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HUAWEI GSM-T GTSOFTX3000

Technical Manual Signaling and Protocols Contents

Issue 03 (2008-07-15)Huawei Proprietary and Confidential

Copyright Huawei Technologies Co., Ltd.i

Contents

14 DSS1 and R2............................................................................................................................14-1

14.1 DSS1 Signaling ................................................................. ....................................................................... .14-2

14.1.1 Overview of DSS1 Signaling...........................................................................................................14-2

14.1.2 Basic Concepts.................................................................................................................................14-2

14.1.3 Application of DSS1 .............................................................. .......................................................... 14-7

14.1.4 Protocol Structure of DSS1..............................................................................................................14-8

14.1.5 Call Control Message.....................................................................................................................14-11

14.1.6 Basic Signaling Process ............................................................... .................................................. 14-13

14.2 R2 Signaling............................................................................................................................................14-15

14.2.1 Basic Concepts...............................................................................................................................14-15

14.2.2 Line Signaling................................................................................................................................14-16

14.2.3 Register Signaling..........................................................................................................................14-20

14.2.4 Application of R2 Signaling...........................................................................................................14-29

14.2.5 Basic Signaling Flow ..................................................................... ................................................14-30

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Technical Manual Signaling and Protocols Figures


Copyright Huawei Technologies Co., Ltd.iii

Figures

Figure 14-1 Structure of ISDN................................................................... ...................................................... 14-2

Figure 14-2 Reference configuration for ISDN user-to-network interfaces..................................................... 14-3

Figure 14-3 Correlation between a binary code and an AMI code...................................................................14-4

Figure 14-4 ISDN subscriber number and sub-address....................................................................................14-7Figure 14-5 Typical application of DSS1 in NGN ...................................................... .....................................14-8

Figure 14-6 Correlation between DSS1 signaling and the OSI reference model ............................................. 14-9

Figure 14-7 Reference configuration of ISDN user-to-network interfaces ...................................................... 14-9

Figure 14-8 Format of ITU-T Q.931 messages ............................................................... ............................... 14-11

Figure 14-9 Basic signaling process of DSS1 (circuit switching) ............................................................... ...14-14

Figure 14-10 The transmission process of R2 register signaling....................................................................14-21

Figure 14-11 Typical application of R2 signaling in NGN.............................................................................14-30

Figure 14-12 Signaling process of a local call................................................................................................14-31

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Technical Manual Signaling and Protocols Tables


Copyright Huawei Technologies Co., Ltd.v

Tables

Table 14-1 Bandwidth allocation in the 2B1Q line code mode ........................................................................ 14-4

Table 14-2 Bandwidth allocation in the 2B1Q line code mode ........................................................................ 14-6

Table 14-3 Types of call control layer messages of Q.931 ..................................................................... ........14-12

Table 14-4 Nominal values of the in-band single frequency pulses and their intervals..................................14-16Table 14-5 Signal structure of line signaling with in-band single frequency pulse ........................................14-17

Table 14-6 Use of TS16 in a PCM multiframe ...................................................................... .........................14-19

Table 14-7 Meaning of forward signaling in digital lines...............................................................................14-19

Table 14-8 Meaning of backward signaling in digital lines............................................................................14-19

Table 14-9 Signaling bits in the automatic and semi-automatic connection of a toll office ...........................14-20

Table 14-10 Forward signaling.......................................................................................................................14-22

Table 14-11 Backward signaling.....................................................................................................................14-22

Table 14-12 Meanings of the four groups of signaling...................................................................................14-23

Table 14-13 Forward group I signaling .............................................................. ............................................ 14-23

Table 14-14 Backward group A signaling.......................................................................................................14-24

Table 14-15 Forward group I signaling and backward group A signaling...................................................... 14-25

Table 14-16 Forward group II signaling and backward group B signaling .................................................... 14-28

Table 14-17 Contents and role of KD signaling .................................................................... .........................14-29

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Technical Manual Signaling and Protocols 14 DSS1 and R2


Copyright Huawei Technologies Co., Ltd.14-1

14 DSS1 and R2About This Chapter

The following table lists the contents of this chapter.

Section Describes

14.1 DSS1 Signaling The basic concept, application, and protocol structure ofthe DSS1 signaling, and call control message.

14.2 R2 Signaling The basic concept and application of the R2 signaling,and basic signaling process.

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14 DSS1 and R2


Technical Manual Signaling and Protocols

14-2Huawei Proprietary and Confidential

Copyright Huawei Technologies Co., Ltd.Issue 03 (2008-07-15)

14.1 DSS1 Signaling

14.1.1 Overview of DSS1 SignalingISDN features multiple capabilities, including circuit switching, packet switching,

non-switching connection, and common channel signaling. Normally, a network only providesfunctions of lower layersphysical layer, data link layer, and network layer - of the opensystems interconnection (OSI) model. Intra-network higher layer (layers 4 to 7 of model OSI)

functions required by some supplementary services can be implemented inside ISDN orprovided by an independent service center.

The basic structure of ISDN is shown in Figure 14-1. The terminal equipment (TE) of ISDN

is connected through the standard user-to-network interface.

Figure 14-1Structure of ISDN

TEISDN

switch

User-networkinterface

Circuitswitchingcapacity

Packetswitchingcapacity

Non-switchingcapacity

Commonchannelsignalingcapacity

TEISDN

switch

User-networkinterface

14.1.2 Basic Concepts

Reference Points and Functional GroupThe reference configuration (reference model) of the ISDN user-to-network interface is

shown in Figure 14-2. The model is an abstract arrangement of the user-to-network interfacestandardized by CCITT (ITU) regulations. It offers reference points to be standardized and

functional groups related to the reference points.

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Figure 14-2Reference configuration for ISDN user-to-network interfacesTE1

SNT2

TNT1

U

Transmission line

TAS

TE2R

Reference point Functional g roup

TE1S

NT2T

NT1U

Transmission line

TAS

TE2R


TE1S

NT2T

NT1U

Transmission line

TAS

TE2R


z Reference point

In Figure 14-2, crosses stands for reference points. A cross is a conceptual referencepoint for dividing functional groups. In the user accessing, crosses stand for physical

interfaces between device units. For the implementation of multiple functional groupscombined in one device, reference points between functional groups exist onlyconceptually. The physical interfaces cannot be observed.

