47 CFR § 52.20 - Thousands-block number pooling.
(a)Definition. Thousands-block number pooling is a process by which the 10,000 numbers in a central office code (NXX) are separated into ten sequential blocks of 1,000 numbers each (thousands-blocks), and allocated separately within a rate center.
(b)General requirements. Pursuant to the Commission's adoption of thousands-block number pooling as a mandatory nationwide numbering resource optimization strategy, all carriers, except those exempted by the Commission, must participate in thousands-block number pooling where it is implemented and in accordance with the national thousands-block number pooling framework and implementation schedule established by the Commission.
(c)Donation of thousands-blocks.
(1) All service providers required to participate in thousands-block number pooling shall donate thousands-blocks with ten percent or less contamination to the thousands-block number pool for the rate center within which the numbering resources are assigned.
(2) All service providers required to participate in thousands-block number pooling shall be allowed to retain at least one thousands-block per rate center, even if the thousands-block is ten percent or less contaminated, as an initial block or footprint block.
(d)Thousands-Block Pooling Administrator.
(1) The Pooling Administrator shall be a non-governmental entity that is impartial and not aligned with any particular telecommunication industry segment, and shall comply with the same neutrality requirements that the NANPA is subject to under this part.
(2) The Pooling Administrator shall maintain no more than a six-month inventory of telephone numbers in each thousands-block number pool.