Signaling Connection Control Part

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Signaling Connection Control Part (hereinafter SCCP ) is in telecommunication networks such as the telephone network in the context of Signaling System No. 7 (abbreviated as SS7 used) network layer . It is used in the signaling network for routing , error correction and flow control and is based on the Message Transfer Part ( MTP ) level 3 ( MTP level 3 , MTP-3 ) in the context of the OSI layer model .

The original specifications of SCCP were set for the fixed network area by the ITU-T within the framework of the standards Q.711 , Q.714 and Q.715 . In addition, there are additional regional extensions, such as ETSI EN 300-009-1 published by the European Institute for Telecommunications Standards (ETSI) and the standard T1.112 in the USA by the American National Standards Institute (ANSI). There are also extensions such as the Generic Signaling Transport Service , which enables SCCP via the Internet Protocol (IP) and establishes the connection to IP telephony . It is specified in the Q.2150.0 standard.

Routing

An essential function of SCCP is routing that goes beyond MTP-3. SCCP offers various possibilities for this, which are summarized under the technical terms such as Point Code (PC), Subsystem Number (SSN) or Global Title (GT).

A Point Code addresses a particular SS7 network node while Subsystem Number references a particular application at the relevant network nodes. Global Title is used to globally determine the point codes for the mediation. The messages from SCCP consist of various parameters (indicators) such as the Address Indicator , Global Title Indicator and the Routing Indicator .

Protocol classes

In order to separate tasks, SCCP is divided into different protocol classes:

  • Class 0: Connectionless basic service ( English Basic connectionless ): Longer messages can be shared. Higher layers are responsible for the correct composition of these parts
  • Class 1: Connectionless service with sequence numbers, ( English Sequenced connectionless ): This number (SLS code) is 4 or 8 bits long (ITU-T or ANSI standard). Related messages use the same SLS code. If several links (linkset) are used for a message, the sequence number differs in the least significant bits.
  • Class 2: Connection-oriented basic service ( English Basic connection-oriented ): The signaling connection must be established and terminated.
  • Class 3: Connection-oriented basic service with flow control ( English Flow control connection oriented ).
  • Class 4: Connection-oriented error correction with flow control, ( English Error recovery and flow control connection oriented ).

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  1. ↑ Q.711 , Functional description of the signaling connection control part , (Engl.)
  2. ↑ Q.714 , Signaling connection control part procedures , (Engl.)
  3. ↑ Q.715 , Signaling connection control part user guide , (Engl.)
  4. ↑ ITU-T , Q-Series Recommendations , (Eng.)
  5. ↑ ETSI EN 300-009-1 , (English)
  6. ↑ Q.2150.0 , Generic Signaling Transport Service , (Eng.)