OMA003001 GSM Signalling System- First Level ..

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OMA003001 GSM Signalling OMA003001 GSM Signalling System-MTPSystem-MTP

OMA003001 GSM Signalling OMA003001 GSM Signalling System-MTPSystem-MTP

2.02.0

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Course ObjectivesCourse Objectives

Upon completion of this course, the trainees should be

able to

Understand the basic concepts in CCS7

Understand the important composition of CCS7 signaling units

Understand the basic signaling procedure of CCS7

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Section 3 Signaling Procedure

Section 2 Signaling Units

Course ArrangementCourse Arrangement

Section 1 Basic Concepts in CCS7

Part 1 Signaling

Part 3 Hierarchy of CCS7 Signaling System

Part 2 CCS7 Signaling Network

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Definition of signalingDefinition of signaling

All the control signals used within or between communication equipment, whose function are to set up communication;

Signals except bearer information (voice information and non-voice information), which are used to control the action of the exchange.

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? Subscriber line signaling: between subscriber and the exchange;

? Interoffice signaling: between exchanges.

Classification of signaling: According to working locationClassification of signaling: According to working location

subscriber line signaling

interoffice signaling

exchange

exchange subscriber

line signaling

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a. CAS(Channel associated signaling): CAS is composed of line signal and register signal. For CAS, the signaling channel is combined with the bear information channel (refers to register signal) or the two have fixed correspondence (refers to line signal).

Classification of signaling: According to signaling channelsClassification of signaling: According to signaling channels

switching equipment

signaling equipment

signaling information carried by speech channel

switching equipment

signaling equipment

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b. CCS(Common channel signaling): the signaling of a group of voice channels are transmitted on a common high speed data link in the form of time multiplexing.

Classification of signaling: According to signaling channelsClassification of signaling: According to signaling channels

switching equipment

signaling equipment

signaling equipment

dedicated channel for carrying signaling

speech channel

switching equipment

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1) CAS: multi - frequency in - band signals, small information volumemutual - control transmission and receiving, slow speed no signaling channel during conversation

The comparison of CAS and CCSThe comparison of CAS and CCS

2) CCS: packet data signal, large information volumenon - mutual - control mechanism, fast speedindependent data link for signaling, signaling could be transmitted during conversation

wide application area, suitable for future development? require low error - code - ratio? require conduction check of the voice channels

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part 1 Signaling

part 3 Hierarchy of CCS7 Signaling System

part 2 CCS7 Signaling Network

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Definition of CCS7 signaling networkDefinition of CCS7 signaling network

In CCS7, signaling links are independent of voice channels. These signaling links form a network dedicated to the transmission of signaling, the so called CCS7 signaling network.

It is a multifunctional supporting network, can be used in telephone network, circuit-switch data network, ISDN network, and intelligent network, etc.. Fundamentally, CCS7 signaling network is a packet switching data network used for dedicated purpose.

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Existing CCS7 signaling networksExisting CCS7 signaling networks

Three supporting networks (in contrast to service networks): CCS7 signaling network; synchronization network; telecommunication management network(TMN).

The existing CCS7 signaling networks International network, International reserved network, national network, national reserved network.In CCS7, each message carries a field called NI (network indicator) to indicate which of the four networks this message works in.

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Three elements in a CCS7 signaling networkThree elements in a CCS7 signaling network

A CCS7 signaling network is composed of three elements:

Signaling Point (SP), Signaling Transfer Point (STP) and Signaling Link.

SP

STP

SP

Link Link

As shown in the figure on the right, in a CCS7 signaling network, SP is represented by a circle, STP is represented by a square, link is represented by a dashed line, voice path is represented by a solid line.

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1) SP (Signaling Point)

SP is the originating or destination point of a CCS7 message. In each signaling network, a SP has an exclusive signaling point code: SPC (14 bits). Since the four signaling networks assign the SPCs independently, only NI+SPC can uniquely locate a SP.Notes: In data setting we usually describe SPC in Hex. Following are some examples of SPC shown in binary and hex.

