How do the IXCs exchagne calls and peer between eachother?
Hello all, I've been trying to better understand the inner workings of the US phone network for some time now, and I think that I have come pretty far in that goal, but there is still one topic which I have been unable to figure out: how do the major IXCs exchange calls with each other for destination numbers using off-net FGD tandems. I understand that, for example, MCI can pick up a call directly from a customer, or from a PICed line at a ILEC FGD tandem, and then cart that call to the FGD tandem for the target LATA (or to a private interconnect with the destination carrier), moving through several switches along the way. What I'm trying to understand is how calls reach alternate FGD tandems (e.x. widevoice, teliax, intelliquent) when the call is being carried by a different IXC (e.x. AT&T). Right now, I could order a CLLI code, and assuming that I could get SS7 connections, put up a switch that would reachable by any other switch, but I would have no actual circuits on which I could accept calls. Must these alternate FGD tandem providers acquire trunking from every outbound provider for their service to be usable? Is there some kind of inter IXC transit service? I would appreciate any insight that you could provide. Thank you, Enzo Damato
LD carriers interconnect to every FGD tandem in the service areas they cover. In areas where they might have minimal traffic, they might have their CICs loaded on other carrier's trunks and pay that IXC to bring their traffic in (or they use someone else's PIC in certain states and have a wholesale agreement set up to pay certain rates for traffic from a list of ANIs they provision in the carrier systems and the LD carrier is just a rebiller in those circumstances. (Verizon and Global Crossing were big on this for years). Realistically speaking, nobody does this anymore, you only see tollfree traffic and the random ILEC landlines. CLECs typically self provision their own LD service by buying transport from several carriers and build a low cost routing table and handing it off. Carriers like Sinch, Peerless and Bandwidth have aggressively low rates for their own numbers and for people who directly subtend them for IPES service, or use their CLEC trunking, and have default rates for anything sent to them not in that list, but then you can go to someone like Verizon Business to get full A-Z rates, and pick up a few other carriers who have better rates to rural areas, etc. PIC traffic is a super rare thing these days. wireless, CLEC and IPES carriers just do what I said above, and since they already have the local loop (or its equivalent) they just send the call to its next destination (or directly to the terminating carrier if they have a direct interconnection. -Paul Paul Timmins paul@timmins.net Ham License: KC8QAY Committee Chair, Pack 1589 MBC (Archery, Aviation, Digital Technology, Electronics, Motorboating, Radio) District Scoutbook Helpdesk, North Star GLFSC I used to be an Eagle (C2-784-18-1)
On Nov 8, 2025, at 20:38, Enzo Damato via VoiceOps <voiceops@voiceops.org> wrote:
Hello all,
I've been trying to better understand the inner workings of the US phone network for some time now, and I think that I have come pretty far in that goal, but there is still one topic which I have been unable to figure out: how do the major IXCs exchange calls with each other for destination numbers using off-net FGD tandems. I understand that, for example, MCI can pick up a call directly from a customer, or from a PICed line at a ILEC FGD tandem, and then cart that call to the FGD tandem for the target LATA (or to a private interconnect with the destination carrier), moving through several switches along the way. What I'm trying to understand is how calls reach alternate FGD tandems (e.x. widevoice, teliax, intelliquent) when the call is being carried by a different IXC (e.x. AT&T). Right now, I could order a CLLI code, and assuming that I could get SS7 connections, put up a switch that would reachable by any other switch, but I would have no actual circuits on which I could accept c alls. Must these alternate FGD tandem providers acquire trunking from every outbound provider for their service to be usable? Is there some kind of inter IXC transit service?
I would appreciate any insight that you could provide. Thank you, Enzo Damato _______________________________________________ VoiceOps mailing list -- VoiceOps@voiceops.org https://lists.voiceops.org/postorius/lists/voiceops.voiceops.org/ To unsubscribe send an email to voiceops-leave@voiceops.org
I agree with everything said. I would only add that PSTN is on the way out, so no one is going to sell SS7 link service to a carrier that didn't already have SS7 links. Syniverse just removed all SS7 services from their network and TNS eventually forces everyone to interconnect via SIP. The only other option missing is that many IXC and Wireless carriers create direct SIP connections with carriers they do a significant amount of business with. MARY LOU CAREY BackUP Telecom Consulting Office: 615-791-9969 Cell: 615-796-1111 On 2025-11-08 07:59 PM, Paul Timmins via VoiceOps wrote:
LD carriers interconnect to every FGD tandem in the service areas they cover. In areas where they might have minimal traffic, they might have their CICs loaded on other carrier's trunks and pay that IXC to bring their traffic in (or they use someone else's PIC in certain states and have a wholesale agreement set up to pay certain rates for traffic from a list of ANIs they provision in the carrier systems and the LD carrier is just a rebiller in those circumstances. (Verizon and Global Crossing were big on this for years).
Realistically speaking, nobody does this anymore, you only see tollfree traffic and the random ILEC landlines.
CLECs typically self provision their own LD service by buying transport from several carriers and build a low cost routing table and handing it off. Carriers like Sinch, Peerless and Bandwidth have aggressively low rates for their own numbers and for people who directly subtend them for IPES service, or use their CLEC trunking, and have default rates for anything sent to them not in that list, but then you can go to someone like Verizon Business to get full A-Z rates, and pick up a few other carriers who have better rates to rural areas, etc.
PIC traffic is a super rare thing these days. wireless, CLEC and IPES carriers just do what I said above, and since they already have the local loop (or its equivalent) they just send the call to its next destination (or directly to the terminating carrier if they have a direct interconnection.
-Paul
Paul Timmins paul@timmins.net Ham License: KC8QAY Committee Chair, Pack 1589 MBC (Archery, Aviation, Digital Technology, Electronics, Motorboating, Radio) District Scoutbook Helpdesk, North Star GLFSC I used to be an Eagle (C2-784-18-1)
On Nov 8, 2025, at 20:38, Enzo Damato via VoiceOps <voiceops@voiceops.org> wrote:
Hello all,
I've been trying to better understand the inner workings of the US phone network for some time now, and I think that I have come pretty far in that goal, but there is still one topic which I have been unable to figure out: how do the major IXCs exchange calls with each other for destination numbers using off-net FGD tandems. I understand that, for example, MCI can pick up a call directly from a customer, or from a PICed line at a ILEC FGD tandem, and then cart that call to the FGD tandem for the target LATA (or to a private interconnect with the destination carrier), moving through several switches along the way. What I'm trying to understand is how calls reach alternate FGD tandems (e.x. widevoice, teliax, intelliquent) when the call is being carried by a different IXC (e.x. AT&T). Right now, I could order a CLLI code, and assuming that I could get SS7 connections, put up a switch that would reachable by any other switch, but I would have no actual circuits on which I could accept c alls. Must these alternate FGD tandem providers acquire trunking from every outbound provider for their service to be usable? Is there some kind of inter IXC transit service?
I would appreciate any insight that you could provide. Thank you, Enzo Damato _______________________________________________ VoiceOps mailing list -- VoiceOps@voiceops.org https://lists.voiceops.org/postorius/lists/voiceops.voiceops.org/ To unsubscribe send an email to voiceops-leave@voiceops.org
_______________________________________________ VoiceOps mailing list -- VoiceOps@voiceops.org https://lists.voiceops.org/postorius/lists/voiceops.voiceops.org/ To unsubscribe send an email to voiceops-leave@voiceops.org
participants (3)
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edamato＠ricetelecom.net -
Mary Lou Carey -
Paul Timmins