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Nice however two things which are not clear.
In case of VCC does the data transfer continues (I suppose it is since both are IP based).
Second what happens in the case of circuit switched fal-back? Does the LTE Data transfer continues on LTE network? Is it handed over to 3G or 2G? If so do you need GSM DTM to continue the data transfer?


Hi dbudbu,

yes, the data transfer can continue in case the fallback is done to a 3G network. In case of GSM the data transfer is interrupted, unless of course DTM is available in the network.



Hi Martin,

Thanks for your great blog!
I have read about UTRAN(HSPA) which supports voice call over PS domain in the 3G network. And the SRVCC for UTRAN(HSPA) to UTRAN is also described in 23.216. But I don't know how to start a voice call over PS domain by 3G RRC signalling, do you have any ideas about this feature?


Hi ShuWen,

Well, if you use Skype for making a voice call over 3G, RRC signaling will not be different from the one you see today for any other kind of data service. But I guess that was not the intent of your question.

For VoLGA and VoLTE: There are some means for both systems to interact with the core and radio network to set the quality of service for the voice packets. In LTE that would be the establishment of a default bearer and in UMTS it would be a secondary PDP context. The same thing, just different words. That in turn then triggers a number of radio bearer reconfigurations, e.g. having one radio bearer in RLC unack. mode for the voice packets. Youll find some details here: http://tinyurl.com/yz86eo5


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