There are three types of reference points: the U reference point, S/T reference point andR reference point.

U reference point

The U reference point, also called the U interface, is the line interface between the

network and the user. According to the regulations of ITU, the U interface is the line

interface between the network and the ISDN basic rate access (BRA) user, but not theline interface between the network and the primary rate access (PRA) user.Comparing the reference model to the actual application, we regard that the E1 line inthe PRA application as the U interface in Figure 14-2.

The BRA U interface determines the transmission line code. The U interface uses theoriginal analog subscriber line (ASL). To transmit digital signals through twisted

pairs, you need to reduce transmission attenuation. One way for reducingtransmission attenuation is to reduce the line transmission rate, that is, to transmit a

2-bit binary code with one level. The transmission line code adopted by the Uinterface in China is 2B1Q. This code indicates that the line transmission uses four

levels, each level being a combination of two bits. Correlation between binary codesand line levels:

Binary code Line level

00 3V

01 1V

10 +3V

11 +1V

In this way, the line rate is reduced by half compared with the binary code rate, thusreducing the transmission attenuation.

When the 2B1Q line code is used, the line element rate (baud rate) is 80 kbit/s, and

the corresponding bandwidth is 160 kbit/s. The bandwidth allocation is described inTable 14-1.

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Table 14-1Bandwidth allocation in the 2B1Q line code modeChannel Rate (Bit/s) Function

2B channel 128k Traffic channelD channel 16k Signaling channelM channel 40k Transmitting the maintenance

information between the network and theterminal

Used for U interfacesynchronization

12k Transmitting clock information

S reference point and T reference point

The S reference point, also called S interface, is the line interface between the ISDNterminal (terminal equipment type 1 (TE1) or terminal adaptor (TA)) and the networkterminal (NT). The T reference point, also called T interface, is the line interfacebetween network terminal type 1 (NT1) and network terminal type 2 (NT2). In the

ITU regulation, the specifications of the S interface is the same as that of the Tinterface.

If the NT2 device does not exist, S and T together form S/T reference point, alsocalled S/T interface.

The S/T interface uses a four-line transmission mode, two lines for sending and twolines for receiving. The line code is a pseudo-AMI (alternate mark inversion) code. InAMI code, binary bit "1" is converted to positive pulse or negative pulse, which

alternate forward and backward; binary bit "0" is converted to level 0. Figure 14-3

illustrates the correlation between a binary code and an AMI code.

Figure 14-3Correlation between a binary code and an AMI codeBinary code 1 0 0 1 1 1 0 1 0 1

AMI code

Sending direction

Binary code 1 0 0 1 1 1 0 1 0 1

AMI code

Sending direction

Binary code 1 0 0 1 1 1 0 1 0 1

AMI code

Sending direction

R reference point

The R reference point, also called R interface, is a non-standard ISDN terminal

interface, for example, RS-232 interface, IEEE-488 interface, and analog telephoneinterface.

z Functional group

In Figure 14-2, blocks stand for functional groups. A functional group is the combinationand arrangement of functions required on ISDN user interfaces. In application, a numberof functional groups may be implemented in one device.

NT1

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NT1 provides U interfaces and S/T interfaces for connecting ISDN terminals anddevices of the ISDN exchange. The function of NT1 is the code conversion betweenthe U interface and S/T interface, for example, the 2B1Q/AMI code conversion in theChinese standard.

NT1 is purely a physical layer device without software intelligence, but it has the linemaintenance and performance monitoring functions. It ensures the clocksynchronization of the ISDN terminal and network.

If the NT1 includes the function of the TA, it is called NT1+.

NT2

NT2 is an intelligent terminal device. A common NT2 device can be a terminal

control device such as a private automatic branch exchange (PABX) that has thefunctions of ISDN, and a LAN router.

TE1

The TE1 is a standard ISDN terminal, with standard S interfaces. It can be connected

directly with the NT1 or NT2 through S interfaces. Common TE1 devices includeISDN digital telephone sets, G4 fax machines, and video phones.

Terminal equipment type 2 (TE2)

TE2 is a non-standard ISDN terminal without S interfaces. It cannot be directlyconnected with the NT1 or NT2. An S interface can be connected to the TE2 through

a terminal adapter (TA). Common TE2 devices include PCs, ordinary telephone sets,X 25 packet terminals and G3 fax machines.

TA

There is an S or U interface on one end of the TA, and an interface for connecting anon-standard ISDN terminal on the other end. The role of the TA is for rate

adaptation and protocol conversion. The non-standard ISDN terminal (TE2) does not

have the function of the common channel signaling (D channel). It can be connectedwith the S or U interface only after the rate adaptation and protocol conversion withthe TA.

Some TAs contain the built-in AT command set. The AT command set is a general

command format for operating on the Modem on a computer. It supports calloriginating and answering on a computer. In other words, the AT command isconverted to D channel signaling. With a TA, the user can make calls and transmitdata simultaneously through a computer.

The B channel protocol of the TA is V.110. It converts the low-speed serial port datato the data with the speed of 64 kbit/s to enter the B channel. It enables the

non-standard ISDN terminal to communicate with the network through a standardISDN interface.

ISDN Channel

The ISDN channel type refers to the channel path type of the user-to-network interface. It

includes bearer channel (B channel), demand channel (D channel) and H channel.

z B channel

The B channel is used for transmitting user information (including voice, data and

images) at the rate of 64 kbit/s. It can implement circuit switching, packet switching andsemi-permanent connection (SPC).

z D channel

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The D channel transmits signaling messages and packet messages for circuit switching.According to the number of B channels supported by D channels, D channels are dividedinto 2B+D and 30B+D.

Table 14-2Bandwidth allocation in the 2B1Q line code mode

Channel Rate (Bit/s) Function

D16 16k D channel in 2B+D

D64 64k D channel in 30B+D

z H channel

The H channel is for transmitting user information (including stereo programs, imagesand data) at a rate over 384 kbit/s.

ISDN Interface

The ISDN interface falls into three types: BRA (2B+D), PRA (30B+D) and ISUP.

z BRA interface

BRA is short for the basic rate interface/access (BRI/BRA). It is specified when the

ordinary subscriber line in PSTN is used as the ISDN subscriber line. It has a rate of 144

kbit/s. It supports two 64 kbit/s user channels (B channel) and one 16 kbit/s signalingchannel (D channel).

The BRA interface is provided by the digital subscriber line board (DSL) of the opticalnetwork unit (ONU) or remote subscriber processor (RSP) under the UMG8900. Each

DSL can provide eight BRA interfaces. One BRA interface can be connected with eightISDN terminals at most. It allows two telephones (each occupying a B channel) and a

packet terminal (occupying the D channel) to communicate with the networksimultaneously. When the ISDN-PC communicates with the network, it can occupy twoB channels at the maximum rate of 128 kbit/s.

As shown in Figure 1-6, the eight ISDN terminals attached to the 2B+D interface can

call another terminal in the "subscriber number + sub-address" mode. Two subscriber

numbers must be allocated to a BRA interface on the network side and set on theterminal. Each subscriber number can have four sub-addresses (14 digits) at most. Onthe network side, sub-address numbers need not be set. Only the authorities for

sub-address numbers need to be registered. Sub-addresses are set on terminals.

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Figure 14-4ISDN subscriber number and sub-address

2B+D subscriber line

N1=6600000N2=6600001

NT1

S/T

SUB1=1

SUB1=2

SUB1=3

SUB1=4

N1=6600000

SUB1=1

SUB1=2

SUB1=3

SUB1=4

N2=6600001


N1=6600000N2=6600001

NT1

S/T

SUB1=1

SUB1=2

SUB1=3

SUB1=4

N1=6600000

SUB1=1

SUB1=2

SUB1=3

SUB1=4

N2=6600001


N1=6600000N2=6600001

NT1

S/T

SUB1=1

SUB1=2

SUB1=3

SUB1=4

N1=6600000

SUB1=1

SUB1=2

SUB1=3

SUB1=4

N2=6600001

z PRA interface

According to different gaping (E1=32TS, T1=24TS) divided by the PCM system, theprimary rate interfaces/accesses (PRI/PRA) are classified into the 30B+D interfaces(China and Europe) and the 23B+D interfaces (North America and Japan).

The 30B+D interface is the PRA interface in China with a rate of 2048 kbit/s. It supportsthirty 64 kbit/s user channels (B channels) and a 64 kbit/s signaling channel (D channel).

The physical channel of the PRA interface is provided by the digital trunk module(DTM). The board type must be set to "PRA" during hardware data configuration. Each

PRA board provides two 30B+D PRA interfaces. The subscriber line is a coaxial cablethat can meet the requirement of users with heavy traffic. The PRA interface can be

connected to the PABX that has the functions of ISDN, a LAN, or Internet interiminter-switch signalling protocol (ISP) system. It can also provide channels for videoconference users to transmit high quality pictures.

z ISUP interface

The ISDN user part (ISUP) interface is needed for enabling the ISUP circuit betweentwo exchanges.

14.1.3 Application of DSS1

Figure 14-5 is a typical application of DSS1 signaling in NGN.

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Figure 14-5Typical application of DSS1 in NGN

GTSOFTX3000

IP Metropolitan-Area

Network

UMG8900 UMG8900

POTS POTS

H.248/IUA

ISDN 2B+D Access

RSP

PBX and NAS Equipment

PRI PRI

NASPBX

H.248/IUA

ISDNISDN

BRIBRI

The UMG8900 provides the BRIs and PRIs specified inISDN User to Network InterfaceSpecifications, for processing Q.921 messages. It transparently transmits Q.931 signaling to

the GTSOFTX3000 through ISDN Q.921-User Adaptation Layer (IUA) to implement thefollowing ISDN services:

z Providing BRIs for the accessing of ordinary ISDN users (2B+D);

z Providing PRIs for accessing PABXs and network access servers (NAS).

For the DSS1 signaling system, this document introduces only the PRI. For the BRI, refer to

relevant standards.

14.1.4 Protocol Structure of DSS1

DSS1 signaling has three layers: physical layer, data link layer and call control layer. Figure14-6 illustrates the correlation between DSS1 signaling and the OSI reference model.

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Figure 14-6Correlation between DSS1 signaling and the OSI reference model

Data link layer

Physical layer Layer 1

Layer 2

Layer 3

Layers 4-7

DSS1 signaling OSI reference model

Call control layer

Physical Layer

The physical layer specifies the procedure and electrical and functional features of the ISDN

user-to-network interface. It provides the technical basis for the interconnection, operation

and maintenance, equipment design, network planning and acceptance test of theuser-to-network interface. For example, the reference configuration of the PRI is shown inFigure 14-7.

Figure 14-7Reference configuration of ISDN user-to-network interfaces

TE1

R

NT2

T

NT1

UTransmission media

TE2

R S

Reference point

Functional group

TE1: Standard ISDN terminal

TE2: Non-standard ISDN terminal

NT1: Network terminal type 1

NT2: Network terminal type 2 (For example, PBX, LAN, Router)

TA: Terminal adaptor

TA

The meanings of the B channel and D channel supported by the PRI:

B channel: bearer channel of the user information with the rate of 64 kbit/s, used for carrying

voice and data for circuit switching, packet switching and SPC.

D channel: bearer channel of the signaling information with the rate of 64 kbit/s, used totransmit the signaling information and packet data information of circuit switching. The PRI

physical channel is in the PCM structure. It has the same rate as the PCM primary rate,namely, 2048 kbit/s. The PRI can use twisted pairs as the transmission media. In the 30/32

channels of PCM, each frame is divided into 32 basic time slots. TS0 is used for framesynchronization and error control, and TS16 for signaling transmission.

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Data Link Layer

The data link layer specifies the specification attributes of the data link layer of the ISDN

user-to-network interface (PRI). These specification attributes include the concept and terms

of the data link layer protocol, and the frame structure, procedure, procedure element and field

format of the data link layer protocol under normal operation.

On the ISDN user-to-network interface, the data link layer protocol accesses the LAPD

protocol through the link on the D channel. The LAPD protocol defines rules for the layer 2entity on the user-to-network interface to exchange information through the D channel. The

layer 2 entity may exchange information between the TE and the NT2 (such as PABX, LANand a router), between the NT2 and an exchange, or between the TE and an exchange.

Therefore, LAPD is to provide means of information transmission between combinations of

data link connection ends. Functions of LAPD are as follows:

Providing data link connections on one or more D channels; Discrimination of data linkconnections depending on the data link connection identifier (DLCI) contained in each frame;

Delimitation, location and transparent transmission of frames, hence allowing recognizing a

string of bits sent on the D channel in the form of a frame;

Sequence control for keeping the sequence of frames connected through data links;

Checking of the transmission and format of and operation onto data link connections;

Error recovery after the transmission, format and operation check;

Notifying the management entity of unrecoverable errors;

Performing flow control;

Management of the activation of the physical layer.

For details, refer toISDN User to Network Interface Specifications Part 2: TechnicalSpecifications on Data Link Layer (YDN 034.3-1997).

Call Control Layer

The call control layer specifies the procedure for establishing, keeping and removing network

connections on the ISDN user-to-network interface. It also specifies the process of message

exchange on the D channel.

With the functions and services provided by the data link layer, the call control layer providesfunctions for establishing and operating on network connections to users. These functions

support the basic call control program and the call control program related to supplementaryfeatures provided by the network. These functions include:

Processing the primitive used for the communication with the data link layer;

Generating and translating layer-3 messages for intra-layer communication;

Managing the timer and logical entity used in the call control program;

Managing accessing resources, including the B channel, and the logical path of the packetlayer (for example, X.25 recommendations);

Ensuring the consistency between the provided services and the services required by the user

(for example, the bearer capacity, address, and the compatibility between the lower layers andthe higher layers);

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Routing and trunks;

Network connection control;

Transmitting information between the network and the user;

Multiplexing of network connections;

Error checking;

Error recovery;

Sequencing;

Blocking control and user data stream control;

Restart.

For details, refer toISDN User to Network Interface Specifications Part 3: Technical

Specifications on Basic Call Control of Layer 3 (YDN 034.3-1997).

14.1.5 Call Control Message

The Layer 3 (call control layer) entity of the user side needs to communicate with the Layer 3entity of the network side for call control. The communication is realized by exchanging

messages on the D channel. The call control layer message is composed of data blocks ofdifferent lengths. It is produced and processed by the call control layer, and carried andtransmitted by the data link layer.

The format of the call control layer message specified by the recommendations of ITU-TQ.931/Q.932 is illustrated in Figure 14-8. The call control layer message consists of a number

(an integer) of bytes. Each message has a common part, and optional or mandatoryinformation elements.

Figure 14-8Format of ITU-T Q.931 messages8 7 6 5 4 3 2 1

Protocol discriminator

0 0 0 0Length of callreference value

Call reference value

0 Message type

Other information elements

1 byte

2 bytes atmost

Commonpart

Optional ormandatoryinformationelements

FLAG

1 byte

1 byte

Other information elements

The common part consists of three sub-parts with the format identical with that of allmessages.

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Protocol Discriminator

The protocol discriminator separates the call control message from other messages on the

user-to-network interface. The length of the protocol discriminator is one byte. The value of

the Q.931 call control layer message fixedly is 00001000.

Call Reference Value

The reference identifies calls involved by messages or facility registration/un-registration

requests on the local user-to-network interface. Call reference value does not have themeaning of overriding ISDN from end to end.

The call reference value is allocated by the call originating interface. Inside the layer-2 logical

link connection of a specific D channel, call reference values are unique on the originatingside. They are allocated at the start of calls and kept till the end of these calls (except in the

cases of call suspension). After the end or successful suspension of a call, the call referencevalue can be re-allocated to a new call. On layer 2 logical links of a same D channel, two calls

of different directions can have the same call reference value.

The eighth byte of the second eight-byte set is the call reference flag. The value of the flag is0 or 1. The call reference flag identifies the end of the layer 2 logical link to send the call

reference value. The call reference flag on the originating side is always set to 0, and that onthe terminating side is always set to 1. The sole purpose of the call reference flag is to solve

the problem of two ends attempting to allocate the same call reference value at the same time.The call reference flag is also applied when using the global call reference (for example, torestart a program).

Message Type

Message types identifies messages that are being sent. They include different informationelements. The message part is the third part of a message, and its length is one byte. Bit 8 is

reserved for future expansion.

Call control layer messages of Q.931 are classified into four types: messages for call setup,messages used at the call information stage, messages for call clearing, and other messages.

The coding of different types of messages is described in Table 14-3.

Table 14-3Types of call control layer messages of Q.931MessageCode

Message Type

0000 0001 ALERTING0000 0010 CALL PROCEEDING

0000 0111 CONNECT

0000 1111 CONNECT ACKNOWLEDGE

0000 0011 PROGRESS

0000 0101 SETUP

0000 1101

Messages for call setup

SETUP ACKNOWLEDGE

0010 0110 Messages used at the call RESUME

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MessageCode

Message Type

0010 1110 RESUME ACKNOWLEDGE

0010 0010 RESUME REJECT

0010 0101 SUSPEND

0010 1101 SUSPEND ACKNOWLEDGE

0010 0001

information stage

SUSPEND REJECT

0100 0101 DISCONNECT

0100 1101 RELEASE

0101 1010 RELEASE COMPLETE

0100 0110 RESTART

0100 1110

Messages for call clearing

RESTART ACKNOWLEDGE

0111 1011 INFORMATION

0110 1110 NOTIFY

0111 1101 STATUS

0111 0101

Other messages

STATUS ENQUIRY

14.1.6 Basic Signaling Process

The following takes the process of the simplest call control with circuit switching as anexample to describe the basic signaling process of DSS1. Suppose both the calling end and

the called end use ISDN terminal devices. If ISUP is used as the signaling protocol betweenthe originating and terminating offices, the process of a typical call is illustrated in Figure

14-9.

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Figure 14-9Basic signaling process of DSS1 (circuit switching)Originating

officeTerminating

office

IAM

Conversation or data

Callerhookson first

Callerhooks on

first

ISUPCalling terminal

Called terminal

SETUP

SETUP ACK

INFO

INFO

ACMALERT

CONNANM

CONN ACK

SETUPCALL PROC

ALERT

CONN

CONN ACK

DISC(cause value=16)REL DISC(cause value=16)

RLCREL

REL

REL COMP

REL COMP

DISC(cause value=16)

REL

REL COMP

RLC

RELDISC(cause value=16)

REL

REL COMP

TEx TEy

ALERT

REL COMP

REL

Call Setup Process

A call request is sent in the form of the SETUP message. The message is transmitted on anestablished data link.

When the SETUP message reaches the network side of the originating office, the network

entity of layer 3 checks whether the called address is complete. If it is complete, theoriginating office returns the CALL PROCEEDING message to hold the caller waiting. If the

called address is incomplete, the originating office returns the SETUP ACK message torequest subsequent information. The caller sends the INFORMATION message to provide the

remaining information.

When the originating office network side receives the complete address information, itnotifies the exchange for routing and resource allocation. In this example, the call must go

through another exchange before being connected to the callee. Therefore, the originatingoffice exchange must send a message containing the call-related information to the

terminating office exchange through SS7 signaling (ISUP). When the terminating officereceives this message, it sends the SETUP message to the callee. The SETUP message

contains all the information sent by the originating office, including the bearer service

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capacity, terminal lower layer and higher layer attributes, and end-to-end information. It alsocontains the subscriber information channel selected by the terminating office.

On the basic interface of the callee, the SETUP message is transmitted on the broadcast data

link (TEI = 127). Therefore, all the terminals connected to the passive bus receive the SETUP

message. These terminals will check whether they meet the content requirements of theSETUP message. For example, whether they have the same bearer service features as the

message, whether the lower layer and higher layer protocols are consistent, whether theirterminal types match that of the calling terminal, and whether the sub-address (if there is one)

is conformant. The following case is possible. For a call, there are several terminals havingthe information compatible with the SETUP message. Then, these terminals simultaneously

return the ALERTING message to the network and send the ringing tone to the callee. Theterminating office sends the first ALARTING message to the originating office. When the

ALARTING message finally arrives at the calling terminal, the calling terminal sends theringback tone (or displays the ALARTING information) to the caller. When a called terminal

responds to the call, it immediately sends the CONNECT message to the network. Theexchange of the terminating office transfers the CONNECT message to the caller side, and at

the same time sends the CONNECT ACK message to the responding called terminal. Then,the B channels selected by both exchanges are connected. The circuit connection is set up

between the caller and the callee and the circuit is ready for transmitting subscriberinformation.

Call Release Process

The call release process with the caller hooking on first is as follows.

The caller sends the DISCONNECT message (cause value = 16) to the originating office.After the originating office receives the message, it sends the REL message to the terminating

office to disconnect the inter-office circuit. The terminating office returns the RLC message,indicating the completion of call release.

When the originating office sends the REL message to the terminating office, it also responds

to the calling terminal with the RELEASE message to disconnect the inter-office circuit. Thecalling terminal returns the RELEASE COMPETE message, indicating the completion of

disconnection.

After the terminating office receives the REL message from the originating office, it sends theDISCONNECT message (cause value =16) to the called terminal. The called terminal

responds with the RELEASE message to disconnect the circuit between the caller and theterminating office. The terminating office returns the RELEASE COMPLETE message to the

callee, indicating the completion of disconnection. Now, the call is completely released.

For the call release process with the callee hooking on first, DSS1 call control messages on

the user-to-network interface are the same as the above. Refer to Figure 14-9for an analysis.

14.2 R2 Signaling

14.2.1 Basic Concepts

As the telecom network is very large in scale, it is hard to replace channel associated signalingcompletely with SS7 signaling in a short time span. By far, the channel associated signaling

system is still widely used in the international telecom network and telecom networks of

various countries. No. 1 signaling is a subset of R2 signaling.

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R2 signaling consists of line signaling and register signaling. Of these two kinds of signaling,the definition varies from country to country.

Line signaling is transmitted between line devices (repeaters). It is composed of line

monitoring signals. It is used for monitoring the status of connection of trunks and controlling

the connection. A line device cannot be shared among trunks. Instead, each trunk must have aline device. Therefore, line signaling is relatively simple to reduce costs, and the types of line

signaling are few.

Register signaling is transmitted between registers. It is composed of selection signals andservice signals. It is used for selecting route and callee and managing the telephone network.

A register is a shared device. Few registers are needed in a signaling network. Therefore, aregister can be a complex device for matching more kinds of signaling.

14.2.2 Line Signaling

There are three forms of line signaling: DC line signaling, line signaling with in-band single

frequency pulse and digital line signaling.

DC Line Signaling

DC line signaling is used for the real line trunks of electromechanical switches. In China,

local call networks are all stored program-controlled; therefore DC line signaling actually is

not used. DC line signaling will not be introduced in this document.

Line Signaling with In-Band Single Frequency Pulse

In a toll automatic telephone network, if the inter-office transmission system uses carrier,microwave or satellite circuits of frequency-division multiplexing, the inter-office line

signaling usually uses the audio signal, namely, the in-band single frequency pulse signal.

The single frequency used by line signaling is 2600 Hz. It consists of the short signal unit,

long signal unit and continuous signal unit. The short signal unit is a short pulse signal withthe nominal value of 150 milliseconds. The long signal unit is a long pulse signal with thenominal value of 600 milliseconds. The nominal interval of sending two signals is 300

milliseconds. Table 14-4 lists the nominal values of pulse signals and intervals.

