Optical Fiber Basic.ppt

7/22/2019 Optical Fiber Basic.ppt

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Public Switched

Telephone Network (PSTN)

BY

M C KOLADIYA


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The PSTNArchitecture

PSTNPublic Switched Telephone Network

Uses digital trunks between Central Office switches (CO) Uses analog line from phones to CO

Digital Trunks

Analog line

Central

Office

(CO)

Analog DigitalAnalog


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The PSTNDigitization

Voice frequency is 100 - 5000 Hz, with the main portionfrom 3003400 Hz

Nyquist Theorem states that sampling must be done at

twice the highest frequency to recreate. 4000 Hz was

chosen as the maximum frequency, thus sampling at8000 Hz

PCM = 8kHz * 8 bits per sample = 64 kbit/s


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Public Switched Telephone Network

Three major components of PSTN:

Local loops

Trunks

Switching Offices

Local CO

408-527-xxxx

22,000 in US

1-10 Km

CAT 3

Tandem

(class 4)

Mostly fiber or

microwave running

ATM or IP

(MCI, Sprint, ATT)


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PSTN

A: Switching types

Connectionless/ connection oriented

Packet/circuit

B: PSTN exchanges and interfaces interface Q.512

using access and trunk networks

signaling

network mana ement

Node 1 Node 2

Node 3

Access

Trunk Network

TerminalsTerminals

Access


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Switching in public networks

CSPDN: Circuit switched public data net*

PSPDN: Packet switched public data net**

DQDB: Distributed queue dual bus

* Used by European Telecoms that use X.21 in circuit switched nets**Used by British Telecoms Packet-switched Service (PSS), Data Pac (Canada) ...

(fixed

length)

Cel l sw i tch ing- resembles packet switching

- difference: cells (packets) have a fixed size :

offers bounded delay guarantees

(QoS compatible, long packets wont stuck cells)


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Circuit switching

Time swi tch

- Makes switching between time slots

- In the figure incoming slot 3 is moved to

outgoing slot 3 for one voice direction

- Each coming timeslot stored in Speech Store (SS)

- Control store (CS) determines the order the slot

are read from SS

- The info in CS is determined during setup

phase of the call

Space swi tch

- makes switching between PCM lines

- works with electronic gates controlled by CS Cross-pointcontrolled

by CS

Circu i t swi tch ing

- dedicated path

- constant delay/bandwidth

- voice/data

- paid by time

- examples: PSTN, VPN

TDMA


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Time Division Multiplexing (E1)

The T1 frame is composed of 230 channelsThe frame is 193 bits = 1 framing bit + 8 bits * 32 Time Slots (TS)

Framing bit creates an additional channel of 8 kb/s

Frame rate is 8 KHz, each channel is 8K * 7 bits = 56 Kbps

The extra bit is used for CAS (Channel Associated Signaling)

E1 32 channels, 2.048 MHz = 32 ch * 8K * 8 bits/ch, CCS

PCM voice

or data


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Packet switching

Node structure

Packet structureSeq: sequence number

Op code: message/control

identifier

CRC: Cyclic Redundancy

Code

Note:

- source address

required for retransmission

in ARQ

- byte count could be also an

end flag


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Connection-oriented and connectionless

switching

Connect ion o r iented

- Applies same route

- QoS well defined

- Phases

- Connection setup

- Data transmission

- Release

- Packets received in same order

- Example: ATM, frame relay, PCM

Connect ion less

- Use of different routes foreach packet possible

- Each packet have address fields

- QoS not guaranteed

- Packets may come in different order

- Example: IP (Internet Protocol),

TCP takes care of cleaning the mess


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Transfer modes & connections

summarized

Circuit switching

Packet switching

Connection oriented

Connectionless

- hand-shaking

- strict error requirements

- for fast data transfer

- broadcasting- modest error rates

often accepted

- fast data in good channels

Transfer modes Connection types

- developed for data- nowadays also for voice

- Statistical multiplexing

- variable delays

- developed for voice

- nowadays also for data

- well-specified delays

- echo problems

PSTN

ISDN

PCM

IP, Frame-relay

ATM

X.25

ATM

Frame-relay

IP, UDP*

*User Datagram Protocol


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Packet Switching

A comparison of circuit switched and packet-switched

networks.


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The Local Loop (Last Mile)Modems, ADSL, and Wireless

Use both analog and digital transmissions (E1)Conversion is done by the modems and codecs.

Transmission problems :Attenuation (loss of energy), delay distortion (propagation speed vs freq), noise

(white noise, crosstalk, impulse noise)


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Integrated Services Digital Network(ISDN)

Telephone

network

Digital data

network

Facsimile

network

Telex

network

Services and network integrations

ISDNDigital technologiesComputer control

technologies


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I SDN Basic Rate I nter face (BRI )

B

B

D

64 kbit/s

64 kbit/s

16 kbit/s

Basic rate interface

(2B+D)

144 kbit/s

B ch for information transfer

D ch for signaling transfer

2B+D


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Primary Rate I nterface(PRI)

D

B

B

B

30B+D

64 kbit/s

64 kbit/s

64 kbit/s

64 kbit/s

Primary

Rate

Interface

(2.048 Mbit/s)30 B channels


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Broadband ISDN

Todays N-ISDN

Circuit switched

network

Packet switched network


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To be integrated by B-ISDN

ATM and

OpticalFiber

Network

Broadband ISDN (continued)


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ATM (Asynchronous Transfer Mode)

Information(48 Bytes)

Header(5Bytes)

ATM Cell Structure

Incoming data is chopped every 48 bytes, added a header thenan ATM cell is formed. Transmission and switching are

conducted by cell basis.


