EWSD - DIGITAL SWITCHING SYSTEM

Communications networks are changing rapidly, placing vast new demands on

switching systems. Once single-function machines designed simply to connect voice

circuits, central office switches must now deliver a wide range of services, create

customized services on demand, and manage network operations. In addition to these

changes in functionality, changes to how these switches are deployed have also taken

place. Once locked into central offices, they are now distributed into numerous network

nodes, close to communications users and customized to the end users' needs.

..

EWSD USE:

Because of its inherent versatility, the EWSD system has become the universal switch,

capable of responding to the full range of telecommunications standards and the full

variety of global service demands. Over 160 million lines of EWSD switch capacity are

now in service in more than 100 countries. In North America, EWSD systems are leading

the introduction of integrated digital services, Advanced Intelligent Network (AIN)

capabilities and open interfaces to multi-service terminal platforms.

The Siemens EWSD Switching System is well ahead of the challenge with a uniquely

flexible architecture that anticipates change and adapts easily.

Personal Communications Services

The EWSD switch offers Bellcore AIN 0.2 Personal Communications Services. In

addition, the EWSD switch also provides Global System for Mobile communications

(GSM) based PCS. Siemens has established itself as the world leader in GSM by its key

role in European wireless communications and is building on that experience to link PCS

and wired networks with the same fundamental EWSD technology.

Growing in Capacity and Connectivity

The EWSD Switching System is based on a modular hardware platform,

completely integrated under generic software. Processing is distributed throughout the

modular components, and the components can be assembled into a single central office,

or they can be distributed to move call processing close to subscriber communities.

DIGITAL LINE UNIT (DLU)

The DLU can be operated either locally or remotely in the network node. Remote DLUs

are installed in the vicinity of concentrated groups of subscribers. This reduces the length

of the subscriber lines and concentrates traffic to the network node on digital

transmission links, which has the effect of rationalizing the cost of the distribution

network

Functional areas with the subsystems in the node

PRINCIPAL FEATURES OF THE DLU

· Connection capacity of a rack

Depending on which modules are equipped and what traffic volume is to be carried

– up to 952 analog subscriber lines or

– up to 928 digital subscriber lines (ISDN basic access)

– 16 x 2 V5.1 interfaces

· Line types

The following analog line types can be connected:

– subscriber lines (individual lines) with rotary dialing, DTMF dialing, subscriber's

private meter operating at 16/12 kHz

– payphones (coinbox)

– analog PBXs with/without direct dialing

The following digital line types can be connected:

– ISDN basic access

– small and medium-sized PBXs

· Expansion capability

In small modular increments which consist of adding

– one analog subscriber line module (SLMA), which may be equipped with 4, 6 or 8

analog subscriber line circuits (SLCA), according to line type

– one digital subscriber line module containing 8 digital subscriber line circuits (SLCD)

– one subscriber line module (SLMX) for two V5.1 interfaces, each with 30 subscribers

(Access Network (AN))

· Signaling

Via common channel signaling (CCS) for transmission of control information between

the DLU and line/trunk groups (LTGs). Channel 16 is used in both directions for

signaling. For the local DLU interface, channel 32 is used for CCS on both 4096-kbit/s

links.

· High reliability

A high level of reliability is ensured by:

– connecting each DLU to two LTGs

– duplicating all DLU units performing central functions, with load sharing

– continuous self tests

· All features are available, regardless of whether the DLU is deployed locally or

remotely.

· Integral test unit (TU) for automatic and manual testing of line circuits, access lines and

analog telephone terminals, extended-range subscribers or special modules.

· Metallic test access (MTA) for external subscriber line test systems relating to the

subscriber lines (a/b wires) connected to the DLU.

· DLU stand-alone mode for remote DLUs (RCUs) in the event that all transmission links

to the network node should fail.

STRUCTURE OF DLU

In functional terms, the DLU is subdivided as follows:

Central functional units

The central functional units in the DLU are duplicated and together form DLU systems

0 and 1. A DLU system consists of:

– control for DLU (DLUC)

– digital interface unit for DLU (DIUD) or alternatively

digital interface unit for local DLU interface, module D (DIU:LDID)

– clock generator part of the bus distributor module BD with clock generator CG.. for

DLU (BDCG)

The bus distributor BD units also belong to the central functional units.

Signal distribution

Communication with the central and peripheral functional units of the DLU takes place

with the BD units via the duplicated bus systems 0/1.

The BD units comprise:

– Bus distributor function BD on the functional unit (BDCG)

– Bus distributor basic modules (BDB)

– Bus distributor extension modules (BDE)

The DLU bus systems consist of:

· Control buses

The control buses 0/1 carry control information, i.e. line signals and commands from

the DLUC to the subscriber line modules (SLM), line signals and messages in the

other direction.

· 4096-kbit/s buses (speech/data buses)

The 4096-kbit/s buses 0/1 transmit speech/data information to and from the SLMs.

· Collision buses

The duplicated collision bus is used for control purposes when packetized X.25 data

is transmitted over the D channel of the ISDN basic access.

· Ringing and metering bus

The ringing and metering bus feeds ringing and metering voltage from the ringing

generator and metering voltage generator (RGMG 0/1) via the bus distributors (BDB

and BDE).

Ringing generator and metering voltage generator (RGMG)

The ringing generator and metering voltage generator (RGMG) generates the sinusoidal

ringing and metering voltages needed in the DLU for analog subscribers. It also generates

a synchronizing signal for application of ringing.

Peripheral functional units

The peripheral functional units are:

· Subscriber line modules (SLMs)

– subscriber line module, analog (SLMA), for connecting analog subscribers

– subscriber line module, digital (SLMD), for connecting ISDN subscribers

– subscriber line module, V5.1 interface (SLMX)

For remote operation:

· Stand-alone service control (SASC-E)

During emergency service in the DLU the stand-alone service control, abbreviated

as SASC-E, controls call setup and release for analog and ISDN subscribers (single

remote DLU or remote control unit (RCU)) and enables DTMF dialing for pushbutton

users.

· External alarm set module (ALEX)

The external alarm set module (ALEX) forwards external alarms (e.g., power supply

failures) to the network node.

Test equipment

The DLU test equipment includes:

· Test unit (TU)

The test unit (TU) can be used to perform tests and measurements of lines and line

circuit modules.

· Functional units for metallic test access (MTA)

The metallic test access (MTA) allows external line testing systems to access the

analog lines connected to the DLU.

Block diagram of the DLU

(1) For local use of DLU , DIU:LDID0 and DIU:LDID1

(2) Ringing and metering voltages for analog subscribers only

(3) Functional units for the MTA

(4) RGMG only for self-testing the test unit (TU)

(5) Connection of two V5.1 interfaces, each with 32 channels

(6) Emergency service (for remote use)

(7) For external alarms, e.g. power supply failure (for remote DLU only)

LINE TRUNK GROUP (LTG)

The line/trunk group (LTG) forms the interface between the digital environment of the

node and the digital switching network (SN).

The connection between the LTG and the duplicated switching network (SN) is made

by a secondary digital carrier (SDC). The transmission rate on the SDC from the LTG to

the SN and vice-versa is 8192 kbit/s (abbreviated to 8 Mbit/s). Each of these 8-Mbit/s

multiplex systems has 127 time slots, each with 64 kbit/s for useful information, and one

64kbit/s time slot for messages.

Operation and maintenance functions

The operation and maintenance functions of the LTG comprise:

– transmitting messages to the CP for traffic measurement and observation

– switching test calls

– testing the trunks and port-specific parts of the LTG with the aid of the integrated

automatic test equipment for trunks (ATE:T) and the automatic test equipment for

transmission measurement (ATE:TM)

– indication of important operating states (e.g. channel assignment) with respect to

the functional equipment

– creation, blocking, release of equipment via man-machine language (MML)

commands.

