SS7 - REQUEST and INDICATION primitives

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A low-level object or operation from which higher-level, more complex objects and operations can be constructed. In graphics, primitives are basic elements, such as lines, curves, and polygons, which you can combine to create more complex graphical images. In programming, primitives are the basic operations supported by the programming language. A programmer combines these primitives to create more complex operations, which are packaged as functions, procedures, and methods.

CCS (Common Channel Signaling)

CAS (Channel Associated Signalling)

TBD

SS7-SCCP (Signalling Connection Control Part)

Introduction



Terms/Abbreviations
SLR
DLR

DTAP

SS7 - ISUP Notes

Fully Associated Signaling
Quasi Associated Signaling

SS7 - ISUP

Terms/Abbreviations

CIC: Circuit Identification Code
OPC: Origination Point Code
DPC: Destination Point Code
SLS: Signalling Link Selection

COT (Continuity Test): To test continuity of bearer channel



ISUP Messages

Complete list of ISUP messages and descriptions:
http://www.asknumbers.com/SS7ISUPMessages.aspx

ACM (Address Complete Message)
An Address Complete Message (ACM) is sent in the "backward" direction to indicate that the remote end of a trunk circuit has been reserved.

The originating switch responds to an ACM message by connecting the calling party's line to the trunk to complete the voice circuit from the calling party to the called party. The terminating switch sends a ringing tone to the calling party's line.



ANM (Answer Message)
When the called party answers, the destination switch terminates power ringing of the called line, removes audible ringing tone from the calling line and sends an Answer Message (ANM) to the originating switch. The originating switch initiates billing after verifying that the calling party's line is connected to the reserved trunk.



Call Progress Message (CPG)
CPG is sent in either direction during the set-up or active phase of the call, indicating that an event, which is of significance, and should be relayed to the originating or terminating access, has occurred.


Circuit Group Response Message (CQR)
Sent in response to a Circuit/CIC Group Query message to indicate the state of all circuits/CICs in a particular range.


Circuit Group Reset Acknowledgement Message (GRA)
GRA is sent in response to a Circuit/CIC Group Reset message indicating that the requested group of circuits/CICs has been reset. The message also indicates the maintenance blocking state of each circuit/CIC.


Confusion Message (CFN)
CFN is sent in response to any message (other than a confusion message) if the node does not recognize the message or detects a part of the message as being unrecognized.


Connect Message (CON)
CON is sent in the backward direction indicating that all the address signals required for routeing the call to the called party have been received and that the call has been answered.

Continuity Message (COT)
COT is sent in the forward direction indicating whether or not there is continuity on the preceding circuit(s) as well as of the selected circuit to the following exchange, including verification of the communication path across the exchange with the specified degree of reliability.

Facility Reject Message (FRJ)
FRJ is sent in response to a facility request message to indicate that the facility request has been rejected.

Information Message (INF)
INF is sent to convey information in association with a call, which may have been requested in an information request message.


Information Request Message (INR)
INF is sent by a node to request information in association with a call.

ISUP - Continuity bit

ISUP - CPG

SS7 - Flow Control - SIB LSSU

SS7 - Signalling Link Alignment

There are two forms of alignment procedures: the emergency procedure and the normal alignment procedure. The emergency procedure is used when the link being aligned is the only available link for any of the routes defined within the SSP. Otherwise, the normal alignment procedure is used.

SS7 - MTP3 (Message Transfer Part 3)

MTP3 does message handling and network management.

Message handling


Signaling Link Management
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Signaling link activation,deactivation
SLTM - Signaling Link Test Message
SLTA - Signaling Link Test Acknowledge


Traffic Management
~~~~~~~~~~~~~~~~~~~~~~~~~~
Changeover (COO and COA)
COO - Change Over Order
COA - Change Over Acknowledgment
Changeback (CBD and CBA)
CBD - Change Back Declaration
CBA - Change Back Acknowledgment
Management inhibiting/Uninhibiting
MTP restart
Signaling traffic control
Forced rerouting
Controlled rerouting




Route Management
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
TFP (Transfer Prohibited)
FTR (Transfer Restricted)
TFC (Transfer Controlled)
TFA (Transfer Allowed)
SRSM (Signaling-route-set-test)




Clusters
~~~~~~~~~~~~~~



MTP3 Timers -
~~~~~~~~~~~~~~


Timer T17 : Timer T17 (MTP3) prevents the rapid oscillation from in service to out of service. Timer T17 is started when the link begins the alignment procedure. No further alignment attempts are accepted from a remote or local SP until T17 has expired.

SS7 - MTP2 (Message Transfer Part 2)

MTP2
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SIO - status indication out of alignment
SIN - status indication normal alignment
SIE - status indication emergency alignment
SIOS - status indication out of service
SIPO - status indication processor outage
SIB - status indication busy


BEC - Basic Error Correction
PCR (Preventive Cyclic Retransmission) Technique
Difference between BEC and PCR
Forced Retransmission
Signaling Link Alignment
Proving Period (T4)
AERM - Alignment Error Rate Monitor
SUERM - Signal Unit Error Rate Monitor
PO - Processor Outage


Link Alignment (Normal and Emergency Alignment)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~







MTP2 Flow Control (SIB - Status Indication Busy)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~




MTP2 Timers
~~~~~~~~~~~~~~~~~~~~~~~
T1
T2
T3
T4
T5 -- sending SIB (80 to 120 ms),
T6 -- remote congestion
T7 -- excessive delay of acknowledgment
T8

