> VOIP is less reliable than traditional public switched telephone network
> (PSTN).
So, let me tell you a story...
Last Friday, I was giving a "run for your life" introduction tour of a
telephone switching office to a new employee in our group. This
particular telephone switching office had a massive Nortel DMS 100/200
switch in it and was the host switch for many telephone exchanges
across the state. Well, "massive" is relative, but we still have a
dozen Nortel racks installed, but the main brain has been replaced. We
replaced about 30 racks of equipment with one, and this new switch is
capable of about 10x the load of the old one.
In another location in the same state, we decommissioned an entire
switching office and moved everything to another location 90 miles
away. In that case, we went from about 120 racks to two racks and at
that other location, we also eliminated about 60 racks. So 180 racks
to 2. This is repeated over and over again across the country. Sadly,
it doesn't actually change our power load, but it does change our
physical load. The heat coming out of this rack (chilled cabinet) is
equal to what was generated by 300 linear feet of equipment. It's not
uncommon to have 12000 watts of power consumption in a single
home-refrigerator sized cabinet.
These are all VoIP switches.
But here is the deal. That is NOT the same as the Internet. The
connectivity between switches in the PSTN system is still over
dedicated trunks. Most of the trunks are still TDM (T1, DS3, OC3)
based, but more and more are being converted to Ethernet 1G or 10G
pipes. The basic architecture of the PSTN system is not changing, only
the equipment itself. But that's only on the switch level.
What IS changing is on the access level. Instead of TDM muxing "at the
edge", the industry is converting over to IP transport to the edge. In
the case of a business with multiple telephone lines, we'll run a
single (or dual-diverse, depending on how suicidal the customer is)
Ethernet connection to the customer over fiber, copper or even
third-party service provider. This connection can be direct connected
to the switch, but in nearly all cases, it is transported and
terminated to the switch through MPLS routers. Again, no public
internet involved yet, except for low-grade redundancy which doesn't
really work. I don't want the Internet flying my airplane.
On the consumer level, things get even screwier. FttH (Fiber to the
Home) seems like a great advancement, but it really isn't as the
current strength is only through the excess bandwidth available. It is
a shared environment and requires robust traffic management in the
switched Ethernet environment as well as the routers involved. To give
you an idea of how hard it is to stay on top of the growth and loads,
we have to replace our routers about every 4.5 years. (Moore's Law,
three cycles worth of aggregate bandwidth growth). It doesn't matter
what I put in, my absolute state-of-the-art transport network has to
be replaced or overlayed, in entirety, before six years, with the
first additions at 3 years.
So, VoIP itself is not the evil. How it is used is the evil. And then
you have consumer-grade VoIP products that use the public Internet for
communication. That's pure garbage. More to that in a moment.
All that said, I'm going to opinionate for a moment. Throughout the
history of PSTN, each new generation of telephone switch has brought
on major enhancements, features and capabilities. Each generation of
switch or switching technology has about a 20-25 year lifespan. This
is the first time that we've actually gone BACKWARDS in the PSTN. VoIP
has brought advancement in terms of options on the access circuit side
(as well as the ability to consolidate assets), but in terms of raw
features, voice quality, etc., it is either the same as or worse.
Voice quality is a massive step backwards. Echos, delays, buzzes, and
other evils are common issues, as is the ability to handle dial-up
modems and fax machines.
Ok, here is my antidote on when belt+suspenders+rope+staples will end
up strangling you: Somewhere in the USA, there is a state-wide
emergency communications network that needed absolute redundancy and
protection. The tried-and-true (relatively speaking, as there is
always issues with fiber cuts, and so forth) system worked for them
almost glitch-free for 15 years. This was replaced with a robust VoIP
network that was highly advanced in the redundancy and protection
environment. Not only are there parallel fiber and copper connections
to every location, but there is also a cellular connection too. OK,
fine. Three physical connections to each site. Everything feeds back
into an MPLS routed network for termination to the head-end location
in the state. Incidentally the majority of the cell towers ALSO
physically backhaul over the same fiber network as terrestrial system
and even passes through the exact same equipment. Oh well... But the
big issue is latency. The cellular network ends up routing about 200
miles out of the way to an entirely different VoIP switch, and the
router-to-router connections have even more additional delay. The
fiber-network itself also has redundant paths with auto-switching on
failures, but can result in swings of 100-200 miles of additional
latency. (The biggest difference between working and protect paths
I've ever seen is about 2000 miles, but that's another story). So, at
the end of the day, what happens is that all this redundancy and
protection is for naught because even in the best of conditions, a
fault-recovery will result in the loss of ALL calls from affected
portions of the network. One such outage literally dropped every
in-progress 911 call and every other call out of the offices state
wide. I cannot say which state this happened or what companies
(multiple) were involved, but I can say that steps (very very
expensive steps) are being done to make sure that this doesn't happen
again and this will become a case-study for the industry.
AG Schnozz
--
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