Subscriber connections are connections that convey useful information. The

subscribers may be telephone subscribers, or also, for example, telecopying devices,

fax machines. For setting up subscriber connections, each LTG has at its disposal 127

time slots (1 - 127), also called channels, per 8-Mbit/s multiplex system.

The User information is the for the communication relevante information (speech, text,

data, picture).

Messages serve the purpose of inter-processor communication with the coordination

processor (CP), other LTGs and the CCNC. User information and messages are

transmitted together.

Signaling is communication between network nodes.

Call processing functions

The call processing functions of the LTG comprise:

– receiving and interpreting the signaling from the trunk and subscriber line

– transmitting the signaling

– transmitting audible tones

– transmitting messages to the coordination processor (CP) and receiving commands

from the CP

– transmitting and receiving reports from the group processors (GP) of other LTGs

– transmitting orders for common channel signaling network control (CCNC);

receiving orders from the CCNC

– controlling the signaling to DLU, PA

– matching the line conditions to the 8-Mbit/s standard interface to the duplicated

switching network (SN)

– through-connection of messages and useful information

Structure OF LTG

The line/trunk group G (LTGG) is divided into the following several functional units

– group processor (GP)

– group switch and link unit (GSL)

– line/trunk unit (LTU)

– signaling unit (SU)

Group processor (GP)

The group processor (GP) converts the incoming information from outside the network

node into the intrasystem message format and controls the functional units of the LTG.

Group switch and link unit (GSL)

The group switch and link unit (GSL) connect the line/trunk unit (LTU) to the signaling

unit (SU) or the switching network (SN).

Line/trunk unit (LTU)

The task of the line/trunk unit (LTU) is to adapt connected lines to the internal LTG

interfaces add equalize propagation delays (synchronizing network node and line clock).

SWITCHING NETWORK (SN)

The Digital Electronic Switching System (EWSD) is equipped with a very powerful

switching network (SN). By virtue of its high data transmission quality, the switching

network can switch connections for various types of service (for example telephony,

facsimile, teletext, data transmission). This means that it is also ready for the Integrated

Services Digital Network (ISDN).

The switching network, to which up to 504 line/trunk groups (LTG) can be connected

(SN:504LTG), can be employed in a number of optimized capacity stages .

The most significant features of the switching network are:

low space requirement

negligible internal blocking

high degree of functional integrity provided by duplication

modular hardware and software

only eight module types for all capacity stages of the switching network

ease of expansion

use of the latest technology (NMOS and TTLLS)

one switching format for both speech and data signals (octets)

single-channel connections broadcast connections (for application of signal

sources)

microprocessor control with read-only software (firmware)

self-supervision

multilayer printed circuit backplanes in the module frames

Structure OF SWITCHING NETWORK

The modular structure of the EWSD switching network allows it to be partly

equipped and then expanded in small stages if required.

The following basic structures are used in EWSD switching networks:

In large and very large exchanges the capacity stages of the switching network include

– one time stage incoming (TSI)

– three space stages (SS)

– one time stage outgoing (TSO)

Medium-sized and small exchanges (SN:63LTG and SN:15LTG) contain

– one time stage incoming (TSI)

– one space stage (SS)

– one time stage outgoing (TSO)

In a time stage, the 8-bit code words (octets) can change time slots and highways

between the input and output.

In a space stage, the 8-bit code words can change highways between the input and

output but remain in the same time slot.

The EWSD switching network has full availability. This means that every 8-bit code

wordon an incoming highway entering the switching network can be switched to any

time sloton an outgoing highway leaving the switching network.

Fig shows a simplified diagram of a switching network for 63 LTGs. The grouping

parameters shown refer to the number of 8192-kbit/s highways. All 8192-kbit/s highways

have 128 channels with a transmission capacity of 64 kbit/s each (12864 = 8192 kbit/s).

Switching network for 63 LTGs incoming time stages (TSI) and outgoing time stages

(TSO)

The switching network is fully transparent to the 8-bit code words switched from the

incoming channels to the outgoing channels that lead to the desired destination. This

means that every bit in every 8-bit code word is transmitted to the output of the switching

network unchanged, just as it appears at the input (bit integrity). The time slots in the

switching network used for one through-connection form a 64-kbit/s connection path.

