what is the purpose of default bearer in LTE?

Question

Probably is newbie question -
What is the purpose of default bearer in LTE and why this concept is missing in UMTS?

Answer 1

In LTE, there is a concept of always on IP connectivity. It means even if UE becomes idle after a successful attach with core networ, assigned IP address will be there for UE until and unless it gets detached from network. default bearer is a non-guaranteed bearer. It means even UE gets connected with eNB and Core network. It is not necessary that data should flow through default bearer.

Comments

Though I am not sure but for me default bearer is there because of voice flows onto datapath in the LTE where as in UMTS it was not.

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Usually default bearer is established with QCI 9, which can't serve conversational voice in lte.
http://blog.3g4g.co.uk/2009/06/lte-qci-and-end-to-end-bearer-qos-in.html

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Thanks Vimal, I am not sure. I made a guess because it was not there in UMTS, not sure who asked this question but surely this Q needs many upvotes.

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Hi Salil , Even in UMTS we had a primary PDP context, Default bearer is similar to the same. Since UMTS had IU-CS and IU-PS separately so the UE can be latched to the network only for voice and sms (IU-CS) and no data, In LTE there is no such concept of CS so if a UE is connected to the network it must have at least one PDN connection. To be more specific , for the UE to be in EMM registered state , it must have a default bearer connection active.