Architectural Guidelines for Multipath TCP Development
draft-ietf-mptcp-architecture-05

[Ballot discuss]
The Gen-ART Review by Joel Halpern on 14-Jan-2011 raises one concern
  that needs to be addressed.  That is, "break-before-make" is added in
  the security design decisions in section 5.8.  Even if this is merely
  a desirable behavior, it should be described in the behaviors before
  being referenced in the design decisions.

[Ballot comment]
This is a useful document.

I believe that it would useful to the community to note much earlier, and with greater clarity, in the document that it is applicable to the ECMP case.  Whilst few hosts are dual attached most networks have ECMP, and better ECMP is the subject of work in the Routing area.

[Ballot comment]
I think this document is well-written and support its publication.

1)  The architecture document has no discussion of how MPTCP should be managed, or what types of information should be made accessible for management purposes. I believe it should - at an architectural level.

However, since this is the architecture document for a protocol being put forth as Experimental, it would be beneficial to take the results of the experiment into consideration when designing an appropriate management solution. Therefore, I have reduced this to a comment.

TCP is intrumented with a MIB that is widely implemented on devices and used by network management applications. MPTCP should share that MIB for aspects that are designed to be transparent to the application. However, there should be extensions specific to MPTCP so an operator can monitor the operational state and impact of MPTCP.
For example,
a) MPTCP should be able to be enabled/disabled, the enabled/disabled state should be able to be queried, and the fallback mentioned in section 2.1 should be indicated in operational state.
b) if there are errors or congestion on a path and MPTCP can detect those errors or congestion, it should make that information available to an operator via the MIB.
c) if MPTCP can determine the performance of each path, that information should be made available via the MIB for use by performance monitoring applications.
d) if MPTCP can determine the different security state of different paths, that information should be made available via the MIB. It would probbaly be good if an operator can choose to provide a weight for different paths based on the security properties of the path.

[Ballot discuss]
The Gen-ART Review by Joel Halpern on 14-Jan-2011 raises one concern
  that needs to be addressed.  That is, "break-before-make" is added in
  the security design decisions in section 5.8.  Even if this is merely
  a desirable behavior, it should be described in the behaviors before
  being referenced in the design decisions.

[Ballot discuss]
I think this document is well-written and support its publication. There are a few points I would like to discuss before indicating my approval.

1) TCP is intrumented with a MIB that is widely implemented on devices and used by network management applications. MPTCP should share that MIB for aspects that are designed to be transparent to the application. However, there should be extensions specific to MPTCP so an operator can monitor the operational state and impact of MPTCP. The architecture document has no discussion of how MPTCP should be managed, or what types of information should be made accessible for management purposes. I believe it should - at an architectural level.

For example,
a) MPTCP should be able to be enabled/disabled, the enabled/disabled state should be able to be queried, and the fallback mentioned in section 2.1 should be indicated in operational state.
b) if there are errors or congestion on a path and MPTCP can detect those errors or congestion, it should make that information available to an operator via the MIB.
c) if MPTCP can determine the performance of each path, that information should be made available via the MIB for use by performance monitoring applications.
d) if MPTCP can determine the different security state of different paths, that information should be made available via the MIB. It would probbaly be good if an operator can choose to provide a weight for different paths based on the security properties of the path.

2) for the connection identifier described in 5.6, would there be an IANA registry? That would seem to be an architectural consideration.

[Ballot comment]
5.6.  Connection Identification

  Legacy applications will not, however, have access to this identifier
  and in such cases a MPTCP connection will be identified by the
  5-tuple of the first TCP subflow.  It is out of the scope of this
  document, however, to define the behaviour of the MPTCP
  implementation if the first TCP subflow later fails.  If there are
  MPTCP-unaware applications that make assumptions about continued
  existence of the initial address pair, their behaviour could be
  disrupted by carrying on regardless.  It is expected that this is a
  very small, possibly negligible, set of applications, however.  In
  the case of applications that have used an existing API call to bind
  to a specific address or interface, the MPTCP extension MUST NOT be
  used, since the applications are indicating a clear choice of path to
  use and thus will have expectations of behaviour that must be
  maintained, in order to adhere to the application compatibility
  goals.

I am not convinced your use of MUST NOT is correct here. In fact, it seems that it is in direct conflict with the following paragraph:

  Since the requirements of applications are not clear at this stage,
  however, it is as yet unconfirmed what the best behaviour is.  It
  will be an implementation-specific solution, however, and as such the
  behaviour is expected to be chosen by implementors once more research
  has been undertaken to determine its impact.

I.e., it is actually possible to know from the current socket API what is the application intent in this case?

State changed to In Last Call from Last Call Requested.

The following Last Call Announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Subject: Last Call:  (Architectural Guidelines for Multipath TCP Development) to Informational RFC


The IESG has received a request from the Multipath TCP WG (mptcp) to
consider the following document:
- 'Architectural Guidelines for Multipath TCP Development'
  as an Informational RFC

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 2011-1-11. 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.

