Like the ISUP layer, the TUP (Telephone User Part) layer provides an interface for applications to establish, maintain, and clear circuit switched connections with the SS7 network. The TUP layer is also responsible for circuit group management, such as blocking, unblocking, and resetting of circuits and circuit groups.
The TUP layer operates in accordance with the CCITT (ITU-T) recommendations Q.721 - Q.724 and China GF001 - 9001 (Technical Specifications of SS7 for the National Telephone Network of China). TUP is not used in ANSI networks, so there is no applicable ANSI standard for TUP.
TUP implements services through the configuration of general parameters and the following entities:
|
Entity |
Description |
|
Physical bearer circuits controlled by the TUP layer. Like the ISUP layer, circuits are identified by both a circuit index and a circuit identification code (CIC). The circuit index is a number unique across all circuits configured on a particular TX board. This number has only local significance. It is used between the TUP layer and the local call processing application to identify a particular circuit. The CIC (the kick or kick code) is used between signaling points (the SS7 TUP layer and the far exchange that terminates the other end of the circuit) to uniquely identify a particular circuit. The CIC must be configured at both ends of the circuit to identify the exact same bearer facility, for example, the same T1 span and timeslot. CICs need not be unique across circuits that terminate on different far exchanges. Circuits are specified in the TUP configuration file in groups. A group is one or more circuits with contiguous circuit indexes and contiguous CICs that terminate on the same far exchange and have common characteristics. A single circuit group is frequently used to represent all the timeslots on a single T1 or E1 span, for example. When defining a circuit group, only the circuit index and CIC of the first circuit in the group, along with the number of circuits in the group, are specified. The TUP layer derives the circuit index and CIC for subsequent circuits since they are considered to be contiguous. The starting circuit index and starting CIC for a group need not be the same value. | |
|
Define the interface between the TUP layer and the user applications. TUP supports only a single user application. Configure only one user SAP. | |
|
Define the interface between the TUP layer and the MTP layer. NSAPs identify the MTP network SAP to be used by the TUP layer, allowing multiple user parts (TUP, ISUP, and SCCP) to share access to the MTP layer services. |
The following illustration shows the concept of user SAPs and NSAPs: