6 No.7 Signaling System

8/9/2019 6 No.7 Signaling System

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No.7 Signaling SystemV0701

ZTE UniversityMobile-MSS/WDSS Group


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Understand Basic Concepts ofNo.7 Signaling System

Know Stack of No.7 Signaling

System

Familiar with No.7 NetworkingStructure and Elements

Course Objectives


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Agenda

NO.7 Signaling System overview The Protocol stackNetwork architecture and elements


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What is Signaling?

SignalingSignaling

It is the dialog language for the communication between

various parts of the telecom network.

Signaling systemSignaling system

Signaling system includes a set of signaling and operation

procedure.Signaling system is the collection of software and hardware

which generate transmit receive and recognize the

signaling.


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CAS Vs CCS

Channel associated signaling:(CAS)

In addition to carrying the conversation or bearer, all

telephone bearer trunks also carried the signaling

information necessary to control the call concerned. Common channel signaling:(CCS)

Messages are carried on a separate digital signaling

network, logically apart from the actual voice traffic.

No.7 signaling system is a kind of Common Channel

Signaling System.


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Channel Associated Signaling

Exchange A

Exchange B

v+s

v+s

v+s

v+s


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Common Channel Signaling System

ExchangeA

ExchangeA

ExchangeB

ExchangeB

SignalingSignalingterminalterminal

S

v

v

v

v

SignalingSignalingterminalterminal


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Basic Concepts of No.7 Signaling

System

Signaling link SS7 messages are exchanged between network elements over

64k/s 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

is typically shared between the active links.

There can be up to 16 links in a linkset. The Links in the same LinkSet are sharing load.


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Route

When one SP is in communication with another, there is said to be aroutebetween the two. A route is the path that exists between any twoSPs. The

route may include 1 or 2 linksets.

The Links in the same Route are sharing load.

Routeset

A collection of routes to the same destination is known as a Routeset. Routes in the same RouteSet are priority-ranked.

Basic Concepts of

No.7 Signaling System _Cont.

Link

LinkSet

Route

RouteSet


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Networking Design Example 1

Link

Route2LinkSet2

Route 1 LinkSet 1

AB

RouteSet


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Networking Design Example 2

Link

LinkSet2

LinkSet 1

AB

Route


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Agenda

NO.7 Signaling System overview

The Protocol stack

Network architecture and elements


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NO.7 Signaling System

TUP DUP

ISUP

MTP3

SCCP

MTP2

MTP1

TCAP

INAP OMAP

MAP BSSAP

Physical

Layer

Data Link

Layer

Network

Layer

Application

Layer


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MTP1 is at the physical layer. The 1st level defines thephysical, electrical, and functional features of thesignaling data link .

Primarily serving as a two-way data transmissionchannel, it contains digital transmission channels witha basic rate of 64kb/s and signal terminal equipment.

Function of MTP1


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Function of MTP2

MTP-2 ensures accurate end-to-end transmission of a

message cross a signaling link. Level 2 implements flow

control, message sequence validation, and error checking.

When an error occurs on a signaling link, the message is

retransmitted.


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Function of MTP3

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 discrimination and message distribution.

Signal network management: involves management

of signal traffic, signal link and signal routing.


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Signal unit

An SS7 message is called a signal unit (SU).

There are three kinds of signal unit:


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Flag (F)

The starting flag indicates the start of a signal unit. The start

flag of a signal unit is usually the ending flag of the precedingsignal unit. The ending flag indicates the end of a signal unit,and has a flag code type of 01111110.

F F F F F

signal unitssignal unitssignal unitssignal units

01111110

start

start end

delimitation


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Length indication code (LI)

The 6-bit LI can store values between zero and 63.

If the number of octets which follow the LI and precede theCRC is less than 63, the LI contains this number. Otherwise,the LI is set to 63. An LI of 63 indicates that the messagelength is equal to or more than 63 octets (up to a maximumof 273 octets).

The maximum length of a signal unit is 279 octets: 273 octets(data) + 1 octet (flag) + 1 octet (BSN + BIB) + 1 octet (FSN+ FIB) + 1 octet (LI + 2 bits spare) + 2 octets (CRC).

