Voice: The Litmus Test for LTE Handsets

The more I think about it the more I am convinced that voice service will make or break LTE in the mid-term. While most industry observers agree that the first devices for LTE are likely to be USB dongles and PC cards the real LTE story only starts once the technology makes it into mobile Internet devices and handsets.

While on mobile Internet devices it might be acceptable to have Skype or some other VoIP technology, smaller handsets who’s main purpose is voice service might have a much more difficult time with VoIP. Such devices must also be capable of roaming to 2G and 3G networks when running out of LTE coverage. Especially in 2G networks, VoIP is a no go so voice service must fall back to good old circuit switched telephony. So apart from the question of how VoIP will be done on LTE handsets the much bigger question is how to make the experience seamless over 2G, 3G and LTE.

Sure, there is Voice Call Continuity and the IMS can be configured to forward an incoming call via a circuit switched connection when no suitable wireless IP network is available. However, from what I can see so far it seems that achieving this is much more difficult then rolling out LTE in the first place.

Another alternative would be for a LTE handset to be simultaneously attached to a LTE network for data and a 2G or 3G network for circuit switched voice. This way the telephony application on the handset could be simple. Not sure if that will work in practice though!?


4 thoughts on “Voice: The Litmus Test for LTE Handsets”

  1. hi,martin
    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)

  2. 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…

  3. 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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