Data User Part (DUP), an application protocol in the SS7/C7 protocol suite, defines the necessary call control and facility registration and cancellation related elements for circuit-switched data transmission services. The data signaling messages are divided into two categories:
- Call and circuit related messages: used to set up and clear a call or control and supervise the circuit state.
- Facility registration and cancellation related messages: used to exchange information between originating and destination exchanges to register and cancel information related to user facilities.
While Data User Part (DUP) is still in use currently, but it is fallen out of favor except in certain parts of the world such as China.
The pouting label of DUP contains the DPS, OPC, BIC and TSC fields. It is contained in a signaling message and used to identify particulars to which the message refers. This is also used by the message transfer part to route the message towards its destination point.
The general format of the header of call and circuit related messages is shown as follows:
The general format of the header of facility registration and cancellation messages is shown as follows: