Signalling Connection Control Part: Difference between revisions

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{{distinguish|Skinny Client Control Protocol}}

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The '''SignalingSignalling Connection and Control Part''' ('''SCCP''') is a [[transportnetwork layer]]<ref>[http://www.itu.int/rec/T-REC-Q.1400/en/ ITU-T Recommendation Q.1400].</ref> protocol whichthat 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.

==Introduction==

'''Signaling Connection and Control Part''' ('''SCCP''') is a [[transport layer]] protocol which provides extended [[routing]], [[flow control]], segmentation, [[connection-oriented|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 recommendationrecommendations [http://www.itu.int/rec/T-REC-Q.713711/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/ whilstQ.713] as ANSI T1.112. The [[Telecommunication Technology Committee|TTC]] publishes as JT-Q.711 to JT-Q.714, inand Europe [[ETSI]] publishes ''[http://webapp.etsi.org/workprogram/Report_WorkItem.asp?WKI_ID=6605 ETSI EN 300 -009-1]:'', both of which documentsdocument itstheir modifications to the [[ITU-T]] specificationspecifications.

==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)

==ClassesProtocol of serviceclasses==

SCCP provides 54 classes of serviceprotocol 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.

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 serviceprotocol class is the most basic of the SCCP transportsprotocol classes. No provisionNetwork isService madeData forUnits breakingpassed blocksby ofhigher datalayers whichin the originating node are largerdelivered thanby the maximumSCCP sizeto ofhigher anlayers SCCPin messagethe intodestination node. They are transferred independently of smallereach piecesother. ClassTherefore, 0they ismay typicallybe useddelivered forto non-criticalthe messagingSCCP user out-of-sequence. AsThus, this protocol class corresponds to a pure [[connectionless protocol|connectionless network service]]. As a connectionless protocol, no transport-levelnetwork dialogconnection is established between the sender and the receiver.

===Class 1: Sequenced connectionless===

SCCP Class 1 builds on the capabilities of Class 0, with the addition of a sequence control parameter in the NSDU which allows the SCCP User to instruct the SCCP that a given stream of messages should be delivered in sequence. Therefore, Protocol Class 1 corresponds to an enhanced connectionless protocol with assurances of in-sequence delivery.

SCCP Class 1 allows for sending blocks of data which are larger than the maximum size of a single SCCP message. It permits this by splitting the data into pieces small enough to fit into an SCCP message and sending each piece separately. Upon receipt of a sequence of class 1 messages, the receiver will re-assemble the original data block in the correct order. As with SCCP Class 0, the Class 1 service is also connectionless.

===Class 2: Basic connection-oriented===

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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==

===Class 4: Error recovery and flow control connection oriented===

In the [[SIGTRAN]] suite of protocols, there are two primary methods of transporting SCCP applications across [[Internet Protocol]] networks: SCCP can be transported directlyindirectly using the [[M3UA|''MTP level 3 User Adaptation'' protocol (M3UA)]], a protocol which provides support for users of [[Message Transfer Part|MTP-3—including3]]—including SCCP. Alternatively, SCCP applications becan operate directly over the ''SCCP User AdapationAdaptation'' protocol (SUA) which is a form of modified SCCP designed specifically for use in IP networking.

Whilst SCCP Class 3 allows for error ''detection'', Class 4 supports re-transmitting messages when errors occur.

[[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 ==

==Transport over IP Networks==

<references/>

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

[[Category:Telephony]]

[[Category:ITU-T recommendations]]

[[Category:Signaling System 7]]