RE: Lossless fail-over

I thing there was a lot of misunderstandings yesterday. I used incorrect
terminology. Words like fail-over or change-back belong to SS7 when
changing the signalling link within a signalling link set. This was very
misleading. I'm sorry for it.

There may exist two levels of ASP1 backup. ASP1 may be backuped on SCTP
and/or M3UA/ SUA level. 

a) When the SCTP level is used than the ASP1 and ASP2 (which backups
ASP1, uses different IP connection and may be geographically far from
ASP1) operate over the same SCTP level. Although ASP1 and ASP2 may be
realized on different computers their SCTP levels looks like one SCTP
level on multihomed AS from ASP3 point of view. This type of backup is
analogy to the Tolga's mentioned SS7 backup.

b) There may exist also different type of ASP1 backup. Lets to imagine
the M3UA/SUA only is synchronized between ASP1 and ASP2. In this case
the SCTP level on ASP1 is not the same entity like SCTP level on ASP2
from ASP3 point of view - it looks like two single-homed SCTP entities.
I think this situation has no analogy in SS7.

The difference between a) and b) is in network failure handling. In case
a) the SCTP handles it. In this case there is not necessary something
new. There exist everything what SCTP need for it. Different situation
is in case b). In this case M3UA/SUA must handle any network failure.
And (in my opinion) the CORID mechanism is very helpful in such
situations. The right question is if it is necessary to make ASP backup
according to case b) and not according to case a)? When somebody is able
to create synchronization on M3UA/SUA level what may be a reason for
non-creation synchronization on SCTP level also?

The difference is also in reaction time on network failure. Both
detection and reaction time is much shorter in case a), but case a) is
more difficult for realization.

So my question is if there is something helpful (like CORID) for network
failure recovery in situations like b)? 

The benefit of CORID I see also in possibility in usage when network
failure is repaired and the original entity (ASP1 in our example) tries
to takeover traffic back - in case of b) of course.

Jan

-----Original Message-----
From: Brian F. G. Bidulock [mailto:[email protected]] 
Sent: Monday, June 19, 2006 10:02 PM
To: Tolga Asveren
Cc: [email protected]
Subject: Re: [Sigtran] Lossless fail-over

Tolga,

Tolga Asveren wrote:                            (Mon, 19 Jun 2006
12:37:03)
>
> a) Relying on a single router for IP connectivity is really very very
bad

You still miss the point: it doesn't require one router: all that it
requires is one back-hoe.

--brian

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

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