There is no restriction on the possible variations of consecutive binary ”0”s and ”1”s on

any 64-kbit/s connection path. In other words, there is bit sequence independence on

all 64-kbit/s connection paths through the switching network.

The time stages incoming (TSI) and time stages outgoing (TSO) are accommodated in

pairs on common time stage modules (TSM). The diagram of the switching network in

and subsequent figures takes account of this physical pairing of TSI and TSO.

Each block in the switching stages T and S represents a time stage module (TSM) or a

space stage module (SSM).

Each of the two grouping parameters 4 of a TSM means:

– four 8192-kbit/s incoming highways

– four 8192-kbit/s outgoing highways

COORDINATION PROCESSOR (CP)

A network node is divided into different function areas. The functions of these areas

are implemented for the most part by independent subsystem. Each subsystem has its

own microprocessor controls, for example, the group processors (GP) in the line/trunk

groups (LTG) in the function area for access.

The coordination processor (CP) is responsible for the common functions in the

network node, such as the coordination of the distributed microprocessor controls and the

data transfer between them.

The CP performs the following functions in a network node:

Call processing

– Digit translation

– Routing

– Zoning

– Path selection through the switching network

– Call charge registration

– Traffic data administration

– Network administration

Operation and maintenance

– Input and output from/to external memories (EM)

– Communication with the operation and maintenance terminal (OMT)

– Communication with the operation and maintenance center (OMC)

Safeguarding

– Self-supervision

– Fault detection

– Fault treatment

One CP type is available for all sizes and configurations of a network node, namely the

113D coordination processor (CP113D).

The CP113D meets all the applicable safety and performance requirements.

Main features of the CP113D are:

– Use of a modular multiprocessor system

– can be adapted to different sizes of exchange

– Performance (dependent on configuration): typically, more than 1 000 000 BHCA

(The effective, dynamic performance depends on the features available, the traffic

distribution and the call mix; it must be defined individually for each case

– Combination of task and load sharing

– Redundancy achieved by duplication of important functional units as well as

creation of call processor pools

– Use of high-performance micro-processor types

– processing width of 32 bits

– Addressing capacity of 4 Gbytes (for the CP113C)

– Common memory with a capacity of 64 Mbytes to 512 Mbytes

(based on 4-Mbit DRAM)

– Local memory per processor with a maximum capacity of 32 Mbytes

(expansion up to the required capacity is affected by the use of an appropriate

number of memory modules)

– 8 interrupt levels with fixed priorities

– Flexible in allowing connection of peripheral devices

Major functions in the area of coordination in a network node are also undertaken

by:

– the system panel (SYP)

– the message buffer (MB)

– the central clock generator (CCG), and

– the input/output processor (IOP).

Structure OF CP113D

The CP113D is designed as a modular, multiprocessor system. The modular structure

allows it to be easily adapted to different sizes of network node. The CP113D has a large

degree of redundancy as a result of the duplication of important functional units.

Moreover, various safeguarding measures in the hardware and software ensure a high

level of availability.

Structure of the CP113D

The CP113D comprises the following functional units

· base processors (BAP)

· call processors (CAP)

· input/output controls (IOC)

· bus for common memory (BCMY)

· common memory (CMY)

· input/output processors (IOP)

CENTRAL CLOCK GENERATOR (CCG)

In order to switch and transmit digital information, the sequence of operations must be

synchronous throughout the equipment involved. This requires a clock supply with a

high level of reliability, precision and consistency for all the nodes in the digital network.

This task is fulfilled by the central clock generator (CCG), which is assigned to the

coordination section of a node .

In view of its vital role, the central clock generator is always duplicated. One is always

switched as master and the other as slave. This ensures that in the event of a malfunction

or failure affecting the master CCG, the master/slave roles can be switched over

immediately and automatically, and that the clock supply to the connected subsystems

continues uninterrupted.

