SS7 also known as Common Channel Signaling System 7 (CCS7) that uses channels separate from the communications channels for signaling and control purposes. SS7 significantly speeds call setup and call completion processes, allows access to databases that enable toll-free calling and number portability, and supports the CLASS (Customer Local Access Signaling Services) services such as caller ID, name ID, selective ringing (or priority ringing), selective call forwarding, call block (or call screen), repeat dial, call trace, and automatic call-back (call return).
It is optimized for use in digital telecommunication networks and designed to meet present and future information transfer requirements to provide reliable means for the transfer of information.
Here I try to discuss about elements of SS7 : Signalling Network, Signalling Point, Signaling Link, signaling Linkset and Signaling Route, and SS7 Transfer Mode.
Signalling Network
The signaling network consists of signaling point (SP), signaling transfer point (STP) and signaling link (Link). It is a supporting network independent from the communication network. The SS7 network consists of 3 levels. The architecture of SS7 can be shown in this picture :
SS7-architecture
Notes :
SCP Signaling Control Point
SSP Signaling Switching Point
STP Signaling Transfer Point
ED External Databases
IP Intelligent Peripherals
SMS Service Management System
SS7 Uses the first four layers of OSI model, which the first three to assure reliability (Message Transfer Part)
Signalling Data Link: Physical, Electrical and Procedural Characteristics. Signalling Link is for errorDetection/Correction,Sequencing, Alignment, Link Synchronization and Flow control.
Signalling Network is for messages and Procedures for Network Management and responsible for end-to-end routing.
The 4th for users applications using these protocols :
SCCP: Signaling Connection Control Part
TCAP: Transaction Capabilities Application Part
ISUP: ISDN User Part
TUP: Telephone User Part
If we compare SS7 layer and OSI layer can be shown like this :
SS7-OSI-Layer
Back to Signalling Network, we have four type Signalling Network : the international network, international standby network, national network, national standby network.
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Signaling type
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SPC type
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International network
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14-bit SPC
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II International Standby network
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14-bit SPC
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National network
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24-bit SPC
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National Standby network
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14-bit SPC
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SPC type describe Length of SPC in Signalling network.
I will continue then to discuss about Signalling Point ( SP ) in SS7 Network in the next article.
Slide 8
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[...] Link, Signaling Linkset and Signaling Route After reading basic concept of SS7, we can see the seven layer of SS7. The first three Layer SS7 has function to assure reliability [...]