In general, I advise my clients to *not *generate ringback tone on phones. Best practice is to have phones indicate alerting state by responding with 180 RINGING with no SDP, and require PRACK method. Media flow from phones /before /200 OK may cause other problems, especially in a simultaneous ringing environment. One common practice is that 180 RINGING is sent without SDP, and a media gateway closer to the caller furnishes the ringback tone. PRACK is optionally used to ensure that the provisional response is reliable. Another common practice is to send 183 PROGRESS with SDP indicating the availability of early media and progress tone, but that practice isn't bullet proof. Hope this helps. If you would like additional discussion, please feel free to contact me off list. John S. Robinson /jsr at communichanic.com <mailto:jsr at communichanic.com>/ Communichanic Consultants, Inc. On 11/5/2012 23:40, John Botha wrote:
We are debating on having our Broadsoft media server generating RBT on a SIP 180 vs having the phone generate it locally, which is currently the case.
We have found sporadic ringback issues when the phones generate local RBT when it plays one ring and then goes silent or no RBT at all. This only happens once out of approximately 10 calls though, and signalling looks normal (ie no 180 followed by 183 or duplicate messaging).
The end-user hardware devices are mostly Polycom.
Does anyone have some experience, advice and information this?
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