Each subsystem generates fresh synchronization pulses, which it synchronizes with the

output pulses of the equipment unit preceding it in the circuit, in order to then

synchronize the equipment unit following it in the circuit.

In addition to internal clock distribution, there is also the option of external clock

distribution, in which the CCG controls synchronization.

This overview deals with the CCG and its functional units, clock distribution, and the

prepositioned reference frequency hierarchy in networks.

Throughout the rest of this overview, we will be more specific and use the current

designation "central clock generator A (CCG(A))" instead of the general term "CCG".

Structure of the Central Clock Generator

The central clock generator (CCG) comprises the following functional units:

– clock generator

– clock synchronization unit

– clock transfer unit

– interface buffer

Clock Generation

The clock generator generates a nominal reference clock (4096 kHz) for the clock

generator in the clock synchronization unit.

The clock generator also sends an 8192-kHz reference clock to the clock generator of

the partner CCG(A). If both external reference frequencies fail, the partner CCG(A) is

synchronized to this 8192-kHz signal. Moreover, the partner CCG(A) is also supplied

with a synchronization clock of 2048 kHz. In plesiochronous operation, this clock is

switched from the clock generator of the active CCG(A) to the external reference clock

input of the standby CCG(A). (Module type CCG11A is required for this purpose.)

Clock Synchronization

The clock synchronization unit synchronizes itself to the nominal reference clock (4096

kHz) of the clock generator oscillator and generates a synchronization clock (8 kHz).

This clock is fed not only to the internal clock transfer unit, but also to the subsystems

Clock Transfer

The clock transfer unit transfers the 8-kHz synchronization clock (SYCLK) from the

clock synchronization unit to outputs for further message buffer groups (MBGs) of the

MB(B) for the purpose of frequency and frame synchronization and to reserve outputs.

These outputs are isolated from the clock synchronization unit by drivers.

Interface Buffer

The CCG(A) contains microprocessors which are responsible for control and

supervision. The interface buffer adapts the internal bus structure of the CCG(A) to the

bus structure of the IOP:MB in CP113 .

The interface buffer enables the exchange of data and control signals between the

CP113 and the CCG(A). The line drivers responsible are synchronized by the

synchronous signal (4096 kHz). Commands are transferred from the CP113 to the

CCG(A). Messages are transferred from the CCG(A) to the CP113 .

SYSTEM PANEL (SYP)

In the digital electronic switching system EWSD the system panel (SYP) belongs to

the coordination processor 113 (CP 113).

The purpose of the system panel is to display alarms and advisories of internal and

external supervisory units (outside the system) both visually and acoustically. In contrast

to the detailed error messages, which can be retrieved from the CP113 via the operation

and maintenance terminal (OMT) in the event of a malfunction, the system panel

provides a continuous overview of the current functional status of the system.

The functional status of exchanges in an entire areas can be monitored from a

superordinate operation and maintenance center (OMC). For this purpose, a central

system panel (CSYP), which displays all alarms and advisories reported by the

exchanges, can be used in the OMC.

SYSTEM PANEL LAYOUT

The system panel (SYP) consists of a system panel control (SYPC) and at least one

system panel display (SYPD). Other system panel displays can be operated in the

exchange itself, a superordinate exchange or an operation and maintenance center.

System Panel Layout

System panel control

The system panel control receives alarms and advisories as well as additional data

(date, time and call-processing CP load) from the CP113. External alarms and advisories

are received from external supervisory units. The system panel control processes

the received information and forwards it to all system panel displays simultaneously. If

necessary, the system panel control can forward some of the received alarms and

advisories to external fault signaling devices (outside the system) as well. In addition, the

system panel control reports certain actions at the system panel displays (e.g. alarm

confirmation) back to the CP113.

In its basic configuration, the system panel control has the ability to connect up to four

system panel displays and up to 24 external supervisory units (outside the system).

Depending on the requirements, mechanisms for connecting an additional four system

panel displays and up to 24 external fault signaling devices (outside the system) can be

provided.

