VoIP Provider to PSTN Advice

It would be specific to the carrier. Generally most of the back-haul carriers (IXC) are IP. The locals (ILEC) may use either, but I suspect PRI would be more common.

You should ask someone on the Small Business or National account team at your ILEC.

II am also seeking some clarification on where exactly the "area code" exists in terms of physical hardware.  Does the area code reside on a physical switch that has routes to other area codes (analagous to how IPs are routed)? In other words, if i am a VoIP provider and want to provder telephone service to area code 123,  what is it that i actually interface with?  would this be an IP connection to a single switch that is responsible for routing calls for the 123 area code?

appreciate clarification here.

Are you planning your own ILEC? ;-)

SS7 is the protocol used  http://en.wikipedia.org/wiki/Signaling_System_No_7

Area Code and NXX numbers are like IP routes. The Area Code identifies a LATA and the NNX identifies the central office

You would have a route out to your LEC for that Area Code or have a default route for all unknowns

Read up the Wikipedia article and some of the  See Also  links at the bottom
http://en.wikipedia.org/wiki/Voice_over_Internet_Protocol

when you say "you would have a route to your LEC for that Area Code",  i assume that you mean there would be an interface/route from my VoIP service platform to the LEC's switch or other piece of hardware?  is this interface IP?  or this an SS& connection from my equipment to the LEC's switch?

Any other experts out there with this subject matter expertise?

As some have suggested here, a signaling relationship is usually required with the LEC. This can be achieved through an aggregator that has those singaling realtionships with the carrier. Such an aggregator would be able to provide an ss7 link set that would enable all LEC connections in various markets needed to provide service.

Besides the signaling requirement, you most likely will need 3 other components in the architecture. A least cost router, a media gateway, and a billing solution.

The media gateway will sit in each LEC and connect to the LEC's PSTN circuits using T1 or DS3 circuits. Yes, those T1 or DS3 trunks will probably need some DIDs. You can connect each MGW to your VoIP network and provide VoIP transport between LEC markets. The least cost router will help you figure out how best to direct traffic in the way that keeps your costs low and earns you the most money. The billing solution, of course, should be logging every call that enters and exits your network so you can bill accordingly for the service.

The tricky part involving the media gatway is that it needs to work with the signaling piece so that when a call originates or terminates at a LEC, the call itself is in synch with the SS7 signaling between you and the LECs.

There are several approaches to this, my description may vary depending on what type of architecture and the type of service you wish to provide. Some vendor sell Class 4 and Class 5 soft-switching solutions that handle most of your concerns but will cost you heavily. Other vendors will try to do most of the magic with Session Border Controllers. SBCs are versatile, but usually expect everything to already be IP oriented. Some vendors already have the infrastructure in place and are willing to rent part of their infrastructure to you on some rate-table contract basis. Your rates will be better if you are handling more traffic.

If your an ITSP, meaning you already have a vast IP infrastructure and are now looking to use it to carry VoIP traffic (SIP trunking?), you can look at some of the usual suspects for answers: Cisco, Broadsoft, AcmePacket, Dialogic, etc.

Thanks chris,  but my fundamental question remains unanswered. How does an ITSP interface with the PSTN to route calls?  let's say than I am an ITSP and i want to be able to route 30 calls simultaneously to endpoints on the PSTN.  Meaning 30 calls originate via IP and reach my soft switch and they all need to go an endpoint on the PSTN.

Does this require that i purchase a physical circuit (for example two PRIs in this case to cover 30 calls) from an LEC?  if so, is this typically how it works?

Or are the calls desitined to the PSTN throuhg my softswitch route via some other interface to the LEC ?

Asked another way, does a company such as vonage simply purchase enough physical telephone lines so that they can route calls to the PSTN if needed?

edit: So 24 DS0s * 2 = 48 DS0s total. 2 DS0s for D-channel, 46 DS0s for actual voice traffic.

Thanks.  To be clear, I am (was) aware of how many channels are in a PRI and that a T1 has 24 channels.  My point in the example was that two PRIs would cover my 30 call requirement.  

But i feel like we are getting on the right track now.  Focusing on what you stated below:

"In the case of Vonage they are considered a VoIP retailer. So they provision service for end users and do the billing and all that good stuff. How they carry their traffic is probably a mix of things, they may actually own their infrastructure, or lease/rent it from a company like Level 3. If that was the case, Level 3 would have the media gateways in each of the LECs."

can you clarify what you mean by infrastructure?

Let's say for example that i am a small vonage, in a small city that is served by one LEC (the incumbent) and there are no other CLECs in the picutre.  therefore i am forced to interface with the sole LEC so that i can route calls to the PSTN. I assume I purchase a media gateway and put at the LEC's CO.  assuming i've go that part correct, how do the media gateway interface with the LEC's equipment?  what protocol, physical circuit is used there?

The basic answer is within the specifications of the media gateway. You are looking for a carrier-grade media gateway. preferrably one that give you the most options in how you configure the IP-side and PSTN side. For VoIP retailing, usually the TDM side is SS7 ISUP protocol + T1 (no need for ISDN if SS7 is used). The IP side can be H.323 or SIP. I would recommend you use SIP if you can, but many carriers still use H.323 and you may be limited by what the carrier can offer. There are special varieties of SIP that address the interworking for a SIP to SS7 ISUP use case. SIP-I is a notable example.

There are a myriad of other topcis involved here. If you are providing residential phone service over IP like Vonage, you need to comply with certain regulations such as 911. I think I've addressed the question as posed, but your desire to become an operating phone company - and all the detail involved - is beyond the scope of just a single question : )

Found this for you to read as an overview: http://www.voip-info.org/wiki/view/How+to+start+the+next+Vonage

You may also want to read-up in some trade publications such as InternetTelephony and go to some trade shows like VON, IT Expo, etc.