Re: [sipcore] 4244bis-05: additional technical comments
Shida Schubert <shida@ntt-at.com> Sun, 10 July 2011 08:14 UTC
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From: Shida Schubert <shida@ntt-at.com>
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Date: Sun, 10 Jul 2011 17:14:19 +0900
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To: "Worley, Dale R (Dale)" <dworley@avaya.com>
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Cc: "draft-ietf-sipcore-rfc4244bis@tools.ietf.org" <draft-ietf-sipcore-rfc4244bis@tools.ietf.org>, "sipcore@ietf.org WG" <sipcore@ietf.org>
Subject: Re: [sipcore] 4244bis-05: additional technical comments
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Hi Dale; My comments inline.. On Jun 23, 2011, at 5:47 AM, Worley, Dale R (Dale) wrote: > Thanks for writing this, as both points you made lead me to realize > errors I was making! > >> From: Hadriel Kaplan [HKaplan@acmepacket.com] >> >> 1) Section 10.3, page 19, says: >> In the case that a SIP entity (intermediary or UAS) adds an hi-entry >> on behalf of the previous hop, the hi-index MUST be set to 1. >> >> Taken literally, this means when a request already marked with H-I >> entries happens to cross a legacy non-HI system, the next downstream >> element will add an additional H-I entry starting at 1 again. Is that >> intentional/on-purpose?? At first I thought this was just an >> editorial mistake, but section 11, page 22, says : >> >> Gaps are possible if the request is forwarded through >> intermediaries that do not support the History-info header field and >> are reflected by the existence of multiple hi-entries with an index >> of "1". >> >> So a single SIP request can actually have multiple H-I trees with >> multiple root indexes of 1? Wouldn't this make UAS logic code more >> complicated, because now the "mp=X" and "rc=X" index values are >> relative "X" values, scoped to within their particular tree, as >> opposed to being an absolute number for the whole H-I list? > > I had mis-read this to mean that the receiving entity would construct > an H-I entry on behalf of the previous hop by adding a new H-I entry > with index "[whatever].1", that is, the entry the previous hop would > have added, had it forwarded to only one destination. > > But that's not what the draft says, the draft says that the new index > is just "1". > > Given the specifications, that new H-I entry must be the child of the > immediately preceeding H-I entry, so the H-I header is not ambiguous. > But it does destroy the principle that the three of H-I entries is > described simply by the index values. Your understanding is correct AFAIK. The index added for entity which didn't log H-I (didn't support H-I) SHOULD be "[last-hi-entry's index].1". > >> 2) Section 9.4, page 16 says: >> When sending a response other than a 100, a SIP entity MUST include >> all the cached hi-entries in the response, subject to the privacy >> consideration in Section 10.1.2 with the following exception: If the >> received request contained no hi-entries and there is no "histinfo" >> option tag in the Supported header field, the SIP entity MUST NOT >> include hi-entries in the response. >> >> Note the "If the received request contained no hi-entries and...". I >> don't know what having H-I entries has to do with it. We have an >> option-tag for this purpose: histinfo. If the option-tag is in the >> Supported, then you can send H-I entries in response. Else not. Even >> if the request contained H-I entries but no "histinfo" option tag, you >> can't send 'em back. (e.g., such would be the case if proxies added >> the entries but the UAC does not support it) > > Hmm, I would be inclinded to agree with you, but, as written, the > draft solves a "problem" I was wondering about: > > phone A (no H-I supt.) --> proxy B (H-I supt.) --> proxy C (H-I) --> phone D (H-I) > > Phone A does not insert H-I in the request. > > Proxy B inserts H-I in the request to proxy C: One entry, index > 1, containing the original request-URI, and a second entry, index > 1.1, containing the request-URI it sends to proxy C. > > Proxy C inserts H-I in the request to phone D: index 1.1.1, > containing the request-URI it sends to phone D. > > Phone D copies the H-I into its response -- because it received > H-I in the request (which implies that some upstream entity can > understand the H-I). > > Proxy C copies the H-I into its response, adding Reason to index > 1.1.1 -- because it received H-I in the request. > > Proxy B *does not* include H-I in its response. The absence of > "Supported: histinfo" and an incoming H-I in its request shows that no > upstream entity understands H-I. > > Phone A receives a response without H-I, as it expected. > > This arrangement satisfies these requirements: > > 1) No phone will receive H-I in a response if it does not support it. > Thus, no pre-H-I phone will receive a response that is unexpectedly > large. > > 2) Every H-I-aware entity will receive H-I information from every > upstream and downstream entity H-I-aware entity. > > An implication of this is that "Supported: histinfo" is redundant and > can be eliminated from the protocol; a phone can indicate whether or > not it supports H-I by whether it includes a History-Info header. > > Dale We still need "Supported: histinfo" for backward compatibility as you stated yourself in the following e-mail. Regards Shida > _______________________________________________ > sipcore mailing list > sipcore@ietf.org > https://www.ietf.org/mailman/listinfo/sipcore
- [sipcore] 4244bis-05: additional technical commen… Hadriel Kaplan
- Re: [sipcore] 4244bis-05: additional technical co… Worley, Dale R (Dale)
- Re: [sipcore] 4244bis-05: additional technical co… Worley, Dale R (Dale)
- Re: [sipcore] 4244bis-05: additional technical co… Shida Schubert
- Re: [sipcore] 4244bis-05: additional technical co… Shida Schubert