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Whats so difficult about ISSU

Compared to our CMTS, our class 5 softswitch cost us less money.  Yet our
CMTS vendor stopped talking about hitless software upgrades 2 years ago
because the upgrade path (from, to, and which software releases you can use)
is so limited it's hardly practical.




From: Kasper Adel [mailto:karim.adel at gmail.com] 
Sent: Monday, November 12, 2012 12:22 AM
To: Frank Bulk
Cc: NANOG list
Subject: Re: Whats so difficult about ISSU


Hi Frank,


Is it because C5 softswitches have expensive hardware, advanced software and
dual asics? I would have never imagined that any vendor is capable of
upgrading fpd's/ASICs ucode without a hit unless there are multiple chips
continuously syncing with each other.




On Monday, November 12, 2012, Frank Bulk wrote:

We do it on our Class 5 softswitch ... and it works consistently.  There may
be a few seconds, once, where a new call can't be made, but most people will
re-dial.  It just works.

It can be done, but the product has to be built with that in mind.


-----Original Message-----
From: Kasper Adel [mailto:karim.adel at gmail.com <javascript:;> ]
Sent: Thursday, November 08, 2012 5:23 PM
To: NANOG list
Subject: Whats so difficult about ISSU


We've been hearing about ISSU for so many years and i didnt hear that any
vendor was able to achieve it yet.

What is the technical reason behind that?

If i understand correctly, the way it will be done would be simply to have
extra ASICs/HW to be able to build dual circuits accessing the same memory,
and gracefully switch from one to another. Is that right?