Friday, May 2, 2008

Mobile Number Portability

MNP Techniques
Onward routing (OR): The call is delivered first to the network to which the ported number belonged (donor network). The call is identified in the donor network as being a call to a ported number and the call is routed onward to the new destination.
Call drop back (CDB): CDB is an enhancement of OR. When the donor network receives the call, it releases the call and returns a message indicating that the number has been ported (and providing routing information). This drop back message is used by a transit or an originating network to route the call onward to the new destination.
Intelligent-network-related (IN-related): IN-related solutions use a database which is interrogated to identify whether the called number has been ported and, if so, to which destination. A range of IN-related solutions are possible, including all call query (ACQ) and query on release (QoR). ACQ requires all calls to visit the central database. QoR allows the calling network to try the donor network (more precisely the "number range owning network") first - since the vast majority of numbers are not ported. Only if the donor network says "this number has been ported" does the calling network dip into the central database.
Signalling relay (SR): SR is a solution for GSM using existing GSM functions. The donor network uses the GSM signalling relay function (SRF) to send a routing enquiry to the recipient network, which returns the routing information required to properly route the call. The routing information can be used either to reach the recipient network or the current visited network (the network where the called party is roaming). If mobiles with ported numbers are often roaming in other networks then this obviously has efficiency advantages since it "kills two birds with one stone".

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