The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-mptcp-architecture/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-mptcp-architecture/

  (1.a) Who is the Document Shepherd for this document? Has the
        Document Shepherd personally reviewed this version of the
        document and, in particular, does he or she believe this
        version is ready for forwarding to the IESG for publication?
Philip Eardley is the Document Shepherd for draft-ietf-mptcp-architecture. I have personally reviewed this version of the document and believe it is ready for forwarding to the IESG for publication.

  (1.b) Has the document had adequate review both from key WG members
        and from key non-WG members? Does the Document Shepherd have
        any concerns about the depth or breadth of the reviews that
        have been performed? 
The document has been extensively reviewed by key WG and non-WG members and I have no concerns about the reviews. Olivier Bonaventure, Gorry Fairhurst, Iljitsch van Beijnum, Philip Eardley, and Michael Scharf made detailed reviews.

  (1.c) Does the Document Shepherd have concerns that the document
        needs more review from a particular or broader perspective,
        e.g., security, operational complexity, someone familiar with
        AAA, internationalization or XML?
No.

  (1.d) Does the Document Shepherd have any specific concerns or
        issues 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. Has an IPR disclosure related to this document
        been filed? If so, please include a reference to the
        disclosure and summarize the WG discussion and conclusion on
        this issue.
I have no concerns about the document. No IPR disclosures have been filed.

  (1.e) 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 a very solid WG consensus behind the document. It captures the key high-level design decisions about MPTCP, which have been reached after extensive discussion and agreement at the IETF meetings and on the list.

  (1.f) 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
        entered into the ID Tracker.)
No-one has threatened extreme discontent.

  (1.g) Has the Document Shepherd personally verified that the
        document satisfies all ID nits? (See the Internet-Drafts Checklist
        and http://tools.ietf.org/tools/idnits/). Boilerplate checks are
        not enough; this check needs to be thorough. Has the document
        met all formal review criteria it needs to, such as the MIB
        Doctor, media type and URI type reviews?
There is one warning,
  == Unused Reference: '9' is defined on line 1108, but no explicit reference
    was found in the text
However, reference '9' is used!
No formal reviews are needed by MIB doctor etc.

  (1.h) Has the document split its references into normative and
        informative? 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
        strategy for their completion? Are there normative references
        that are downward references, as described in [RFC3967]? If
        so, list these downward references to support the Area
        Director in the Last Call procedure for them [RFC3967].
It has split its references. Normative references are only to existing RFCs.

  (1.i) Has the Document Shepherd verified that the document IANA
        consideration section exists and is consistent with the body
        of the document? If the document specifies protocol
        extensions, are reservations requested in appropriate IANA
        registries? Are the IANA registries clearly identified? If
        the document creates a new registry, does it define the
        proposed initial contents of the registry and an allocation
        procedure for future registrations? Does it suggest a
        reasonable name for the new registry? See [RFC5226]. If the
        document describes an Expert Review process has Shepherd
        conferred with the Responsible Area Director so that the IESG
        can appoint the needed Expert during the IESG Evaluation?
Yes the IANA considerations section exist; there are none and this is consistent with the body of the document.

  (1.j) Has the Document Shepherd verified that sections of the
        document that are written in a formal language, such as XML
        code, BNF rules, MIB definitions, etc., validate correctly in
        an automated checker?
Not applicable

  (1.k) The IESG approval announcement includes a Document
        Announcement Write-Up. Please provide such a Document
        Announcement Write-Up? Recent examples can be found in the
        "Action" announcements for approved documents. The approval
        announcement contains the following sections:

    Technical Summary
        Relevant content can frequently be found in the abstract
        and/or introduction of the document. If not, this may be
        an indication that there are deficiencies in the abstract
        or introduction.

    Working Group Summary
        Was there anything in WG process that is worth noting? For
        example, was there controversy about particular points or
        were there decisions where the consensus was particularly
        rough?

    Document Quality
        Are there existing implementations of the protocol? Have a
        significant number of vendors indicated their plan to
        implement the specification? Are there any reviewers that
        merit special mention as having done a thorough review,
        e.g., one that resulted in important changes or a
        conclusion that the document had no substantive issues? If
        there was a MIB Doctor, Media Type or other expert review,
        what was its course (briefly)? In the case of a Media Type
        review, on what date was the request posted?

Technical Summary
Hosts are often connected by multiple paths, but TCP restricts communications to a single path per transport connection.  Resource usage within the network would be more efficient were these multiple paths able to be used concurrently.  This should enhance user experience through improved resilience to network failure and higher throughput.
This document outlines architectural guidelines for the development of a Multipath Transport Protocol, with references to how these architectural components come together in the development of a Multipath TCP protocol.  This document lists certain high level design decisions that provide foundations for the design of the MPTCP protocol, based upon these architectural requirements.

Working Group Summary
This is a product of the MPTCP WG. There is a consensus in the WG for publication as an informational RFC.
There is a very solid WG consensus behind the document. It captures the key high-level design decisions about the MPTCP protocol, which have been reached after extensive discussion and agreement at the IETF meetings and on the list.

Document Quality
There is already an implementation of the protocol (draft-ietf-mptcp-multiaddressed) that implements the architecture and high-level design decisions in this document, https://scm.info.ucl.ac.be/trac/mptcp/wiki.
There were five detailed reviews of versions of the document. No substantial issues were raised. Expert reviews (MIB doctor etc) were not applicable.