[VoiceOps] TDM -> IP Migration

[Alex Balashov]

Hello Mike,

> On Oct 21, 2024, at 2:35 pm, Mike Hammett via VoiceOps <voiceops at voiceops.org> wrote:
> 
> Well, nobody cares. The largest user in the area moved everything to Teams, so what point is there in me pushing something that no one cares about.

I think that about sums up the state of things.

> what are the advantages of staying CLEC-based instead of moving to IPES-based? From what I can tell, they're very similar. In both methods, I'm still responsible for 911, for number blocks, for porting, for a SIP interconnect, for my own switching, etc., etc. In both worlds (as is the PSTN), I'm limited to being single-homed. For instance, I couldn't use BOTH Inteliquent and Peerless simultaneously for a given TN. 

Well, what you have called "single-homing" here is not a hallmark of CLEC or IPES status, but rather an almost ontological limitation of how PSTN routing works. The number is simply homed to one underlying carrier, period.

> We don't yet have our IPES OCN, but that's hardly a large barrier.
> 
> What are some things that I might not be thinking of? For those of you that have made similar migrations, which path did you choose and what did you wish you knew before the move?
> 
> Yeah, lots of things in the air...  looking to change basically how every aspect of voice in the network works...  all at once (or nearly at once). About the only things that wouldn't be changing would be a couple of existing SIP providers and our subscriber gateways. Even our hosted PBXes would be changing, though more of a phased-in model.

Based on my (somewhat dated) CLEC experience going through this in the late 2000s, it's best to take it in tiers. Tackle the core, the interconnects and the customer access edge (if relevant) as distinct phases. 

In our particular case, which, again, I think is anchored to a certain era and may not be exactly applicable to the current way of doing things, we had SS7 (TDM) coming in from the ILEC POI and kept all that in place on big Class 4 tandem switch iron (I think a Telica/LCS), but then broke out DS3s onto STS-1 cross-connects to Cisco AS5400s. From there, there was a very intentional initiative to turn everything SIP, including to the Metaswitch and other Class 5 platforms, and to SBCs onto which customer trunks landed. There was some older H.323 stuff to CallManager; that was jettisoned and replaced with SIP. That made the network SIP interconnect-ready, if the ILEC would ever allow it. I'm sure they still don't.

I'll never forget how I worked myself out of a job. I advised a customer in 2008 to do a ISDN-to-SIP gateway buildout in a data centre for their call centre stuff. They were on the fence about SIP trunking, and I tilted them away from it. For the next ten years, I got no calls about telephony; literally none. They had no use for me. No interop issues, no DTMF issues, no call quality problems. I think the one call I did get was about a dead CMOS battery in one of the eBay'd Cisco AS5400XMs they used as gateways, so it wasn't retaining the config. All their problems started when they finally broke down, decommissioned those and switched to SIP. 

If my other customers had done that, I wouldn't have had a job, nor a business! It's horrifying to think what would happen if everyone had stuck with the rock-solid reliability of TDM.

-- Alex

-- 
Alex Balashov
Principal Consultant
Evariste Systems LLC
Web: https://evaristesys.com
Tel: +1-706-510-6800