prezentare sumara ss7

8/10/2019 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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CS 31 SY 2005-2006

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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Provide caller ID

Call forwarding

Malicious call identification

Request to hold the connection


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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

prezentare sumara ss7

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