The ROLO charge is the charge that a BT Wholesale customer pays BT Wholesale for transit of the call through its network to another Communications Provider. Typically the ROLO charge also includes the POLO and TWIX charges, though not always, as certain in types of call such as freephone numbers the TWIX and POLO charges are not charged to the originating CP.
Once the ROLO charge is received, BT keeps the TWIX portion of the charge as payment for carrying the call through its network and rest is paid to the terminating CP as a POLO charge.
Assume, for the purposes of this example, Garytel and gr0mtel are both BT Wholesale customers and they are not connected to each other's network. A customer of Garytel makes a call to a gr0mtel geographic number. Garytel pays BT Wholesale the ROLO charge. BT Wholesale then route the call to gr0mtel's network, taking the TWIX charge as payment for doing so. BT Wholesale then pays gr0mtel what's left of the ROLO charge after taking TWIX, and this is the POLO charge.