04 no.7 signaling system

7/31/2019 04 NO.7 Signaling System

1/58

NO.7 SignalingSystem


2/58

NO.7 Signaling System overview

The Protocol stack Message Transfer Part

call control protocol

Network architecture and elements


3/58

overview :Signaling System SS7 is the predominant signaling system

for the Public Switched Telephone Network (PSTN) andalso Public Land Mobile Networks (PLMNs). SS7 defines

the procedures for setting-up, managing and clearing downcalls between users, as well as non-circuit related signaling.

NO.7 Signaling System


4/58

Channel associated signaling:(CAS)In addition to carrying the conversation or bearer

content ,all telephone bearer trunks also carried

the signaling information necessary to control thecall concerned.

Common channel signaling:(CCS)

messages are carried on a separate digital signaling

network, logically apart from the actual voice traffic"


5/58

Voice group

switch

net

Switch

net

..

.

MPMP

Sign

alin

gterm

inal

Sign

alin

gterm

inal

signaling

link

DT DT



6/58

Advantage :

Speed is fast Information can be switched between

processors much faster than in channel-associated

signaling.

Signaling capacity is larger With a huge signal

capacity, it can hold dozens or even hundreds of

different kinds of signals, it is the basic of PLMN

network.

advantage and disadvantage of no.7 signaling



7/58

disadvantage

1) 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.

2) The SS7 systems that every transnational

corporation produces are having some problems

in compatible.



8/58

signaling link:

SS7 messages are exchanged between network elements over 64 kilobitper second (kbps) bidirectional channels called signaling links.

Signaling occurs out-of-band on dedicated channels rather than in-bandon voice channels.

Signaling linkset:Links are usually organized into groups known as linksets. A linkset is acollection 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


9/58

route:

When one SP is in communication with another, there is saidto be aroute between the two. A route is the path that existsbetween any twoSPs. The route may include a single linkset,or multiple linksets;

routeset:

A collection of routes to the same destination is known as a

Routeset.


10/58

BA

Signaling link

C

SP ASP B

SP C

three SPs (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.


11/58

LinkLink Set 1

Link Set 2

ROUTE1

ROUTE2

ROUTE3

ROUTE SET


12/58

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

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

routesets.

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.


13/58


The Protocal stack Message Transfer Part




14/58

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


15/58

OSI model

MTP1MTP2MTP3

TCAP

SCCP

CCITT No.7 Signaling functional class

TUP DUPISUP

Transport layer,

session layer and

presentation

layer

Applicationlayer

Physical layer,data linklayer andnetwork layer

OSI 1,2,3

OSI 4,5,6

OSI 7

MAP INAP OAMP



16/58


The Protocal stack Message Transfer Part




17/58

MTP(message transfer part):

MTP is further divided into mtp1 ,mtp2 and mtp3,respectively

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

1. Function of MTP1:

MTP1 is at the data link level, corresponding to the physicallayer 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.


18/58

2. Function of MTP2:MTP Level 2 ensures accurate end-to-end transmission of amessage cross a signaling link. Level 2 implements flowcontrol, message sequence validation, and error checking.When an error occurs on a signaling link, the message is

retransmitted.MTP Layer 2 is also responsible for the assembly of

outgoing messages into packets known as signaling units,

of which there are three types .


19/58

3. Function of MTP3:

MTP3 performs the functions of a signaling network. It is combinedwith

the SCCP to form the OSI L3 functional level. The major functions of

this layer are signal message processing and signal network

management.Signal message processing involves message routing, message

identificationandmessage distribution.

Signal network management involves management of signal traffic, signal

link and signal routing.

MTP Level 3 routes messages based on the routing label in the

signaling information field (SIF) of message signal units.


20/58

4. Signal unitAn SS7 message is called a signal unit (SU). Thereare three kinds of signal units:

Fill-In Signal Units (FISUs),

Link Status Signal Units (LSSUs)

Message Signal Units (MSU)


21/58


22/58

1) Fill-in signal unit (FISU)

FISUs are transmitted continuously on a signaling link in both directions

When there are no other signal units (MSUs or LSSUs) to transmit. FISUscarry basic level 2 information only (e.g., acknowledgment of signal unitreceipt by a remote signaling point).

