Camel Subscription Information (CSI) explained.
In another tutorial, we have discussed the camel protocol. The tutorial mentions introductory information about the camel subscription information(CSI) along with other protocol details. Here we will discuss in detail the structure and components of the camel subscription information.
In CSI, subscription means, that a subscriber needs to have camel information in the subscriber profile on HLR or home location register. On the SS7 level, the information represents the address of gsmSCF and other parameters. A mobile subscriber may have camel information for various camel services. Examples are MO call, MT call, MO SMS, MT SMS, and Data. Each service has its own type of camel information. There may be different types/values for each parameter. To make it easy to understand, we will take the example of O-CSI or Originating Camel Subscription Information. O-CSI subscriber parameter is downloaded at gsmSSF during map protocol location update, if the location update procedure gets successful, upon MO call, gsmSSF sends the triggers to the gsmSCF.
Camel Subscription Information(CSI) parameters
- Detection Points (DPs): A DP is like a state for an activity from the mobile device e.g dialing a number. When DP occurs, gsmSSF interrogates gsmSCF for further actions. In O-CSI, there can be two detection points (DPs), collected info, and route select failure. First DP is triggered when a user dials a number and other when there is a call setup not possible.
- Service Key: A four bytes integer value. The same gsmSCF may serve multiple services. For example key one for MO-Call and the other for MT-Call.
- Default Call Handling: The parameter has two possible values, release or continue. When there is a communication failure between gsnSSF and gsmSCF, default call handling is used. Mostly it is configured as a release.
- gsmSCF address: This is the global title (Digits ) of gsmSCF.
On the collect info DP, SSF sends the Camel IDP to the SCP. The IDP has called a party SCCP address as gsmSCF address and a calling party address is the GT of gsmSSF. In IDP, there is a service key along with other many call-related parameters (eg calling, called numbers, etc.).