47 C.F.R. § 61.39
(a) Scope. Except as provided in paragraph (g) of this section, This section provides for an optional method of filing for any local exchange carrier that is described as a subset 3 carrier in § 69.602 of this chapter, which elects to issue its own Access Tariff for a period commencing on or after April 1, 1989, and which serves 50,000 or fewer access lines in a study area as determined under § 36.611(a)(8) of this chapter. However, the Commission may require any carrier to submit such information as may be necessary for review of a tariff filing. This section (other than the preceding sentence of this paragraph) shall not apply to tariff filings of local exchange carriers subject to price cap regulation.
(b) Explanation and data supporting tariff changes. The material to be submitted to either a tariff change or a new tariff which affects rates or charges must include an explanation of the filing in the transmittal as required by § 61.15. The basis for ratemaking must comply with the following requirements. Except as provided in paragraph (b)(5) of this section, it is not necessary to submit this supporting data at the time of filing. However, the incumbent local exchange carrier should be prepared to submit the data promptly upon reasonable request by the Commission or interested parties.
(1) For a tariff change, the incumbent local exchange carrier that is a cost schedule carrier must propose Traffic Sensitive rates based on the following:
(2) For a tariff change, the incumbent local exchange carrier that is an average schedule carrier must propose Traffic Sensitive rates based on the following:
(3) For a tariff change, the incumbent local exchange carrier that is a cost schedule carrier must propose Common Line rates based on the following:
(i) For the first biennial filing, the common line revenue requirement shall be determined by a cost of service study for the most recent 12-month period. Subscriber line charges shall be based on cost and demand data for the same period. Carrier common line rates shall be determined by the following formula:

Where:
And where: CCL Rev Req = carrier common line revenue requirement for the most recent 12-month period; CCL MOUb = carrier common line minutes of use for the most recent 12-month period; CCL MOU1 = CCL MOUb; and CCL MOU0 = carrier common line minutes of use for the 12-month period preceding the most recent 12-month period.
(ii) For subsequent biennial filings, the common line revenue requirement shall be determined by a cost of service study for the most recent 24-month period. Subscriber line charges shall be based on cost and demand data for the same period. Carrier common line rates shall be determined by the following formula:

Where:
And where: CCL Rev Req = carrier common line revenue requirement for the most recent 24-month period; CCL MOUb = carrier common line minutes of use for the most recent 24-month period; CCL MOU1 = carrier common line minutes of use for the 12-month period; and CCL MOU0 = carrier common line minutes of use for the 12-month period preceding the most recent 12-month period.
(4) For a tariff change, the incumbent local exchange carrier which is an average schedule carrier must propose common line rates based on the following:
(i) For the first biennial filings, the common line revenue requirement shall be determined by the incumbent local exchange carrier's most recent annual Common Line settlement from the National Exchange Carrier Association. Subscriber line charges shall be based on cost and demand data for the same period. Carrier common line rates shall be determined by the following formula:

Where:
And where: CCL Rev Req = carrier common line settlement for the most recent 12-month period; CCL MOUb = carrier common line minutes of use for the most recent 12-month period; CCL MOU1 = CCL MOUb; and CCL MOU0 = carrier common line minutes of use for the 12-month period preceding the most recent 12-month period.
(ii) For subsequent biennial filings, the common line revenue requirement shall be an amount calculated to reflect the average schedule pool settlements the carrier would have received if the carrier had continued to participate in the carrier common line pool, based upon the average schedule Common Line formulas developed by the National Exchange Carrier Association for the most recent 24-month period. Subscriber line charges shall be based on cost and demand data for the same period. Carrier common line rates shall be determined by the following formula:

Where:
And where: CCL Rev Req = carrier common line settlement for the most recent 24-month period; CCL MOUb = carrier common line minutes of use for the most recent 24-month period; CCL MOU1 = carrier common line minutes of use for the most recent 12-month period; and CCL MOU0 = carrier common line minutes of use for the 12-month period preceding the most recent 12-month period.
(d) Rates for a new service that is the same as that offered by a price cap local exchange carrier providing service in an adjacent serving area are deemed presumptively lawful, if the proposed rates, in the aggregate, are no greater than the rates established by the price cap local exchange carrier. Tariff filings made pursuant to this paragraph must include the following:
[76 FR 43212, July 20, 2011, as amended at 76 FR 73882, Nov. 29, 2011; 84 FR 57652, Oct. 28, 2019]