SS7 - Difference between SLS and SLC

SS7 - Links and books

SS7 Standards

List of SS7 Standards: http://www.c7.com/ss7/ss7_standards.htm

ITU-T Q Series standards: http://www.itu.int/rec/T-REC-Q/en



Books


Signaling System No. 7 (SS7/C7): Protocol, Architecture, and Services
by Lee Dryburgh, Jeff Hewett





























Signaling System 7
By Travis Russell

SS7 - Signalling System 7 - Introduction

Introduction
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~







Power point slide for this picture: SSP-STP-SCP.ppt








SSP: Service Switching Point
STP: Signal Transfer Point
SCP: Service Control point




Terms/Abbreviations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PC (Point Code) : Wikipedia page for point code




SS7 Stack
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~




MTP - Message Transfer Part
SCCP - Signalling Connection and Control Part
ISUP - ISDN User Part
TUP - Telephone User Part
TCAP -Transaction Capabilities
MAP - Mobile Application Part
INAP - Intelligent Network Application Part


Power point slide of this picture: SS7-stack.ppt













MTP Layer
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
FISU - Fill In Signal Unit
LSSU - Link Status Signal Unit
MSU - Message Signal Unit


Flag - 01111110 - Separates two message units.
BSN - Backward Sequence Number
BIB - Backward Indicator Bit
FSN - Forward Sequence Number
FIB - Forward Indicator Bit
The value of the LI (Length Indicator) field determines the signal unit type.

SIO - Service Information Octet
SIF - Signaling Information Field


Power point slide of this figure: FISU-LSSU-MSU.ppt






The FISU is sent when no other signal units are available.

The LSSU is used by the signalling link level to bring the link into alignment.

The MSU carries the actual upper-level information. For example, if ISDN User Part (ISUP) information is to be sent, it will be carried in an MSU.



Service Switching Point (SSP)

Signal Transfer Point (STP)

Service Control Points (SCP)

SS7 - notes

Few salient points
~~~~~~~~~~~~~~~~~~~~~~~






Terms and more
~~~~~~~~~~~~~~~~~~~~~~~


BEC (Basic Error Correction)


Telcordia administers ANSI Point Codes.
User Part Unavailable (UPU)
Mixed Linkset
Combined Linkset
Alias Point Code/Capability Point Code

quasi-associated route

Class3 Switch/Class 4 Switch



Switches are also known as exchanges; within the United States, the term exchange is used interchangeably with Central Office (CO) or End Office (EO).

Network signaling is also known as inter-switch signaling, network-network signaling, or trunk signaling.

PSTN (public switched telephone network) = Plain Old Telephone Service (POTS).

How voice circuit is reserved?
~~~~~~~~~~~~~~~~~~~~~~~~~~


What is the voice path?
~~~~~~~~~~~~~~~~~~

SS7 Signaling can do lot more ---
~~~~~~~~~~~~~~~~~~~~~~~~~~

• translate toll-free numbers into "routable" numbers
• validate credit and calling cards
• provide billing information
• remove faulty trunks from service
• provide the support for supplementary services (such as caller ID),
• roaming with your cellular telephone
• local number portability (LNP)

Non-circuit related signaling
~~~~~~~~~~~~~~~~~~~~~~~~~~

modern telephone networks can perform signaling while a call is in progress, especially for supplementary services—for example, to introduce another called party into the call, or to signal the arrival of another incoming call (call waiting) to one of the parties. In fact, since the 1980s, signaling can take place even when there is not a call in place. This is known as non-circuit related signaling and is simply used to transfer data between networks nodes. It is primarily used for query and response with telecommunications databases to support cellular networks, intelligent networks, and supplementary services. For example, in Public Land Mobile Networks (PLMNs), the visitor location register (VLR) that is in charge of the area into which the subscriber has roamed updates the home location register (HLR) of the subscriber's location. PLMNs make much use of non-circuit-related signaling, particularly to keep track of roaming subscribers.


TUP versus ISUP
~~~~~~~~~~~~~~~~~~~
ISUP resides at Level 4 of the SS7 stack with its predecessor, the Telephone User Part (TUP). TUP is still used in many countries, but ISUP is supplanting it over time. TUP also provides a call setup and release that is similar to ISUP, but it has only a subset of the capabilities. TUP is not used in North America because its capabilities are not sufficient to support the more complex network requirements.