LTE and the SMS Question

As standardized today, LTE does not have built in SMS capabilities. In a recent webinar on VOLGA (Voice over LTE via GAN), Franz Seiser of Deutsche Telekom (formerly T-Mobile International) argued that this might be a significant issue in the future for a number of reasons.

First, he said, there are a lot of systems in the network that rely on SMS such as SIM card provisioning, for updating the roaming operator list and other data on the SIM card for example, SMS subscription to activate/deactivate add-ons, etc.

Second is the EU mandated SMS user interaction while roaming. Introduced during the first wave of roaming regulation, operators are obliged to inform their subscribers by SMS about roaming costs when they start using a network abroad. In the future, notification to prevent "bill shock" (e.g. when using mobile data abroad) might also be based on SMS.

While the roaming tariff SMS announcements for voice and SMS are probably meaningless for LTE networks that do not support voice and SMS, the notification about bill shock might very well apply to LTE as well. Unless of course, the same tariff applies abroad like at home. Unlikely I would say…

So I quite agree with Franz, if a network allows VOLGA roaming in the future, the SMS solution already comes included at no extra price.

Another option is using SMS as part of the CS fallback (CSFB) feature that is already standardized. However, if the roaming country does not support CSFB and the mobile device is mostly data centric, then the SMS can't be delivered. While it's pretty obvious that a USB data dongle is a data centric device, I wonder what an iPhone or an N97 qualifies as.

And then there is SMS over IMS. However, I doubt we will see IMS and mobile IMS clients anytime soon.

5 thoughts on “LTE and the SMS Question”

  1. Hi Martin!

    I have seen you often refer to the Voice & SMS over LTE issue I guess its a topic that is in the mind of many of your readers. Beside Volga and the CSFB there is from 3GPP this CS Domain Services over EPS (3GPP TR 23.879) which I do not remember if you have mentioned in your posts.
    As I understand, this approach is very similar to Volga but instead of the BSC or RNC (Volga A or Iu modes) it modifies the MSC.
    The clear advantage of Volga is that it bases on GAN which is already done.

    Anyway the usage of SMS for provisioning or updating the roaming lists etc.. should be at sometime substituted for OMA DM (Device Management) which is over IP and fits better in the IP-only world.
    But this is of course still a bit of science fiction, I also believe Volga is nearer to reality.

  2. Hi Mr.Martin,
    iam newbee to protocols..pls excuse if blabbered some thing…
    I heard u say in your blog that SMS services in LTE are delivered even without CSFB.and now iam confused..
    Is SMS possible over the PS connection in LTE?
    and what about CISS and call dependant SS.

  3. Hi Lilly,

    With the CSFB feature, SMS messages are transported over LTE. Not over IP however but as part of the NAS signalling between the mobile device and the MME. For Call Independent Supplementary Services, a fallback is required to GSM or UMTS. Have a look at 3GPP TS 23.272 (CSFB spec) for the details.


  4. Thank You Martin 🙂
    and one more doubt :
    From your blog:LTE and the Voice Gap: CS Fallback,
    It is mentioned that:

    “SMS and CISS

    For receiving text messages, the mobile device can remain the LTE nework, the SMS is forwarded by the MSC to the MME via the Gs/SGs interface and from there via RRC signaling over the LTE radio network to the mobile device. Sending text messages works in a similar way, there is no need to fall back to a legacy network.
    For call independent supplementary services (CISS) such as changing call forwarding configuration, checking prepaid balance via USSD messaging, etc., a fallback to the legacy network is required.”

    Doubt: 1.You said for sending/receiving text messages,there is no need for fallback to GSM/UMTS.with this statement,SMS should be using the same PS connection is it?
    Iam not still clear about this.But from your reply to my doubts, you mentioned that”With the CSFB feature, SMS messages are transported over LTE”
    which is true?
    2.For CISS: for changing call forwarding configuration, why do we need to fallback to 2G/3G.
    we can configure it from LTE domain only know,so that when call comes till MME, then MME can inform to that particular MSC to redirect the call to forwarded mobile(be it in [LTE, redirected to another MME],[2G/3G,redirected to another MSC]).
    Hope my questions are valid,pls excuse me if iam wrong..these are my doubts.
    Thank you.

  5. Hi Lilly,

    With CSFB, SMS can be transported as part of the signaling over the SGs interface from the MSC to the MME and from there via NAS signaling (not IP!) to the LTE mobile. That is part of the CSFB standard. For CISS, a fallback is required as such messaging is not standardized over the SGs interface.

    Have a look at 3GPP TS 23.272, which is freely available at for the details.

    Kind regards,

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