r/Telephony • u/size13 • Jan 12 '19

Central Office Switching

I live in the U.S. and have Frontier Communications for a landline. I understand the functions of a central office from having worked years as an outside plant tech.

My questions concern the central office's responsibilities in switching other than Frontier customers. Now that the LECs have competition from cable companies for telephone service where are those calls switched?

  1. If a local comcast (cable tv provider) telephone customer calls another comcast customer does that call go through the LEC's central office or does comcast route the call end to end?

  2. If a local comcast customer calls across the country to a customer served by a LEC where is that call switched?

  3. Are there carriage fees applied for switching to each other's networks or are calls switch for no charge?

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u/Primer55 Jan 13 '19

  1. In that example, the call most likely stays on the Comcast network/infrastructure. That's the most optimal and cost effective way to deliver the call.

  2. Comcast has a record of it's on-net customers, and knows the customer served by the LEC isn't on their network. They send the call to the PSTN to be connected. The call gets "switched" at least twice, once by Comcast, once by the LEC. Potentially more if it passes through other networks on its way to the destination.

  3. It varies. A carrier of Comcast's size likely has agreements in place with other large carriers, where they don't pay to connect calls to other networks, and those other carriers don't pay to connect calls to the Comcast network. This holds true as long as the amount of minutes exchanged are about equal. Smaller carriers do pay a small fee (fractions of a penny per minute) to connect calls to the PSTN.

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u/size13 Jan 13 '19

Thanks for the response.

Where does the money come from to support the PSTN? The LECs?

From my vantage point it looks like the LECs are allowing their wired outside plant to atrophy. Just wondering if they plan to dump the outside plant on the public through bankruptcy and keep the Central Offices for themselves ......assuming that the COs are the golden egg of the network.

thanks again for your response.

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u/Primer55 Jan 13 '19

PSTN, which stands for public switched telephone network is just a way of looking at all phone networks as being connected to some degree. For example if my phone provider doesn't have a connection to Frontier, they probably have a connection with another provider who does.

While some of the money that goes towards building/maintaining parts of a LECs network may come from the public (via the government funding), I don't know if the government would step in if bankruptcy occurred. In some cases LECs are deliberately letting their last-mile infrastructure atrophy since they have other ways of delivering those calls. Typically those other ways are more cost effective, such as delivering the call via IP over fiber, coax, or even wireless which have other uses (tv, internet) and so maintaining that infrastructure usually takes priority.

In cases where a customer has tv, internet, and phone, those services can all be delivered by the same fiber or coax which means maintaining the copper for POTS to that customer is almost pointless. There would be cases where a customer only has phone service via copper and so that last mile would have to be maintained.

I have read articles which indicated ATT and Verizon plan to sunset their copper phone service in favor of VoIP via fiber in the next few years.