FISU is used to keep the synchronization of signal links, so it is also

called the synchronization signal unit.

The first transmitted bit

F LI FIB FSN BIB BSN FCK

LI0


23/58

2) Link status signal unit (LSSU)

Link Status Signal Units (LSSUs) 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.

LSSULI1~2

Note: SF---- Status Field The first transmitted bit

F CK SF LI FIB FSN BIB BSN F


24/58

3) Message signal unit (MSU)

The fill-in signaling unit and the link status signaling unit are sentfrom 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.

MSULI>2The first transmitted bit

F CK SIF SIO LI FIB FSN BIB BSN F


25/58

The meanings of the various fields are as follows:

1) 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 preceding

signal 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 units

signal units

01111110

start

start end

delimitation


26/58

F F F01111110

01111110 01111110

F F F010111110

In order to ensure that 01111110 code do not appear in other parts

of the unit, after fifth 1 (with more than 6 continuous 1s) we

appended a 0 in outgoing end, and remove it in receiving end.

False flag

F??


27/58

2) 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 the CRC is less than 63, the LI contains this

number. Otherwise, the LI is set to 63. An LI of 63 indicates that the message

length is equal to or more than63 octets (up to a maximum of 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 type0 Fill-in signal unit

1-2 Link Status signal unit

3-63 Message signal unit


28/58

3) Sequence number (FSN, BSN):

the forward sequence number (FSN) is the No. of the signal unit

itself.

the backward sequence number (BSN) contains the sequence

number of the signal unit being acknowledged.

Both forward sequence number and backward sequence number

are binary numbers with a length of 7 bits, in the circular

sequence from 0 to 127.




29/58



4) The indication bits (FIB, BIB):

together with FSN and BSN, the forward indication bit (FIB)

and the backward indication bit (BIB) are used for basic error

control, with a length of 1 bit, so as to perform the signal unit

sequence number control and acknowledgment.

5) The check code (CK): each signal unit has the 16-bit check

code ,The CRC value is used to detect and correct data transmission

errors.


30/58

SPA SPB


FLIFIBFSNBIBBSNF CK

FIB0

FSN

0

BIB?

BSN?

FIB0

FSN

0

BIB?

BSN?

010 0 0 0 1 0

21

3 2020 0

10 2 0

0 3 0 1

1 0 3 0

21 4 0

BIB

reverse

0 4 0 2

0 5 0 3

1 3 0 4

4

3

5

CK

error

1


31/58

6) The service information octet (SIO): in the message signal unit,

the service information octet includes the Service Indicator and sub-

service field.

The service indicator specifies the MTPs users,

DCBA

Sub-service

field

Serviceindication

code

DCBAThe first transmitted bit


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

SSF SI


32/58

service indicator: MTP User

0000 signaling network management message

0001 signaling network test and maintenance message0010 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

101010111100 reserved

1101

11101111


33/58

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:

DC

00 international network

01 reserved (for international use only)

10 domestic network

11 reserved for domestic use


34/58



7) The 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, TCAP, and ISUP message data)
http://www.pt.com/tutorials/ss7/tcap.htmlhttp://www.pt.com/tutorials/ss7/tcap.html


35/58

the routing lable:

The routing label is comprised of the destination point code(DPC), originating point code (OPC), and signaling link

selection (SLS) field.


SLS OPC DPC

4 14/24 14/24

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.


36/58

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 that destination.


37/58

5. Processing of signaling messages

Message routing:

To select a signaling link for each signaling message to be sentout.

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.


38/58

Message identification:

The process in which the signaling point determines whether this pointis 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 signaling link.


39/58

Go to the fourth level

DPC and SI

Message

identification

Messagerouting:

Messagedistribution:

Come from the second level

Go to the second lever

Come from the fourth level SLS and DPC

LINK BY LINKSIO(SSF ,SI


40/58

ZXC10ZXC10

transmission system D TD T

2048kb/s

Level 1

Signaling link

Level 2

M PM P

Level 3

Message transfer part

Level 4

S T BS T B

semi-permanent connecting

64kb/s

NET NET


41/58

Corresponding relation about

ZXC10 and NO.7 system

No.7 DTI board----------- MTP1

No.7 signaling board

----- MTP2

MP board MTP3

MP board U P


42/58

NO.7 Signaling System overview The Protocal stack

Message Transfer Part




43/58

One or more of the available Layer 4 protocols provides the data that is

transmitted by MTP in the form of MSUs. These can bedivide into

two basic classes:

circuit-related call control protocols (e.g. ISUP and TUP)

non-circuit-related protocols (e.g.SCCP).


