A TX board can support as many as 32 SS7 links numbered 0 through 31, depending on the board model and board configuration. Additional TX boards can be added for more links.
MTP 2 uses SAPs (service access points) to support one or more applications. Each SAP corresponds to a single SS7 link controlled by the MTP 2 task. An application binds to a particular SAP at initialization time, specifying the link number (0 through 31). An application implementing MTP 3 repeats the bind process for all SS7 links on a TX board. Only one application is allowed to bind to each MTP 2 SAP (link). The following illustration shows MTP2 SAPs: