05 no.7 signaling system

8/2/2019 05 NO.7 Signaling System

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Part5

NO.7 Signaling System


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Agenda

NO.7 Signaling System overview

The Protocol stack

Message Transfer Part

Network architecture and elements


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Overview :

Signaling System SS7 is the predominant signaling

system for the Public Switched Telephone Network(PSTN) and also Public Land Mobile Networks (PLMN).

SS7 defines the procedures for setting-up, managing and

clearing down calls between users, as well as non-circuit

related signaling.



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Voice group

Switch

net...

MPMP STB

signaling link

DT DT

Switch

net

STB



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Basic concept:

Signaling link:

SS7 messages are exchanged between network elements over 64

kilobit per second (kbps) bidirectional channels called signaling

links.

Signaling linkset:

Links are usually organized into groups known as linksets. A

linkset is a collection of links that share the same destination .

When links are collected in linksets, the total load of messages istypically shared between the active links.

There can be up to 16 links in a linkset


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Route:

When one SP is in communication with another, there is said to be a

route between the two. A route is the path that exists between any

twoSPs. The route may include a single linkset, or multiplelinksets;


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BA

Signaling link

C

SP ASP B

SP C

A, B and C areconnected to each other via signaling links.

In each case, we see twolinks, united in a linkset. Each SP node can be said

to have a route toeach other. However, the arrangement also allows for the

possibilitythat any two points can be reached indirectly via a third, as well as

directly.


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Link

Link Set 1

ROUTE1

ROUTE2

ROUTE3


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In the signaling hierarchy, we can see that the most fundamental

unit is link. Links are grouped in linksets, which make up routes,

to the same office ,we can built several different routes.

In the same way that links within a linkset can work together to

ensure secure transmission of information, the possibility of

supporting alternative routes to the same destination serves to

promote network security.


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Agenda


The Protocol stack




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The earliest structure of No.7 signaling protocol system

SCCPMTP3network layer

MTP2Data link layer

MTP1Physical layer

TUPISUP DUP

The earliest No.7 signaling technical specifications were based on

the circuit related phone control requirements.



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OSI model

MTP1MTP2MTP3

TCAP

ISP

(Intermediate

service part)

SCCP

CCITT No.7 Signaling functional class

TUP DUPISUP

presentation layer

session layer

Transport layer

Application layer

network layerdata link layerPhysical layer

OSI 1,2,3

OSI 4,5,6

OSI 7

MAP INAP OAMP



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Agenda


The Protocol stack




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MTP is further divided into MTP 1, MTP 2 and MTP 3,respectively

corresponding to layers 1, 2 and 3 of the 7-layer protocol.

1. Function of MTP1:

MTP1 is at the data link level, corresponding to the physical

layer in OSI. The 1st level defines the physical, electrical, and

functional features of the signaling data link . Primarily serving

as a two-way data transmission channel, it contains digital

transmission channels with a basic rate of 64kb/s and signal

terminal equipment.

MTP (message transfer part)


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MTP Level 2 ensures accurate end-to-end

transmission of a message cross a signaling link.

Level 2 implements flow control, messagesequence validation, and error checking. When

an error occurs on a signaling link, the message

is retransmitted.


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MTP3 performs the functions of a signaling network.

It is combined with the SCCP to form the OSI L3 functional

level.

Major functions:

Signal message processing: involves message routing, message

identification and message distribution.Signal network management: involves management of signal

traffic, signal link and signal routing.

.


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3.1 signaling messages Processing

Message routing:

To select a signaling link for each signaling message to be sent out.

Message distribution:

The process in which the destination point decides, after receiving

messages, to send messages to which user part or to the third level.

The decision shall be made by the service analysis indication code.


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Message Discrimination:

The process in which the signaling point determines whether this point is the destination point

of that message after receiving the message. Such decisions are based on analyzing the

destination point codes in message channeling.

If the signaling point is the destination point, the message is then sent to the message

distribution function part.

If it is not, and if the signaling point has the signaling transfer capacity, then the message shall

be sent to the message channeling function part so that it is then sent out on another signalinglink.


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MDC

MRT

MDTDPC=own SPC

DPCown SPC

MTP2

SCCP,TUP,IS

UP,DUP SI

DPC&

SLS

MTP3

MDC: Message Discrimination

MDT: Message Distribution

MRT: Message Routing


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Service Indicator: MTP User

0000 signaling network management message0001 signaling network test and maintenance message

0010 reserved

0011 SCCP

0100 the telephone user part (TUP)

0101 the ISDN user part (ISUP)

0110 the data user part (messages related to call and circuit)0111 the DUT (performance registration and canceling message)

1000 reserved for MTP to test the user part

1001

1010

1011

1100 reserved1101

1110

1111


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The routing label:

The routing label is comprised of the destination point code (DPC),

originating point code (OPC), and signaling link selection (SLS) field.

The first transmitted bit

SLS OPC DPC

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DPC is the destination signaling point code, indicating the signaling point the message

shall reach.OPC is the original signaling point code showing the original message signaling point.


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SLS is used for:

Ensure message sequencing. Any two messages sent with the same

SLS will always arrive at the destination in the same order in which

they were originally sent.

Allow equal load sharing of traffic among all available links. In

theory, if a user part sends messages at regular intervals and assigns

the SLS values in a round-robin mode, the traffic level should be

equal among all links (within the combined linkset) to thatdestination.


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ZXC10ZXC10

transmission system D TD T

2048kb/s

Level 1

Signaling link

Level 2

M PM P

Level 3

Message transfer partLevel 4

S T BS T B

semi-permanent connecting64kb/s

NET NET

C di l i b


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Corresponding relation about

ZXC10 and NO.7 system

No.7 DTI board MTP1

No.7 signaling board MTP2

MP board MTP3

MP board

UP


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AgendaNO.7 Signaling System overview

The Protocol stack




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1)Signaling point (local exchange)

It refers to the node in the signaling system that provides common

channel signaling.

SP can also be divided into 2 types:

Source points : OPC (Originating points code)

Destination points: DPC (Destination point code)

Actually, SP is part of a switching system.


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2)Signal transfer point (STP)

It refers to SP that transfer signaling messages from one signaling

link to another. They are the middle signaling points during signaling

transfer.

STPs are usually setted in pairs, as they are linked to ensure

redundancy and achieve routing reliability.

One key advantage of STP is that it enables a SP to signal to other

SPs without being directly connected to them.


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B

Voice channels

A

Signaling link

C

SP ASP B

STP

2_2_2 3_3_3

8_8_5


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Signaling code

OPC or DPC is 14-bit address for CCITT (24-bit for China)

International3bit-8bit-3bit

In CHINAthe frame is 8bit-8bit-8bit


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OPC and DPC is a opposite conception, but signaling point code (SPC) is absolute.

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 DSP for A. If other work in switch B, then

3_3_3 is OPC for B, and 2_2_2 is DPC for B.

B

Voice channels

A

Signaling link

C

2_2_2 3_3_3


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1)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, as shown in the Figure.

B

Voice channels

A

Signaling link

Signaling Mode


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2)The quasi-associated modeThis can be called a special case of the non-associated mode.In this mode, signaling messages between switches A and B gothrough the several preset concatenated signaling links.

B

Voice channels

A

Signaling link

CSTP

SP SP

Th 3 l l i li k


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B2

A2

A1

LSTP

HSTP

HSTPHSTP

D DD

DDD

DD

B1

C1

C2

A B

C

A

C

B

B

BB

B

SPSP

SP

SP

A A A A

A areaC area

B area

The 3-level signaling network


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The End

05 no.7 signaling system

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