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SS7 Basics

Signaling System 7 - SS7 Book

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   Signaling System 7 - SS7

The signaling system #7 (SS7) is an international standard network signaling protocol that allows common channel (independent) signaling for call-establishment, billing, routing, and information-exchange between nodes in the public switched telephone network (PSTN). SS7 system protocols are optimized for telephone system control connections and they are only directly accessible to telephone network operators.

Common channel signaling (CCS) is a separate signaling system that separates content of telephone calls from the information used to set up the call (signaling information). When call-processing information is separated from the communication channel, it is called "out-of-band" signaling. This signaling method uses one of the channels on a multi-channel network for the control, accounting, and management of traffic on all of the channels of the network.

An SS7 network is composed of service switching points (SSPs), signaling transfer points (STPs), and service control points (SCPs). The SSP gathers the analog signaling information from the local line in the network (end point) and converts the information into an SS7 message. These messages are transferred into the SS7 network to STPs that transfer the packet closer to its destination. When special processing of the message is required (such as rerouting a call to a call forwarding number), the STP routes the message to a SCP. The SCP is a database that can use the incoming message to determine other numbers and features that are associated with this particular call.

In the SS7 protocol, an address, such as customer-dialed digits, does not contain explicit information to enable routing in a signaling network. It then will require the signaling connection control part (SCCP) translation function. This is a process in the SS7 system that uses a routing tables to convert an address (usually a telephone number) into the actual destination address (forwarding telephone number) or into the address of a service control point (database) that contains the customer data needed to process a call.

Intelligence in the network can be distributed to databases and information processing points throughout the network because the network uses common channel signaling A set of service development tools has been developed to allow companies to offer advanced intelligent network (AIN) services

This diagram shows the basic structure of the SS7 control signaling system. This diagram shows that a customer's telephone is connected to a local switch end office (EO). The service switching point (SSP) is part of the EO and it converts dialed digits and other signaling indicators (e.g. off-hook answer) to SS7 signaling messages. The SS7 network routes the control packet to its destination using its own signal transfer point (STP) data packet switches using separate interconnection lines. In some cases, when additional services are provided, service control point (SCP) databases are used to process requests for advanced telephone services. This diagram also shows that the connections used for signaling are different than the voice connections. This diagram shows that there are multiple redundant links between switches, switching points, and network databases to help ensure the reliability of the telephone network. The links between points in the SS7 system have different functions and message structures. Access links (A-links) are used for access control between EOs and SCPs. Bridge links (B-links), cross links (C-links), and diagonal links (D-links) interconnect STPs. Extended links (E-links) are optionally used to provide backup connections from an EO to the SS7 network. Fully associated links (F-links) share (associate with) the connection between EOs.

SS7 System Diagram

Signaling System 7 - SS7 Diagram

   Related Signaling System 7 - SS7 Terms

A&B Signaling
Access Link - A Link
Access Tandem - AT
Active Signaling Link
Address Complete Message - ACM
Address Translation Gateway
Adjacent Signaling Points
Adjunct Processor - AP
Advanced Intelligent Network - AIN
Analog Signaling Link
Answer Message - ANM
Application Service Element - ASE
Application Service Provider - ASP
Backward Indicator Bit - BIB
Backward Sequence Number - BSN
Bridge Link - B Link
Broadband Integrated Services Digital Network - B-ISDN
Broadband Integrated Services Digital Network User Part - B-ISUP
CAMEL Application Part - CAP
Carrier Identification Code - CIC
Circuit Identification Code - CIC
Circuit Validation Test - CVT
Common Language Location Identification - CLLI
Cross Link - C Link
Customized Applications For Mobile Enhanced Logic - CAMEL
Destination Point Code - DPC
Diagonal Link - D Link
Extended Link - E Link
Extension Link
Fill In Signal Unit - FISU
Forward Indicator Bit - FIB
Fully Associated Link - F Link
Geographic Number Portability - GNP
Global Title - GT
Global Title Translation - GTT
Initial Address Message - IAM
Initial Alignment Procedure - IAP
Integrated Service Unit - ISU
Integrated Services Control Point - ISCP
Integrated Services Digital Network - ISDN
Integrated Services Digital Network User Part - ISDN-UP
Integrated Signal Transfer Point - ISTP
Intelligent Network - IN
Intelligent Network Application Part - INAP
Intelligent Network Server - INS
Intelligent Peripheral - IP
Intercept Access Point - IAP
Interexchange Carrier - IXC
Interim Link Management Interface - ILMI
International Gateway Facilities - IGFs
International Signaling Point Code
ISDN User Adaptation Layer - IUA
ISDN User Part - ISUP
Layer Management Entity - LME
Layer Management Interface - LMI
Line Information Database - LIDB
Link Status Signal Unit - LSSU
Management Information Base - MIB
Message Signal Unit - MSU
Message Transfer Part MTP
Message Transfer Part Level 3 - MTP3
Mobile Application Part MAP
MTP3 User Adaptation Layer - M3UA
Multifrequency Signaling - MF
Network Automatic Call Distribution - NACD
Network Gateway - NGW
Network Indicator
Network Layer
Number Portability
Operation, Maintenance and Administration Part OMAP
Originating Point Code - OPC
Permanent Virtual Circuit - PVC
Point Code - PC
Pre-Intelligent Network - Pre-IN
SCCP User Adaptation - SUA
SCTP Packet
Service Creation Environment - SCE
Service Information Octet - SIO
Service Management System - SMS
Service Number Portability - SNP
Service Switching Point - SSP
Session Description Protocol - SDP
Signal Unit - SU
Signaling Connection Control Part - SCCP
Signaling Control Point - SCP
Signaling Gateway - SG
Signaling Information Field - SIF
Signaling Link
Signaling Link Code
Signaling Link Selection Code - SLS
Signaling Point - SP
Signaling System 7 - SS7
Signaling Transfer Point - STP
Signaling Transport - SIGTRAN
Signaling Unit Error Rate Monitor - SUERM
Simple Network Management Protocol - SNMP
SS7 Protocol Stack
Stream Control Transport Protocol - SCTP
Switched Virtual Circuit - SVC
Telephone User Part - TUP
Temporary Location Directory Number - TLDN
Transaction Capabilities Application Part - TCAP
Trunk Side Connection

   Signaling System 7 - SS7 Books

Signaling System 7 - SS7 Book

more details

SS7 Basics, 3rd Edition

This book explains the operation of the Signaling System 7, and how it controls and interacts with public telephone networks and VoIP systems. SS7 is the standard communication system that is used to control public telephone networks. In addition to voice control, SS7 technology now offers advanced intelligent network features.

$34.99 Printed, $29.99 eBook


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