Replacing PSTN with VoIP wise? Was Re: Phone networks struggle in Hurricane Katrina's wake

Wed Aug 31 21:07:45 UTC 2005

On 31-aug-2005, at 21:19, Andy Davidson wrote:

>> There are two types of VoIP: voice over a private, tightly  
>> controlled  IP network, and voice over the public internet. Now  
>> obviously the  latter is a risky proposition, as it imports all  
>> the limitations of  the internet into the voice service.

> I'm not so sure; someone cuts an ISDN-30 into our building and the  
> sky falls down.

Yes, single homing sucks.

> Someone cuts some fibre carrying IP and life (and communications)  
> carry on ..

You can get your ISDN 30 over redundant fibers too, that's not the  
problem.

> Perhaps you've made a fair and good comment on the marurity of most  
> off-the-shelf voip products or implementations.  But the key, in my  
> mind, is that VoIP across the internet, when done well, imports all  
> of the opportunities of internet routing into voice service.

You say that as if it's a good thing.  :-)

I think in the long run, it makes sense to have end-to-end IP calls  
over the internet. However, this is not going to be as reliable as  
the PSTN for many years to come, because there are is no inter-AS QoS  
deployment, routing protocols take their sweet time (180 seconds BGP  
timeout anyone?) and the internet is becoming fairly non-transparent  
because of all the goo people keep pouring into the machinery in the  
name of security and the like.

However, using the public internet as a local loop is bad. Here in  
the Netherlands, the incumbent telco isn't allowed to lower its  
prices, but everyone (including the incumbent telco) can sell voice  
minutes to PSTN destinations over an IP "local" loop for any price  
they want. So basically they're forced to kill off the local leg of  
the PSTN to be able to compete on medium/long distance. This is not  
good. Not so long ago, when there was a failure in the long distance  
infrastructure, you could still make local calls. With the current  
"intelligent" networks that's not always the case anymore, but if the  
emergency number stuff is done properly, you can still call 911/112  
when the long distance stuff is down. With inet local loop that will  
no longer be the case in most cities.

But then, people don't really care about this, as cell is in the  
exact same boat and huge numbers of people rely on just their cell  
phone and no longer have a fixed line (in Europe at least).