Re: [dtn-interest] [irsg] IRSG review of draft-irtf-dtnrg-tcp-clayer-06.txt

"Eggert, Lars" <lars@netapp.com> Wed, 31 July 2013 12:17 UTC

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From: "Eggert, Lars" <lars@netapp.com>
To: Dirk Kutscher <Dirk.Kutscher@neclab.eu>
Thread-Topic: [irsg] IRSG review of draft-irtf-dtnrg-tcp-clayer-06.txt
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Date: Wed, 31 Jul 2013 12:16:29 +0000
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Cc: "Internet Research Steering Group \(irsg@irtf.org\)" <irsg@irtf.org>, "dtn-interest@irtf.org" <dtn-interest@irtf.org>, "draft-irtf-dtnrg-tcp-clayer@tools.ietf.org" <draft-irtf-dtnrg-tcp-clayer@tools.ietf.org>
Subject: Re: [dtn-interest] [irsg] IRSG review of draft-irtf-dtnrg-tcp-clayer-06.txt
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Lars

On Jul 28, 2013, at 13:18, Dirk Kutscher <Dirk.Kutscher@neclab.eu> wrote:

> Hi Simon,
> 
> Very good -- I agree with what you proposed in your reply -- looking forward to the new revision.
> 
> Best regards,
> Dirk
> 
> 
>> -----Original Message-----
>> From: Simon Perreault [mailto:simon.perreault@viagenie.ca]
>> Sent: Mittwoch, 17. Juli 2013 13:33
>> To: Dirk Kutscher
>> Cc: Internet Research Steering Group (irsg@irtf.org); draft-irtf-dtnrg-tcp-
>> clayer@tools.ietf.org; dtn-interest@irtf.org
>> Subject: Re: IRSG review of draft-irtf-dtnrg-tcp-clayer-06.txt
>> 
>> Thanks for your very detailed review! I agree with almost all your proposed
>> changes. I'll publish a new revision.
>> 
>> Le 2013-07-16 22:41, Dirk Kutscher a écrit :
>>> - section 3:
>>>  <comment>
>>>   The protocol overview needs to say that a TCPCL can be used to
>>>   transmit several bundles, but that multiple bundles MUST be
>>>   transmitted consecutively (i.e., no inter-leaving of bundle
>>>   segments). In addition, I think, you also have to say that the
>>>   blocks of a particular bundle MUST be sent sequentially (no change
>>>   of block order).
>>>  </comment>
>> 
>> Agreed. I would also add that interleaving can be accomplished with bundle
>> fragmentation.
>> 
>>> - section 3:
>>>  <oldtext>
>>>   This protocol provides bundle conveyance over a TCP connection and
>>>   specifies the encapsulation of bundles as well as procedures for TCP
>>>   connection setup and teardown.
>>>   </oldtext>
>>> 
>>>   <comment>
>>>    "The service of this protocol is the transmission of DTN bundles
>>>     over TCP. This document specifies the encapsulation of bundles,
>>>     procedures for TCP setup and teardown, and a set of messages and
>>>     node requirements."?
>>>   </comment>
>> 
>> Agreed.
>> 
>>> - section 3.1:
>>> 
>>>  <comment>
>>>   The first paragraph is not very clear. You want to say that there
>>>   are different specific messages for sending and receiving
>>>   operations (in addition to connection setup/teardown).  TCPCL is
>>>   symmetric, i.e., both sides can start sending data segments in a
>>>   connection, and one side's bundle transfer does not have to
>>>   complete before the other side can start sending data segments on
>>>   its own. Hence, the protocol allows for a bi-directional mode of
>>>   communication.
>>>  </comment>
>> 
>> Agreed.
>> 
>>> - section 3.2:
>>> 
>>>  <oldtext>
>>>   Note that the sending node may transmit multiple
>>>   DATA_SEGMENT messages without necessarily waiting for the
>>>   corresponding ACK_SEGMENT responses.  This enables pipelining of
>>>   messages on a channel.
>>>  </oldtext>
>>> 
>>>  <comment>
>>>   This is a too important property to just mention it on the side of
>>>   an example description. You should mention this in the protocol
>>>   overview. You should also mention that there is no explicit flow
>>>   control on the TCPCL layer.
