1.0. DIGITAL SWITCHING CONCEPTS:- Telephony was invented in 1876 and automatic telephone exchanges were

developed in 1895.All these exchanges were analog.Now we have only digital exchanges in the

network,which work on time switching or time and space switching.The digital exchanges are

compatible to provide value added services and Intelligent services.

Communication can be defined as the transfer of information from one point to

another point as per desire of the user under the control of some system.

The key aspects of a communication network are:

1.Switching

2.Transmission

3.Call control or signaling

4.End terminals or network elements

2.0. SWITCHING:- Switching is basically estabilishing temporary path or connection between two

points or it can also be defined as writing at one point of time and reading at another point of

time.

There are two modes of switching employed in our network.

Circuit Switching

Packet Switching

2.1. CIRCUIT SWITCHING:-

In normal telephone service,basically,a circuit between the calling party and

called party is set up and this circuit is kept reserved till the call is completed.Here two speech

time slots are involved,one of calling subscriber,other of called subscriber.It is called CIRCUIT

SWITCHING.

Circuit switching is based on the principle of SAMPLING THEOREM.

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2.1.1. SAMPLING THEOREM:-

Sampling Theorem states

“If a band limited signal is sampled at regular intervals of time and at a rate equal to or more

than twice the highest signal frequency in the band,then the sample contains all the information

of the original signal.Mathematically,if fh is the highest frequency then sampling frequency Fs

needs to be greater than or equal to 2fh.”

i.e; Fs>=2 fh.

2.2. PACKET SWITCHING:-

In packet switching,the information(speech,data etc.) is divided into packets,

each packet containing piece of information also bears source and destination address.These

packets are sent independently through the network with the destination address embedded in

them.Each packet may follow different path depending upon the network.

3.0. SWITCHING CONCEPT:-

To connect any two subscribers,it is necessary to interconnect the time-slots

of the two speech samples which may be on same or different PCM highways.

The digitized speech samples are switched in two modes:

. Time Switching

. Space switching

3.1. TIME SWITCHING:-

“A Digital Time Switch consists of two memories,viz,a speech or buffer

memory to store the samples till destination time-slots arrive,and a control or

connection or address memory to control the writing and reading of the samples

in the buffer memory and directing them on to the appropriate time-slots.”

Speech memory has as many storage locations as the number of time slots

in input PCM,e.g; 32 locations for 32 channel PCM system.

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3.2. SPACE SWITCHING:-

“A space switch is used to simply change the PCM of a incoming time slot

keeping the time slot number same in the outgoing PCM.”

4.0. SWITCHING TECHNOLOGIES OF BSNL:-

OCB-283

EWSD

5ESS

AXE-10

C-DOT

E-10B

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5.0. EWSD: AN OVERVIEW:-

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 Digital switching system has been designed and manufactured by M/s Siemens,

Germany. The name is the abbreviated form of German equivalent of Electronic

Switching System Digital (Electronische Wheler Systeme Digitale). EWSD switch can

support maximum 2,50,000 subscribers or 60,000 incoming, outgoing or both way trunks,

when working as a pure tandem exchange. It can carry 25,200 Erlang traffic and can

withstand 1.4 million BHCA. It is claimed that with the latest hardware and software

version (Ver. 16), the system can withstand a BHCA of 16 million , can connect 6,50,000

subscribers or 2,40,000 trunks and handle 1,00,800 Erlang traffic. It can work as local

cum transit exchange and supports CCS No.7, ISDN and IN and V5.X features.

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OMT PRINTER

SN

DLU LTG(B)

LTG(C)

CCNC

CPMB

CCG

SYP

LINES

TRUNKS

MOD MDD

5.1. EWSD: BLOCK DIAGRAM:-

6.0. SYSTEM ARCHITECTURE:-

6.1)DIGITAL LINE UNIT(DLU):-

It is a functional unit on which analog and digital subscribers (ISDN-BRI)

lines are terminated.

DLUs are connected to EWSD sub-systems via a uniform interface standardized by

CCITT, i.e., Primary Digital Carrier (PDC) to facilitate Local or Remote connection

of subscriber lines. A subset of CCS# 7 is used for CCS on the PDCs. One DLU is

connected to two different LTGs for the reasons of security. A local DLU is

connected to two LTGs via two 4 Mbps (64 TSs) links, each towards a different

LTG. In case of remote DLUs, maximum 4 PDCs of 2 Mbps (32 TSs) are used per

DLU, two towards each LTG (PDC0 & PDC1 from DLU System 0, PDC2 &PDC3

from DLU System 1. Signaling information is carried in TS16 of PDC0 and PDC2.

In case of a local DLU interface, TS32 carries the signaling information.

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In case the link between a remote DLU and the main exchange is broken,the

subscribers connected to the remote DLU can still dial each other but metering will

not be possible in this case.

6.1.1) PRINCIPLE FEATURES OF DLU:-

. Connection capacity of a rack:

-Upto 952 analog subscriber lines

-Upto 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

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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

6.1.2) STRUCTURE OF DLU:-

Subscriber lines and PBX lines in EWSD are connected to digital line units

(DLU). (Fig. 1)

The DLUs can be operated locally in an exchange or remotely (Fig.2).

The DLUs are connected to the Switching Network via LTG(B-function). A

remote DLU is connected to an LTG by 2 Mbps Primary Digital Carriers (PDC).

However, the local DLUs ( the DLUs located in the main exchange ) are

connected to the LTG(B) by 4 Mbps carriers.

For security reasons, a DLU is connected to two LTGs. A subset of CCS#7

according to CCITT is used for signaling between a DLU and the Group

Processor (GP) in the two LTGs.

