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Camel Protocol

What is CAMEL?

CAMEL is oftenly the termed as ‘Intelligent Network’ (IN), an enhancement of an existing network services that can be offered to mobile subscribers.

Because mobile subscribers could not use these service provider specific IN services when roaming outside their home network, there was the need to standardize the parameters that identify an IN service and the signaling protocol used to transmit service information between switch and the IN platform. This standard is called

Customized Applications in Mobile Networks, Enhanced Logic (CAMEL)

and applies to mobile networks only.

Today, the term ‘Intelligent Network’ is used for IN services based on a national solution as well as for CAMEL based IN services.

Subscribed IN Services

A subscriber-specific IN service according to the CAMEL standard is possible just for mobile subscribers. The subscribers must be subscribed on one side in the IN database and on the other side in the HLR database.

Friends and Family

With Friends & Family, customers enjoy an especially attractive rate for the numbers they call most frequently. The subscriber can update the Friends & Family list at any time. The numbers and speed-dialing codes on the personal Friends & Family profile apply to fixed or mobile phones alike.

Some operators realize this service solely by means of postprocessing the MCR tickets.

Prepaid Service

The prepaid service is a real bestseller. For prepaid services no contracts, no basic charges and no bills exist. The service provider may not even know the customer. Travelers who are temporarily in a foreign country can also use the service. Depending on the subscriber’s tariff, the dialed number and the remaining prepaid account, the IN calculates a maximum calling period that is granted to the caller.

Personal Number Service

This service is also known as ‘Mobile Access Hunting MAH’. It guarantees for the subscriber that he can be reached on one single number at any terminal, regardless of whether it is in a fixed or in a mobile network. Usually he can administrate these numbers himself. In his subscriber profile the subscriber also determines which calls must always be put through and which are to be rejected by diverting them to a voice mail system.

Virtual Private Network Service

Virtual Private Networks allow business customers, regardless of the company size, to optimize their communication costs. VPN allows subscribers to set up their own private networks using public network resources. Virtual Private Networks represent a cost-saving alternative to private networks, since they do not require Private Branch Exchanges (PBX) and leased lines. The private networks can easily be integrated into a VPN. VPN is also advantageous for companies with several smaller locations spread over a large area. VPN users are furnished with their own private numbering plan and private exchange features.

The flexible charging options enable the service provider to customize the service to individual new target groups.

CAMEL Subscription Information (CSI)

Via the HLR provisioning, it is possible to specify individual CSI to mobile subscribers. For example,  that all mobile originating calls (MOC) and/or mobile terminating calls (MTC) always result in interrogation of the Camel Services Environment (CSE).

Services of this kind are identified by the CAMEL Subscription Information (CSI).

Furthermore, the CSE may be informed about the invocation of  supplementary service ‘Multiparty’ in order to inform the prepaid service logic about this event.

The HLR-relay function allows to forward received USSD-strings from HLR to an external entity if a general or subscriber specific global title was assigned to that USSD-code in the HLR.

Each subscriber can be marked with more than one CSI. All CSIs contain the following supplements:

  • Trigger Detection Point (TDP)
  • gsmSCF address (E.164 number)
  • Service Key
  • Default Call Handling


The O-CSI belonging to an IN service for MOC is sent to the VLR together with the other mobile subscriber data during a location update. With the help of this O-CSI the subscriber is identified as a CAMEL subscriber.

The T-CSI belonging to an MTC service is retained in the HLR and is made available during the interrogation procedure.

The GPRS-CSI is received within the SGSN when processing GPRS attach requests or routing area updates. On setup of a session this CSI will be evaluated and a dialogue between the SGSN and the SCP/CSE is established.

The SS-CSI is sent to the VLR together with the other mobile subscriber data during a location update. With the help of this SS-CSI a MAP notification message to the CSE is triggered in order to inform a service logic about the invocation of the supplementary service Multiparty.

A received USSD string (sent by the MS) is evaluated in the HLR and, depending on the specified service code, relayed to e.g. a gsmSCF. USSD CAMEL Subscription Information (U-CSI) and USSD General CAMEL Subscription Information (UG-CSI) are applied to determine the gsmSCF address depending on the service code.


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