>>>  </comment>
>> 
>> Agreed.
>> 
>>> - section 3.2:
>>> 
>>>  <oldtext>
>>>    However, interleaving data segments from different bundles is not
>>>    allowed.
>>>  </oldtext>
>>> 
>>>  <comment>
>>>   Again, this is too important to not mention it earlier.
>>>  </comment>
>> 
>> Agreed.
>> 
>>> -section 4:
>>> 
>>> <oldtext>
>>>   The manner in which a bundle node makes the decision to establish
>>>   such a connection is implementation-dependent.
>>> </oldtext>
>>> 
>>> <comment>
>>>  I think you want to say that the implementation can decide, possibly
>>>  case-by-case, at runtime (unless it is fixed). Perhaps better so
>>>  say: "It is up to the implementation to decide how and when
>>>  connection setup is triggered. For example..."
>>> </comment>
>> 
>> Agreed.
>> 
>>> -section 4:
>>> <oldtext>
>>>   Therefore, the node MUST retry
>>>   the connection setup only after some delay and it SHOULD use a
>>>   (binary) exponential backoff mechanism to increase this delay in case
>>>   of repeated failures.
>>> </oldtext>
>>> 
>>> <comment>
>>>  You should specify what is meant by "some delay". Is it completely
>>>  up to the implementation? Do you want to RECOMMEND a minimum
>> delay?
>>> </comment>
>> 
>> How about recommending 1 second minimum?
>> 
>>> - section 4.1:
>>> 
>>> <oldtext>
>>>   magic:  A four byte field that always contains the byte sequence 0x64
>>>        0x74 0x6e 0x21, i.e., the text string "dtn!".
>>> </oldtext>
>>> 
>>> 
>>> <newtext>
>>>   magic:  A four byte field that always contains the byte sequence 0x64
>>>        0x74 0x6e 0x21, i.e., the text string "dtn!" in US-ASCII.
>>> </newtext>
>> 
>> Agreed.
>> 
>>> - section 4.1:
>>> 
>>> <oldtext>
>>>   version:  A one byte field value containing the current version of
>>>        the protocol.
>>> </oldtext>
>>> 
>>> 
>>> <newtext>
>>>   version:  A one byte field value containing the value 3 (current version of
>>>        the protocol).
>>> </newtext>
>> 
>> Agreed.
>> 
>>> - section 5.2
>>> 
>>> <oldtext>
>>>  However, a node MUST be able to receive a bundle that has been
>>>   transmitted in any segment size.
>>> </oldtext>
>>> 
>>> <comment>
>>> 
>>>  How feasible is this, for example for constrained devices? Even if a
>>>  node does not intend to store and reassemble bundles, there may be
>>>  certain limits for the maximum size of segments that it can
>>>  receive. Has there been a discussion to make this
>>>  negotiable/configurable? How should a node react if it cannot
>>>  receive/process any more bytes for a transmitted segment?
>>> </comment>
>> 
>> The intent here is not to override a node's intrinsic limitation on bundle sizes.
>> The intent is that if a node is able to receive, over TCP, a bundle of size X with
>> segment size Y, then it MUST also be able to do it with any segment size <= X.
>> I'll adjust the text.
>> 
>>> - section 5.2
>>> 
>>> <oldtext>
>>>   Following the message header, the length field is an SDNV containing
>>>   the number of bytes of bundle data that are transmitted in this
>>>   segment.  Following this length is the actual data contents.
>>> </oldtext>
>>> 
>>> 
>>> <comment>
>>>  This should be mentioned earlier in section 5.2  </comment>
>> 
>> Agreed.
>> 
>>> - section 5.3
>>> 
>>>  <oldtext>
>>>   To transmit an acknowledgment, a node first transmits a message
>>>   header with the ACK_SEGMENT type code and all flags set to zero, then
>>>   transmits an SDNV containing the cumulative length of the received
>>>   segment(s) of the current bundle.
