[VoiceOps] Geographic redundancy

David Birnbaum davidb at pins.net
Tue Aug 11 21:45:19 EDT 2009


A number of different options exist for redundancy, but they all depend 
on your underlying network architecture and connectivity options.  The 
newest switches tend to have call agents and media gateways that are 
separate, so you can have redundancy across your hardware and call 
control geographically.  Some older switches are more monolithic, so you 
have more redundancy in your network since that has to survive more.

You also find the world changes pretty dramatically when you go from 
Asterisk (which I use generically to refer to any small-scale solution 
of under 2k endpoints or so) to Big Iron - you pay a lot more money for 
all sorts of redundancy and scalability, and as a result you solve 
problems very differently (and have different options to solve 
problems).  Right now Asterisk can't exist without the big iron (5E, 
MetaSwitch, Broadsoft, etc.) because it can't handle the call routing, 
SS7 interop, etc.  One can think of the smaller VoIP providers as basic 
class 5 switches providing the traditional end-user connectivity and not 
worrying about the bigger issues that will bedevil people as they head 
into the interconnection world.

If you can split your call control and media between geographical 
locations, then you can set up as a CLEC in two colocations, and 
interconnect to the necessary tandems to exchange traffic with two 
unrelated circuits, and then have lots of room to lose one half of your 
network without affecting core call control (how you get to your 
customers is a different problem, of course).  Switches can also 
function in an emergency-standalone world as well.  SS7 already has all 
of the redundancy options via multiple A-links to the outside world.  I 
don't believe it's possible to interconnect with IP anywhere as a CLEC 
since the PSTN infrastructure doesn't exist outside of the SS7 
environment for all practical purposes.  (Obviously, you can peer with 
IP but that's not the same as interconnection from a PSTN perspective).

If you can't split your call control, then you use SONET and other 
self-healing architecture to buttress your network as much as possible 
against fiber cuts, MUX outages, and other crashes with the hope that 
you never lose both ends of your ring at the same time.




Kenny Sallee wrote:
> Yes IP makes it easier but you still have to 'plugin' to the PSTN 
> somewhere and in some fashion correct?  Unless you have nothing but 
> SIP peering it does get a little more complicated (although I'm new to 
> the VoIP world and do not know SS7).  Then you still have to worry 
> about your call processing platform: can it live with being greater 
> than x ms apart from it's redundant pair?  What about CDR's and 
> reporting - how do you merge those coming from multiple sources?  I 
> would think there's also rate center and latency issues as well with 
> outbound routing of calls (send calls out the cheapest carrier that 
> will allow it).  I don't think any of it's impossible, but the 
> presence of IP doesn't remove all complexity.
> I like David's idea of a VoiceOps working group to help define 
> options.  Sounds like fun
> Kenny
> On Tue, Aug 11, 2009 at 7:23 AM, Alex Balashov 
> <abalashov at evaristesys.com <mailto:abalashov at evaristesys.com>> wrote:
>     Seems to me like one of the main arguments for moving to IP
>     infrastructure - alongside the numerous arguments telco people
>     have against it - is that it makes this type of redundancy a lot
>     more achievable and cost-effective.
>     -- 
>     Alex Balashov
>     Evariste Systems
>     Web    : http://www.evaristesys.com/
>     Tel    : (+1) (678) 954-0670
>     Direct : (+1) (678) 954-0671
>     Mobile : (+1) (678) 237-1775
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