Roaming in telecom



Roaming allows mobile subscriber to visit foreign network and continue to allow send and receive calls as they were within home network. Depending upon network services they subscribe they can use them as well e.g. Voicemail.
A subscriber can only roam in foreign network if their home operator has roaming agreement with foreign network. In such case foreign operator called roaming partner for home operator.
The foreign network send the call detail of visiting subscriber to their home network and invoice them for terminating  the call, then home network subsequently charges to subscriber for providing this facility.
When a foreign subscriber roam in home network the home network send call details of foreign subscriber to their respective foreign network and billed them.
Roaming agreement between different network are governed by number of different standered eg: TAP, CIBER, BARG
CASE: 1 :-> When Home subscriber in foreign network: Make a MOC call
In this case home network subscriber visited foreign network and originate a call.Foregin network route the call to their respective home network and finally home network terminate the call to destination partner.
AT HOME NETWORK:
1: Create/Maintain roaming agreement with foreign network
2: Collect and validate CDR send by foreign network of MOC call detail originating within their network and finally home subscriber rate the customer CDR and billed.
3: Return any dispute record within the agreement.
4: Making payment of invoice /settlement of invoices billed by foreign network.
AT FOREIGN NETWORK:
1: Rating of call and event records for subscriber of home network who visited into foreign network.
2: Providing CDR of subscriber to home network, Invoice them as per roaming agreement and settlement of invoices /disputes.
Case2: When home network subscriber in foreign network and receive incoming calls.
AT Home network MOC call generates first and check for called party profile on HLR. If called party is in foreign network then its VLR profile updated accordingly. The call then routed to foreign network.A roaming call forwarding call (RCF) is generated at Home MSC.
Roaming call forwarding call (RCF):RCF is  service by which the network forwards calls made to a subscriber who is roaming outside his HPMN.While the calling party pays for the part of the call in the subscriber’s HPMN, the subscriber in roaming has to pay for the roaming leg, i.e. the part outside his HPMN. It creates a MTC record from the <RCF> base part, which must be alone. The difference in between a MTC record from a MTC base part is the charge origin indicator being ‘R’ instead of ‘H’ or ‘F’ .
RCF record comes in MSC CDR and finally we rate RCF CDR as well and billed accordingly.
Roaming Testing:
Types:
A: IREG (International Roaming Expert Group)
B: TADIG (Transferred Account Data Interchange Group)

MONITORING OF ROAMING CALLS( ROLE OF DCH in GSM)
Data Clearing House (DCH) is a third party solution based on the GSMA specifications and guidelines. Various operator exchange billing information of the roaming calls as per agreement between them.
DCH provide various services to operators like TAP file conversion, TAP file validation, Inter operator tariff validation, Visitor customer activities, Fraud, Roaming agreement management between roaming partners, Invoicing to operators.
Near Real-Time Roaming Data Exchange (NRTRDE)
Near Real Time Roaming Data Exchange (NRTRDE) is CDR interchange workflow developed by GSMA to monitor customers’ activities in the VPMN (Visited Public Mobile Network) networks, and enables the HPMN (Home Public Mobile Network) to detect unauthorized network usage and other fraud issues near real time.
Operator generates NRTRDE files and sends to DCH for monitoring subscriber’s activities in visitor’s network.