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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