Subject: [MMUSIC] Propose A Non-18x Provisional Response Used for ICE Connectivity Check

From: <[email-masked]>
Date: Thu, 29 Nov 2007 13:56:53 +0800

Hi, there:

In section 12, “Usage with SIP”, ICE-19 suggests the use of rfc3262 (100rel extension) for reliable provisional responses with SDP transmission as well as an ICE optimization by sending 18x with SDP 4 times ‘till receiving an ICE binding request (section. 12.1.1 “Offer in INVITE”). 

Prior to ICE invention, a terminal (such as an SIP IP phone) may locally generate ringback tone to notify its user upon receiving a 180 provisional response; and it will cease playing locally generated ringback tone upon receiving a 183 with SDP (even when a 180 with SDP) because the far-end side may decide to send call-progress tone or an audio announcement in an early media stream.  Generally, a 183 with SDP is reliably or unreliably transmitted by a PSTN gateway to transmit PSTN-side call-progress tone (it may be just a tone or some music) in an early media. 

Therefore, the reliable provisional 1xx responses with SDP transmitted aimed for ICE-connectivity check should not use 180~184 provisional responses; otherwise, the terminals receiving such 18x provisional responses while making outbound calls may wrongly cease playing locally generated ringback tone even such 18x reliable provisional responses are for ICE connectivity check instead of for far-end side call-progress tones. 

I would suggest explicitly nail down or recommend another non-18x provisional response for such ICE usage in the revised ICE-20. 

Albert

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