VoLTE: Does a network need to establish a separate default bearer for IMS call ?

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

Usually, for the services like TCP, ftp, gmail, chat and browsing, network prefers to establish a default bearer with QCI '9'. For the IMS signalling message exchange , QCI '5' is required. So If network establish one default bearer of qci '5' then both the services IMS as well as normal internet access can be provided by the network by just using a single default bearer. But if network establishes a single bearer with QCI '9' to save network resources since both the QCI's have different packet delay requirement, in that case network will have to establish another bearer with the QCI value '5'.

Answer 2

Usually in the field there are two default bearers established when UE attaches to network - QCI 9 - Internet services and QCI 5 - IMS signalling

Comments

Is it always ? On what basis this decision is taken ? It is network driven decision or Does UE ask to establish two default bearers one for IMS signalling and another one for internet access ?

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This all depends on operators configuration and how they want to provide services.
They can have single APN for both Internet and IMS or different APNs.

When there are two APNs, two default bearers will be established. APNs are configured in UE

Answer 3

QCI 5 (non-GBR) & QCI-1 (GBR) is mandatory. one of them is default IMS bearer and other is dedicated bearer. Before IMS attach, QCI-9 or QCI-6 (that part is due to operator configuration. vendors use different QCI non-GBR types ) is being used as default EPS bearer. So, at least 3 bearers are mandatory for VoLTE; 4 bearers per user for ViLTE call session.

Answer 4

I think for each apn, there is a default bearer created.

For volte call, it uses the default bearer created for apn, "ims"..

Correct me if I am wrong..

Comments

Where these APNs are configured ?
- UE SIM or
- UE gets details from the network (Does the network broadcast all these APN's information ? )
- Can a user configure manually ?

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I can tell you from what basic testing expirience I had done with my code :) .

I had to configure the apn in the UE and so  UE requests that Apn when contacting network

N.w may have  info (or a table) saying that for this apn, it needs to use this particular QOS. (I mean, QCI and AMBR in case of default bearer.).
N/w can also use the requested QCI . So it is based on network configuration