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What is the difference between these two (in distance and function)? I understand that a Central Office is a place where the ISP stores equipment that connects many clients. But the POP has a similar definition. It is a place where many clients connect and there are multiple POP's for each ISP.

What am I missing?

  • Your understanding is incorrect. Central Offices and ISPs are unrelated. Central office is a telephony term. ISPs related to Internet. – InterLinked Jun 25 '17 at 23:02
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What is the difference between this two (in distance and function).

Short answer:

  • Distances - not very much, these days
  • Function - Basic / Enhanced 911 is still processed through the Central Office; however other CLECs can trunk customers' 911 calls back to the Public Service Answering Point (PSAP) via the local Central Office... I also think Intrado has equipment for CLECs to provide 911 services...

Long answer:

The differences between them have much more to do with historical context...

  • Central Office is a term that has deep roots in the Bell companies, where the Central Office also called a telephone exchange. Originally they housed circuit-switching technologies; these days they have similar routers and switches as you'll see in a Point of Presence. Telephone copper pairs star out of the Central Office to normally about 15,000-18,000 feet; however, you can also star the copper out from a DLC can to cover a much larger area, because the DLCs can be connected via fiber. The key points to remember:

    1. Because the Central Office is associated with the Bell companies, they are heavily regulated by the government. Incumbent carriers in many other countries are also regulated in a similar manner.
    2. Construction and installations within a Central Office normally comply with Telecordia standards, such as GR-63 NEBS. NEBS-compliant equipment is a big deal to RBOCs and incumbents... NEBS requires routers / switches to have front-to-back cooling and other features that comply with Telecordia's requirements.
    3. They always have responsibility for maintaining last-mile transport to customers.
    4. Basic / Enhanced 911 is routed through the Central Office
    5. Most of the labor is unionized.
  • Point of Presence does not always carry the same loaded meaning that Central Office does. Most of the time, it refers to a building that is carefully selected to host internet circuits between various carriers. Customer connectivity to a Point of Presence these days is usually over Metro ethernet or SONET rings.

    1. These facilities are often not regulated by the government.
    2. Construction and installations don't need to comply with Telecordia standards, such as GR-63 NEBS
    3. The carriers within a POP often are not associated with the remains of the original Bell companies, and they are not required to host last-mile transport to a customer (although they often do). It's quite common for the local AT&T / Verizon / other bellco to offer T-carrier services from a POP because they will co-locate within the POP to spoon as much transport business as they can from the other carriers who might need last-mile transport to customers.
    4. POPs don't have to handle 911
    5. Labor might not be unionized.

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