44/58

The telephone user part:(TUP)

TUP establishes a frameworkprotocol for the exchange of

messages designed to describe call set-up and teardown.

LEAD CODES

SI H1 H0 LABEL

8n 4 4 64

CIC OPC D PC

4 12 24 24


8 16 8n(n2) 8 2 6 1 7 1 7 8 The first transmitted bit

SSF SI


45/58

S I F

message n 8bit Head code 8bit flag 64bit

H1 H0 CICOPCDPC

TUP message is composed of three parts as flag,head code

and messagefollowing as:

7 bits 5 bits

32 TS

128 E1


46/58

flag used for message route (level three of MTP) to select

appropriate signaling route and used to recognizing certain

call of a message for TUP. It includes three fields:

DPC24bitdestination signaling point codinga sign for

destination of message.

OPC24bitorigination signaling point a sign for

source of message.

CIC 12bit identify a voice circuit of voice circuits

between DPC and OPC.


47/58

Head code is for specifying the message type ,made up of

H1,H0

H0 (4 bits) message group code for identifying message group

H1 (4 bits) message code ,used to identify message in one

message group .


48/58

message

group

H1

H00000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111

0000 Reserved for domesticFAM 0001 IAM IAI SAM SAO

FSM 0010 GSM COT CCF

BSM 0011 GR

SBM 0100 ACM CHG

UBM 0101 SEC CGC NNC ADI CFL SSB UNN LOS SST ACB DPN MPR EUM

CSM 0110 ANU ANC ANN CBK CLF RAN FOT CCLCCM 0111 RLG BLO BLA UBL UBA CCR RSC

GRM 1000 MGB MBA MGUMUA HGB HBA HGU HUA GRS GRA SGB SBA SGU SUA

1001 reservedCNM 1010 ACC

1011

Reserved for international anddomestic

NSB 1100 MPMNCB 1101 OPR

NUB 1110 SLB STB

NAM 1111 MAL

Reserved for domestic


49/58

IAM

ACM

ringing

ANC

CLF

RLG

Inter office

signaling

CBK

CLF

RLG

Called

party hang

off

Caller hang

off

Initiate address message

Address complete message

Answer callbilling

Clear line forward

Release guard

Called hang downClear line

forward releaseRelease guard


50/58


The Protocal stack

Message Transfer Part




51/58

1)Signaling point (local exchange)

It refers to the node in the signaling system that providescommon channel signaling.

SP can also be divided into source points (the SP that

generate signaling messages)OPC(Originating points code) and

destination points (i.e.,the SP that receives signaling

messages)DPC(destination point code). Actually, SP is part of a

switching system.


52/58

2)Signal 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 signaling points during signaling transfer.

STPs are usually setted in pairs, as they arelinked to ensureredundancy. A device connecting to a STP will connect to both

in the pair to 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.


53/58

B

Voice channels

A

Signaling link

C

SP ASP B

STP

2_2_2 3_3_3

8_8_5


54/58

Signaling code

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

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

In international

3bit-8bit-3bit

OPC and DPC is a opposite conception, but signaling

point cod (SPC) is a absolute


55/58

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

C2_2_2 3_3_3

signaling mode


56/58

1)The associated modeIn 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

g g


57/58

2)Non-associated mode

Signaling messages between A and B are transferred by

several signaling links according to the current network status,but the voice circuit is the direct route between A and B. In other

cases, the common channel signaling messages are transferred on

different paths.

B

Voice channels

A

Signaling link

This mode is normally not used, as it is rather

difficult to exactly identify a route at any given

time.


58/58

3)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 gothrough the several preset concatenated signaling links, butvoice signals go through the direct channels between A and B.Normally, different transmission carriers are used in thecommon channel signaling systems and their related voice

links.

B

Voice channels

A

Signaling link

CSTP

SP SP

04 no.7 signaling system

Documents