Aditya, That all depends on the switch. Asterisk sends a 503 if you look at it the wrong way, that is, under many conditions. In my experience most carriers will send a 503 when their upstream paths are full (or your concurrent calls to them is full) and they expect you to route advance to another carrier. A 503 could cause a proxy or a switch to blacklist the host that sent it for a period, so proxies (Opensips included) will convert a 503 to a 500 before relaying.
When a switch has trouble processing the request because of some internal issue, say, a database error, it will reply with a 500. This list is by no means all inclusive. Hopefully it will point you in the right direction. - Jeff On Jan 4, 2010, at 10:13 PM, Aditya Kumar wrote: Thanks Jeff for the link. I did see 3261. Question is : RFC will tel high level about response codes. I am trying to understand in particular when a End User (UAS) will sent. I am clear from a proxy perspective. Was looking some one can share your experiences when a UAS will send 5xx ________________________________ From: Jeff Pyle <[email protected]<mailto:[email protected]>> To: OpenSIPS users mailling list <[email protected]<mailto:[email protected]>> Sent: Mon, January 4, 2010 7:01:34 PM Subject: Re: [OpenSIPS-Users] 3rd party Client sending 5xx Please see: http://www.apps.ietf.org/rfc/rfc3261.html#sec-21.5 On Jan 4, 2010, at 9:53 PM, Aditya Kumar wrote: Hi all, I am inter working with a 3rd party SIP UA and I see they are sending 503/500. Can any one tell me what are the cases at which a SIP UAS will sent 503 or 500
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