Global Title Translation
SS7 Tutorial
Global Title
Copryright SS8 Networks - 2002
Before we get deeply into the subject of Global Title, it might help to get a very broad view of exactly what Global Title is. Simply defined, it is an address. But it is not an address of a node in the SS7 network (DPC, SSN). Instead, it is an alias for such an address that needs to be translated into an SS7 network address. With that definition out of the way, let’s quickly review what we know about SS7 addressing in general. To begin with, each User Part approaches addressing in a different way. The MTP (Message Transfer Part) has a job that is limited to reliably transferring messages over the links in a link set. That is, MTP only cares about the address of the node at the other end of the links it is tending. Therefore the only addressing the MTP requires is the SPC (Signalling Point Code) of the node at the end of its links. MTP sees this address as the Destination Point Code (DPC) of all messages it sends over the links. The only concern MTP has for any other location in the network is to be able to make use of the final destination of the message to help it pick out one link set from all the available linksets as the best one to use for sending the message. This is what MTP routing is all about. ISUP addressing is different. In normal Call Control use, ISUP addresses a switch at the other end of its trunk connections. For the SS7, this too means using a Destination Point Code (DPC). But the switch ISUP talks to (which is the next switch in a circuit being set up or torn down) is not necessarily (and really not likely) to be located at the other end of its own SS7 links. The job of addressing all other locations falls to the SCCP. Actually SCCP could be used to address the same switching locations as ISUP. If it were used in this way, SCCP could be used for end-to-end signal routing in conjunction with ISUP. But since the usual switch-to-switch routing of ISUP provides complete circuit
Global Title
Copryright SS8 Networks - 2002
Before we get deeply into the subject of Global Title, it might help to get a very broad view of exactly what Global Title is. Simply defined, it is an address. But it is not an address of a node in the SS7 network (DPC, SSN). Instead, it is an alias for such an address that needs to be translated into an SS7 network address. With that definition out of the way, let’s quickly review what we know about SS7 addressing in general. To begin with, each User Part approaches addressing in a different way. The MTP (Message Transfer Part) has a job that is limited to reliably transferring messages over the links in a link set. That is, MTP only cares about the address of the node at the other end of the links it is tending. Therefore the only addressing the MTP requires is the SPC (Signalling Point Code) of the node at the end of its links. MTP sees this address as the Destination Point Code (DPC) of all messages it sends over the links. The only concern MTP has for any other location in the network is to be able to make use of the final destination of the message to help it pick out one link set from all the available linksets as the best one to use for sending the message. This is what MTP routing is all about. ISUP addressing is different. In normal Call Control use, ISUP addresses a switch at the other end of its trunk connections. For the SS7, this too means using a Destination Point Code (DPC). But the switch ISUP talks to (which is the next switch in a circuit being set up or torn down) is not necessarily (and really not likely) to be located at the other end of its own SS7 links. The job of addressing all other locations falls to the SCCP. Actually SCCP could be used to address the same switching locations as ISUP. If it were used in this way, SCCP could be used for end-to-end signal routing in conjunction with ISUP. But since the usual switch-to-switch routing of ISUP provides complete circuit