Table 14-4Nominal values of the in-band single frequency pulses and their intervalsNominal Values of Pulse Signal or Interval

Pulse Signal

Length (ms)

Interval

(ms)

Sending TimeDeviation atTransmitting

End (ms)

Recognition TimeRange atReceiving End

(ms)

Short signal

unit

150 150 30 80 20Sending

interval

300 60 Long signalunit

600 600 120 375 75

There are two kinds of line signaling: forward signaling and backward signaling. Forwardsignaling is sent from the originating office to the terminating office. Backward signaling is

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sent from the terminating office to the originating office. The structure of signaling signals isdescribed in Table 14-5.

Table 14-5Signal structure of line signaling with in-band single frequency pulseSending DirectionSN. Connection

Status(SignalingName)

Forward Backward

Signaling Signal Structure(ms)

Remarks

1 Occupationsignal

Single pulse 1502 Disconnection

signal

Single pulse 600

150 300 600 Used

betweentoll officesand

between

toll/localoffices

3 Repeated

disconnectionsignal

600600600 Used

betweenlocal

offices

4 Answer signal Single pulse 1505 Clear signal Single pulse 6006 Release guard

signal Single pulse 600

7 Blocking signal ContinuousRe-ringing orforced

disconnectionsignal

150 150150 150150

At leastthreepulses

8 Operator signal

Ringbacksignal

150 150150 150150

At leastthreepulses

A

Single pulse 600 Equivalent

to clearsignal

9 Forced release signal

B

Single pulse 600 Equivalent

to release

guardsignal

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The connection states in Table 14-5 are described as follows:

z Occupation signal is a forward signaling. When the outgoing trunk of the originating

office sends an occupation signal, an incoming trunk of the peer office will change itsstate from idle to occupied.

z Disconnection signal is a forward signaling sent by the outgoing trunk to the incomingtrunk of the peer office. It means that the switch can release the call in abnormal calldisconnection in addition to normal disconnection. The disconnection signal is sent inany of the following cases:

1 The caller hangs up in call control recovery mode

2 The operator of original toll office in toll semi-automatic connection

3 The original office receives a backward register signaling such as connectionbusy.

4 Callee not pickup after alerting timeout, or caller not hang up for more than

90 seconds after callee hangs up

z The repeated disconnection signal is sent by the outgoing trunk of the original officewhen it does not receive the release control signal 3 to 5 seconds after its sending the

disconnection signal. If the release control signal is still not received after sending therepeated disconnection signal, an alarm will be generated.

z The answer signal indicates that the callee picks up the phone. It is a backward signalingsent by the incoming trunk.

z The clear signal indicates that the callee hangs up. It is a backward signaling sent by theincoming trunk from the terminal office to the original office in relay.

z The release control signal is a backward confirmation signal of the disconnection signal.It indicates that the caller of the originating office releases.

z The blocking signal is a backward signaling sent by the incoming trunk of the incomingoffice, indicating that the trunk has been blocked.

z The re-ringing signal is a forward operator signaling. After the toll office operator

establish call connection with the callee and the callee answers, if the callee hangs upand the operator need to call the callee, the operator can send the re-ringing signal.

z The forced disconnection signal is also a forward operator signal. When the toll office

operator tries to connect the call, and finds that the callee is engaged in a local call, theoperator will send the signal after receiving confirmation from the callee.

z The ringback signal is a backward operator signaling. It is sent by the operator back to

the caller.

z The forced release signal is used in the following case. In a bi-directional trunk circuit,sometimes it is occupied in both direction due to disturbances. If no register signaling is

received in 15 seconds, one end will send a forward forced release signal (acting as a

release signal), and the other end will send a backward forced release signal (acting as arelease control signal), and the trunk circuit is released.

Digital Line Signaling

The line signaling monitors the occupation, release, and blocking state of the trunk lines. To

support transmission of 30 voice channel line signaling in the PCM system, a multiframeconcept is introduces. A multiframe consists of 16 individual frames, each of which is 125 s

and contains 32 timeslots. A multiframe has 16 TS16. In the TS16 of the frame 0, the first four

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bits are used for synchronization in the multiframe, the last four bits are used forloss-of-synchronization report, and the TS16 of the other 15 frames are used to transmit theline signaling of the 30 voice channels. Table 14-6describes the usage of TS16 in a PCM

multiframe.

Table 14-6Use of TS16 in a PCM multiframeFrame 0 Frame 1 Frame 2 ...

00 00 XY XX abcd

Voice

channel 1abcd

Voice

channel 16abcd

Voice

channel 2

abcd

Voice

channel 17

z TS16 of frame 0

X: Spare bit, and is set to 1.

Y: Loss-of-synchronization report bit. 0 means normal, and 1 means loss ofsynchronization.

z TS16 of other frames

A 30-voice-channel PCM system sends the line signaling by sampling and transmitting

the TS16 in a multiframe. There are four bita, b, c, and davailable in both

transmission directions for each voice channel. Only the first three bits are used for boththe forward signaling and the backward signaling.

The bit af, bf, and cfare for the forward signaling, and the ab, bb, and cb are for thebackward signaling. Table 14-7 and Table 14-8list the meaning of the signaling.

Table 14-7Meaning of forward signaling in digital linesBit Meaning

af=0 Caller picks up (occupied)

af=1 Caller hangs up (released)

bf=0 Not faulty

bf=1 Faulty

cf=0 Operator re-rings or forced releases

cf=1 Operator does not re-ring or forced release

Table 14-8Meaning of backward signaling in digital linesBit Meaning

ab=0 Callee picks up

ab=1 Caller hangs up (backward released)

bb=0 Idle

bb=1 Occupied or blocked

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Bit Meaning

cb=0 Operator rings back

cb=1 Operator does not ring back

Obviously, no operator intervention is needed in the connection between local offices, and theautomatic connection between a local office and a toll office. Therefore, Cfand Cb are notneeded. Table 14-9 shows the differences between different digital line signaling in the three

bits.

