Re: [RFC 4235 & draft-kuthan-sip-derive] 481 "Call doesn't exist" for initial SUBSCRIBE ?

I agree that 481 seems an unsuitable response in this case.
Its not clear to me what response is best suited. Perhaps 403 or 603.

	Thanks,
	Paul

Iñaki Baz Castillo wrote:
> Hi, I've a doubt about what should be the correct response for an initial 
> SUBSCRIBE (Event: dialog) if the indicated dialog doesn't exist in the 
> recipient of the SUBSCRIBE.
> 
> This doubt comes after reading the today submitted draft "Dialog Event foR 
> Identity VErification":
>   http://www3.ietf.org/proceedings/staging/draft-kuthan-sip-derive-00.txt
> 
> In page 14 of this draft there is a flow about a suspicious call (spoofed 
> From). The flow is correctly displayed using fixed length typography, if it's 
> not your case refer to page 14 of the draft.
> 
> 
>     Attacker        Alice   Proxy 1 (atlanta.com) Proxy 2 (biloxi.com) Bob
>     |               | INVITE F5      |                |                |
>     |------------------------------------------------>|                |
>     |               | 100 F6         |                |                |
>     |<------------------------------------------------| INVITE F7      |
>     |               |                |                |--------------->|
>     |               |                |                | 100 F8         |
>     |               |                |                |<---------------|
>     |               |                |                | SUBSCRIBE F9   |
>     |               |                | SUBSCRIBE F10  |<---------------|
>     |               | SUBSCRIBE F11  |<---------------|                |
>     |               |<---------------|                |                |
>     |               | 481 F12        |                |                |
>     |               |--------------->| 481 F13        |                |
>     |               |                |--------------->| 481 F14        |
>     |               |                |                |--------------->|
> 
> 
> So, Bob sends an initial SUBSCRIBE to Alice AoR (the received From uri in the 
> INVITE F5/F7) with the half-dialog data:
> 
>    SUBSCRIBE sip:[email protected] SIP/2.0
>    From: Bob <sip:[email protected]>;tag=8672349
>    To: <sip:[email protected]>
>    Call-ID: [email protected]
>    Contact: <sip:[email protected]>
>    Event: dialog;[email protected];to-tag=9fxced76sl
>    Expires=0
>    Accept: application/dialog-info+xml
>    Content-Length: 0
> 
> Note that "Event" header contains specific half-dialog information.
> 
> This SUBSCRIBE arrives to Alice's UA which is not aware of that dialog. Which 
> response should it reply? The flow suggests "481 Call/Transaction doesn't 
> exist", but... is it correct?
> 
> AFAIK, a 481 should be replied when an *in-dialog* request arrives to an UAS 
> which is not aware of that dialog. But in the above case we have an *initial* 
> request and the 481 refers to the specific dialog in the "Event" header.
> 
> 
> Well, I suggest a possible issue with the above behaviour:
> 
> - Alice invites Bob.
> - Before sending a provisional response, Bob sends an *initial* SUBSCRIBE to 
> Alice with the current half-dialog information in the "Event" header.
> - Alice accepts the SUBSCRIBE, replies 200 and later a NOTIFY with the 
> specific dialog status.
> 
> a)
> - After 40 seconds Alice's UA crashes and is restarted (dialog info lost).
> - Bob sends a SUBSCRIBE refresh (an in-dialog request).
> - That dialog (the SUBSCRIBE dialog) doesn't exist in Alice anymore, so Alice 
> replies 481.
> 
> b)
> - Dialog between Alice and Bob ends because Alice sends a BYE, but before 
> Alice receives the BYE and the dialog NOTIFY update, Bob sends a SUBSCRIBE 
> refresh (an in-dialog request) for that dialog.
> - This SUBSCRIBE arrives to Alice, the SUBSCRIBE request dialog exists but the 
> dialog indicated in "Event" header doesn't exist anymore.
> - As the above flow suggests, Alice replies 481.
> 
> In both cases a) and b), Alice replies 481 but the scenario is completely 
> different. The 481 in a) means that the in-dialog SUBSCRIBE belongs to a non 
> existing dialog in Alice, while the 481 in b) means that a dialog indicated 
> in the Event header doesn't exist.
> But there is no way for Bob to realize which is the case a) or b).
> 
> 
> The main question is: is 481 the approiate (and valid) reply in the above flow 
> (case b)? Is 481 really valid as a reply for an initial request?
> 
> 
> 
> 
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