SS7 DUP: Data User Part

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 signalling 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.

Protocol Structure - SS7 DUP: Data User Part

The pouting label of DUP contains the DPS, OPC, BIC and TSC fields. It is contained in a signalling message and used to identify particulars to which the message refers. This is also use 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:

OPC - The originating point code (14bits) is the code applicable to the data switching exchange from which the message is sent.

DPS - The destination point code (14bits) is the code applicable to the data switching exchange to which the message is to be delivered.

BIC - Bearer identification code (12 bits).

TSC - Time slot code (8 bits). If the data circuit is derived from the data multiplex carried by the bearer, identified by the bearer identification code:

Heading code - The heading code (4 bits) contains the message type code which is mandatory for all messages. It uniquely defines the function and format of each DAP message.

Message specific parameters - Contains specific fields for each message.

DUP is defined by the ITU-T Q.741 (or X.61).

http://www.itu.int/rec/recommendation.asp?type=folders&lang=e&parent=T-REC-Q.741 : SS7 Data User Part