SPC (binary) SPC (Hex)

00 0000 1011 0101 00b5

10 0011 1101 0111 23d7


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OPC and DPC (1)OPC and DPC (1)

DPC: Destination Point CodeOPC: Originating Point Code

A message going from one SP to another SP should bearing the SPC of the originating SP and the terminating SP, which are called OPC and DPC respectively. If we compare sending a message to sending a letter, OPC and DPC are similar to the sender's address and receiver's address.

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2) STP (Signaling Transfer Point)

STP is the network node which transfers CCS7 messages.

3) Link

Link is the data channel which connects the nodes (SPs and STPs) in CCS7 signaling network.Digital link, 64 kb/s


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Working mode refers to the relationship between the signaling link and the voice channels the link serves.Presently two modes are in use:

1) Associated modeThe messages between two adjacent points are conveyed over a link-set directly interconnecting those signaling points, i.e., the link is parallel to the voice path.

Working modes of CCS7 signaling networkWorking modes of CCS7 signaling network

SPA BSP

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2) Quasi-associated mode

In the quasi-associated mode

the message which is going to

arrive at a SP goes through a

path which is predetermined and

via one or more STPs.

Working modes of CCS7 signaling networkWorking modes of CCS7 signaling network

SPA B

STP

SP

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When the links between any two offices are transferred by a STP, how will be the link path?


Remember, the sole purpose of using signaling is to serve the voice path.

SPA

SPB

TandemC

STP

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Note: the arrows show the paths that signaling messages go through. Remember, a signaling path always starts from one end of the voice path it is going to serve, and ends up at the other end of the voice path.

SPA

SPB

TandemC

STP

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OPC and DPC (II)OPC and DPC (II)

MSU1OPC=?DPC=?

: voice path: signaling link

SPB

SPA SPC SPA SPC

STPB

MSU2OPC=?DPC=?

MSU1OPC=?DPC=?

MSU2OPC=?DPC=?

Tandem Office

In the following two figures, what's the DPC and OPC of the messages?

(a) (b)

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OPC and DPC (II)OPC and DPC (II)

MSU1OPC=ADPC=B

: voice path: signaling link

SPB

SPA SPC SPA SPC

STPB

MSU2OPC=BDPC=C

MSUOPC=ADPC=C

MSUOPC=ADPC=C

Tandem Office

Answer:

(a) (b)

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part 1 Signaling



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The hierarchy of CCS7 system can be functionally divided into two parts, i.e. Message Transfer Part (MTP) and User Part (UP).

1) MTP (Message Transfer Part)The Message Transfer Part (MTP) provides the functions that enable User Part's significant information to be transferred across the signaling network to the required destination. In addition, functions are included in the MTP to overcome network and system failures that would affect the transfer of signaling information.

Hierarchy of CCS7 signaling systemHierarchy of CCS7 signaling system

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2) UP (User Part)

The User Part (UP) is the "user" of

MTP. It includes TUP (Telephone

User Part), ISUP (ISDN User Part),

etc.

In the following, our explanation will

focus on TUP, which transmits and

receives interoffice control signals

to/from the MTP for telephone calls

during call process.

The figure on the right describes the

relation between UP and MTP.

Hierarchy of CCS7 signaling systemHierarchy of CCS7 signaling system

UP

MTP

TUP

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MTP could be further divided into 3 levels, namely, level 1-- signaling data link, level 2 -- signaling link, level 3 -- signaling network.These three levels are similar to the first three levels of OSI model.

Three levels of MTPThree levels of MTP

A signaling data link is a bi-directional transmission path for signaling, comprising two data channels operating together in opposite directions at the same data rate. It constitutes the lowest functional level (level 1) in the Signaling System No. 7 functional hierarchy.

1) Level 1: Signaling Data Link

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The second level provides such functions as signal

unit delimitation, signal unit alignment, error detection,

error correction, initial alignment, signaling link error

monitoring and flow control. It, working together with

level 1, ensures the reliable transmission of

messages between two adjacent SPs.


