LTE: Why does need a bearer of QCI 5 to exchange SIP signalling messages ?

Question

Is it mandatory to establish a separate default bearer to exchange IMS signaling messages between UE and IMS network nodes ? Can't internet default bearer be used for the same ?

Answer 1

A LTE subscriber may use different types of applications. Each application has different packet delay budget and packet loss error rate requirements. Usually network establishes non-GBR bearer (Packet Delay - 300 ms and (1/1000000) packet error loss rate) for the internet access bearer by an UE.

For IMS signalling and IMS voice data different packet delay budgets (100 ms) and packet error loss rate 1/1000000) are defined . If you see IMS packet delay budget is different from the normal internet bearer that is the reason to establish a new bearer which fulfill the requirement of IMS signaling. Along with IMS signalling bearer, another bearer with QCI "1" need to establish .