Signalling Connection Control Part: Difference between revisions

Revision as of 01:56, 15 May 2007

Revision as of 15:20, 15 May 2007

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* '''Class 3''': Flow control connection oriented

* '''Class 4''': Error recovery and flow control connection oriented

The connectionless protocol classes provide the capabilities needed to transfer one Network Service Data Unit (NSDU) in the "data" field of an XUDT, LUDT or UDT message. When one connectionless message is not sufficient to convey the user data contained in one NSDU, a segmenting/reassembly function for protocol classes 0 and 1 is provided. In this case, the SCCP at the originating node or in a relay node provides segmentation of the information into multiple segments prior to transfer in the "data" field of XUDT (or as a network option LUDT) messages. At the destination node, the NSDU is reassembled.

The connection-oriented protocol classes (protocol classes 2 and 3) provide the means to set up signalling connections in order to exchange a number of related NSDUs. The connection-oriented protocol classes also provide a segmenting and reassembling capability. If an NSDU is longer than 255 octets, it is split into multiple segments at the originating node, prior to transfer in the "data" field of DT messages. Each segment is less than or equal to 255 octets. At the destination node, the NSDU is reassembled.<ref name="q714">[http://www.itu.int/rec/T-REC-Q.714/en ITU-T Recommendation Q.714] - Signalling connection control part procedures</ref>

===Class 0: Basic connectionless===

The SCCP Class 0 service is the most basic of SCCP transports. No provisionNetwork isService madeData forUnits breakingpassed blocksby ofhigher datalayers whichto arethe largerSCCP thanin the maximumoriginating sizenode ofare andelivered by the SCCP messageto intohigher smallerlayers piecesin the destination node. ClassThey 0are istransferred typicallyindependently usedof foreach non-criticalother. messagingTherefore, they may be delivered to the SCCP user out-of-sequence. AsThus, this protocol class corresponds to a pure [[connectionless protocol| connectionless network service]]. As a connectionless protocol, no transport-level dialog is established between the sender and the receiver.

===Class 1: Sequenced connectionless===