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STM/ATM

# 1

# 4

# 3

# 2STM

MUX

ATM

MUX

# 1

# 4

# 3

# 2

STM

MUX

STM: Synchronous Transfer Mode

E l f ll it hi


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Example of cell switching:

Distributed queue dual buss (DQDB)

LAN

access

unit

accessunit

accessunit

LAN

accessunit

Function

- transport unitsconstant length

- access unitsaccess

info in the ring:

- know subscribers in access units

subnets and route packets for them

- access protocol applies token ringProperties

- distributed switching (Compare

to FDDI*)

- ATM compatible

- rates: 64 kb/s ... 45 Mb/s

- geographical limit up to 200 km

*FDDI: Fiber Distributed Data Interface

see: http://www.iol.unh.edu/training/fddi/htmls/

Transport Unit (same as in ATM)

C ti i t PSTN h


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Connecting into PSTN exchange:

Equipment in the access network

ISDN connection

example: 30B+D

(2.048 Mb/s)

Twisted pair - connection

Private Branch Exchange

Multiplexer

On-line subscriber

with several telephones

Business

subscriber

Wireless

access

(or radio access

point)

Distribution point

Cross connection point

ISDN 2B+D

144 kb/s

Q.512 specifiesexchange interfaces


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Switch

Local exchange

Subscriberstage

Groupswitch

ETC

Announcementequipment

Signalingequipment

Test/measure-ment equipment

Control system

to other exchanges

Third-partyequipment

PBX

ETC: Exchange terminal circuit

IN: Intelligent network

conference calls, call waiting,

broadcasting ...

Signaling (SS7) with users and

other exchanges

Traffic concentration- Operation & maintenance support (Q.513)- Charging

- Supplementary (IN) services

- Subscriber data, switch control Control


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Subscriber stage

To

ETC

ETC: Exchange terminal circuit

Speech store: shift registers storing bits for time switching

Control store: gates guiding speech store switches

Connects to: digit receivers, info

tones, test equipment

Control System: subscriberauthentication, routing, billing, O & M, ...

Concentrator

internet access

(DSLAM)

centrex serviceMUX

E h t l f ti


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Exchange control functions

Maintenancefunctions

supervision of subscriber lines and trunk circuits Operationalfunctions

adminis t rat ivedata as

subscriber database

routing database

stat ist icaldata as

from where and whom subscribers call

holding times for different equipment types

utilization of IN services

User servicesSample of IN services


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Exchange user services (examples)

Absent-subscriberservices as the answering

machine

Call booking: connection at the desired time

Person-to-person call: ensures that call goes to aright person

Serial call: setting up several calls

Telephone conferencing: several persons

participate to call in real-time (compare: tele-conferencing)

Directory inquiries: also speech recognition,

recorded messages

(many of these nowadays available in terminals)

Th it h


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The space-switch(used as a cross-switch and concentrator)

Number of cross-connections reduced compared if a simple

space division matrix of NxM (input x output) would be used

Usually performs concentration: Blocking possible

Same signal can be routed via different paths: increased

reliability


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The time-switch

One of the time slots of any full-duplexlines is connected tosome other line (at a time)

Thus two switches / time slot connect a line

For 100 full-duplex lines at 19.6 kbps a 1.92 Mbps bus is thusrequired for no blocking

If no fixed assignment of input lines to time slot but ondemand allocation -> blocking switch that reduces number ofswitches and switch clock frequency. For instance 200 lines of19.6 kbps with bus of 1.92 Mbps-> about half of the devices can connect at any time, egconcentration is 2:1


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The time-space-time (TST) switch

Works in local exchange and subscriber stage Performs PCM concentration, usually 10:1 3:1

Connects subscribers also to information tones

and test equipment

Time switch contains one bus for incoming and outgoingcalls (full-duplex)

Subscriberstage

Space switch

Time switch

Time switch

PSTN ISDN e change interfaces


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CN

CN:ConcentratorET:Exchange T.LT:Line T.AN:Access Net.

LT

NT ET

X

ET

ET

ET

LT

LTLT

ETLT

ETLTISDN PABX

ETLTAN

V1

V2

V3

V5

A

B

NT:NetworkT. (in ISDN)

T:Terminal

PSTN ISDN exchange interfaces

Q.512)

Peek to Q-recommendations

V4
http://localhost/var/www/apps/conversion/tmp/scratch_2/Q.512.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_2/Q.512.pdf


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Exchange interfaces and tasks, V1

Purpose of exchange is to organizes connectionbetween exchange terminators!

