How CAMEL helps in establishing a VPN Call

How is VPN call established using CAMEL support.

The VPN service translates the dialled number into the public number associated with the destination subscriber, who belongs to the same VPN group as the calling subscriber. Hence,
subscribers of one VPN group, e.g. an enterprise, may call one another by GSM, by dialling the
PABX extension number.

In case (1), the CAMEL service connects the calling subscriber to a mobile VPN subscriber. The mobile VPN subscriber belongs to the same VPN group as the calling subscriber. The call is routed to the GMSC of the HPLMN operator, from where the call is routed to the VMSC, where the called subscriber currently resides.

In case (2), the calling subscriber is connected to an extension of the PABX at the company.

In example (3), the calling subscriber is connected to a VPN colleague in an office in the visited country.

In all three cases, the ISUP signalling may take the shortest possible path between the VMSC of the calling subscriber and the PSTN/PLMN of the called subscriber. In these examples, the VPN service may ensure that the called party receives the calling party’s VPN number on her display, instead of the calling party’s public number (Table 3.6).

On-net calls are calls between users of the same VPN group;

Off-net calls are calls from a user of a VPN group to a user outside the VPN group or vice versa.

Referring to the diagram below:

When the calling party (+31 6 516 34 567) dials 3341, the VPN service determines that this number belongs to a subscriber of the same VPN group. The VPN service translates the dialled
number into the public GSM number of the destination subscriber (+31 6 516 34 568). The VPN
service also provides an additional calling party number (3342) in CAP CON. The called subscriber receives 3342 on her display, instead of +31 6 516 34 567. Should the called VPN subscriber return the call, i.e. dial 3342, then the VPN service will connect the call to +31 6 516 34 567. If the calling subscriber dials an off-net number (e.g. +31 70 456 6782), then the VPN service allows the call to continue to the dialled destination, without affecting the routing of the call. VPN does not provide an additional calling party number, since the VPN number should not be presented to a called party that does not belong to the (same) VPN group.
When a call crosses an international boundary, it may occur that the calling party number or the
additional calling party number is not transported in the ISUP signalling link.
A VPN subscriber may receive an on-net call when she is roaming in a non-CAMEL network. In
that case, the VPN service for that called subscriber may remove the additional calling party number from the ISUP signalling flow. The rationale is that the called VPN subscriber might otherwise return a call to the displayed VPN number of the calling party. However, since the network where the called party is currently roaming does not support CAMEL, the VPN service does not have the capability to connect a call from that subscriber to a VPN destination.

Call Forwarding -- Early or Late

What is difference between Early and Late Call Forwarding? Here is a possible explanation ....
Cellular telephones have become increasingly prevalent in today's society. The cellular telephone makes use of a cellular network and traditional telephone networks to route calls using radio communication signals. Two types of cellular networks have evolved—Global Systems for Mobile communications (GSM) and American National Standards Institute-41 (ANSI-41) type networks. ANSI-41 is also sometimes referred to as IS 41 (TIA/EIA [Telecommunications Industry Association/Electronic Industries Association] Interim Standard 41).
The two types of cellular networks use message formats that are not completely compatible with one another as they are. Thus, if a mobile subscriber (MS) using cellular communication, roams from one type of network to another, the messages sent by the MS may not be understood by the network into which it roams unless some sort of conversion is performed. In order to allow roaming between “foreign” type networks, a signaling message converter, referred to herein as an IWU (InterWorking/interoperability Unit) operates to interconnect calling and called Mobile services Switching Centers (MSCs). The IWU passes signaling messages back and forth between network entities while converting the format of these messages such that the messages can be properly interpreted by the receiving MSC.
However, even with known signal message converters, GSM standards are inherently different from the ANSI-41 standards mentioned above. One of these differences is in the operation of “late call forwarding” or the action of the system when a call to a mobile subscriber (MS) cannot be terminated, i.e. connection completed, for any of several specific reasons like call collision, no page response of a page request sent to the called MS, and the like. A GSM system expects the terminating Mobile service Switching Center (MSC) to handle the call forwarding while an ANSI-41 system expects the originating or home MSC of the MS to handle the call forwarding.
As is known by those skilled in the art, call forwarding may occur when a call, to a given MS, cannot be terminated. The call forwarding can be “early” or “late”. Early call forwarding is defined as occurring when a contact with the MS has failed due to predetermined circumstances occurring while attempting to extend the call to another network. Late call forwarding is defined as occurring when call forwarding is initiated after the call has been extended to the last known “foreign” public land mobile network location and contact with the MS has failed due to predetermined circumstances.
In view of the above, it would be advantageous to have a converter mechanism that provides for late call forwarding from the originating MSC when a MS roams from an ANSI-41 network to a GSM network.

In summary, If call is forwarded by HPLMN then it is ECF if by VPLMN then it is LCF.

Source: http://www.freepatentsonline.com/6615037.html