Remote DLUs are installed in the vicinity of groups of subscribers. The

resultant short subscriber lines and the flexible concentration of subscriber

traffic to the exchange onto digital transmission links makes for an economical

subscriber line network with optimum transmission quality.

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Analog 2 wire interface for a/b connection

Analog subscribersSmall PSTN P(A)BX

Digital 2 wire interface for basic access (BA)Digital subscribersSmall ISDN P(A)BX2 Mbit/s PDC V5.1 interface to the AN

DLUConcentration of the subscriber accesses Analog/digital conversion for analog subscribers Modules SLM for the connection of - a/b interfaces (SLMA with 8 or 16 subscriber line circuits - SLCA) - U interfaces (SLMD with 8 or 16 subscriber line circuits - SLCD)

- v 5.1 interfaces (SLMX with two V5.1 interfaces)

a/b or U or V5.1 interfaces

Fig. 1

.

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LTGDLU

LTGDLU

Fig2. Structure of DLU interface with LTG

6.1.3) DLU H/W TYPE:-

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Since the first issue of a DLU the frame and rack hardware was redesigned

several times in order to optimize the DLU HW concerning the required size and

the number of connected subscriber lines.

DLU A :This is the oldest DLU HW type. It contains SLM modules with max. 8

subscriber circuits (e.g. SLMA : COS or SLMDB). It may also contains SLM

modules with max. 6 home metering / reversal subscriber circuits (e.g. SLMA :

CMRL. One fully equipped DLU A is housed in one rack R : DLU. A maximum

of 952 analog or 928 digital subscribers with a traffic volume of 0.1 ERL each can

be connected to a DLU A. One DLU A can consist of:

1 frame F:DLU (A)

0,1,2 or 3 frames F:DLU(B) depending on the number and the traffic

volume of the subscribers

DLU B :This is the DLU HW type used in most EWSD switches. It contains

SLM modules with max. 16 subscriber circuits (e.g. SLMA:FPE or SLMD:QFB).

Two fully equipped DLUBs are housed in one rack R:DLUB. A maximum of

1760 analog or 1536 digital subscribers with a traffic volume of 0.1 ERL each can

be connected to a rack R:DLUB. One DLU B can consist of:

1 frame F:DLU(D)

0 or 1 frame F:DLU(E) depending on the number and the traffic volume

of the subscribers (alternatively frame F:DLU(F) for less high construction )

DLU D ( also called DLU B type D) :This was the latest DLU HW type. The

main difference to the DLUB is a new more integrated solution for the central

parts of the DLU. This offers mounting locations for 4 additional SLMA:FPE

modules to connect one remote DLU to EWSD. One DLU D can consist of :

1 frame F : DLU(G)

0 or 1 frame F:DLU(E) depending on the number and the traffic volume

of the subscribers (alternatively frame F:DLU(F) for less high construction)

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6.2) LINE AND TRUNK GROUP:-

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:-

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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

6.3) SWITCHING NETWORK:-

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

IntegratedServices 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:

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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

6.4) CO-ORDINATION PROCESSOR:-

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

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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

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number of memory modules)

– 8 interrupt levels with fixed priorities

– Flexible in allowing connection of peripheral devices

6.5) 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.

6.6) 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.

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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.

6.7) 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

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–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

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6.8) COMMON CHANNEL SIGNALLING 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).

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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.

7.0) COMMON CHANNEL SIGNALLING 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

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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 medi 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).

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8.0) 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.

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CONCLUSIONS

EWSD is a digital electronic switching system upgraded by Siemens, taking into account the

latest tendencies of services and communication means development. It is the solution that

makes it possible to satisfy any current and future requirements.

The new applications implemented on the EWSD platform are the EWSD Inter Node and the

EWSD Broadband Node. The EWSD Inter Node integrates Internet technology into the EWSD

system, it creates the basic conditions required for speech and data networks to grow together. It

offers unrestricted access to Internet services.

The EWSD Broadband Node is the foundation stone for a future oriented network in which

various types of technology, such as ISDN in the public network (PSTN) and broadband

communication, harmoniously operate together. Broadband technology offers the network

operator the opportunity to introduce completely new services, e.g. services with high-quality

graphics and multimedia applications as well as video telephony.

EWSD system is based on the most advanced technologies in the field of communication and

provides the networks operators with the possibility of prompt and cost-effective response to the

market needs. The growing need for the powerful networks is also conditioned by the subscriber

traffic growth evoked primarily by new communication services implemented with the transfer

rates of up to 2 Mbit/s. These services include ISDN, online services, Internet services, and the

services implemented in n x 64 Kbit/s configuration.

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APPENDIX

TECHNICAL DATA

Call-handling capacity

No. of Subscriber lines max. 250 000

No. of Trunks max. 60 000

Switchable traffic max. 25 200 E.

Call attempts in busy hour 10 million

Supply voltage

-48 V nominal direct voltage

Clock accuracy

Maximum relative frequency deviation:

plesiochoronous 10-9

synchronous 10-11

Signaling systems

All conventional signaling systems, e.g. CCITT R2, No.5, No.7

Analog subscriber line and trunk accesses

Various loop and shunt resistance possible.

Push-button dialing, Multi-freq. signaling to CCITT

Rotary dialing: 5 to 22 pulse/s

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ISDN accesses

Basic access 160 kbps(2B+D+sync.)

B= 64 kbps, D= 16 kbps

Primary rate access 2048 kbps(30B+D+sync.)

Digital trunk accesses 2048 kbps

Traffic routing

Per destination one primary route and max. 15 alternate routes.

Sequential or random selection of idle trunk of a trunk group

Number of trunk groups per exchange:

Max. 1000 incoming and

Max. 1000 outgoing and

Max. 1000 both way

Environmental conditions

Ambient temperature 5°C to 40°C

Relative humidity 10% to 80%

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