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glad to find your site here for all the infos concerning the mobile and the networks. I am just wondering about one questions: as we know that with GSM and GPRS/EDEG, we can not use voice and data simultaneously. When we have a incoming call, the data link is suspended and resumed after the call. So I want to know whether it is possible that during a GSM call, i can send out SIP message like invite notify through GPRS ? may you give me some ideas? thank you. (hongwu.lu@gmail.com)


The feature is called DTM (Dual Transfer Mode). Quite a number of phones are compatible already but I don't know a single network that supports packet + circuit simultaneously today. It will come eventually but not tomorrow...


Hi! Martin
Your posting is quite informative. I enjoy it.

Dean Bubley

Hi Martin

Yes, I agree with this. For me, the killer app for VCC is handover between cellular packet voice & cellular circuit, not with VoWLAN.

I also think all of this highlights the complexities in VoLTE - which is why operators should attempt to "soft launch" VoIP on HSPA or HSPA+ first, to gain experience & fill in any gaps in the end-to-end systems, before they're forced into it by all-IP LTE.

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