LI Value Signal unit type

0 Fill-in signal unit

1-2 Link Status signal unit

3-63 Message signal unit


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Fill-in signal unit (FISU)

FISU is transmitted continuously on a signaling link in bothdirections when there are no other signal units (MSU or LSSU) totransmit. FISU carry basic level 2 information only (e.g.,acknowledgment of signal unit receipt by a remote signaling point).

FISU is used to keep the synchronization of signal links, so it isalso called the synchronization signal unit.

The first transmitted bit

F LI FIB FSN BIB BSN FCK

LI

0


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Link status signal unit (LSSU)

Link Status Signal Unit (LSSU) carry one or two octets (8-bit bytes)

of link status information between signaling points at either end of a

link. The link status is used to control link alignment and to indicate

the status of a signaling point (e.g., local processor outage) to the

remote signaling point.

LI

1~2Note: SF---- Status Field


F CK SF LI FIB FSN BIB BSN F


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Message signal unit (MSU)

The fill-in signaling unit and the link status signaling unit are sent

from the link control terminal (the second level), but the message

signaling unit is generated by the user part, and used to send the

user part messages. The length of MSU is variable, with a

maximum length of 272 bytes.

LI>2The first transmitted bit

F CK SIF SIO LI FIB FSN BIB BSN F


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Service Information Octet (SIO)

DCBA

Sub-service

Field(SSF)

Service

indication(SI)

DCBA


F CK SIF SIO LI FIB FSN BIB BSN F

8 16 8n(n2) 8 2 6 1 7 1 7 8

SSF SI


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Service Indicator

0000 signaling network management message

0001 signaling network test and maintenance message

0010 reserved

0011 SCCP

0100 TUP

0101 ISUP

0110 DUT(messages related to call and circuit)

0111 DUT (performance registration and canceling message)

1000 reserved for MTP to test the user part

1001 reserved

1010 reserved

1011 reserved

1100 reserved

1101 reserved 1110 reserved

1111 reserved


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Sub-Service Field

The sub-service field includes the indication code (bits C and D)

and two reserved bits (bits A and B). The network indication

codes are distributed as follows:

DCBA

00 international network

01 reserved (for international use only)

10 domestic network

11 reserved for domestic use


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Signaling Information Field (SIF)

The signaling information field consists of an integral number of [2,272] octets. The SIF in an MSU contains the routing label and

signaling information (e.g., SCCP, TUP, and ISUP message data)


F CKSIF SIO LI FIB FSN BIB BSN F


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Routing Label

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

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


SLS OPC DPC

4 14/24 14/24


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Principle of MTP3

MDC

MRT

MDTDPC=own SPC

DPCown SPC

MTP

2S

CCP,TUP

,ISUP,

SI

DPC&

SLS

MTP3

MDC: Message Discrimination

MDT: Message Distribution

MRT: Message Routing


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Relationship between

ZXC10 and NO.7 System

ZXC10ZXC10

transmission systemDTDT

2048kb/s

Level 1

Signaling link

Level 2

MPMP

Level 3

Message transfer partLevel 4

SPBSPB

semi-permanent connecting64kb/s

NET NET


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Agenda

NO.7 Signaling System overview

The Protocol stack

Network architecture and elements


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Signal transfer point (STP)

It refers to SP that transfer signaling messages from one signaling

link to another. They are the middle signaling points duringsignaling transfer.

STPs are usually setted in pairs, as they are linked to ensureredundancy and achieve routing reliability.

One key advantage of STP is that it enables a SP to signal to otherSPs without being directly connected to them.

B

Voice channels

A

Signaling link

C

SP A SP B

STP


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Signaling Mode _ Associated Mode

In this mode, messages related to the voice channelconnecting two switches are sent on the signaling link that

directly connects two switches, as shown in the Figure.

B

Voice channels

ASignaling link


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Signaling Mode _Quasi-Associated Mode

This can be called a special case of the non-associatedmode. In this mode, signaling messages between switchesA and B go through the several preset concatenatedsignaling links.

B

Voice channels

A

Signaling link

C


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6 No.7 Signaling System

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