ?

Question

Is it the wish of HSS or MME or UE ?

Answer 1

If u will see the Diameter protocol message in whcih MME asks to HSS for authentication vector u can see that MME has an option about how many vectors he want.

Requested- EUTRAN-Authentication-Info ::=
[ Number-Of-Requested-Vectors]
[ Immediate-Response-Preferred ]
[ Re-synchronization-Info ]

So if he will ask for at a time then each time when ENB / MME decides to change the security context no need to ask HSS (Where each time he has to to calculation for generating the KASME).
If MME asked more than one AV in the message so that later when he want to changes then he can change the KSIASME so that the key KAME can be changed and applied.

Comments

Sachidananda, You have given a nice explanation. Does MME has configuration of number of requested vectors at the network level ? or Is it depend on UE's subscription profile ?

---

I think MME will be deciding based on UE's profile as If he include nothing about Number-Of-Requested-Vectors means zero still HSS will send one.

It is also true that if u are asking for 5 also he can give less than 5 also based on processing.