2) Level 2: Signaling Link

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Functions on this level include signaling message handling and signaling network management. In the transmission of messages, the function of signaling message handling sends the messages to the proper link or user part; while when malfunctions come up, the network management function realizes the reorganization of the signaling network, and when congestion appears, the network management function carries out flow control at the network level, so as to ensure the reliable transmission of signaling under extreme conditions.


3) Level 3: Signaling Network

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The 4-level structure of CCS7 systemThe 4-level structure of CCS7 system

Logicalchannel

Logicalchannel

Logicalchannel

Physicalchannel

Message Discrimination

Message Distribution

Message Routing

User Part

L4 SP A

Signaling NetworkL3

L2 Signaling Link

L1 Signaling Data Link

SP B

User Part

Signaling Network

Signaling Link

Signaling Data Link

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The distribution of CCS7 system in C&C08The distribution of CCS7 system in C&C08

AM/CM

OPT

MPU

LPN7

BNET

DT

OPT

MPU

SMSM

LEVEL 4

LEVEL 3

LEVEL 2

LEVEL 1

LINKS

LEVEL 4

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part 1 Signaling



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Signaling unit (SU) is the minimum unit used to carry the various signaling messages in

CCS7 signaling system.

Definition of CCS7 signaling unitDefinition of CCS7 signaling unit

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1. MSU (Message Signaling Unit)

Used to transfer the signaling message from the 4th level or the signaling network management message from the 3rd level.

2. LSSU (Link Status Signaling Unit) Originating and terminating at the 3rd level, it carries no detailed signaling message, used to indicate the link status when the link is put into use or malfunctions, so as to set up or recover the signaling links.

3. FISU (Fill-in Signaling Unit) Originating and terminating at the 2nd level, it is used to fill in the vacant locations when the link is free or congested, so as to keep the link in the status of communication, and sometimes it is also used to confirm the receive of message from the opposite side.

The classification of signaling units--According to the sourcesThe classification of signaling units--According to the sources

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The structure of MSU, LSSU and FISUThe structure of MSU, LSSU and FISU

FF CK LI FIB FSN BIB BSN

8 16 2 6 1 7 1 7 8

SIF SIO

8n(n≥2) 8 SendingDirectionStructure of MSU

FF CK SF LI FIB FSN BIB BSN

8 16 8 2 6 1 7 1 7 8 Sending DirectionStructure of LSSU

F CK LI FIB FSN BIB BSN F

8 16 2 6 1 7 1 7 8 Sending DirectionStructure of FISU

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As shown in the above figure, there are multiple circuits (e.g.. one time slot is one circuit) connecting two adjacent SPs. To distinguish them, we should assign each of them a code, CIC. So CIC is unique in each direction, and is coded in 12 bits. Therefore, in each direction we can have as many as 212=4096 circuits, and the value range of CIC is [0~4095].

Important fields in TUP MSU-- CIC, SLCImportant fields in TUP MSU-- CIC, SLC

link

speech channel

switching equipment

signaling equipment

switching equipment

signaling equipment

CIC: Circuit Identification Code (12 bits)SLC: Signaling Link Code (4 bits)

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Correspondence of CIC

and E1:

For E1, the lowest 5 bits of

CIC represent PCM time slot

number, and the higher 7 bits

represent PCM system

number.

7 bits 5 bits CICPCM system number PCM time slot number

CIC E1#1 E1#0 CIC

TS0 0000000 00000TS1 0000000 00001

TS31 0000000 11111

0000001 00000 TS0 0000001 00001 TS1

0000001 11111 TS31


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Similarly, if there are multiple links connecting two adjacent SPs, to distinguish them, we should assign each of them a code, SLC. So SLC is unique in each direction, and is coded in 4 bits. Therefore, in each direction we can have as many as 24=16 links, and the value range of SLC is [0~15].

......

... ...

CIC=0,CIC=1,

CIC=m1

CIC=0,CIC=1,

CIC=m2

SLC=0,SLC=1,

SLC=n1

SLC=0,SLC=1,

SLC=n2

local SP one direction

another direction


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Different from CAS, in CCS7 we usually use bi-directional trunk circuits. This induces the possibility of selecting the same circuit from the two offices at the same time, which is called "dual seizure". To prevent this, for each circuit, we assign its "master" control right to one office, and the "non-master" or "slave" control right over this circuit to the office at the other end. Usually we assign the master control rights according to the circuit's CIC number : if the CIC number is even then its master control right is given to the office which has larger SPC (Signaling point code), and if the CIC number is odd then its master control right is given to the office which has smaller SPC.Following is an example of CIC and master right distribution.

