RE: Reliable Messaging Spec v0-078

[Ajay K Sanghi <sanghi@giasdl01.vsnl.net.in>]

Hi Rik,

The neck-break speed with which the ebXML team is working is simply amazing.
I have been finding it difficult to keep upto date.

> we decide to make this transport independent.

making it transport independent is fine, but providing reliability over
unreliable transports like UDP, in my opinion should be dropped. I don't
think that RM specs should build "flow control", which it will require if
reliability is to be supported over unreliable transports. "sequence"
numbering is a different issue.

>i have been
> thinking about it
> work directly over tcp/ip, as we are now doing with smtp and
> http... what do
> you think of that? and are there any concerns?

I assume, you mean making ebXML as first class application (or application
protocol) over TCP/IP, just like SMTP, HTTP and issues/concerns associated
with the same.

Yes, I would like to see ebXML sit directly on top of TCP/IP (at later
date), with SMTP as an excellent starter.

I noticed Martin using the term "logical channel" in response to Sanjay's
email, which is a key point. In my earlier mail, I suggested going through
BX.25 specs ("B" stands for Bell Labs), which are very comprehensively
done - used by AT&T for their NEMOS and 800 DCS project (that was 1992).
Basically, one LAPB link can contain multiple X.25 virtual circuits (logical
channels) and each virtual circuit is dedicated to one BX.25 session (I
think - it has been a while I worked on it). Over and above all the
reliability that X.25 provides, BX.25 was mainly used for session recovery
(if lost virtual circuit) and resynchronisation (continue from the point
where it let off). Key thing leveraged from X.25 was "flow control" besides
"reliability". ebXML should also leverage flow control and reliablity from
TCP.

Following is just loud thinking-
Assumption: well known port for ebXML is defined (say 1000).
Context: <sender ip, reciever ip, sender port number, receiver port number>
forms unique combination to connect to an instance of application
Scenario:
One ebXML receiver (server) is listening on port 1000
One sender sending 2 ebXML messages concurrently,
case 1: on 2 different sender port numbers
case 2: on 1 (same) sender port number but the 2 ebXML messages are
multiplexed

case 1 does not have the problem associated with flow control. i.e. one
ebXML  session blocking the other

case 2 would involve building flow control in the ebXML RM layer so that the
other ebXML message is not blocked - defining flow control would increase
complexity, besides invloving negotiation at application protocl layer for
the window size, etc.

more cases can also be introduced like the receiver re-connecting on a
different port for each ebXML message once the ebXML listener identifies a
ebXML message request...

Issues:-
1. should ebXML RM support auto resyncronisation and recovery after the
session has been timed-out.
2. if yes, how to identify the resynchronisation point. resync should be
supported for "best effort" cases also, once the decision is yes (may be as
optional feature).
3. sequence number is ok for resync purpose but then a "session-id" (logical
channel) should also get added. who allocates the session-id? sender or
receiver? since it's going to be common to both. Also, some more resync
protocol messages have to be added.
4. Who initiates the recovery and resync process (sender or receiver or
combination of both)? for example,sender recovers but receiver resyncs. Note
recovering has to do with only identification of the lost session, while
resync has to identify the point within the session from where data transfer
is to begin.
5. should ebXML RM assume window size of 1, or should a window be defined. I
think, window complexity should not be added.
6. does session establishment involve any negotiation for QoS. Can receiver
deny "at most once" effort to downgrade the session to "best effort".
7. Delivery confirmation can be achieved even without sequence numbering but
for resynchronisation, sequence numbering  (or some identification) with
every packet is required
8. I find timing-out at RM level quite dicy, without the knowledge of timers
at lower level as mentioned in my earlier email. I think retrying to send
the data at RM level should be replaced by re-establishing for resync and
recovery in case that is to be supported.
9. arhcitecturally, it seems there would be one ebXML listener and each call
reqquest would be handled by a different thread

these are some of the points that i can immediately think of...

