Ori000004 Ccs7 Signaling System Issue2.0

ORI000004 CCS7 Signaling System ISSUE 2.0

Wireless Wireless Curriculum Curriculum Development Development Section Section

Course 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

Course Arrangement

Section 1 Basic Concepts in CCS7 Part 1 Signaling Part 2 CCS7 Signaling Network Part 3 Hierarchy of CCS7 Signaling System

Section 2 Signaling Units Section 3 Signaling Procedure

Definition 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.

Classification of signaling: According to working location

1. Subscriber line signaling: between subscriber and the exchange;

2. Interoffice signaling: between exchanges.

subscriber line signaling

exchan ge

interoffice signaling

exchan ge

subscriber line signaling

Classification of signaling: According to signaling channels switchin g equipme nt signaling equipme nt

signaling information carried by speech channel

switchin g equipme nt signaling equipme nt

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 channels switchin g equipme nt signaling equipmen t

speech channel dedicated channel for carrying signaling

switching equipmen t signaling equipmen t

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.

The comparison of CAS and CCS 1) CAS: multi - frequency in - band signals, small information volume mutual - control transmission and receiving, slow speed no signaling channel during conversation

2) CCS: packet data signal, large information volume non - mutual - control mechanism, fast speed independent 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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Course Arrangement

Section 1 Basic Concepts in CCS7 part 1 Signaling part 2 CCS7 Signaling Network part 3 Hierarchy of CCS7 Signaling System

Section 2 Signaling Units Section 3 Signaling Procedure

Definition 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.

Existing 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.

Three 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. 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.

SP

Link

SP

Link STP

Three elements in a CCS7 signaling network 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

OPC and DPC (1)

DPC: Destination Point Code OPC: 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.

Three elements in a CCS7 signaling network

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

Working modes of CCS7 signaling network 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 mode The 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.

SP A

SP B

Working modes of CCS7 signaling network 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.

STP

SP

A

SP B

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

STP

SP A

SP B

Tandem C

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

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

STP

SP A

SP B

Tandem C

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.

OPC and DPC (II)

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

Tandem Office

SPB

SPA

MSU1 OPC=? DPC=?

MSU2 OPC=? DPC=?

(a)

: voice path : signaling link

SPC

SPA

STPB MSU1 OPC=? DPC=?

MSU2 OPC=? DPC=?

(b)

SPC

OPC and DPC (II)

Answer: Tandem Office

SPB

SPA

MSU1 OPC=A DPC=B

MSU2 OPC=B DPC=C

(a)

: voice path : signaling link

SPC

SPA

STPB MSU OPC=A DPC=C

MSU OPC=A DPC=C

SPC (b)

Course Arrangement

Section 1 Basic Concepts in CCS7 part 1 Signaling part 2 CCS7 Signaling Network part 3 Hierarchy of CCS7 Signaling System

Section 2 Signaling Units Section 3 Signaling Procedure

Hierarchy of CCS7 signaling system

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 system

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.

UP

MTP

T U P

Three levels of MTP

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.

1) Level 1: Signaling Data Link 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.

Three levels of MTP 2) Level 2: Signaling Link

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.

Three levels of MTP

3) Level 3: Signaling Network 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.

The 4-level structure of CCS7 system

L4

SP A User Part

L3 Signaling Network

L2

Signaling Link

L Signaling Data Link 1

Logical channel Logical channel Logical channel Physical channel

SP B User Part Message Distribution

Signaling Network Message Discrimination

Message Routing

Signaling Link

Signaling Data Link

The distribution of CCS7 system in STE AM/CM SM

SM

OPT MPU LPN7

OPT LEVEL 4 LEVEL 3 LEVEL 2

BNET DT LINKS

LEVEL 1

MPU

LEVEL 4

Course Arrangement

Section 1 Basic Concepts in CCS7 part 1 Signaling part 2 CCS7 Signaling Network part 3 Hierarchy of CCS7 Signaling System

Section 2 Signaling Units Section 3 Signaling Procedure

Definition of CCS7 signaling unit

Signaling unit (SU) is the minimum unit used to carry the various signaling messages in CCS7 signaling system.

The classification of signaling units --According to the sources 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 structure of MSU, LSSU and FISU

F

CK

SIF

8

16

8n(n≥2)

SIO 2

8

LI

FIB

FSN

BIB

BSN

6

1

7

1

7

F 8 Sending Direction

Structure of MSU F

CK

SF

8

16

8

2

LI

FIB

FSN

BIB

6

1

7

1

BSN 7

Structure of LSSU

F

CK

8

16

2

LI

FIB

6

1

FSN 7

Structure of FISU

BIB 1

BSN

F

7

8

F 8 Sending Direction

Sending Direction

Important fields in TUP MSU-- CIC, SLC CIC: Circuit Identification Code (12 bits) SLC: Signaling Link Code (4 bits)

switching equipment

switching equipment speech channel

signaling equipment

link

signaling equipment

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, SLC

7 bits PCM system number

5 bits

CIC

PCM time slot number

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.

CIC

E1#1

0000001 00000 TS0 0000001 00001 TS1

0000001 11111 TS31

E1#0

CIC TS0 TS1

0000000 00000 0000000 00001

TS31

0000000 11111

Important fields in TUP MSU-- CIC, SLC

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]. one direction

local SP CIC=0, CIC=1,

... CIC=m1 SLC=0, SLC=1,

... SLC=n1

CIC=0, CIC=1,

. . CIC=m2 . SLC=0, SLC=1,

... SLC=n2

another direction

Dual seizure

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 seizure

SP B SPC=0001

SP A SPC=0002 0 1 2

master slave master

2n

master

2n+1

slave

slave 0 master 1 slave 2

slave

2n

master 2n+1

Dual seizure 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...

Dual seizure 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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Course Arrangement

Section 1 Basic Concepts in CCS7 part 1 Signaling part 2 CCS7 Signaling Network part 3 Hierarchy of CCS7 Signaling System

Section 2 Signaling Units Section 3 Signaling Procedure

Basic signaling procedure SPA

SPB IAM (6660008)

IAM:

initial

address

message, the part or all of the called number are sent

the caller listen to the ring back tone

in this message ACM:

address

ACM ANC

complete

message

the called phone rings the called party pick up the phone

communication

ANC: answer signal, charge CLF: clear forward message RLG: release guard signal

the caller hooks on first

CLF RLG

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

Call connection through tandem office LE

TM

LE

IAM* (66) SAM ( or SAO ) (60)

..

SAO (8) IAM** (6660008) ACM ACM ANC

ring back tone ANC conversation CBK

CBK CLF

RLG

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

CLF RLG

the called party hooks on first

Send caller number initiatively the originating toll office

LE

the destination toll office

IAI(66, 8880003) SAM( or SAO) (60)

..

SAO (8) IAM**(6660008) ACM ACM ring back tone ANC ANC conversation CLF CLF RLG RLG

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

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

LE

LE

IAM(6660008)

GRQ

IAM(6660008) GRQ

GSM(8880003)

ACM

GSM(8880003) ACM ring back tone ANC

ANC CLF

conversation CLF RLG

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.

The cooperation of CCS7 and R2 LE

CCS7 IAM (666) SAO . (0)

.

SAO (8)

TM

R2 SEIZE 6 (the 1st digit) A1 6 (the 2nd . digit)

.

ACM ANC CBK CLF RLG

A1 8 (the last digit) A3 II-1 B6 ring back tone ANSWER conversation CBK CLF RLG

LE

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