SMS and calls theory

If the incoming SMS delivery calls have a caller ID in the BT Text, the chances are there that it understands ETSI ES 201 912, and for incoming SMS, refers to the caller as the SM-SC and recipient as SM-TE, or use the implementation in Asterisk

This may be true even where the call is really SIP and RTP over IP, so there is digital (SMS) over analogue (FSK) over digital going on. (voice codec)

Having the message recovered digitally by the Voip service provider may be helpful for the "tight delay bounds" issue on the asterisk article, even if it is then relayed via a role switch:

Incoming messages

This mainly relies on voicemail being able to activate based on caller phone number, so if it is a SMS relay service such as BT Text or AQL calling, divert to voicemail:
Then optionally play the initial FSK communication of ETSI ES 201 912, in the SM-TE role, to have a chance to get the SMS digitally
If the caller (SM-SC) replies with FSK quickly in accordance with ETSI ES 201 912 then accept the SMS digitally and deliver as an Inbound SMS, otherwise:
send dialpad digits to have SM-SC play SMS as text-to-speech
then record it like voicemail, attempt send the recording via email and if successful, ask the SM-SC to delete the delivered SMS, then end the call.

End user equipment interaction

End user SIP equipment may support ETSI ES 201 912 over RTP, if so then:

VoIP supplier could implement that by divert outgoing calls to well known SM-SC numbers to the provider SM-SC
Also have an option to rôle switch to SM-SC to deliver messages to it, after having logged them, if customer wanted that.

Experimenting

Trying to send SMS from Vodafone to a BT number ported to AAISP does result in text-to-speech calls that come from 08456021111, which is different from the numbers in gigaset sl450a-go that is use to get calls, so there likely be no need to support both the text to speech and FSK based SMS delivery.

The factory numbers are 1470P17094009* to send (as in active send=yes) and 0800587529* to receive (as in active send=no), it can be set to process these numbers on IP1 instead of "Fixed" The asterisk apparently means to accept any follow-on digits, although it could mean asterisk literally also.

Therefore, the outstanding matters are to get BT to send AAISP SMS either via SMS over PSTN, (by us [sending "register" to 00000 or BT delivering SMS over inter-operator transports such as text files over ftp over ipsec.

Michael (talk) 22:17, 12 October 2021 (BST)

Block SMS text to speech

The user may prefer to lose incoming SMS completely than have them delivered as voice calls, such as where the ability to intercept calls from +448456021111 and +443333440000 to voicemail is not set up.

To do that the opt-out functions are used on both BT and AQL, with both pages used to opt back in later, such as to do further tests if progress on inbound digital delivery of SMS is known about.