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

Facts about IN and CAMEL

Source: Book - Camel Intelligent Networks for the GSM, GPRS and UMTS Networks by Rogier Noldus

Intelligent networks (IN) is a technique that augments digital telecommunication networks with a method to lift the control over CS calls to a higher-layer control platform. These digital networks, which are based on signalling principles defined by ISUP, may include networks such as the integrated service digital network (ISDN), the public switched telephone network (PSTN) and the PLMN. Applying IN to any of these networks has in common that call establishment is intercepted at a designated node in the network. Control over the call is handed over to a control platform. The control platform determines how the establishment of this call shall continue.

What is CAMEL: Customized Applications for Mobile networks Enhanced Logic

CAMEL Services:

• Calling Name Presentation: The ability to provide the name of the calling party to the called party, allowing the called party to decide how to handle the call (e.g. the subscriber decides either to answer the call or let it go to voice mail). CAMEL is used to query a database that contains name information, which allows for a network-based service rather than programming the GSM phone to recognize caller names.
• Prepay and Account Spending Limit (ASL): Prepay and ASL utilize CAMEL to allow for metering usage on a prepaid basis and post-paid basis respectively. ASL has applications for those markets that are not debit based or credit-challenged but rather want to just manage usage. Markets include parental controls and corporate resource management.
• Incoming Call Management (ICM): CAMEL is leveraged to manage call termination attempts to customize subscriber’s inbound calling experience. The subscriber can decide how inbound calls will be automatically managed. Features include automatic call handling (example: route all calls except boss to voice mail for the next hour) fixed-to-mobile convergence capabilities such as routing to mobile when a fixed network number is called.
• Virtual Private Network (VPN): CAMEL enables a mobile VPN that replicates PBX-like
  dialling in a mobile environment. For example, this (typically) group-based feature allows one to hit the digits “2706” and then SEND to actually place a call to Gerry Christensen at 650-798-2706.
• Call Redirect Services (CRS): CAMEL is utilized to provide a variety of CRS services including redirecting international roamers to their own customer care when they dial “611”
• Location-based Services (LBS): CAMEL has been used in the United States to support FCC
  mandates for wireless emergency calling (e.g. dialling 9-1-1) from a mobile phone. CAMEL
  thus allows for call control, information to be passed to databases, call assistance for routing
  to a Public Safety Answer Point, and for query of LBS infrastructure such as the Gateway
  Mobile Location Center (GMLC) for more precise positioning data based on A-GPS or TDOA. Commercial (non-regulatory) LBS applications are emerging that will rely on CAMEL based directory services and location-based search and information.
  

CAMEL also enables hybrid applications that allow for both voice and data interaction.
CAMEL enables a simple and standard user interface for the end-user to engage in wireless data including SMS, MMS, and WAP.

CAMEL services may also be office-based, which means that any mobile phone user may use
the service, whether in their home system or while roaming, without pre-subscription. CAMEL
application triggering is based on events recognized by the Mobile Switching Center (MSC) rather
than relying on communication and instruction from the HLR/VLR to arm a trigger detection point.