Public Safety Answering Point (PSAP) Callback
draft-ietf-ecrit-psap-callback-13

[Ballot comment]
Version -13 addresses my comments, and thanks very much for that.

When I asked for changes to the example domains, to follow the recommendations in 2606, I had intended changing "town.com" and "state.org" to "town.example" and "state.example" to keep the sense of the relationship (rather than "example.com" and "example.net", which don't).  Of course, the change that was made does follow 2606, so if you're happy, I'm happy.  You're certainly right that it's a pity that 2606 didn't reserve a shorter TLD, such as "xmp", for examples.  Waddyagonnado?

[Ballot comment]
While these are non blocking comments regarding the document publication, let's have a discussion about those.
Note: I already discussed those two points with Hannes over the phone.

1.
  In the case where the SIP
  Priority header value, 'psap-callback', is supported by the SIP UA,
  it would override user interface configurations, such as vibrate-only
  mode, to alert the caller of the incoming call.

Is it a good idea?

I'm witnessing a crime: I call or page the police, put the silent mode, hide in a corner while waiting for the police, and now the police calls me back: no more silent mode. I'm now dead.

2.
In the SIP proxy case, what prevents the VoIP provider to use this mechanism for support calls.
It's not emergency, but it will save the VoIP provider time and money. So they might tempted to use it.

Richard's new sentence:

    The indicator described in Section 4 can be inserted by any SIP entity, including attackers.  So it is critical that the indicator only lead to preferential call treatment in cases where the recipient has some trust in the caller, as described in the next section.

I've have some trust in my VoIP provider, but it doesn't mean that he should get priority to call me back, by-passing all my policies.

What prevents some state/government to say: "I'm important. I want this priority feature when I call one of my citizen".

I believe that you need to impose, that, even in the proxy case, this mechanism only works in case of callback.

Editorial:
- Not sure what LoST is:

  In
  this scenario we consider a SIP UA that uses LoST to learn the next
  hop destination closer to the PSAP.

[Ballot comment]
I support Barry's Discuss wrt FQDN. note that town.com is an ongoing business and should not be abused in this way.

There is no reasonable reason not to conform to RFC 2606

[Ballot comment]
I share Barry's concerns regarding security. It sounds like that DISCUSSion is moving along.

I implore you to take Barry's advice regarding the Introduction. Please shorten it.

[Ballot discuss]

(1) This seems to scream out "I want stir!" and that
confuses me. If this is meant as an interim solution
until stir is available, then that should be stated.  And
that raises another question - if stir were available
then I don't think you'd even need this indication, but
maybe some people would want both and then would ask for
the stir signture to cover this as well, which could
complicate (and maybe damage) stir. So having this as an
interim solution might have a downside. And if this is
not an interim solution, then I don't get why it doesn't
e.g. have its own (realistically usable, i.e.  not 4744)
signature scheme.  All that leaves me wondering: why not
just wait for stir and use that?

(2) - The reference to 4744 is misleading since nobody
does that. Does anyone do 3325? In any case, the
text there should reflect reality.

[Ballot comment]

- I think there's a missing security consideration.  The
Irish emergency calling service can accept a (voice) call
where the caller says "I need to hang up now, please
don't call back but send me an SMS - the burgler is in
the other room and will hear." I think you could mention
that that's a potential danger that would need to be
mitigated via implementations and/or operational
practices.

- Question for the AD/shepherd: The IPR declaration was
posted before IETF LC but (I think) after the draft left
the wg. I assume that the wg are ok with that, since its
more or less the same IPR declaration as was made on
6443. Is that correct? I note that the shepherd write-up
says there's no IPR of which the shepherd was aware at
that time, hence the question.

[Ballot comment]
One thought.

  When there is a local relationship between
  the VoIP provider and the PSAP then populating the whitelist is
  fairly simple.  For SIP UAs there is no need to maintain a list of
  PSAPs.  Instead SIP UAs are assumed to trust the correct processing
  of their VoIP provider, i.e., the VoIP provider processes the PSAP
  callback marking and, if it cannot be verified, the PSAP callback
  marking is removed.  If it is left untouched then the SIP UA should
  assume that it has been verified successfully by the VoIP provider
  and it should therefore be obeyed.

This seems to presume that UA's in fact have trust with respect to what their voip provider does when in fact that may not be the case. if this facility can be abused and can't be ignored it will become untenable rather quickly.

[Ballot comment]
I agree with Barry's Discuss concerns on Security Considerations. I'm not a Discuss because I think the problems Barry identified are more general than the problems ECRIT is chartered to solve.

For example, a STIR Secure Telephony Identity would help prevent spoofed use of psap-callback, but is much more broadly applicable than just assisting with PSAP Callbacks.

The conversations I've had with carriers make me think penalizing spoofed psap-callbacks by doing anything worse than treating them as ordinary calls is too risky to deploy.

