What is Signaling Connection Control Part (SCCP)?

The Signaling Connection Control Part (SCCP) is an improvement to the MTP Level 3 which is known to provide connection-oriented and connectionless services, and the SCCP also provides an enhancement to address translation capabilities.

Given Diagram provides a clear view of the improvements that SCCP provides over MTP services and the SCCP also provides a network service that is equivalent to the OSI Network third Layer.

SCCP 

SCCP Addressing Translation:

MTP has a limited or ranged capability of routing and delivering messages to the exact signaling point based on the (DPC) destination point code. Once it has received the message, then the message is forwarded to the user with the correct MTP user within the signaling point which depends on the value of the service indicator that is residing within the signal information octet.

The SCCP manages an additional global title address translation function. an address as dialed digits for voice, data, ISDN, or mobile networks, like the addresses which cannot be routed directly are known as Global title. This number is converted into a DPC and sub-system number (SSN) by the SCCP. SCCP user at a signaling point is identified by the SSN.

The SCCP management, OMAP, and ISDN-UP are examples of SCCP users. A similarity between the SSN and the service indicator in the MTP routing is there but the MTP routing allows for 255 unique sub-systems to be declared at the signaling point.

Protocol class in SCCP:

SCCP provides four protocol classes which are: 

• Class 0: Basic connectionless.
• Class 1: Sequenced connectionless.
• Class 2: Basic connection-oriented.
• Class 3: Flow control connection-oriented.

The connectionless protocol classes are able to provide the capabilities that are needed to transfer one Network Service Data Unit (NSDU) in the “data” field of a XUDT, LUDT, or UDT message. When one connectionless message is not enough to send or transfer the user data which is stored in one NSDU, then a segmenting/reassembly function for protocol classes 0 and 1 is enabled.

For exchanging a number of related NSDUs the connection-oriented protocol classes (protocol classes 2 and 3) provides the facilities to set up the signaling connection. Reassembling and segmenting capabilities are also provided by the connection-oriented protocol classes. If the NSDU exceeds 255 octets, it is split into multiple segments at the corresponding originating node then the “data” field of DT messages is transferred. Where each segment is equal to or less than 255 octets. NSDU is reassembled at the destination node.