From http://www.ss7-training.net/sigtran-training/ch07lev1sec3.html

"An alias Point Code is a secondary PC used, in addition to the unique primary Point Code, for identifying a node. Another common name for an alias is a Capability Point Code. Multiple nodes (usually two) share the alias PC; this allows messages to be routed to either node using a common PC. The alias PC is typically used to identify a pair of STPs. Its primary purpose is to allow the load sharing of SCCP traffic across the STP pair. Because SMH discrimination at either STP will accept a message with the alias PC, the message can be delivered to the SCCP User Part, where GTT is performed. Figure 7-11 shows an example using an alias PC. The PC for STP 1 is 200-1-1, and the PC for STP 2 is 200-1-2. The alias PC 200-1-10 is used to identify both STP 1 and STP 2. As a result, SSP A can route messages requiring SCCP GTT to 200-1-10 while load sharing across STP 1 and STP 2. Since STP 1 and STP 2 each must have a unique PC, SSP A cannot perform load sharing of SCCP traffic to the STP pair using the unique PC of either STP. However, the alias PC allows either node to accept and process the message."