Thanks and regards,

Ajay



> -----Original Message-----
> From: Rik Drummond [mailto:rvd2@worldnet.att.net]
> Sent: Wednesday, September 27, 2000 9:53 AM
> To: Ajay K Sanghi; ebxml-transport@lists.ebxml.org
> Subject: RE: Reliable Messaging Spec v0-078
>
>
> Ajay. thanks for the nice comments on the draft everyone has been working
> their butts off...
>
> we decide to make this transport independent. i have been
> thinking about it
> work directly over tcp/ip, as we are now doing with smtp and
> http... what do
> you think of that? and are there any concerns?
>
> best regards, rik
>
> -----Original Message-----
> From: Ajay K Sanghi [mailto:sanghi@giasdl01.vsnl.net.in]
> Sent: Monday, September 25, 2000 6:46 AM
> To: Jim Hughes; ebxml-transport@lists.ebxml.org
> Subject: RE: Reliable Messaging Spec v0-078
>
>
>
> Hi Jim,
>
> Since this is my first communication with the ebXML group, I take this
> opportunity to congratulate ebXML team for excellent work being done. In a
> very recent Bill Gates talk in New Delhi, I asked him the question of
> Microsoft's position w.r.t ebXML, particularly in relation with Biztalk. I
> don't hink he has heard of ebXML, unless he was unable to understand my
> Indian accent ;-) All he said was that Interoperabilty is more important
> (agreed) and that XML will facilitate that (he was speaking on Microsoft's
> .NET strategy).
>
> I am reading Sep 22, 2000 spec for ebXML TRP Reliable Messaging.
> I feel that
> Sequence Numbering is NOT required for achieveing Reliablity at ebXML MSH
> layer. We must leverage reliablilty provided by the protocol themselves.
>
> Assumption for Reliable Messaging should only be that it should use a
> (reliable) connection oriented protocol (CONS like X.25, TCP - they are
> reliable, meaning "ordering" is guaranteed). However, this reliablity does
> not "guarantee" that the ebXML MSH has received the message, for which a
> "delivery confirmation" element/attribute may be added instead of sequence
> number. Whenever delivery confirmation element/attribute is set
> to YES, the
> receiving MSH will respond with ebXML message (just the ebXML header,
> confirming receipt). Note (Key Point) - on account of this
> message (delivery
> confirmation request message) riding on top of CONS, a response to this
> message would necessarily mean that all previously sent messages has been
> received. Infact, if the recieving MSH is sending back some data, this
> delivery confirmation response can be piggybacked. There is absolutely no
> need for persisting packets as suggested in the specs. This delivery
> request/response can be thought of as a ebXML-MSH-ping.
>
> Suggestion for Timeout/Retry is ok provided MSH-timeout is of greater
> interval than what it is at the tranport level (tranport-retries*timeout),
> otherwise it will cause grieve. If retires are to be done by MSH, then
> sequence numbering "may" be required for checking duplicates (not for the
> purpose of delivery confirmation), since for the sending transport layer,
> it's fresh data. In first phase of ebXML specs, I'll be tempted
> to drop this
> idea too - the logic being that if it can't be delivered even with
> transport's retries and timeout, then there is a good chance it won't be
> delivered with ebXML-MSH-retries as well. Sending application
> should simply
> abort and send the message at some other time.
>
> I am in favor of ebXML-MSH, but it should only be used to enable certain
> services (as glue) that CONS transport is supporting or to build something
> on top of what reliable transports support, if absolutely required. For
> example Q-ualified data (used for out of band signalling in X.25) can be
> used for signalling End of File for file transfers. Alternate to
> Q-data way
> of sending End of File would be to first send the size of file.
> The Delivery
> confirmation (D-bit) logic in X.25 protocols should be looked
> into. Also, of
> interest may be some other attributes like fast-select (sender sends
> connection request along with small data and the receiver sends back data
> along with call termination - verifone (I think) used to use this
> for credit
> card verification)
>
> However, if the goal is to provide Relibility over Unrealible
> connectionless
> protocols (CLNS - like UDP) then use of sequence numbering is ok.
> I suggest
> that X.25 protocol is looked at to see the problems assoicated
> with sequence
> numbering, especailly in case MSH is queuing data and not sending
> it to the
> application (see how RNR is used). My suggestion is that ebXML should not
> address reliability over unreliable protocols.
>
> Just a suggestion.
>
> Thank you and regards,
>
> Ajay
>
> Ajay K Sanghi
> Managing Director
>
> ABO Software Private Limited
> B102 Gulmohar Park, New Delhi 110049
> Tel: +91 11 6512816, 6512822 Fax: 6518873
> Website: http://www.abosoftware.com
> email: ajay@abosoftware.com
>
> > -----Original Message-----
> > From: Jim Hughes [mailto:jfh@fs.fujitsu.com]
> > Sent: Sunday, September 24, 2000 4:30 AM
> > To: ebxml-transport@lists.ebxml.org
> > Subject: Reliable Messaging Spec v0-078
> >
> >
> > Attached are Word and PDF copies of the latest version of the Reliable
> > Messaging Spec, for discussion on Wednesday in the F2F.
> Shimamura-san has
> > added much more detail on reliability issues, and of course the
> > earlier use
> > of Message Groups is now deleted for simplicity. Since there were many
> > changes, I deliberately did not mark changes in this document,
> > but you can
> > easily see them by using Word's compare utility against the
> > previous version.
> >
> > [Ralph, could you have some copies of the document available on Tuesday,
> > for those that might not have access to a printer before
> > travelling to Dallas?]
> >
> > Jim
> >
>
>