47 C.F.R. § 36.321
Central office expenses—Accounts 6210, 6220, and 6230
(a) The expenses related to central office equipment are summarized in the following accounts:
| Central Office Switching Expense | Account 6210. |
| Operator Systems Expense | Account 6220. |
| Central Office Transmission Expense | Account 6230. |
(b) The expenses in these accounts are apportioned among the operations on the basis of the separation of the investments in central office equipment—Accounts 2210, 2220 and 2230, combined.