Subject: [SUA issue 15]: Segmentation/Reassembly/Sequencing Part 4

From: [email-masked]
Date: Thu, 6 Sep 2001 11:43:21 +0300

Hi all,

> > 4.   Should reassembly be supported at ASP.
> > In case SCCP at SG is a non terminating SCCP,  SCCP will 
> > not do reassembly incoming SCCP messages, for this case we 
> > need to decide if reassembly needs to be done by NIF or by ASP. 
> > This case is under consideration with IPSP - IPSP
> > case. As for all cases where SCCP is a terminating SCCP, 
> > SCCP at SG will perform reassembly of messages, Can there be any 
> > other case where ASP needs to support reassembly ?
> 
> It is clear that reassembly must be supported at the ASP for 
> the "stream" case where the "more" bit is always set.

So, is it sufficient to add text to 4.1 that states:

For CODT messages, reassembly must be supported at the ASP where 
the "more" bit in the Sequence Number parameter is set.  This
occurs when the SCCP layer at the SG is a non-terminating
SCCP.

John

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From: [email-masked]
Date: Thu, 6 Sep 2001 20:52:27 +0530

Brian, John,

Some comments below ..

> > In case SCCP at SG is a non terminating SCCP,  SCCP will not do reassembly
> > incoming SCCP messages, for this case we need to decide if reassembly needs
to
> > be done by NIF or by ASP. This case is under consideration with IPSP - IPSP
> > case. As for all cases where SCCP is a terminating SCCP, SCCP at SG will
perform
> > reassembly of messages, Can there be any other case where ASP needs to
support
> > reassembly ?
>
> It is clear that reassembly must be supported at the ASP for the "stream" case
> where the "more" bit is always set.
>
> Sandeep >> That will be for CO messages, my question was asking for CL
messages.

For CL messages this is the disruption case.  Where there are multiple SG/STP
the SG/STP may fail to perform reassembly if the SLS stream that the
protocol class 1 segments shift to the other SG during reassembly.  This
disruption doesn't happen in the SS7 network, because reassembly is performed
only at the terminating SEP.  In our case, this disruption can be avoided
by having the ASP reassemble CL messages.

Sandeep >>   We agree to handle the scenario where SCCP message from SEP is
directly addressed to ASP point code by assigning ASP point code to SG as alias
point code. In this case if there are multiple SGs acting as STPs , all SGs will
be assigned ASP point code as alias point code. So SCCP at SG will be
terminating SCCP in this case  and hence SCCP at SG will try to reassemble the
messages. In this case if some segments of the same message reach some other SG,
they can not be passed to other SG , where SCCP is doing the reassembly.  So
disruption of traffic may not be the case for supporting reassembly at ASP.

Only for the case where SCCP at SG is non terminating SCCP ( which was SEP - SG
- ASP1 - ASP2 case ) , SCCP will pass all segments to ASP  for reassembly. These
segments can either be passed by same SCCP to a ASP or passed by SCCP at
different SGs to same ASP. If we decide to support this case , reassembly at ASP
is needed otherwise not.

Best Regards,
-Sandeep

[email-masked] on 09/06/2001 03:13:21 PM

Please respond to [email-masked]

To:   "sigtran" <[email-masked]>
cc:   [email-masked] (bcc: Sandeep Mahajan/HSS)

Subject:  [SUA issue 15]: Segmentation/Reassembly/Sequencing Part 4

Hi all,

Sandeep >> More bit will be the CO message case.

John

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From: "Brian F. G. Bidulock" <[email-masked]>
Date: Thu, 6 Sep 2001 13:33:44 -0500

Sandeep,

On Thu, 06 Sep 2001, [email-masked] wrote:

> > > incoming SCCP messages, for this case we need to decide if reassembly needs to
> > > case. As for all cases where SCCP is a terminating SCCP, SCCP at SG will perform
> > > reassembly of messages, Can there be any other case where ASP needs to support
> > > reassembly ?
> >
> > Sandeep >> That will be for CO messages, my question was asking for CL messages.
> 

This would depend largely on the SCCP implementation and the NIF
implementation.

> In this case if some segments of the same message reach some other SG,
> they can not be passed to other SG , where SCCP is doing the reassembly.

For multiple SG/STP, I would recommend using an SCCP which is capable of
passing unsegmented.  Because STPs normally need to meet a whole host of
other very stringent requirements, I don't see a problem here.

> So disruption of traffic may not be the case for supporting reassembly at
> ASP.

Yes it is the case.  The reassembly function at SG2 cannot pick up in the
middle from partial reassembly at SG1.  SLS flows can swing from SG1 to
SG2 at any time in the SS7 network.

> different SGs to same ASP. If we decide to support this case , reassembly at ASP

That is part of Issue 17.

--brian

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

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