A global title translation (GTT) translates an array of phone numbers into an associated point code and subsystem for routing to another machine.
This topic presents the following information:
The following example is from a TCAP sample program that uses a global title. This example shows the setting of only the called address SCCP address structure:
tInfo.cdAddr.presInd = PRESENT;
tInfo.cdAddr.swType = SW_ANSI;
tInfo.cdAddr.subsystemInd = SUBSYS_NONE; /* A subsystem does not need to be defined */
tInfo.cdAddr.pointCodeInd = PTCODE_NONE; /* A point code does not need to be defined */
tInfo.cdAddr.glTitleInd = GLT_TT; /* A global title format MUST be selected */
tInfo.cdAddr.routingInd = ROUTE_GLT; /* The routing flag MUST be set to ROUTE_GLT */
tInfo.cdAddr.natIntInd = ADDRIND_INT;
//tInfo.cdAddr.subsystem = destssn; /* The subsystem is not required */
//tInfo.cdAddr.pointCode = pointCode; /* The point code is not required */
tInfo.cdAddr.glTransType = 1; /* The global title fields MUST be filled */
tInfo.cdAddr.encoding = ENC_BCD_EVEN;
tInfo.cdAddr.numPlan = NP_ISDN;
tInfo.cdAddr.natAddrInd = NATIND_NATL;
tInfo.cdAddr.glTitleLen = 5; /* The global title length is the BCD-encoded length*/
/* BCD encode the phone number */
for ( i = 0; i < 5; i++)
{
ch = gtitle[((i*2)+1)] - 0x30;
tInfo.cdAddr.glTitle[i] = (ch << 4) & 0xF0;
ch = gtitle[(i*2)] - 0x30;
tInfo.cdAddr.glTitle[i] += ch;
}
The global title must be BCD-encoded. The global title 8471234567 is BCD encoded as:
tInfo.cdAddr.glTitle[0] = 0x48;
tInfo.cdAddr.glTitle[1] = 0x17;
tInfo.cdAddr.glTitle[2] = 0x32;
tInfo.cdAddr.glTitle[3] = 0x54;
tInfo.cdAddr.glTitle[4] = 0x76;
The original global title was 10 digits long. When the global title is BCD-encoded, it is 5 bytes in length. This length is used as the global title length:
tInfo.cdAddr.glTitleLen = 5;
Once the application sends the TCAP message with the route by global title flag set, the SCCP task receives the message and attempts the global title translation. The SCCP task uses three steps to translate a global title:
The SCCP task masks the outgoing global title with the ADDR_MASK field in the USER SAP section of the SCCP configuration file.
In the previous example, the global title was 8471234567. An ADDR_MASK of FFF masks the first three digits of the global title. The result of the masking in the example is the first three digits - 847.
On incoming messages, the ADDR_MASK in the NSAP section of the SCCP configuration file masks global titles.
The SCCP task matches the masked result with the ADDRESS sections in the SCCP configuration file. If a matching section is not found, the SCCP message is returned to the application.
In the example, an ADDRESS 847 section is configured in the SCCP configuration file and matches the masked global title:
ADDRESS 847 # global title matching characters
REPLACE_GLT FALSE # do NOT replace the global title
SWITCH_TYPE ANSI # one of ITU, ANSI
NI_IND NATIONAL # one of NATIONAL, INTERNATIONAL
DPC 1.1.2 # translated destination point code
SSN 254
ROUTING_IND PC_SSN # set outgoing routing flag (PC_SSN or GLT)
END #
The SCCP task modifies the SCCP called address of the outgoing message. In the example, the outgoing message has a called address of:
cdAddr.pointCode = 1.1.2
cdAddr.subsystem = 254
cdAddr.routingInd = "Route by PC_SSN"
The global title specified by the application is also carried in the outgoing message.
Note: The point code used in the translated message must be listed as a ROUTE in the SCCP configuration file.
The most common variations to global title translation are presented.
A global title translation is forwarded to another node. The following example is a sample global title translation block (ADDRESS section) in the SCCP configuration file. 1.1.2 is the point code of the node that performs the global title translation:
ADDRESS 847 # global title matching characters
REPLACE_GLT FALSE # do NOT replace the global title
SWITCH_TYPE ANSI # one of ITU, ANSI
NI_IND NATIONAL # one of NATIONAL, INTERNATIONAL
DPC 1.1.2 # forward translation to this point code
ROUTING_IND GLT # set outgoing routing flag(PC_SSN or GLT)
END #
This translation forwards a message to another node (1.1.2) to do the global title translation.
The ROUTING_IND field is set to GLT (route by global title), which sets the routing flag in the outgoing message. The DPC field contains the point code of the node that receives the message and translates the global title. The SSN field does not need to be defined. The called address of the outgoing message is set to:
cdAddr.pointCode = 1.1.2
cdAddr.subsystem = "not encoded"
cdAddr.routingInd = "Route by Global Title"
The global title specified by the application is also carried in the outgoing message.
Note: The point code of the forwarded node must be listed as a route in the SCCP configuration file.
Set the ADDR_MASK in the USER SAP section of the SCCP configuration file to 0 (zero). Create an ADDRESS 0 translation block. This block now matches all global titles.
Remove the DPC field from the ADDRESS translation block. The called address DPC is not encoded in the outgoing message. Use the default routing option to provide an MTP header DPC.
Remove the SSN field from the ADDRESS translation block. The subsystem field specified by the application in the SCCP called address (if it exists) is inserted in the SCCP called address of the outgoing message.