During design team discussions on Automatic Call Handling (ACH), a question arose concerning the impact of B2BUAs on ACH.
At present, the ACH draft (draft-ietf-bliss-ach-analysis-00) discusses ACH at UAs and ACH at proxies, and interactions between these. In principle the discussion on ACH at proxies applies equally to ACH at B2BUAs, where B2BUAs perform the role of domain proxy. The issue that was raised concerned other B2BUAs on the path of a call, either between the UAS and the proxy or between the proxy and the UAC. In the first case these might have impact on information between the UAS and the proxy, which the proxy needs in order to perform ACH successfully. In the second case it might have impact on information sent to the UAC for delivery to the calling user. One such issue is the HERFP issue, where there is a forking B2BUA on the path and as a result only one of several final response codes can be sent backwards. However, in my opinion this is no different from the case of a forking proxy on the path. The next version of the ACH analysis draft will mention the HERFP issue. However, the point was made that there may be other types of behaviour, specific to certain types of B2BUA, which might have an impact. These are to do with B2BUAs that fork but hide from the upstream side the multiple early dialogs that are generated on the downstream side. I will leave the originator of these comments to expand further on this. The charter of BLISS/ACH (or indeed the charter of BLISS) does not require us to address B2BUA issues. Also, certain B2BUA behaviours can impact other aspects of SIP, not specifically ACH. Furthermore, B2BUAs vary widely in their behaviour and we cannot hope to address all possible architectures. However, it might be beneficial to mention any particular behaviours that are known to cause problems for ACH, even if we don't attempt to solve such problems. Comments? John _______________________________________________ BLISS mailing list [email protected] http://www.ietf.org/mailman/listinfo/bliss