>>>  </oldtext>
>>> 
>>> 
>>>  <newtext>
>>>   To transmit an acknowledgment, a node first transmits a message
>>>   header with the ACK_SEGMENT type code and all flags set to zero,
>>>   then transmits an SDNV containing the cumulative length in bytes of
>>>   the received segment(s) of the current bundle.
>>>  </newtext>
>> 
>> Agreed.
>> 
>>> - section 5.4
>>> 
>>>  <oldtext>
>>>   Note: If a bundle transmission if aborted in this way, the receiver
>>>   may not receive a segment with the 'E' flag set to '1' for the
>>>   aborted bundle.  The beginning of the next bundle is identified by
>>>   the 'S' bit set to '1', indicating the start of a new bundle.
>>>  </oldtext>
>>> 
>>>  <comment>
>>> 
>>>   Should this be turned into a general rule? I.e.: "if a receiver
>>>   receives a segment for a new bundle without having seen the final
>>>   segment of a previous bundle, it SHOULD disregard all segments of
>>>   the incompletely received bundle."
>> 
>> I don't think so. The received segments are valid. The receiver can do
>> whatever it wants with them.
>> 
>>>   (wording may need some work)
>>> 
>>>   It's probably good to use "SHOULD" here, because the node may
>>>   already have forwarded the segments...
>>>  </comment>
>>> 
>>> 
>>> - section 6.1
>>> 
>>>  <oldtext>
>>>   The format of the shutdown message is as follows:
>>> 
>>>                        1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
>>>    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>   |  0x5  |0|0|R|D| reason (opt)  | reconnection delay (opt)      |
>>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>> 
>>>               Figure 8: Format of bundle shutdown messages
>>> 
>>>  </oldtext>
>>> 
>>>  <comment>
>>>   Is it really efficient to have variable length messages here by
>>>   making the reason code optional? How about always requiring it and
>>>   then allow for a default value (0x00)?
>>>  </comment>
>> 
>> I think it's a backward compatibility wart that we need to live with.
>> That is, earlier versions of the protocol did not send those two fields.
>> (not 100% sure)
>> 
>>> - section 6.1
>>> 
>>>  <oldtext>
>>>   If either node terminates a connection prematurely in this manner, it
>>>   SHOULD send a SHUTDOWN message and MUST indicate a reason code
>> unless
>>>   the incoming connection did not include the magic string.
>>>  </oldtext>
>>> 
>>>  <comment>
>>>   Why not send a reason like "illegal syntax"?
>>>  </comment>
>> 
>> Wasn't there talks of a draft registering a bunch of additional reason codes?
>> 
>>> - section 6.7
>>> 
>>>  <comment>
>>> 
>>>  Regarding the peer entity authentication issue, I think you have to
>>>  use a stronger statement, like "a node SHALL NO" use the endpoint
>>>  identifier conveyed in the TCPCL connection message to derive a peer
>>>  node's entity unless it can ascertain it via other means."
>> 
>> Agreed.
>> 
>>>  If it is possible to do that through the Bundle Security Protocol,
>>>  you could be a bit more specific on how the Bundle Authentication
>>>  Block would be used. I assume one TCPCL peer node would become a
>>>  security source in an RFC 6257 sense?
>>> 
>>>  BTW, you are using the term "Bundle Authentication Header" -- I
>>>  think it's "Bundle Authentication Block".
>>> 
>>>  In general, it could be worthwhile stating that TCPCL does not
>>>  provide any security services and that RFC 6257's mechanisms should
>>>  be used.
>> 
>> Agreed.
>> 
>>>  BTW, is the use of TLS for TCPCL defined or excluded? You may want
>>>  to say something about why it's not applicable
>>>  </comment>
>> 
>> Why wouldn't it be applicable? I think we *want* it to be applicable!
>> 
>>> - section 10.2
>>> 
>>>  <oldtext>
>>>   [RFC6256]  Eddy, W. and E. Davies, "Using Self-Delimiting Numeric
>>>              Values in Protocols", RFC 6256, May 2011.
>>>  </oldtext>
>>> 
>>>  <comment>
>>>    Isn't that a normative reference for this spec?
>>>  </comment>
>> 
>> No, because that's an informational RFC.
