Signalling Connection Control Part: Difference between revisions

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{{distinguish|Skinny Client Control Protocol}}

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The '''Signalling Connection Control Part''' ('''SCCP''') is a [[network layer]]<ref>[http://www.itu.int/rec/T-REC-Q.1400/en/ ITU-T Recommendation Q.1400].</ref> protocol that provides extended [[routing]], [[flow control (data)|flow control]], segmentation, [[connection-oriented communications|connection-orientation]], and [[error correction]] facilities in [[Signaling System 7]] telecommunications networks. SCCP relies on the services of [[Message Transfer Part|MTP]] for basic routing and error detection.

==Published specification==

The base SCCP specification is defined by the [[ITU-T]], in recommendations [http://www.itu.int/rec/T-REC-Q.711/en/ Q.711] to [http://www.itu.int/rec/T-REC-Q.714/en/ Q.714], with additional information to implementors provided by [http://www.itu.int/rec/T-REC-Q.715/en/ Q.715] and [http://www.itu.int/rec/T-REC-Q.716/en/ Q.716].<ref name="qseries">[http://www.itu.int/rec/T-REC-Q/en/ ITU-T Q-Series Recommendations].</ref> There are, however, regional variations defined by local standards bodies. In the United States, [[ANSI]] publishes its modifications to [http://www.itu.int/rec/T-REC-Q.713/en/ Q.713] as ANSI T1.112. The [[Telecommunication Technology Committee|TTC]] publishes as JT-Q.711 to JT-Q.714, and Europe [[ETSI]] publishes ''[http://webapp.etsi.org/workprogram/Report_WorkItem.asp?WKI_ID=6605 ETSI EN 300-009-1]:'' both of which document their modifications to the [[ITU-T]] specifications.

==Routing facilities beyond MTP-3==

Although [[Message Transfer Part|MTP-3]] provides routing capabilities based uponon the [[Point Code]], SCCP allows routing using a [[Point Code]] and [[Subsystem number]] or a [[Global Title]].

A Point Code is used to address a particular node on the network, whilstwhereas a [[Subsystem number]] addresses a specific application available on that node. SCCP employs a process called [[Global Title Translation]] (which is similar to determine [[DomainPoint name system|DNSCode]]s resolution infrom [[InternetGlobal Protocol|IPTitle]] networks) in order to determine Point Codes from Global Titless so as to instruct [[Message Transfer Part|MTP-3]] on where to route messages.

SCCP messages contain parameters which describe the type of addressing used, and how the message should be routed:

* '''Address Indicator'''

** ''Subsystem'Routing indicator'': The address includes a Subsystem Number'

*** ''Route on Global Title''

** ''Point Code indicator'': The address includes a Point Code

*** ''Route usingon Point Code/Subsystem numberNumber''

* '''Global title indicator'''

** ''No 'Global Titletitle indicator'''

*** ''No Global Title''
*** ''Global Title includes Translation Type (TT), Numbering Plan IndiciatorIndicator (NPI) and Type of Number (TON)''

*** ''Global Title includes Translation Type only''

** '''RoutingSubsystem indicator'''

*** ''RouteSubsystem usingNumber Global Title onlypresent''

*** ''Subsystem Number not present''

** ''Route using Point Code/Subsystem number''

** '''AddressPoint IndicatorCode Codingindicator'''

*** ''Point Code present''

*** ''Point Code not present''

* '''Global title indicatorTitle'''

** '''Address Indicator Coding'''

** ''Address Indicator coded as national'' (the Address Indicator is treated as international if not specified)

==Protocol classes==

SCCP provides 54 classes of protocol tofor its applications:

* '''Class 0''': Basic connectionless .

* '''Class 1''': Sequenced connectionless.

* '''Class 2''': Basic connection-oriented.

* '''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.

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===Class 0: Basic connectionless===

The SCCP Class 0 protocol class is the most basic of the SCCP protocol classes. Network Service Data Units passed by higher layers to the SCCP in the originating node are delivered by the SCCP to higher layers in the destination node. They are transferred independently of each other. Therefore, they may be delivered to the SCCP user out-of-sequence. Thus, this protocol class corresponds to a pure [[connectionless protocol|connectionless network service]]. As a connectionless protocol, no network connection is established between the sender and the receiver.

===Class 1: Sequenced connectionless===

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Class 3 service builds upon Class 2, but also allows for expedited (urgent) messages to be sent and received, and for errors in sequencing (segment re-assembly) to be detected and for SCCP to restart a connection should this occur.

==Transport over IP Networksnetworks==

In the [[SIGTRAN]] suite of protocols, there are two primary methods of transporting SCCP applications across [[Internet Protocol]] networks: SCCP can be transported indirectly using the [[M3UA|''MTP level 3 User Adaptation'' protocol (M3UA)]], a protocol which provides support for users of [[Message Transfer Part|MTP-3]]—including SCCP. Alternatively, SCCP applications can operate directly over the [[SUA|''SCCP User Adaptation'' protocol (SUA)]] which is a form of modified SCCP designed specifically for use in IP networking.

[[ITU-T]] also provides for the transport of SCCP users over [[Internet Protocol]] using the ''Generic Signalling Transport'' service specified in [http://www.itu.int/rec/T-REC-Q.2150.0/en/ Q.2150.0], the ''signalling transport converter'' for [[Stream Control Transmission Protocol|SCTP]] specified in [http://www.itu.int/rec/T-REC-Q.2150.3/en/ Q.2150.3] and a specialized ''Transport-Independent Signalling Connection Control Part'' (TI-SCCP) specified in [http://www.itu.int/rec/T-REC-Q.2220/en/ T-REC-Q.2220].

TI-SCCP can also be used with the ''Generic Signalling Transport'' adapted for [[Message Transfer Part|MTP3
]] and MTP3b as described in [http://www.itu.int/rec/T-REC-Q.2150.1/en/ Q.2150.1], or adapted for [[SSCOP]] or [[SSCOPMCE]] as described in [http://www.itu.int/rec/T-REC-Q.2150.2/en/ Q.2150.2].

== References ==

<references/>

== External links ==

* [http://www.iec.org/online/tutorials/ss7/ SS7 Tutorial] - SS7 tutorial, including SCCP description.

[[Category:ITU-T recommendations]]

[[Category:Signaling System 7]]

[[Category:Transport layer protocols]]

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