System panel display

The system panel display indicates the alarms and advisories as well as the date, time

and call processing CP load. It has four types of displays and controls

Front panel of the system panel display

· LED fields with one LED pair per display

23 LED fields with one LED pair per display are provided. They are assigned the

following elements:

– Seven permanently specified subsystems and functional units:

Line/trunk groups

Switching network

Coordination processor

Message buffer

Central clock generator

Common channel signaling network control and

System panel

– Eight internal system messages:

Trunk group alarm

Line lockout

Signaling link alarm

Call identification

External DLU alarm

Administration alarm

Recovery

CP time insecure

– Eight freely programmable, external supervisory units (outside the system), e.g.

for:

Fire

Power failure

Failure of the air conditioning unit

· Single-LEDs

20 single LEDs are provided. They are assigned to:

– Three permanently specified internal system messages:

Maintenance alarm

Service alarm

External equipment (e.g. DLU)

– Eight internal system states, e.g.:

Trunk group blocked

Catastrophe levels 1 and 2

System operator (operator call)

Hardware functional units

Signaling link blocked

Alarm indication suppression

– Eight freely programmable, external supervisory units (outside the system), e.g.

for:

Entry supervision

Main power supply

– One internal SYP message

Update running on displays of the connected SYPDs

· 7-segment decimal display

Three 7-segment decimal display panels are provided. They are used for displaying

additional permanently specified data:

– Date (month and day

– Time (hour and minutes)

– Call processing CP load

· Keys

Three keys are provided. These keys have the following functions:

– Update key

For updating the displays on all connected SYPDs from the system panel control

– Test key

For conducting a function test on all visual and acoustic indicators on the SYPD– Accept

key

– For deactivating the horn.

· Horn

The horn is used for acoustic signaling of alarms. It is located in the SYPD housing.

MESSAGE BUFFER (MB)

A network node is subdivided into several functional areas. The tasks of these

functional areas are performed by largely independent subsystems. The subsystem

“Message buffer B (MB(B))” is assigned to the coordination area of a network node .

The task of MB(B) is to control the exchange of messages between the following

subsystems:

– coordination processor (CP113) and line/trunk groups (LTG):

commands and messages

– CP113 and switch group controls (SGCB) of the switching network:

setting commands for the switching network

– LTGs among one another:

reports

– LTGs and the common channel signaling network control (CCNC):

orders

The MB(B) is designed for the more stringent performance requirements. The increased

performance in conjunction with of an MBU:LTG Type C provides operation with an

access network (AN) via interface V5.2 or TR303.

The characteristics of an MB(B) with MBU:LTG Type C include the following:

– excellent reliability due to redundancy

– load distribution in normal operation

– control of broadcasting and collective commands

– higher transmission rate by rerouting reports within an MBUL(C) as well as the

packeting or unpacketing of messages

– microprocessor control with permanently stored software (firmware)

– self-monitoring

– simple expansion in stages

.

Structure of Message Buffer B

Depending on the capacity stage, MB(B) can accommodate up to four message buffer

groups (MBG). It is implemented with redundancy in a network node, i.e. MB(B)0

comprises MBG00...MBG03, and MB(B)1 comprises MBG10...MBG13.

The arrangement of MB(B) and MBGs in a network node, including redundancy is

shown in fig.

For reliability reasons, each MB(B) side (with its MBGs) is supplied via two IOP:MBs

(transposition).

Arrangement of MB(B) in a network node

COMMON CHANNEL SIGNALLNG NETWORK CONTROL

(CCNC)

The EWSD digital electronic switching system can control connections to and from

other network nodes using all the common signaling systems.

One system that is particularly suitable for stored-program-controlled digital nodes is

signaling system no. 7 (SS7). This transports signaling information separately from the

user information (voice, data) on common-channel signaling links.

The advantages of common channel signaling as against channel-associated signaling

are:

– higher speed signaling

– large repertoire of signals

– very reliable signal transmission

– flexibility to adapt to future requirements

SS7 common channel signaling can be used in all types of node: local and transit

exchanges, international gateway exchanges and nodes serving mobile subscribers.

