4G Outbound Roaming

End-to-end flow for a home subscriber roaming on a partner LTE network, from the roaming agreement and IR.21 exchange through S6a attach, home-routed session, CDR generation in the visited network, NRTRDE fraud exchange, TAP3 and RAP, inter-operator settlement, retail billing and revenue assurance.

Roaming is the one flow in this set where the network that measures the usage is not the network that bills it. The visited operator runs the radio, the core and the meter; the home operator holds the customer, the price list and the invoice. Everything between them — NRTRDE, TAP3, RAP, clearing and settlement — exists to move a usage record across a company boundary and make it settle. Read the steps in two halves: everything up to the CDR happens on somebody else's network, and everything after it is the home operator working out what it owes and what it can charge.