Signaling
Basic Concepts of CCS 7
Training Center
Zhongxing Telecom Pakistan (Pvt.) Ltd
Overview
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The relationship between signaling
network and telecom network
The development of No.7 signaling
system
The development goal of No.7 signaling
system
The Development Goal
The general goal of the No.7 signaling system is
to suggest an internationally standardized
common channel signaling system with general
applications fields so that the digital
communication networks with digital SPC
switches can work in the best status.
Furthermore,
such networks can provide
sequential (Forming or characterized by a
sequence)and highly reliable transmission with
no loss and no repetition.
Signaling----Definition
It is the dialog language for the
communication between various parts
of the telecom network.
Signaling----Classification
Subscriber signaling: Between sub. & switch
Working area
inter-office: Control the setup and release of call
Monitoring signals: Monitor the changes of call
states or conditions in the lines
Signaling function
Selection signals： Routing information
Operation signals: Management and
maintenance of telecom networks
Channel Associated Signaling：
Transmitting
path
Common Channel Signaling
Common Channel Signaling (CCS)
In telephony, Common Channel Signaling (CCS), in the US also
Common Channel Interoffice Signaling (CCIS), is the
transmission of signaling information (control information) on a
separate channel from the data, and, more specifically, where
that signaling channel controls multiple data channels…….
Channel Associated Signaling (CAS)
Channel Associated Signaling (CAS), also known as per-trunk
signaling (PTS), is a form of digital communication signaling.
As with most telecommunication signaling methods, it uses
routing information to direct the payload of voice or data to its
destination. With CAS signaling, this routing information is
encoded and transmitted in the same channel as the payload
itself.
Common Channel Signaling System
v
ISDN
line
terminal s
Exchange B
v+s
Exchange A
Line
terminal
v
v
v
v
S
Signaling
terminal
Register
Register
Signaling
terminal
v+s
v
s
Line
terminal
ISDN
line
terminal
Channel Associated Signaling
Register
v+s
Line terminal
Register
v+s
Exchange B
Exchange A
Line terminal
v+s
v+s
v+s
v+s
Advantages of CCS
Compared with Channel Associated Signaling,
Common Channel Signaling has many
important advantages
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Information can be switched between
processors much faster than in channelassociated signaling.
With a huge signal capacity, it can hold
dozens or even hundreds of different kinds of
signals, thus providing more new services.
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With a great flexibility, it can provide more
new services simply by modifying software to
increase signals.
Line signaling device is not needed any more
at any trunk station, which shall greatly
reduce investment costs.
Since line signaling is no longer needed, trunk
devices can be used both in calls from A to B,
and in calls from B to A.
In such bi-directional working modes, even
less circuits are required than when trunk
circuits are respectively used in single call
directions.
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When a call is being set up, signals related to this call
can be sent. In this way, the subscriber can change
the already setup connections. For example, the
subscriber can transfer one call to another place, or
request a third party to join the present connections.
Signals can be switched between processors so as to
be used for maintenance or network management.
The No.7 line signaling can provide powerful support
for ISDN, IN, TMN (telecommunication management
Network)and cellular mobile communication systems,
as this signaling is their basis.
Disadvantages of CCS
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The error rate of the common channel
signaling system must be very low.
Its reliability must be much higher than the
channel associated signaling system. This is
because once the data link fails, all related
calls between the two related switches shall
be affected.
Bi-directional trunk working modes exist
conflict of seizure (A Sudden Disorder).
The SS7 systems that every transnational
corporation produces are having some
problems in compatibleness.
SS7 Protocol System Structure
User Part
ISUP
DUP
TUP
MTP3（NETWORK
SCCP LAYER）
MTP2（DATA Link LAYER）
MTP1（PHYSICAL LAYER）
Message
Transfer
Part
ISUP (ISDN User Part):
ISUP supports basic telephone call connect/disconnect
between end offices. ISUP was derived from TUP, but
supports ISDN and intelligent networking functions.
DUP (Data User part):
DUP defines the necessary call control, and facility
registration and cancellation related elements for
international common channel signalling by use of SS7
for circuit-switched data transmission services.
TUP (Telephone User Part):
TUP is an analog protocol that performs basic telephone
call connect and disconnect.