But I'd love to be wrong, and I look forward to learning during the discussion.

[Ballot discuss]
I have two bits that I'd like to discuss, if you please:

  NOTE: All FQDNs used in the subsections below are used for
  illustrative purposes.  They are examples to demonstrate the
  limitations of the technical solution outlined in RFC 6881.

Notwithstanding that, I find it hard to understand how it would harm this document if you would use the reserved domain names from RFC 2606.  That document *is* a BCP, and I'd like to discuss why you don't think you can follow it.  It would be very easy to simply change all the TLDs in this document to "example" (except for the ones that use "example.com") and be in compliance with 2606.  Please tell me why that won't work, or would harm the document.

I find the Security Considerations unrealistic.  Here: you have defined a header field value that anyone can use to try to get expedited handling.  In Section 5.2 you say that you must treat failures to accept this value as though they were normal calls.  And so: why shouldn't every telemarketer on Earth immediately start setting this in every one of their calls?  At *worst*, their calls will be treated the same as if they hadn't.  And at best, they'll get through with expedited treatment, as though they were emergency callbacks.  What's stopping them from rampantly abusing this?

[Ballot comment]
Opinion, with apologies if this comes off as abrupt:
The Introduction is decidedly and unnecessarily long-winded.  This is a small extension, which needs to describe particular situations only, and doesn't need to re-hash all the ECRIT stuff that's in the other docs.  Almost all of the text before the paragraph that begins "Among the emergency services community" really seems unnecessary, as does much of the detail in that paragraph itself.  What the introduction needs to say is that PSAP callbacks are part of the emergency services architecture and are described in [citations], that the callbacks as currently laid out in 6443 have [this limitation], and that there are important situation in which it does not work.  This document describes those situations and defines a header field that can be used in such situations.  Three paragraphs ought to be enough.  Had I been a reader of this document, and not a reviewer, I'm sure I'd have lost interest long before I got to the punch line.

This is, of course, entirely my opinion, and entirely non-blocking.  So: please consider trimming the Introduction significantly... but there's no need to discuss this with me, and if you decide that I'm full of cow cookies and you like it as it is, then carry on.

IESG/Authors/WG Chairs:

IANA has reviewed draft-ietf-ecrit-psap-callback-10.  Authors should review the comments and/or questions below.  Please report any inaccuracies and respond to any questions as soon as possible.

We received the following comments/questions from the IANA's reviewer:

---
IANA understands that, upon approval of this document, there is a single action which IANA must complete.

In the Priority Header Field Values registry located at:

http://www.iana.org/assignments/sip-parameters

a new priority header field value is to be registered as follows:

Reason Code: psap-callback
Reference: [ RFC-to-be ]

IANA understands that this action is the only one required to be completed upon approval of this document.

---

Note:  The actions requested in this document will not be completed until the document has been approved for publication as an RFC. This message is only to confirm what actions will be performed.

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Public Safety Answering Point (PSAP) Callback) to Proposed Standard


The IESG has received a request from the Emergency Context Resolution
with Internet Technologies WG (ecrit) to consider the following document:
- 'Public Safety Answering Point (PSAP) Callback'
  as Proposed Standard

The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send substantive comments to the
ietf@ietf.org mailing lists by 2013-09-27. Exceptionally, comments may be
sent to iesg@ietf.org instead. In either case, please retain the
beginning of the Subject line to allow automated sorting.

Abstract


  After an emergency call is completed (either prematurely terminated
  by the emergency caller or normally by the call taker) it is possible
  that the call taker feels the need for further communication.  For
  example, the call may have been dropped by accident without the call
  taker having sufficient information about the current situation of a
  wounded person.  A call taker may trigger a callback towards the
  emergency caller using the contact information provided with the
  initial emergency call.  This callback could, under certain
  circumstances, be treated like any other call and as a consequence it
  may get blocked by authorization policies or may get forwarded to an
  answering machine.

  The IETF emergency services architecture specification already offers
  a solution approach for allowing PSAP callbacks to bypass
  authorization policies to reach the caller without unnecessary
  delays.  Unfortunately, the specified mechanism only supports limited
  scenarios.  This document discusses shortcomings of the current
  mechanisms and illustrates additional scenarios where better-than-
  normal call treatment behavior would be desirable.  A solution based
  on a new header field value, called "psap-callback", for the SIP
  Priority header field is specified to accomplish the PSAP callback
  marking.




The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-ecrit-psap-callback/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-ecrit-psap-callback/ballot/


The following IPR Declarations may be related to this I-D:

  http://datatracker.ietf.org/ipr/2180/

Technical Summary

After an emergency call is completed (either prematurely terminated by the emergency caller or normally by the call taker) it is possible that the call taker feels the need for further communication. For example, the call may have been dropped by accident without the call taker having sufficient information about the current situation of a wounded person. A call taker may trigger a callback towards the emergency caller using the contact information provided with the initial emergency call. This callback could, under certain circumstances, be treated like any other call and as a consequence it may get blocked by authorization policies or may get forwarded to an answering machine.