Table 14-9Signaling bits in the automatic and semi-automatic connection of a toll officeForward Signaling Backward Signaling Connection State

af bf cf ab bb

Idle 1 0 1 1 0

Occupied 0 0 1 1 0

Occupation

confirmed

0 0 1 1 1

Answer 0 0 1 0 1

Hang up 0 0 1 1 1

Re-ring (forcedrelease)

0 0 0 1 1

Release 1 0 1 0 1

Release control 1 0 1 1 0

Ring back 1 0 1 0 1

Blocked 1 0 1 1 1

Refer to the previous paragraphs on the definition of connection states.

14.2.3 Register Signaling

Definition of Register Signaling

The R2 register signaling is in multiple frequency control (MFC) mode. It is divided into two

typesforward signaling and backward signaling. In the register signaling, the forward

signaling and backward signaling are both consistent. The forward signaling transmitsaddresses and controls indications, while the backward signaling confirms and controls a call.When sending a digit, the sending party will not stop sending the forwarding signaling until

having received a backward confirmation. Similarly, the receiving end will not stop sending

backward signaling until having detected that the peer end stops sending forwarding signaling.As shown in Figure 14-10, the transmission of R2 register signaling is done in four beats.

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Figure 14-10The transmission process of R2 register signaling

SND RCV

Orginating office

SND RCV

Terminating office

t2

t4

t1

t3

Send the first bit of

forward signaling(Beat 1)

Send the first bit ofbackward signaling

(Beat 2)Stop sending the first bitof forward signaling

(Beat 3)

Stop sending the first bitof backward signaling

(Beat 3)Send the second bit offorwarding signaling

Beat Operations

1 The originating office sends the first bit of forwarding signaling.2 The terminating office (receiving end) receives and identifies the forwarding

signaling, and returns the first bit of backward confirmation signaling. The

terminating office thus replies that it has received the forwarding signaling, and

informs what specific forwarding signaling the originating office shall nextsend.

3 The originating office receives and identifies the backward confirmationsignaling, and stops sending the forward signaling.

4 The terminating office detects that the peer end stops sending the forwardsignaling, and stops sending the backward confirmation signaling. When the

originating office detects that the peer end stops sending the backwardconfirmation signaling, it starts the second control period by sending the next bitof forwarding signaling.

Coding Mode of MFC Register Signaling

There are 15 types of forward signaling of MFC register signaling. Fifteen combinations oftwo from the six high frequencies1380 Hz, 1500 Hz, 1620 Hz, 1740 Hz, 1860Hz, and1980Hz. There are six backward signaling of MFC register signaling. Six combinations of

two from four low frequencies1140 Hz, 1020 Hz, 900 Hz, and 780 Hz. Table 14-10 andTable 14-11 details the combination of frequencies.

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Table 14-10Forward signalingCode

Frq (Hz)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

F0 (1380) F1 (1500) F2 (1620) F4 (1740) F7 (1860) F11 (1980)

Table 14-11Backward signalingCode

Frq (Hz)

1 2 3 4 5 6

F0 (1140) F1 (1020) F2 (900) F4 (780)

Types and Meanings MFC Register Signaling

As described in the above, the MFC register signaling falls into two types: forward andbackward. Both forward signaling and backward signaling have two sub-types: group I and

group II for the forward signaling, and group A and group B for the backward signaling.Group A is the acknowledgement of group I, and group B the acknowledgement of group II.

Table 14-12 lists the meanings of the four groups of signaling.

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Table 14-12Meanings of the four groups of signalingForward Signal Backward Signal

Group Name Meaning Capacity Group Name Meaning Capacity

KA Caller type 10/15

KC Tollconnection

type

5

KE Toll/localoffice and

urbanconnection

type

5

I

Digitalsignal

Digit 10 10

A A Signal Back controlacknowledgement of thenumber receiving statusand connection status

6

II KD Originating

call servicetype

6 B B signal Callee status 6

Note: For a local office using the step-by-step system, there are 10 user types; for a stored program control (SPC) local office using

the crossbar system, there are 15 user types.

z Forward group I signaling

Forward group I signaling consists of connection control signaling and digital signaling.For details, refer to Table 14-13and Table 14-15.

Table 14-13Forward group I signalingType Meaning

KA It refers to the caller type signaling sent from the originating local officeto the originating toll office or originating international switching center

in the forward direction. The purpose of this signaling is to provide the

charging type (periodical, immediate, free) and user level (ordinary, highpriority) information.

The combination of these two kinds of information is indicated with a KAcode, as shown in Table 14-14. The high priority user in the table refers to

those whose calls take precedence over others in the case of networkblocking or overload.

KC It refers to the connection control signaling sent between toll offices in the

forward direction. This signaling has the functions of ensuring thecommunication quality of high-priority users, completing specified calls,and connecting other specified calls (for example, test calls).

KE It refers to the connection control signaling sent from the terminating toll

office to the terminating local office and between local offices in theforward direction. There are two types of KE signaling, as shown in Table

14-14.

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Type Meaning

Digital

signaling

It is a selection signaling. The ten digits, 1, 2, 3, , 0, are used to indicate

the calling number, called area code and called number; "15" is used toseparate the calling number and called number, indicating the end of the

calling number.

z Backward group A signaling

Backward group A signaling is the MFC signaling of forward group I signaling. It

controls and acknowledges forward group I signaling. For details, refer to Table 14-14and Table 14-15.

Table 14-14Backward group A signalingType Meaning

A1, A2, A6 These three kinds of signaling together are called code-sending sequencecontrol signaling. They control the code-sending sequence of forward

digital signaling.

A3 A3 is a conversion control signaling for differentiating forward group Ifrom forward group II, and backward group A from backward group B. In

the toll incoming register at the local office end in the connection fromthe terminating toll office to the local office, or in the multiple frequency

incoming register of the local call connection, A3 signaling is the controlsignaling. In other cases, A3 signaling is a pulse (15030 ms) signaling.

A4, A5 They are the cause analysis signaling when connection to the callee fails.A4 indicates busy, and A5 an unallocated number.

