Signaling Connection Control Part (SCCP), a routing protocol in SS7 protocol suite in layer 4, provides end-to-end routing for TCAP messages to their proper database.

SCCP provides connectionless and connection-oriented network services above MTP Level 3. While MTP Level 3 provides point codes to allow messages to be addressed to specific signaling points, SCCP provides subsystem numbers to allow messages to be addressed to specific applications or subsystems at these signaling points. SCCP is used as the transport layer for TCAP-based services such as freephone (800/888), calling card, local number portability, wireless roaming, and personal communications services (PCS).

SCCP also provides the means by which an STP can perform global title translation (GTT), a procedure by which the destination signaling point and subsystem number (SSN) is determined from digits (i.e., the global title) present in the signaling message. The global title digits may be any sequence of digits, such as 800/888 number, pertinent to the service requested.

Protocol Structure

SCCP messages are contained within the Signaling Information Field (SIF) of an MSU. There are two formats for the SCCP messages: one is defined by ANSI and the other is defined by ITU-T.

SCCP: SS7 Signalling Connection Control Part

The SIF contains the routing label followed by the SCCP message header with the following structure:

• Routing label - A standard routing label C see the picture regarding the ANSI and ITU SCCP message for more information.
• Message type code - A one octet code which is mandatory for all messages. The message type code uniquely defines the function and format of each SCCP message.
• Mandatory fixed part - The parts that are mandatory and of fixed length for a particular message type will be contained in the mandatory fixed part.
• Mandatory variable part - Mandatory parameters of variable length will be included in the mandatory variable part. The name of each parameter and the order in which the pointers are sent is implicit in the message type.
• Optional part - The optional part consists of parameters that may or may not occur in any particular message type. Both fixed length and variable length parameters may be included. Optional parameters may be transmitted in any order. Each optional parameter will include the parameter name (one octet) and the length indicator (one octet) followed by the parameter contents.

Related protocols: SS7/C7, ASP, BICC, BISUP, DUP, ISUP, MTP, TCAP, TUP

Sponsor Source: SCCP is defined by ITU-T documents Q.713.

Reference: http://www.itu.int/itudoc/itu-t/rec/q/q500-999/q713_23786.html: Q.713: SCCP Specification