The IETF emergency services architecture specification already offers a solution approach for allowing PSAP callbacks to bypass authorization policies to reach the caller without unnecessary delays. Unfortunately, the specified mechanism only supports limited scenarios. This document discusses shortcomings of the current mechanisms and illustrates additional scenarios where better-than-normal call treatment behavior would be desirable. A solution based on a new header field value, called "psap-callback", for the SIP Priority header field is specified to accomplish the PSAP callback marking.



Working Group Summary

This document represents strong work group consensus and group participation in having worked out the details of the mechanism described. There were no significant controversies that were not overcome during the development stage. A successful document development history is documented in the email list archive.


Document Quality

No existing implementations are known to exist. Several vendors have shown interest, and have also been involved in the development and review of the document.


Personnel

Document shepherd: Roger Marshall (ECRIT co-chair)
Responsible Area Director: Richard Barnes (RAI AD)


Write-up as follows:


(3) Briefly describe the review of this document that was performed by
the Document Shepherd. If this version of the document is not ready
for publication, please explain why the document is being forwarded to
the IESG.

Careful review by the document shepherd following WGLC. Several nits were found and author was asked to resubmit the document, which has been done.


(4) Does the document Shepherd have any concerns about the depth or
breadth of the reviews that have been performed?

No.


(5) Do portions of the document need review from a particular or from
broader perspective, e.g., security, operational complexity, AAA, DNS,
DHCP, XML, or internationalization? If so, describe the review that
took place.

No.


(6) Describe any specific concerns or issues that the Document Shepherd
has with this document that the Responsible Area Director and/or the
IESG should be aware of? For example, perhaps he or she is uncomfortable
with certain parts of the document, or has concerns whether there really
is a need for it. In any event, if the WG has discussed those issues and
has indicated that it still wishes to advance the document, detail those
concerns here.

None noted.


(7) Has each author confirmed that any and all appropriate IPR
disclosures required for full conformance with the provisions of BCP 78
and BCP 79 have already been filed. If not, explain why.

Yes.


(8) Has an IPR disclosure been filed that references this document?
If so, summarize any WG discussion and conclusion regarding the IPR
disclosures.

None that I'm aware of.


(9) How solid is the WG consensus behind this document? Does it
represent the strong concurrence of a few individuals, with others
being silent, or does the WG as a whole understand and agree with it?

There is strong work group consensus to move this document forward to RFC status.


(10) Has anyone threatened an appeal or otherwise indicated extreme
discontent? If so, please summarise the areas of conflict in separate
email messages to the Responsible Area Director. (It should be in a
separate email because this questionnaire is publicly available.)

No.


(11) Identify any ID nits the Document Shepherd has found in this
document. (See http://www.ietf.org/tools/idnits/ and the Internet-Drafts
Checklist). Boilerplate checks are not enough; this check needs to be
thorough.

None that are impacting. There are 1 instance of lines with non-RFC2606-compliant FQDNs in the document.

(12) Describe how the document meets any required formal review
criteria, such as the MIB Doctor, media type, and URI type reviews.

There are no MIB, media, or new URI types referenced to in this document.

(13) Have all references within this document been identified as
either normative or informative?

Yes.


(14) Are there normative references to documents that are not ready for
advancement or are otherwise in an unclear state? If such normative
references exist, what is the plan for their completion?

No.


(15) Are there downward normative references references (see RFC 3967)?
If so, list these downward references to support the Area Director in
the Last Call procedure.

One listed: draft-tschofenig-ecrit-xmpp-es-00 (expired)


(16) Will publication of this document change the status of any
existing RFCs? Are those RFCs listed on the title page header, listed
in the abstract, and discussed in the introduction? If the RFCs are not
listed in the Abstract and Introduction, explain why, and point to the
part of the document where the relationship of this document to the
other RFCs is discussed. If this information is not in the document,
explain why the WG considers it unnecessary.

No referenced RFCs will change in status due to publication of this document.


(17) Describe the Document Shepherd's review of the IANA considerations
section, especially with regard to its consistency with the body of the
document. Confirm that all protocol extensions that the document makes
are associated with the appropriate reservations in IANA registries.
Confirm that any referenced IANA registries have been clearly
identified. Confirm that newly created IANA registries include a
detailed specification of the initial contents for the registry, that
allocations procedures for future registrations are defined, and a
reasonable name for the new registry has been suggested (see RFC 5226).

All IANA registry requirements have been met.


(18) List any new IANA registries that require Expert Review for future
allocations. Provide any public guidance that the IESG would find
useful in selecting the IANA Experts for these new registries.

None.

(19) Describe reviews and automated checks performed by the Document
Shepherd to validate sections of the document written in a formal
language, such as XML code, BNF rules, MIB definitions, etc.

None applied.