The following are suitable for the transmission medium:

– copper wires,

– optical fibers,

– digital radio links,

– satellite links.

The common-channel signaling links are conducted via an independent signaling

network in which the nodes are integrated in the nodes of the telecommunication

network or form independent nodes in the signaling network.

There are two types of node in a signaling network, performing different functions:

– signaling points (SP),

– signaling transfer points (STP).

An SP represents the origin or destination of signaling messages. An STP receives

signaling messages from an SP or another STP and forwards them to an SP or STP.

Some signaling points may perform both SP and STP functions. The number of

signaling points in a signaling network is determined by project or traffic requirements

and conditions.

The signaling functions in an EWSD network node are handled by the "common

channel signaling network control (CCNC)".

The CCNC handles the exchange of messages between different nodes in order to

control and monitor connections and to administer the signaling network. The processors

in the node pass messages they wish to transmit to the CCNC with the addresses

of the relevant destination processors in the destination node. The CCNC now creates

signaling messages in SS7 format from this information and sends them over the

appropriate signaling links. When it receives incoming messages, the CCNC checks

whether they are intended for a processor in its own node or whether they have to be

forwarded over outgoing signaling links to another node.

The separation of the traffic and signaling channels offers the advantage of being able

to exchange any required signaling messages in parallel with the user information.

Because the CP and CCNC are units which operate independently, no dynamic losses

arise in the CP when there is signaling traffic.

STRUCTURE OF CCNC

Each of the hardware units in the CCNC has its own software/firmware, which is

stored in an EPROM. The SIMP and CPI also contain reloadable software that is

downloaded from the CP. Common software for the control of CP-CCNC tasks is

contained in the CP. The CCNC software is divided into subsystems. These subsystems

are in turn made up of modules (procedures, processes and data) containing the functions.

CCNC: Common channel signaling network control

CP: Coordination processor

DLU: Digital line unit

LTG: Line/trunk group

MH: SIMP: Message handler for the signaling management processor

MUXM: Master multiplexer

OMDS: Operation and maintenance data communication system

PMU: CPI: Processor memory unit for the coordination processor interface

PMU: SIMP: Processor memory unit for the signaling management processor

SILTC: Signaling link terminal control

SILTD Signaling link terminal unit, digital

SIPA: Signaling periphery adapter

SN: Switching network

Common Channel Signaling System No. 7

Communication networks generally connect two subscriber terminating equipment

units together via several line sections for message exchange (e.g. speech, data, text or

images). Control information has to be transferred between the exchanges for call

control and for the use of facilities. In analog communication networks, channel-

associated signaling systems have so far been used to carry the control information. Fault

free operation is guaranteed with the channel-associated signaling systems in analog

communication networks, but the systems do not meet the requirements in digital,

processor-controlled communication networks. Such networks offer a considerably

larger scope of performance as compared with the analog communication networks,

due, for instance, to a number of new services and facilities. The amount and variety of

the control information to be transferred is accordingly larger. The information can no

longer be economically transported by the conventional channel-associated signaling

systems. For this reason, a more efficient signaling system is required in digital,

processor-controlled communication networks.

The signaling system no. 7 (SS7) has therefore been specified. SS7 is optimized for

application in digital networks.

It is characterized by the following main features:

· internationally standardized (national variations possible)

· suitable for the national and international/intercontinental network level

· suitable for various communication services such as telephony, text services, data

services and other services

· suitable for service-specific communication networks and for the integrated services

digital network (ISDN)

· high performance and flexibility along with a future-oriented concept which will meet

new requirements

· high reliability for message transfer

· signaling on separate signaling links; the bit rate of the circuits is therefore exclusively

for communication

· signaling links always available, even during existing calls

· use of the signaling links for transferring user data also

· used on various transmission media

cable (copper, optical fiber)

radio relay

satellite (up to 2 satellite links)

· use of the transfer rate of 64 kbit/s typical in digital networks

· used also for lower bit rates and for analog signaling links if necessary

· automatic supervision and control of the signaling network (signaling links +

signaling points).