[asterisk-dev] Why does chan_sip disable early bridging???

[Chris Ziomkowski]

OK everyone,

I have been banging my head against a wall for 2 days trying to figure 
out why I can't get ringback on my SIP to SIP calls through Asterisk. 
Eventually, I tracked it down. The call to ast_early_bridge actually 
completes without error, but the problem appears in chan_sip, in 
sip_set_rtp_peer() at or about line 17204 in the 1.4.11 version of Asterisk:

if (chan->_state != AST_STATE_UP && !global_directrtpsetup)     /* We 
are in early state */
    return 0;
 
Apparently, any attempt at early media over SIP is thwarted in the  
chan_sip module.  After commenting out  this line, my calls bridge fine 
and I hear the ringback and other progress messages. I have not yet 
noticed any ill effects from doing this.

My question is: what was the purpose of this statement? Is there 
another/better way to get early media on SIP to SIP calls?

Thanks in advance,

Chris