>> 
>>> EDITORIAL COMMENTS
>>> ------------------
>>> 
>>> General:
>>> 
>>> - make usage and capitalization of Bundle Protocol (sometimes referred
>>>  to as "Bundling Protocol", "bundle protocol" etc.) consistent
>> 
>> Agreed.
>> 
>>> - section 2.1
>>>   <oldtext>
>>>     Bundle payload --  A bundle payload (or simply "payload") is the
>>>        application data whose conveyance to the bundle's destination is
>>>        the purpose for the transmission of a given bundle.
>>>   </oldtext>
>>> 
>>>   <comment>
>>>     IMO this can be said in a clearer way: "... application
>>>     data that is transmitted to a BP application at a Bundle
>>>     Endpoint"?
>>>   </comment>
>> 
>> We should just remove this and refer to RFC 5050 section 3.1.
>> 
>>> - section 2.1:
>>>   <oldtext>
>>>   Bundle node --  A bundle node (or simply a "node") is any entity that
>>>        can send and/or receive bundles.  The particular instantiation
>>>        of this entity is deliberately unconstrained, allowing for
>>>        implementations in software libraries, long-running processes,
>>>        or even hardware.  One component of the bundle node is the
>>>        implementation of a convergence layer adapter.
>>>   </oldtext>
>>> 
>>>   <comment>
>>>     I don't think the second sentence ("The particular
>>>     instantiation...") is really needed.  This holds for most network
>>>     elements these days.
>>>   </comment>
>> 
>> We should just remove this and refer to RFC 5050 section 3.1.
>> 
>>> - section 2.1:
>>>   <oldtext>
>>>   Convergence layer adapter --  A convergence layer adapter (CLA) sends
>>>        and receives bundles utilizing the services of some 'native'
>>>        link, network, or internet protocol.  This document describes
>>>        the manner in which a CLA sends and receives bundles when using
>>>        the TCP protocol for inter-node communication.
>>>   </oldtext>
>>> 
>>>   <comment>
>>>      Does it make make sense to define "Convergence Layer" first,
>>>      before defining CLA? Is the CLA definition needed at all
>>>      (assuming CL is defined)?
>>>   </comment>
>> 
>> We should just remove this and refer to RFC 5050 section 3.1.
>> 
>>> - section 2.2:
>>>  <oldtext>
>>>   TCPCL Connection --  [...] The lifetime of a TCPCL connection is one-to-one
>>>        with the lifetime of an underlying TCP connection.
>>> 	[...]
>>>   </oldtext>
>>> 
>>>   <comment>
>>>      "The lifetime of a TCPCL connection is bound to the
>>>      lifetime of the underlying TCP connection."?
>>>   </comment>
>> 
>> Agreed.
>> 
>>> -section 4:
>>> 
>>> <oldtext>
>>>   Once a TCP connection is established, each node MUST immediately
>>>   transmit a contact header over the TCP connection.  The format of the
>>>   contact header is described in Section 4.1).
>>> </oldtext>
>>> 
>>> <newtext>
>>>   Once a TCP connection is established, each node MUST immediately
>>>   transmit a contact header over the TCP connection.  The format of the
>>>   contact header is described in Section 4.1.
>>> </newtext>
>> 
>> Agreed.
>> 
>>> - section 4.1:
>>> 
>>> <oldtext>
>>>   local EID:  An octet string containing the EID of some singleton
>>>        endpoint in which the sending node is a member, in the canonical
>>>        format of <scheme name>:<scheme-specific part>.  A eight byte
>>>        EID is shown the clarity of the figure.
>>> </oldtext>
>>> 
>>> 
>>> <newtext>
>>>   local EID:  An octet string containing the EID of some singleton
>>>        endpoint in which the sending node is a member, in the canonical
>>>        format of <scheme name>:<scheme-specific part>.  A eight byte
>>>        EID is shown for clarity of the figure.
>>> </newtext>
>> 
>> Agreed.
>> 
>>> - section 4.2:
>>> 
>>> 
>>> <oldtext>
>>>        The reactive fragmentation enabled parameter is set to true iff
>>>        the corresponding flag is set in both contact headers.
>>> 
>>>        The bundle refusal capability may only be used iff both peers
>>>        indicate support for it in their contact header and segment
>>>        acknowledgement has been enabled.
