prezentare sumara ss7
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CS 31 SY 2005-2006
Signaling System No. 7
William Emmanuel S. YU
Department of Information Systems andComputer Science
Ateneo de Manila University
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Acronyms
SSP - service switching points
STP - signaling transfer points
SCP - service control points
DTMF dual tone multi-frequency
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Signaling System #7 (SS7)
The protocol that governs the operation of the
PSTN
sets up and tear down local and long distance
phone calls
digital technology which allows extra value-
added features
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History
SS6 was a packet-based network using
messages like those of the X.25 packet network
SS6 used a 2.4kbps at first, then upgraded thisto 4.8kbps data links
SS6 evolved into SS7 which is now the signaling
standard of the whole world
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Network Details
56-kbps or 64-kbps full-duplex digital signaling
dedicated packet data network
Common Channel Signaling - data network isseparate from the voice network
Provides network management functionality
through the data network
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Signaling
Basic functions
addressing
supervision
points of signaling
between subscriber and CO
between COs
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Types of Signaling
Conventional - DC signals using DTMF between
subscriber and CO and SF between COs
DC Signaling - uses direct current to signaldistant offices (e.g. E&M or ear and mouth
signaling)
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Types of Signaling
In-band Signaling - where DC signaling is not
possible like in tandem offices, uses DTMF, MF,
and SF, and transmits over the same voicecircuit used
Out-of-band Signaling - used for analog carrier
systems, it sends tones over a differentbandwidth (e.g. in an unused 3.7kHz bandwidth
in some POTS)
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Connecting to the SS7 CloudSCPSCP
STP
STP STP
STP
SSP SSP
PBX PBXBRI BRIResidential
PRIPRI
CO
LL
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SS7 Network Elements
SSP SCP STP
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Service Switching Point (SSP)
Perform call processing in behalf of the user
(CPE)
Serve as the source and destination for SS7messages
Talks to another SSP or to an STP
Implemented at end offices or access tandem
devices
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Signaling Transfer Point (STP)
Translates SS7 messages
Routes SS7 messages between network nodes
(e.g. STP, SSP) and databases (e.g. SCP)
Relay SS7 messages between SSPs, STPs, and
SCPs
Similar to OSI Layer 3 (Network Layer)
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Service Control Point (SCP)
Contains software and databases for the
management of calls
Provides toll-free (800) call services and routing
Receives queries from and return responses to
SSPs through STPs
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SS7 Operation
Source UP generates a message and sends it to
a destination UP through an STP
STP routes messages using information in themessage like routing labels, source and
destination address
Routes are fixed unless a network failure occurs
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Some Functions of SS7
Setup and clear down a telephone call
Called partys line is free
Provide subscriber busy signal
Indicate when a called partys line is out of
service
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Some Functions of SS7
Provide caller ID
Call forwarding
Malicious call identification
Request to hold the connection
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Some Functions of SS7
Furnishes toll-free services
Charging information
Language of assistance operators
Security access calls (CUG)
Use of echo-suppression
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SS7 Evaluation
Very successful and used by practically all the
(PSTN) carriers in the world
Success was almost assured because itspredecessors were woefully inadequate
Some of the features appear in GSM (Global
Mobile System) and even satellite signaling
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