L4
L3
User part
Logical path
Logical
path
Signal network
function
L2
Signaling link Logical path
function
L1
Signaling data Physical path
link function
User part
Signal network
function
Signaling link
function
Signaling data
link function
Example
The President of a Chinese company is
communicating with the President of a
Pakistani Company , however neither speaks
the other’s language. Each employs an
English translator and the translated
messages are sent by the Fax operator over
physical communication channel. Thus, the
two presidents are communicating with each
other through five layers below them
Company A
(China)
Chinese President
Effective
Communication
Company B
(Pakistan)
Pakistani President
Write to paper
Write to paper
Translator
Translator
Print to paper
Print to paper
Fax Operator
Telegraph
Fax Operator
physical communication channel
Common Channel Signaling Network
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The CCS network consists of the following parts
Signaling point (SP)
It refers to the node in the signaling system
that provides Common Channel Signaling. SP can
also be divided into source points
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OPC (Originating Point Code)
The SP that generate signaling messages
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DPC (Destination Point Code)
The SP that receives signaling point code.
Signaling Transfer Point (STP)
It refers to SP that transfer signaling
messages from one signaling link to another.
They are neither source points, nor
destination points. That is, they are the
middle node points during signaling transfer.
OPC or DPC is 14-bit address (24-bit for China
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OPC or DPC is not absolute. OPC and DPC are
relative, the OPC of certain Office, for other
Offices, is DPC.
For example, the SP of switch A is 2_2_2,
and SP of switch B is 3_3_3. If you work in
switch A then 2_2_2 is OPC for A, and 3_3_3
is DPC for A.
Voice channels
B
A
2_2_2
Signaling link
C
3_3_3
SIGNALING LINK
It refers to the signaling message channel that
connects an SP and another SP( or STP).
SIGNALING LINK SET
A bunch of signaling links directly connecting two SP
(including STP) form one signaling link set.
ROUTE
One such set usually includes all parallel signaling links.
ROUTE SET
It is also possible to set several routes between two SP
ROUTE SET
ROUTE3
Link Set 2
ROUTE1
Link Set 1
ROUTE2
Link
The Associated Mode
In this mode, Messages related to the
voice channel connecting two switches
are sent on the signaling link that
directly connects two switches.
Voice channels
A
B
Signaling link
The Quasi- Associated mode
This can be called a special case of the nonassociated mode. In this mode, signaling
messages between switches A and B go
through the several preset concatenated
signaling links, but voice signals go through
the direct channels between A and B.
Normally, different transmission carriers are
used in the common channel signaling
systems and their related voice links.
Voice Channels
B
A
Signaling link
C
Functions of Signaling Data Link Level
The 1st level defines the physical,
electrical, and functional features of the
signaling data link, and is thus similar to
the OSI physical layer.
It determines the connection method
with the data link, and provides an
information carrier for the signaling link.
In digital transmission, signaling data
links are usually digital channels at
64kbit/s.
Functions of the Signaling Link Level
The second level defines the signaling
message transmission functions and
procedure related to its transfer on a
signaling data link.
The second level and the first signaling data
link used as a whole as an information
carrier, provide a signaling link between two
signaling points for the reliable transfer of
messages.
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Error check
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Error Correction
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FSN, BSN, FIB, BIB, Basic Error Correction and
Preventive Cyclic Retransmission (PCR)
Error Monitoring of Signaling Link
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16 bit Check Code
Prevents the retransmission when error occurs
Flow Control
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Prevent the link congestion if the load on the link
is too heavy
The Signaling Network Level
Within a signaling network, each switching
node is allocated a signaling point code,
which is 14-bit address (24-bit for China).
Every CCITT No.7 message then contains the
point code of the originating node (OPC) and
the destination point code or( DPC).
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Message Routing
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Message Distribution
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Selecting the signaling link that is used by
each signaling message to be transmitted
Send the message to a user part or level3functions after receiving the message
Message Authentication
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To determine whether a signaling point is
the destination point of a message after
the signaling point receives the message.
The User Part
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The user part is the fourth function
level of the NO.7 signaling system. Its
main function is to control the setup
and release of various basic calls.
The major user parts include the
telephone user part (TUP), the ISDN
user part (ISUP) and the signaling
connection control part (SCCP)
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Training Center