Converged Networks Threat (Was: Level3 Outage)

Thu Feb 26 05:52:08 UTC 2004

Convergence, and our "lust" to throw TDM/ATM infrastructure in the garbge
is an area very near and dear to my heart.

I apologize if I am being a bit redundant here... but from our
perspective, we are an ISP that is under a lot of pressure to deploy a
VoIP solution.  I just don't think we can... It's just not reliable enough
yet. Period.

In a TDM environment the end node switch is incredibly reliable.  I can't
ever remember in my 30 years on this earth when the end node my telephone
was connected to was EVER down, not once, not EVER.  A circuit switch
environment gives us inherint admission control (if there are not enough
tandem/interswitch trunks we just get a fast busy).  This allows them to
guarantee end to end quality.  The one problem, is that if any of the
tandems along the path my call is connected get nuked off the face of the
earth, I am completely off the air.

In an IP (packet based) environment, theoretically routing protocols can
reroute my call while it is in progress if a catstrophic event occurs,
like the entire NE losing power. The inherint problem with IP is that it
has no admission control, and that it's fundamental resliant design was to
make sure that the "core" of the network knew nothing about the flows
within, so that it _could_ survive a failure.  This design goal is the
problem when trying to guarantee end to end quality of service.  Without
admission control, we can pack it full, so that nothing works.... 
Variable length frames mean that we have little idea of what is coming
down the pipe next.

This can all be solved by massivly overbuilding our network.

Other than the occasional DoS against an area of the network, outages
caused by overuse are relativley rare....

Yhe big problem is the end node hardware in IP networks.  Routers crash
ALL the time.... it is actually a joke.  Yes, theoretically a user could
have 3 separate connections to the Internet and use their VoIP phone and
be happy, but that is not the case.  They buy Internet service from one
place, that is aggregated in the same building as that TDM end node in the
voice world(usually).  That aggregation (access) layer is the single
biggest vulnerability in both worlds.  It just does not fail in the TDM
world like it does in the IP world.  We need to find ways to make that
work better in the IP world so it can be as reliable as the TMD world.  I
realize that us (the public) are asking IP hardware vendors for new
features far faster than can be released reliably... but surely we can
find ways to fail it over more effectivley than it does now...

Dan.