Why IMS required separate PDN?Why cant default PDN controls voice data?

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

Hello Sakshi, the purpose of default bearer is different from the purpose of bearer that supports IMS. Default bearer is used to provide always on IP connectivity and radio network reserve less radio resources for default bearer compared to the IMS data flow bearer.
Voice services need different treatment in the network nodes when its packets pass though them. The parameters such as delay tolerance, packet loss error late is different from default and IMS (dedicated bearer).
That's is the reason, network needs a different bearer for IMS and if it uses the default bearer to send voice packets then user may experience some kind of distortion and low quality service.

Comments

Hi,
We can use different QOS bearer in the default PDN right? say e.g QCI 5 is for IMS then we can create an dedicated bearer with QCI 5 or 1 and can be used for the voice call. i understood that in default bearer we cannot transfer voice packet but dedicated bearer can be used right ,then why do we need different PDN?