Subject: RE: [Sigtran] recommendations for M3UA/SUA BEATs when running overSCTP

From: "Haresign Lincoln" <[email-masked]>
Date: Tue, 4 Oct 2005 09:39:15 -0400

Brian,

We are deployed in IP networks that sometimes are not 100% perfect.
This is a fact of life.  If you don't plan for poor networks, then your
protocol and/or your implementation has some shortcomings.  Why is it
that the SS7 protocols has so many safeguards in it?  We transmit a
message and then start a timer to verify a response.  These safeguards
were put in to handle network or remote switch problems.  The SS7
protocols has fault tolerance at every level from the physical level all
the way up to the application layers above TCAP (or ISUP).  

Personally, I don't care if the RFC contains recommendations on how to
handle switches that keep heartbeating but not SACKing.  Or how to
reduce message loss when associations fail.  We will continue to modify
our SW to handle these scenarios and we will do it outside the
specification if the specifications won't evolve with the times.  If we
run in to interop problems, we'll modify the SW again (after all, it
keeps me employed).  And I think the SIGTRAN interops are a good way to
iron some of these issues out.  But also, real field experience in
networks good and bad.

Yes, I believe we do need to have the protocols handle bad networks (why
not...in SS7 they do).  And yes, I believe the deploying SIGTRAN as a
replacement to the lower layers of SS7 is viable no matter what the
networks are like.  Why not?  Of course the end customer will need to
constantly be on the hook to improve their IP networks when associations
are failing.  Again, it really depends upon the application.  If the
application is not real-time (call setup), but something like SMS, then
we can get by with occassionally dropping associations.  As long as the
higher layer protocols handle it properly.

Regards,
Lincoln

-----Original Message-----
From: Brian F. G. Bidulock [mailto:[email-masked]] 
Sent: Tuesday, October 04, 2005 2:08 AM
To: Haresign Lincoln
Cc: Jeff Morriss; [email-masked]
Subject: Re: [Sigtran] recommendations for M3UA/SUA BEATs when running
overSCTP

Haresign,

Separate issue?

<pardon_the_sarcasm>

  Let me get this right:

  You are sending M3UA over SCTP over a non-graded (even noisy crappy)
  network (a combination that provides no assurances of meeting any
  deadline whatsoever and can delay packets within any stream
indefintedly,
  or at least for several minutes, at any time), and you are proposing
using
  a BEAT/ACK (which is sent only in one stream) with some fixed timeout
after
  which you are going to ABORT the association, not knowning whether the
  timeout was due to broken equipment at the other end, or normal HOL
blocking
  within the stream due to a dirty network, discarding at least the one
packed
  stream of messages on every ABORT, with no procedure for recovering
from the
  message loss, trying to reestablish the association from scratch in
the midst
  of what could be just a noise burst, and punishing yourself and the
properly
  operating peer, for the sake of a specific broken implementation?

  Did you want us to recommend a value for this T.punish timer?  Even
recommend
  that it be used?  So that everybody can punish properly operating
peers
  and end-point applications?

  Does that about sum it up?

  Oh, that's not all.  You want to replace the SS7 network with it too:
right?

</pardon_the_sarcasm>

--brian

Haresign Lincoln wrote:                         (Mon, 03 Oct 2005
14:41:26)
> Brian,
> 
> That's really a separate issue.  Whenever we loose an association for 
> whatever reason, there exists the possibility of message loss.  I 
> consider this one of the major shortcomings of the current 
> specification.  I have reviewed an early draft (Version 0) of your 
> recommendation for using the COORID to prevent message loss and I 
> think it's a good idea.  I haven't seen any other switches that we 
> have interfaced to using this nor have any customers mentioned this.  
> I believe that, as the customers become more educated, they will begin

> to look for solutions to this problem and I think your recommendation 
> is a good place to start.
> 
> Regards,
> Lincoln
> 

--
Brian F. G. Bidulock
[email-masked]
http://www.openss7.org/

_______________________________________________
Sigtran mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/sigtran

---

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Tue, 4 Oct 2005 12:07:45 -0600

Lincoln,

Haresign Lincoln wrote:                                                           (Tue, 04 Oct 2005 09:39:15)
> not...in SS7 they do).

SS7 will simply not operate on links with greater that 1 x 10E-06 bit
error rate.  I would not call that handling a bad network.  SS7 will
only run over graded facilities.

I agree with Tolga when he says that we envisioned SIGTRAN as running
over graded facilities as well.

--brian

-- 
Brian F. G. Bidulock
[email-masked]
http://www.openss7.org/