Dual seizureDual seizure

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0 master slave 01 slave master 12 master slave 2

SP ASPC=0002

SP BSPC=0001

2n master slave 2n

2n+1 slave master 2n+1

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The principle to avoid dual seizure:When the local office wants to make an outgoing call, it first tries those circuits on which it has master control right; only when all these circuits are busy, will the local SP try the circuits it has slave control right. So when the slave circuits are to be selected, the possibility of "dual seizure" rises again. Hence different "circuit selection modes" are used: for the circuits on which the local office has master control right, "FIFO" mode is adopted, which means the circuit bearing the longest idle period will be selected; while for the circuits on which the local office has slave control right, "LIFO" mode is adopted, which means the circuit bearing the shortest idle period will be selected. In this way, most of the danger of "Dual seizure" can be avoided.


To be continued...

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The principle to avoid dual seizure:But still there is an extreme occasion when there is only one idle circuit left for selection from both sides. Then if both sides try to use this circuit at the same time, the possibility of dual seizure rises again. In this case, the principle is the "slave" side should give way to the "master" side.


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part 1 Signaling



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Basic signaling procedureBasic signaling procedure

IAM: initial address

message, the part or all of

the called number are sent

in this message

ACM: address complete

message

ANC: answer signal, charge

CLF: clear forward message

RLG: release guard signal

After hearing the busy tone, the called party hooks on.

the called phone rings

the caller listen to the ring back tone

the called partypick up the phone

the caller hooks on first

IAM (6660008)

ACM

ANC

communication

CLF

RLG

SPBSPA

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Call connection through tandem officeCall connection through tandem office

SAM: Subsequent address message, following IAM, used to send the subsequent digits of the called number which haven't been sent by IAM. SAO: Subsequent address message with one signal. Similar to SAM, but can send only one digit.CBK: Clear backward signal

the called party hooks on first

LE TM LE

...

IAM* (66)

SAM ( or SAO ) (60)

SAO (8)

ACM

ANC

CBKCLF

RLG

IAM** (6660008)ACM

ring back tone

ANC

conversation CBK

CLFRLG

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Send caller number initiativelySend caller number initiatively




IAI : Initial address message with add- tional information. If the caller number is to be sent initiatively, IAI is used.

the originating the destinationLE toll office toll office

...

IAI(66, 8880003)

SAM( or SAO) (60)

SAO (8)

ACM

ANC

CLF

RLG

CLFRLG

IAM**(6660008)

ACM

ANCring back tone

conversation

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The opposite office ask for caller number (e.g.,Malicious call tracing, CLID)

The opposite office ask for caller number (e.g.,Malicious call tracing, CLID)

the called phone ringsthe called party

pick up the phone


GRQ: General request message. It is used to ask for caller number and some other information.GSM: General forward setup information message. It is used to send caller number and some other information.

LE

ACM

ANC

CLF

GRQ

CLFRLG

IAM(6660008)

GRQ

ANCring back tone

conversation

LETM

GSM(8880003)GSM(8880003)

ACM

IAM(6660008)

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The cooperation of CCS7 and R2The cooperation of CCS7 and R2




...

...

CCS7 R2LE TM LEIAM (666)

SAO (0)SAO (8)

ACM

ANC

CBKCLF

RLG

SEIZE

6 (the 1st digit)A16 (the 2nd digit)

A18 (the last digit)

A3II-1B6

ring back toneANSWER

conversationCBK

CLFRLG

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Summary Summary

This course describes the following important aspects of CCS7:

Basic concepts of CCS7: signaling, CCS7 signaling network, CCS7 hierarchy

Signaling Units, in which CIC, SLC, etc. are the most important concepts.

Signaling procedure

OMA003001 GSM Signalling System- First Level ..

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