[asterisk-users] Text messaging

[Alex Balashov]

Michelle Dupuis wrote:

> I assumed the ATA/gateway would throw away or reject the message since I
> don't think there's an analog equivalent...but I'll wait for the analog
> experts to jump in. 

It appears that Sendtext() simply invokes the callback stub 
ast_channel_tech.send_text, and this is implemented by various channel 
drivers in a proprietary manner.

In the case of chan_sip.c:sip_sendtext(), the implementation indeed 
uses SIP MESSAGE:

static int transmit_message_with_text(struct sip_pvt *p, const char *text)
{
         struct sip_request req;

         reqprep(&req, p, SIP_MESSAGE, 0, 1);
         add_text(&req, text);
         return send_request(p, &req, XMIT_RELIABLE, p->ocseq);
}

In the DAHDI implementation, it appears that some kind of acoustic 
in-band tones are generated using main/tdd.c:tdd_generate().  I am not 
certain what exactly the applicable standard is or how it works.

IAX2 appears to have a "text" frame type:

static int iax2_sendtext(struct ast_channel *c, const char *text)
{

         return send_command_locked(PTR_TO_CALLNO(c->tech_pvt), 
AST_FRAME_TEXT,
                 0, 0, (unsigned char *)text, strlen(text) + 1, -1);
}

-- Alex

-- 
Alex Balashov - Principal
Evariste Systems
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