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Oct 30, 2013 (3 years and 9 months ago)

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Training Center

Zhongxing Telecom Pakistan (Pvt.) Ltd

Signaling

Basic Concepts of CCS 7

Overview


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.

Working area

Subscriber signaling: Between sub. & switch

inter
-
office: Control the setup and release of call

Monitoring signals: Monitor the changes of call
states or conditions in the lines

Selection signals


Routing information

Operation signals: Management and
maintenance of telecom networks

Signaling function

Signaling
----
Classification

Common Channel Signaling

Channel Associated Signaling


Transmitting
path

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
.




v+s

s


v

s


v

Line
terminal

Exchange

A

Register

Exchange

B

v+s

ISDN
line
terminal

Line
terminal

ISDN
line
terminal

Register

Signaling
terminal

S

v

v

v

v

Signaling
terminal

Common Channel Signaling System


Exchange A


Register

Register


Exchange

B


Line

terminal

Line terminal

v+s

v+s

v+s

v+s

v+s

v+s

Channel Associated Signaling


Advantages of CCS


Compared with Channel Associated Signaling,
Common Channel Signaling has many
important advantages



Information can be switched between
processors much faster than in channel
-
associated signaling.


With a huge signal capacity, it can hold
dozens or even hundreds of different kinds of
signals, thus providing more new services.



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.


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


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

SCCP

MTP3

NETWORK LAYER


MTP2

DATA Link LAYER


MTP1

PHYSICAL LAYER


TUP

ISUP

DUP

User

Part

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.



User part

Signal network


function

Signaling link


function

Signaling data


link function

L4

L3

L2

L1

Physical path

Logical path

Logical path

Logical path

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)

physical communication channel

Company B
(Pakistan)

Chinese President

Translator

Fax Operator

Write to paper

Print to paper

Pakistani President

Translato
r

Fax Operator

Write to paper

Print to paper

Effective
Communication

Telegraph


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


OPC (Originating Point Code
)



The SP that generate signaling messages


DPC (Destination Point Code)



The SP that receives signaling point code.

Common Channel Signaling Network

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

B

Voice channels

A

Signaling link

C

2
_
2
_
2

3
_
3
_
3


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.


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

Link

Link Set 1

Link Set 2

ROUTE1

ROUTE2

ROUTE3

ROUTE SET

B

Voice channels

A

Signaling 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.

B

Voice Channels

A

Signaling link

C

The Quasi
-

Associated mode



This can be called a special case of the non
-
associated 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.


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 Signaling Data Link Level

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.


Error check



16 bit Check Code


Error Correction



FSN, BSN, FIB, BIB, Basic Error Correction and
Preventive Cyclic Retransmission (PCR)


Error Monitoring of Signaling Link


Prevents the retransmission when error occurs


Flow Control



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).


Message Routing


Selecting the signaling link that is used by
each signaling message to be transmitted


Message Distribution



Send the message to a user part or level
-
3functions after receiving the message


Message Authentication



To determine whether a signaling point is
the destination point of a message after
the signaling point receives the message.


The User Part



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)

Zhongxing Telecom Pakistan (Pvt.) Ltd


Training Center


THANK YOU