A SEMINAR
ON
Signaling System
PRESENTED BY: SHASHANK DUBEY EC 3RD YR UNIV. ROLL NO.-1014131061
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Introduction to Signaling Systems
Signaling : Signaling is defined as a mechanism by virtue of which network
entities exchange information amongst themselves , which are required to set up a communication path.
Signaling system : Signaling system is defined as a set of methods or rules
followed by network entities to exchange information required for communication set up.
Examples of signaling systems :
CAS (Channel associated Signaling) CCS#7 (Common Channel Signaling #7) (Signaling System Number (SS7) is a form of Common Channel Signaling.)
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Areas of Signaling
There are mainly three areas of signaling during a telephone call : between subscribers and exchanges. within exchanges. between exchanges between exchanges.
Exchange A
Exchange B
within exchange
between Subscriber and exchange
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Channel Associated Signaling (CAS)
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Common Channel Signaling (CCS)
In CCS there is a common signaling channel which takes care of all the signaling information to be exchanged during communication. All other channels can be used for speech or data as required.
Speech
Exchange A
Speech
Exchange B
Common Signaling Channel
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Advantage of CCS over CAS
Faster call setup.
No interference between signaling tones by network and frequency of human speech pattern.
Higher signaling capacity.
Information Transfer:- CCS allows the transfer of additional information along with the signaling traffic providing facilities such as caller identification and voice or data identification.
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SS7 Principle
Out of band Signaling. Higher Signaling data rates (56Kbps & 64 Kbps). Signaling traffic is bursty and of short duration, hence operates in connectionless mode using packet switching. Variable length signal units with maximum size limitation. Optimum use of bandwidth. Reliability and flexibility.
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Why Out-of-Band Signaling are used in SS7?
Allows for the transport of more data at higher speeds. Allows for signaling at any time in the entire duration of the call, not only at the beginning. Enables signaling to network elements to which there is no direct trunk connection.
More efficient use of voice circuits.
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SS7 Components
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SS7 components
Service switching point (SSP) :
SSPs are switches that have SS7 software and terminating signaling links. SSPs create packets (signal units) and send those messages to other SSPs.
Signaling transfer point (STP) :
STPs are packet switches, and act like routers in the SS7 network. Routes each incoming message to an outgoing signaling link.
Service control point (SCP) :
An SCP is usually a computer used as a front end to a database system. It is an interface to application-specific databases.
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Basic Signaling Architecture
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SS7 Link Types
A link (access) B link (bridge) Connects signaling end point (SCP or SSP) to STP. Connects an STP to another STP.
C link (cross)
Connects STPs performing identical functions, forming a mated pair (for greater reliability).
Connects a secondary STP pair to a primary STP pair in a quad-link configuration. Connects an SSP to an alternate STP . Connects two signaling end points (SSPs and SCPs) in the same local network .
D link (diagonal)
E link (extended) F link (fully associated)
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What goes over Signaling Link
Signaling information is passed over the signaling link in form of messages, which are called signaling units (SUs).
Types of SUs are:
Message Link
signal units(MSUs).
status signal units(LSSUs).
signal units(FISUs).
Fill-in
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Signaling Unit Structure
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Features of SS7 over IP
Flow Control. Identification of the originating and terminating signaling points. Identification of voice circuits. Error detection, re-transmission and other error correcting procedures. Controls to avoid congestion on the internet.
Support for security mechanism.
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Thank You
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Questions/ Queries
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