Subject: Re: [Sigtran] M2PA Comment: T7 Timer

From: "Amish Chana" <[email-masked]>
Date: Fri, 21 Jun 2002 19:52:28 +0100

Javier,

Agreed, the appropriate selection of SCTP parameters and configuration can 
perform the required re-routing functions in a private network.

But these parameters have not been standardised for private SS7 networks  - 
the only values an implementor has to work with are the ones given for the 
Internet.

It is very very unlikely that all implementations/deployments will have the 
ideal  set of parameters initially (or not until there have been extensive 
deployments and research). The appropriate choice of parameters may also 
differ depending on whether the hosts are single-homed, dual-homed or 
tri-homed.

I see no harm in using the T7 timer in M2PA. Even if the host is multi-homed 
- it would offer protection against badly selected SCTP parameters (assuming 
all the associations don't use the same path as the primary and a minimum of 
2 associations per linkset are used, each with a different primary path - 
even if they are multi-homed).

Once a standised set of parameters are available for implementors to work 
with and extensive experience has been gained from M2PA/SCTP deployments we 
can consider removing T7 from M2PA version 2. :-)

Regards,
Amish

>From: "Brian F. G. Bidulock" <[email-masked]>
>Reply-To: [email-masked]
>To: "Javier Pastor-Balbas (ECE)" <[email-masked]>
>CC: Andrew Booth <[email-masked]>, [email-masked]
>Subject: Re: [Sigtran] M2PA Comment: T7 Timer
>Date: Fri, 21 Jun 2002 13:15:47 -0500
>
>Javier,
>
>MTP3 expects a fixed maximum delay of acknowledgement from
>MTP to MTP.  T3-rtx can increase almost unbounded.  Settings
>of SCTP protocol parameters to yeild 0.5 - 2.0 seconds max
>delay of acknowledgement are not recommneded.  M2PA and MTP3
>include what some might refer to as application level acks.
>These are above SCTP.  MTP3 and MTP2 have more stringent
>requirements than SCTP can provide for.  This is neither
>strange nor peculiar.  iSCSI for example, has application
>level timers above the transport layer (even SCTP) which may
>be far smaller than T3-rtx as dictated by RTO.Min.
>
>--brian

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