Explicit Subscriptions for REFER

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Explicit Subscriptions for REFER - Description

d. raft-sparks-sipcore-refer-explicit-subscription-00. SIPCORE – IETF90. Robert Sparks. Proposed Plan. Today: Discuss . strawman’s. open questions and issues raised on list. Shortly after IETF90: Flesh out . ID: 383686 Download Presentation

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Explicit Subscriptions for REFER




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Presentations text content in Explicit Subscriptions for REFER

Slide1

Explicit Subscriptions for REFER

d

raft-sparks-sipcore-refer-explicit-subscription-00

SIPCORE – IETF90

Robert Sparks

Slide2

Proposed Plan

Today: Discuss

strawman’s

open questions and issues raised on list

Shortly after IETF90: Flesh out

strawman

based on today’s discussions

Process result as a SIPCORE WG document with a

PubReq

target of late September

Slide3

Summary of Strawman (so far)

Send REFER in- or out-of-dialog

Require:

explicitsub

Accepting server MUST NOT create implicit subscription

Instead, returns a URI for use with SUBSCRIBE in a new Refer-Events-At: header

Slide4

Transfer Example

Alice

Carol

Bob

INVITE bob

Contact:

gruu

-a

dialog 1

INVITE carol

200 OK

Contact:

gruu

-c

d

ialog 2

REFER

gruu

-c

Require:

explicitsubRefer-To: gruu-a; replaces = dialog1

200 OKRefer-Events-At: rev-token-c

dialog 3

SUBSCRIBE rev-token-c

Event: referContact: gruu-b

d

ialog 4

INVITE

gruu

-a

Replaces: dialog 1

dialog 5

NOTIFY

gruu

-bEvent: referSubscription-State: terminated

d

ialog 4

Slide5

Easy Questions from Strawman

Do we use a different method?

NO

: An extension does the work and will likely be easier to deploy

Do we use a different event package?

NO : The meaning of the state and the payload delivered in NOTIFY messages does not change.

Do we further restrict what an appear in Refer-To?

NO : A UA can use the existing ability to reject REFER requests with Refer-To URIs that it doesn’t care for.

Do we deprecate RFC4488?

NO : These extensions can co-exist (but not be used together)

Slide6

When no subscription is wanted

REFER-

er

can simply ignore the Refer-Events-At header, and not subscribe if it doesn’t care about the state.

But the server has had to prepare for a subscription that may never come.

Proposal: Additional option tag ‘

nosub

’ telling server to not bother with those preparations

Slide7

Acting on an Refer-Events-At URI

Header field can contain an arbitrary URI

Could be abused to cause peer to send a subscription to a malicious place

Attack advantage is small

Only one SUBSCRIBE is going to be sent – isn’t a good amplifier for a

DoS

attack

All other security considerations are the same as for

any

mechanism through which a UA might get a URI to subscribe to

Existing mechanisms (particularly Refer-To) are more attractive

Slide8

Accepting an Event: refer subscription

How should the SUBSCRIBE be authorized?

Proposal: If someone knows the URI, they get to subscribe.

These URIs are necessarily short-lived and specific to the state being subscribed to.

They can be generated to be hard to guess

Getting another temp-

gruu

would be a good way to

do this

Slide9


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