1/ Give the fact that the #nashvillebombing took place outside of an AT&T Central Office (CO) called Nashville 'Main' there is a lot of confusion about what a central office is so I thought I'd do a thread on what a CO is and what it is for.

2/ Each city has one or more buildings known as Central Offices (COs). They were built by Incumbent Local Exchange Carriers (ILECs) and contain the Public Switched Telephone Network (PTSN) as well as the networks of other private telecom companies and govt agencies. Map of COs:

3/ Traditionally the CO is where all of the copper wires from our homes and offices terminates. In larger cities, there are intermediate COs called LSOs that are connected to the CO. The CO contains one or more Class 5 switches that route local and long-distance calls.

4/ The Telecom Act of 1994 required the ILECs to open their COs to competitors that included Competitive Access Providers (CAPs), Competetive Local Exchange Carriers (CLECs), and Interexchange Carriers (IXCs).
https://en.wikipedia.org/wiki/Telecommunications_Act_of_1996#:~:text=According%20to%20the%20Federal%20Communications,converging%20broadcasting%20and%20telecommunications%20markets.

5/ The CAPs typically ran fiber throughout a city connecting businesses and office buildings together and to the CO. They colocated interconnect gear in the CO by renting one or more relay racks. They could then purchase cross-connects to the ILEC or other telecom providers.

6/ The CLECs bought local switching services from the ILEC and usually offered additional services such as IP and as a result, usually colocated some of their gear in the CO as well.

7/ The IXCs colocated their interconnect gear in the CO and bought access to another data center type facility from a CAP so they could sell long-distance and IP services to ILEC and CLEC customers.

8/ The typical CO houses VERY few people. It is basically a hardened (bomb proof) building that houses communications equipment. This equipment generates a lot of heat and as a result, the building needs a massive amount of HVAC equipment.

9/ The typical CO is usually connected to multiple power grids AND has enough generator capacity to allow the building to operate even if all power is cut off from the building.

10/ Congress mandated that the ILEC (typically AT&T today) allow competitors to rent relay racks inside of their COs so the typical Central Office will have equipment owned and maintained by hundreds of companies and gov't agencies in their buildings.

11/ In fact, Google Maps often blurs the entrances of COs because their three-letter customers DHS and FBI notify the search giant that sensitive equipment is inside.

12/ Now to debunk some rumors. There is no room in a CO to store or work on voting machines. AT&T has various service divisions, but none of them could (or would want to) use a CO to store or work on non-telecom related equipment as there is no room. https://www.rightjournalism.com/four-days-before-the-bombing-in-nashville-near-the-att-building-american-patriot-alleged-that-att-got-the-contract-to-do-the-forensic-audit-on-the-dominion-voting-machines-and-that-they-are-transpo/

13/ The systems in a CO are very complex. The generator could be functioning but if the fire suppression system activated the generator might not turn on taking a system down. This might result in various services like landlines, cell towers, ATMs, 911 to go down.

14/ I got my start in the telecom business working for a CLEC, IXC, and IP provider before I started my own data center business (now a part of Equinix). Happy to answer questions.