Check the RFC 3326. It allows the Reason to be in Responses as well,
RFC 3326 The Reason Header Field for SIP December 2002 Initially, the Reason header field defined here appears to be most useful for BYE and CANCEL requests, but it can appear in any request within a dialog, in any CANCEL request and in any response whose status code explicitly allows the presence of this header field. Note that the Reason header field is usually not needed in responses because the status code and the reason phrase already provide sufficient information. Thanks, Neel. -----Original Message----- From: sip-implementors-boun...@lists.cs.columbia.edu [mailto:sip-implementors-boun...@lists.cs.columbia.edu] On Behalf Of David Mathe (DS) Sent: Thursday, February 04, 2016 11:18 PM To: sip-implementors@lists.cs.columbia.edu Subject: [Sip-implementors] Cause Code in the 500 Server Internal Error message Good Day. Is it acceptable for a switch to send the cause code as a Reason in the 500 Server Internal Error Message instead of sending the Cause code on its own to the caller in a SIP voice call? Example below [cid:image002.png@01D15FE5.4EB417F0] Thank You and Warmest Regards David Mathe ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This e-mail is subject to the Telkom SA SOC Ltd electronic communication legal notice, available at : http://www.telkom.co.za/TelkomEMailLegalNotice.PDF <http://www.telkom.co.za/TelkomEMailLegalNotice.PDF> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