V1: Access to basic ISDN (This is users ISDN-u

interface that can be used to connect small PBX also)

Basic ISDN V1-functions: 2 B + D (2x64 kbps + 16 kbps) channeling structure

timing and frame synchronization

activate and deactivate terminator

operation and maintenance feeding power supply

ISDN basic access parameters defined in G.961


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Exchange interfaces and tasks, V2-V4

V2: Interface serves typically concentrators 2048 kbit/s eg

30 B + D

Electrical standard G.704

V3: Resembles V2 but intended for interface otherexchanges (PABX)

Electrical standard G.703

30 B + D at 2048 kb/s

also 23 B +D at 1544 kb/s (I.431)

V4:Interface to private networks (not ITU-T specified), for

instance DSLAM (ADSL-interface)
http://localhost/var/www/apps/conversion/tmp/scratch_2/G.704%20Synchronous%20frame%20structures%20used%20at%201544,%206312%20%202048%20%208448%20and%2044%20736%20kbit%20s%20hierarchical%20levels.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_2/G.704%20Synchronous%20frame%20structures%20used%20at%201544,%206312%20%202048%20%208448%20and%2044%20736%20kbit%20s%20hierarchical%20levels.pdf


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Exchange interfaces and tasks, V5

Between access network and exchange 2048 kbit/s

Specifies basic interfaces for

Analog access

ISDN-access

Electrical interface G.703

Channel control and signaling

V5 supports interface rates 2048 kbit/s

8448 kbit/s

C ti th l l l


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Connecting the local loop:

Line interface circuit (LIC)

Used for sign al ing in certaincoin -operated pay-phones and PBX


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Line interface circuit components

Over-voltage protection

Test equipment to connect to monitor the line condition

faults

Voltage feed

ringing

telephone current supply

Detection of

hook stage, pulse generated, or dual-tone receiver The hybrid junction (2 wire - 4 wire interface)

An A/D converter (uses PCM techniques at 64 kbps)

The hybrid circuit


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The hybrid circuit

4-wire connection is used between

exchanges and 2-wire connections fromexchange to subscribers

Amplifier

Amplifier

Bridge Bridge

Two-wire

Exchange A Exhange B

Two-wire


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The hybrid-circuit

If the impedance Zbequals the line impedance noincoming voice (down right) leaks to outgoing voice (up right)

but the signal goes via the two wire connection on the left

To exchange

From exchange

Local loop


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The hybrid circuit summarized

The hybrid circuit transformstwo-wire connection into4-wire connection.

If the hybrid is unbalanced echowill result

Hybrid is balancedwhen no own voice is leaked into

own loudspeaker Hybrid unbalance can result from line impedance

changes due to weather conditions

Unbalance results echo

Echo cancellationcircuits are harmful in dataconnections

Now a days realized by operational amplifierbasedcircuitry that automatically monitors line impedancechanges


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Network echo suppressor

R: transmission gate, A: attenuator, L: logic circuit

When the signal is present on the receiving line thetransmitting line is cut-off

A kind of semi-duplex approach to solve the echo

problem


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Network echo canceller (NEC)

Signal echo is extracted and subtractedfrom the

received signal

More effective than echo suppressor. Often NEC and

NES are however both used


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PSTN operation and maintenance

Different alarm classes

Vital functions and circuits(as SS7 and group switch)

use secured paths andbackups

Procedures provided for: troubleshooting

fault diagnostics

hardware faults canbe isolated

Supervision is realized alsoby connecting maintenanceunits to the network

Important switches haveextensive backup equipment

A supervision plan bynetwork levels:


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Modern PSTN hierarchy

to international level

Regional transport level

Local transport level

Access transport level

Local exchange

Transit exchange

PSTN Hi h t


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PSTN Hierarchy cont.

Local(example, within a city)

Subscriber connections

Switching within the local exchange

Switching to other exchanges

Transit(county level, say between Tampere and

Helsinki)

Switching traffic between different geographical areas

within one country

International

Gateway-type traffic between

different countries

DWDM (Dense Wavelength Division Multiplexing) routes

Rates can follow SONET or SDH standard

Subscriber signaling for local calls


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Subscriber signaling for local calls


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Inter-exchange signaling

Channel associated signaling (CAS) as No.5, R1, R2

analog and digital connections

Modern ISDN exchanges apply SS7(digital), that is a

common channel signaling method (CSS) that is

discussed later in its own lecture

CASis divided into line and register signaling:

Linesignaling:

line state between the trunk-links as

answer, clear-forward*, clear-back

Registersignaling:

routing information as

B-number, A-category, B-status

*A-subscriber on-hook message transmitted to B exchange


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Inter exchange signaling (cont.)

Three categories of information is

transmitted:

setup, supervision clearing

servicerelated information as

forwarding, callback, charging

statuschange information

transmission network congestion neighborhood exchange congestion

E l f i t h i li


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Example of inter-exchange signaling


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Inter-exchange signaling (cont.)

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