ITU-T Q.711 PDF

Scope and field of application

The Signalling Connection Control Part (SCCP) provides additional functions to the Message Transfer Part (MTP) to cater for both connectionless as well as connection-oriented network services to transfer circuit-related and non-circuit-related signalling information and other types of information between exchanges and specialized centres in telecommunication networks (e.g. for management and maintenance purposes) via a Signalling System No. 7 network.

A functional block above the message transfer part performs the functions and procedures of the SCCP. The SCCP is capable of using the services of the MTP as described in ITU-T Q.701 to ITU-T Q.707, and/or in ITU-T Q.2210. The combination of the MTP and the SCCP is called "network service part" (NSP).

The network service part follows the principles of the OSI-reference model as defined in ITU-T X.200, providing a subset of the layer 3 services defined in ITU-T X.213.

It is the intent of ITU-T Q.711, ITU-T Q.712, ITU-T Q.713 and ITU-T Q.714 to specify protocol entities which perform the functions according to the SCCP of the Signalling System No. 7. These protocol entities conform at their lower boundary to the upper boundary conditions specified in ITU-T Q.704 or ITU-T Q.2210 for use of the service offered by the underlying layers.

The SCCP making use of the services of the MTP, as specified in ITU-T Q.2210, provides the connectionless network service as specified in this Recommendation. A connection-oriented network service can only use the services which are common to ITU-T Q.2210 and ITU-T Q.704 for the MTP.

ITU-T Q.715 gives guidance on a number of specific issues related to the incorporation of SCCP in actual networks. These guidelines are in their entirety informal and do not specify any requirement.

The SCCP congestion control procedures may be subject to improvement pending further analysis of the impact of these procedures in different network scenarios and based on the results of operational experience. The overall objectives of the signalling connection control part are to provide the means for:

a) logical signalling connections within the Signalling System No. 7 network;

b) a transfer capability for network service data units with or without the use of logical signalling connections.

Functions of the SCCP are also used for the transfer of circuit-related and call-related signalling information of the ISDN user part with or without setup of end-to-end logical signalling connections. These functions are described in ITU-T Q.714 and ITU-T Q.730. Figure 1 illustrates the embedding of the SCCP within the Signalling System No. 7.