The SCCP layer supports global title translation, enabling applications to address messages with a string of digits such as a telephone number or a mobile identification number. Applications can rely on the network configuration to route the message to the correct destination signaling point and subsystem. Global title translations can help isolate applications from changes in the network structure, such as when a particular network database is moved from one signaling point code to another. This feature is available for both applications directly accessing the SCCP layer and for applications indirectly using the SCCP layer through the TCAP layer.
The SCCP layer can translate a global title into its final destination address (point code and subsystem number) or into the address of a gateway signal transfer point (STP). A gateway STP is typically an STP containing a global title translation capability that acts as the entry point to a network for all requests originating from outside the network. In either case, the global title digits can be carried through in the translated address for subsequent translation by the gateway STP or analysis by the destination application.
In the following example network illustration, the SCCP application uses both the 800 number translation services and the 900 number translation services provided by the databases shown:
In this example, the node does not know the network addresses (point codes) of these databases; only the address of the gateway is configured in the SS7 configuration files.
When the application sends a request for either an 800 number or 900 number translation, it generates a SCCP request (or TCAP request) with the 10-digit 800 or 900 number to be translated as the global title digits and the routing indicator field set to route by global title. The application does not include a point code or subsystem number in the destination address.
The following SCCP sample configuration file illustrates the configuration of the address translation.
The ADDRESS_MASK parameter for the user SAP that corresponds to this application is set to FFF0000000. This setting results in the SCCP layer choosing the first address translation entry with the first three digits matching the first three global title digits in the message address being translated.
The configured address translation for both 800 and 900 numbers specifies the point code of the gateway STP. The gateway STP performs subsequent global title translation on the message destination address to insert the actual point code of the appropriate database. A subsystem number is also included here, although it could also be inserted by the gateway STP.
The configured address translation for both 800 and 900 numbers specifies a routing indicator of route by global title to indicate to the gateway STP to perform global title translation. It also indicates that the original global digits are not to be replaced in the outgoing message so that the gateway STP can perform the subsequent translation.
# Sample configuration of Global Title Translation
< ... General Parameters >
# User SAP configuration for example application
USER_SAP 0 # Application 1
SWITCH_TYPE ANSI92 # protocol variant
CONC_PC 2.199.0 # Gateway STP
ADDR_MASK FFF0000000 # match 1st 3 global title digits
END # User application 0
# Address Translations: 800XXXXXXX numbers
ADDRESS 800 # global title - incoming
REPLACE_GLT FALSE # retain global title in message
SWITCH_TYPE ANSI # Address format - one of ITU, ANSI
NI_IND NATIONAL # national address format
DPC 2.199.0 # translated destination point code
SSN 254 # translated subsystem number
ROUTING_IND GLT # set outgoing routing flag to GLT
END # of address translation for 800xxxxxxx
# Address Translations: 900XXXXXXX numbers
ADDRESS 900 # global title - incoming
REPLACE_GLT FALSE # retain global title in message
SWITCH_TYPE ANSI # Address format - one of ITU, ANSI
NI_IND NATIONAL # national address format
DPC 2.199.0 # translated destination point code
SSN 254 # translated subsystem number
ROUTING_IND GLT # set outgoing routing flag to GLT
END # of address translation for 900xxxxxxx
< Route entry for gateway STP >
The address masks have the following properties:
Incoming messages use the address masks defined in the network SAP section of the SCCP configuration file.
Outgoing messages use the address masks defined in the user SAP section of the SCCP configuration file.
Up to four address masks can be defined in each network SAP or user SAP section.
Address masks are applied in the order they are defined in the configuration file. Therefore, list the most specific mask first and the most general mask last.