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Table 14-15Forward group I signaling and backward group A signalingForward Group I Signaling Backward

Group A

Signaling

Contents of KA Signaling (Including KOA)

Step-by-StepLocal Office

SPC Local Office UsingCrossbar System (AlsoIncluding PAM Office)

KACode

KA KA KA

KCCode

Contents ofKCSignaling

KECode

Contents ofKESignaling

DigitalSignaling

Contents ofASignaling

1 Periodi

cal

Periodi

cal

Periodi

cal

1 A1:

sendnext bit

2 User

table,immediate

User

table,immediate

User

table,immediate

2 A2:

sendstarting

fromthe firstbit

3

Ordin

ary

Printer

,immediate

Ordin

ary

Printer,

immediate

Ordin

ary

Printer,

immediate

3 A3:

shift toBsignal

4 Standby Standby Standby 4 A4:

telepho

ne keyblocking

5 Ordinary, free Ordinary, free Ordinary, free 5 A5:

unalloc

atednumber

6 Standby Standby Standby 6 A6:

send

KA andcallingnumber

7 Standby Standby Standby

8 Standby High priority,periodical

High priority,periodical

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Forward Group I Signaling BackwardGroup ASignaling

Contents of KA Signaling (Including KOA)Step-by-StepLocal Office


KACode

KA KA KA

KCCode


KECode


DigitalSignaling


9 (Have right for

suburbanautomatic call;have right for

toll automatic

call

Standby Standby

10 (Have no right

fortoll/suburbanautomatic call)

High priority,free

High priority,free

11 11 Stand

by

11

*

Voice

mailbo

xnotifiesthe

user to

leave amessage

12

Standby

12 Zindicat

es a

specifiednumbe

r call

12 Standby

13 Test call 13 T

indicates atest

connectioncall

13 T

indicates atest

call

14

Standby 14 High

priority

14 Standby

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Forward Group I Signaling BackwardGroup ASignaling

Contents of KA Signaling (Including KOA)Step-by-StepLocal Office


KACode

KA KA KA

KCCode


KECode


DigitalSignaling


15 15 Contr

ol thenumber of

satellit

ecircuitsegments

15 Voice

mailboxcancels

notifyi

ng theuser toleave a

message

NOTE

Those types with brackets are not sent to the originating toll office; * indicates that the signal is needed for cooperating with

old equipment.

z Forward group II

Forward group II signaling is also called KD signaling. It indicates the originating callservice type. It is used, based on KD, to judge whether the attendant can break in orforcefully release a local call. Table 14-17describes the role of this signaling.

z Backward group B signaling

Backward group B signaling is also called KB signaling. It indicates the status of the

callee. It is sent after the reception of KD signaling to acknowledge the control andconnection of KD signaling.

Refer to Table 14-16 for the contents of backward group B signaling.

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Table 14-16Forward group II signaling and backward group B signalingForward Group II Signaling(KD)

Backward Group B Signaling (KB)

Contents of KB SignalingKD Code Contents of KDSignaling

KB Code

During Toll CallConnection or TestCall Connection(when KD=1, 2 or 6)

During Local CallConnection (when KD=3or 4)

1 Semi-automatic

call of a tollattendant

1 Callee idle Callee idle, first party releaserecovered

2 Automatic toll call,

Used

for tollcallconnecti

on 2 Callee local busy

3 Urban call 3 Callee toll busy

Standby

4 Fax or user data

communication of

the urban user;high priority user

Usedfor

urbancall

connection

4 Telephone key blocked Callee busy or telephone key

blocked

5 Automatically

checking callingnumber

5 Called number is anunallocated number

Called number is anunallocated number

6 Test call 6 Standby Callee idle, calling party

release recovered

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Table 14-17Contents and role of KD signalingRole of KD Signaling

WhetherAttendant CanBreak in LocalCall

Whether Toll AttendantCan Break in

KDCode

Originating CallService Type

Yes No Yes No

1 Semi-automatic

breaking in of tollattendant

2 Automatic toll call 3 Urban call 4 Urban fax or data 5 Automatically checking

calling number

6 Test call

14.2.4 Application of R2 Signaling

Figure 14-11 illustrates the typical application of R2 signaling in NGN.

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Figure 14-11Typical application of R2 signaling in NGN

GTSOFTX3000

IP MAN

Exchange

UMG8900

POTSPOTS POTS POTS

R2 R2

PBX

H.248/IUAH.248/IUA

UMG8900

IP MAN

Exchange

UMG8900

POTSPOTS POTS POTS

R2 R2

PBX

H.248/IUAH.248/IUA

UMG8900

GTSOFTX3000

IP MAN

Exchange

UMG8900

POTSPOTS POTS POTS

R2 R2

PBX

H.248/IUAH.248/IUA

UMG8900

IP MAN

Exchange

UMG8900

POTSPOTS POTS POTS

R2 R2

PBX

H.248/IUAH.248/IUA

UMG8900

The UMG8900 provides the interconnection between R2 trunks and the exchange and PBX. It

packages the R2 message in the H.248 message and sends the R2 message to the Soft3000,thus implementing the interworking between NGN and the exchange and PBX in PSTN.

14.2.5 Basic Signaling Flow

Figure 14-12 takes the connection process of a local call as an example to introduce the basicflow of R2 signaling.

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Figure 14-12Signaling process of a local callOriginatingoffice

Terminatingoffice

Transitoffice

P

Occupy

Q

A1

Occupation acknowledge

A1

R

Talk

AnswerAnswer

Callee hooks on

Caller hooks onCaller hooks on

Idle

A1

A

A1

PA1

B

A1

QA1

C

A1

RA1

D

A1

A

A3

KD=3

A1

B

A1

C

A1

B

A1

C

A3

D

KB=1

KD=3

KB=1

Occupy

Occupation acknowledge

Callee hooks on

Idle

In Figure 14-12, the called number is PQRABCD, in which PRQ is the office directionalnumber, and ABCD is the user number. The figure shows that line signaling and registersignaling are sent segment by segment. After the transit office receives PQR completely, itstarts routing to send register signaling of the originating office. After sending the full number,

the originating office waits for the terminating office to send the A3 signal, and then

completes the signaling flow. This connection mode takes a long time. Therefore, it is usedwhen the transmission line is of a poor quality.

01-14 DSS1 and R2

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