Why UE-AMBR is mandatory IE for Initial Context Setup Request message?

Question

and what eNodeB does, when it receives SRVCC IE in the initial context setup request message ?

Answer 1

To answer your question, I would prefer to discuss about AMBR first.
There are 2 types of bearers -
1. Guaranteed Bit Rate (GBR)
2. Non Guaranteed Bit Rate (Non GBR)

During attach procedure, at least one default bearer is established. And default bearer is of Non GBR type.
Now different subscribers subscribe for different bit rates as per their requirement. Just imagine if there is no AMBR, then any attached UE will try to use the complete available bandwidth. (i.e. the bandwidth provided for other UEs too)
So in lay man's term you can say that AMBR is a reference point beyond which a UE cannot access the bandwidth. (It can have a bit rate maximum upto AMBR).
So it is a mandatory IE.

Comments

nicely explained.

Answer 2

As part of attach procedure, network establishes at least one default bearer. A default bearer can have one of the QCI value ranges from 5-9. There are two categories of bearer in lte network, one is known as GBR bearer and another one is known as non-GBR bearer.

Default bearer is mandatory to establish for an UE and also it is under non-GBR category. Every subscriber may subscribe for different bit rate and eNodeB MAC scheduler consider those things. Reason being, UE-AMBR IE is a mandatory IE within the Initial context setup request messag