Hi Roman, Thanks for the clarification. I have changed the code and now the phone is resilient to “out of the order REFER and ACK”.
Regards, Karthik From: Roman Shpount <ro...@telurix.com> Sent: 06 September 2018 22:56 To: Karthik Sasupalli <sasupal...@hcl.com> Cc: sip-implementors@lists.cs.columbia.edu; Brijesh Mishra - ERS, HCL Tech <brijesh.mis...@hcl.com>; Ajit Kumar Singh <kumarsing...@hcl.com> Subject: Re: [Sip-implementors] REFER received before ACK, What should be done !! Karthik, You desk phone seems to be broken. It should handle REFER or re-INVITE before ACK. There is no reason in any RFC why UA should generate an error message for the next INVITE or REFER request, if it is received before ACK from the previous transaction. The main purpose of ACK is to stop 200 OK re-transmission. It is very often re-ordered by the network or proxies with request that starts the next transaction. If you are going to generate error responses to re-INVITE received before ACK, you are going to have serious interop problems, since a lot of SIP service providers do exactly this (send a re-INVITE at the same time as ACK) when trying to limit call to a single codec. Also, you cannot rely on Retry-After header in error response, since it is not always supported. In a lot of cases Retry-After is ignored and call simply ends. Error response 491 is wrong here as well, since it is intended for two UA sending INVITE to each other at the same time, not same UA sending INVITE twice. It will still work for re-INVITE (not REFER) but it is not the intended usage. Regards, _____________ Roman Shpount ::DISCLAIMER:: -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- The contents of this e-mail and any attachment(s) are confidential and intended for the named recipient(s) only. E-mail transmission is not guaranteed to be secure or error-free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or may contain viruses in transmission. The e mail and its contents (with or without referred errors) shall therefore not attach any liability on the originator or HCL or its affiliates. Views or opinions, if any, presented in this email are solely those of the author and may not necessarily reflect the views or opinions of HCL or its affiliates. Any form of reproduction, dissemination, copying, disclosure, modification, distribution and / or publication of this message without the prior written consent of authorized representative of HCL is strictly prohibited. If you have received this email in error please delete it and notify the sender immediately. Before opening any email and/or attachments, please check them for viruses and other defects. -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