>>> </oldtext>
>>> 
>>> 
>>> <newtext>
>>>        The reactive fragmentation enabled parameter is set to true iff
>>>        the corresponding flag is set in both contact headers.
>>> 
>>>        The bundle refusal capability is set to true if the
>>>        corresponding flag is set in both contact headers and if
>>>        segment acknowledgment has been enabled.
>>> </newtext>
>>> 
>>> <comment>
>>>  I'd raher use the same or similar wording to not irritate the implementer.
>>> </comment>
>> 
>> Agreed.
>> 
>>> - section 5.1
>>> 
>>> <oldtext>
>>>  Table 2: TCPCL Header Types
>>> </oldtext>
>>> 
>>> 
>>> <newtext>
>>>  Table 2: TCPCL Message Types
>>> </newtext>
>> 
>> Agreed.
>> 
>>> - section 5
>>> 
>>>  <comment>
>>>   For the different subsections for the individual messages, please
>>>   use the message type names from table 2 in the headings, for
>>>   example: "Bundle Data Transmission (DATA_SEGMENT)". Also, I'd
>>>   recommend to align the order of the subsections with the order of
>>>   message types in table 2.
>>>  </comment>
>> 
>> Agreed.
>> 
>>>  <comment>
>>>   I would also recommend to use a consistent structure for each of
>>>   the subsections, i.e., perhaps
>>>     - purpose
>>>     - syntax
>>>     - procedures / node requirements
>>>  </comment>
>> 
>> Agreed.
>> 
>>> - section 5.3
>>> 
>>>  <oldtext>
>>>   If so, then
>>>   the receiver MUST transmit a bundle acknowledgment header when it
>>>   successfully receives each data segment.
>>>  </oldtext>
>>> 
>>> 
>>>  <oldtext>
>>>   If so, then
>>>   the receiver MUST transmit a bundle acknowledgment message when it
>>>   successfully receives each data segment.
>>>  </oldtext>
>> 
>> Agreed.
>> 
>>> - section 5.6
>>> 
>>>  <oldtext>
>>>   If no message (keepalive or other) has been received for at least
>>>   twice the keepalive interval, then either party may terminate the
>>>   session by transmitting a one byte message type code of SHUTDOWN (as
>>>   described in Table 2) and closing the TCP connection.
>>>  </oldtext>
>>> 
>>> 
>>>  <newtext>
>>>   If no message (keepalive or other) has been received for at least
>>>   twice the keepalive interval, then either party MAY terminate the
>>>   session by transmitting a one byte SHUTDOWN message  (as
>>>   described in Table 2) and by closing the TCP connection.
>>>  </newtext>
>> 
>> Agreed.
>> 
>>> - section 6.1
>>> 
>>>  <oldtext>
>>>   In case acknowledgments have been
>>>   negotiated, it is advisable to acknowledge all received data segments
>>>   first and then shut down the connection.
>>>  </oldtext>
>>> 
>>> 
>>>  <newtext>
>>>   In case acknowledgments have been
>>>   negotiated, a node SHOULD  acknowledge all received data segments
>>>   first and then shut down the connection.
>>>  </newtext>
>> 
>> Agreed.
>> 
>>> - section 6.1
>>> 
>>>  <oldtext>
>>>   This may, for example, be used to notify
>>>   that the node is currently not capable of or willing to communicate.
>>>  </oldtext>
>>> 
>>>  <newtext>
>>>   This may, for example, be used to notify
>>>   that the node is currently not able or willing to communicate.
>>>  </newtext>
>> 
>> Agreed.
>> 
>>> - section 10.2
>>> 
>>>  <oldtext>
>>>   [refs.dtnsecurity]
>>>              Symington, S., Farrell, S., and H. Weiss, "Bundle Security
>>>              Protocol Specification", Internet Draft, work in progress
>>>              draft-irtf-dtnrg-bundle-security-03.txt, April 2007.
>>>  </oldtext>
>>> 
>>>  <comment>
>>>     This is RFC 6257.
>>>  </comment>
>> 
>> Agreed.
>> 
>> Simon