ch-2 transmission basics

7/29/2019 CH-2 Transmission Basics

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Transmission Basics


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What is transmission

To send information between two points

Connection between two equipments

Termination equipments

Baseband Signal processing

Multiplexing

Coding

Physical signal

Media

Simplex and Duplex

Copper Balanced

Unbalanced

OFC Microwave

Terrestrial

Satellite


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Transmission Basics

Transmit means to issue signals to the network medium

Transmission refers to either the process of transmitting or

the progress of signals after they have been transmitted


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Transmission Basics

Analog and Digital Signaling

On a data network, information can be transmitted via one of twosignaling methods: analog or digital

Both types of signals are generated by electrical current, the pressure ofwhich is measured in volts


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An analog signal, like other waveforms, is characterized byfour fundamental properties: amplitude,frequency,wavelength, and phase

A waves amplitude

Frequency

Phase

Transmission Basics (continued)


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Digital signals composed of pulses precise

positive voltages and zero voltages

Data Modulation used to modify analog signals in order to make them suitable for

carrying data over a communication path



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A Transmission System

Transmitter

Converts information into signalsuitable for transmission Injects energy into communications medium or channel

Telephone converts voice into electric current

Modem converts bits into tones

Receiver

Receives energy from medium

Converts received signal into form suitable for delivery to user Telephone converts current into voice

Modem converts tones into bits

Receiver

Communication channel

Transmitter


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Modem reflects this devices function as a modulator/demodulator

Modulates digital signals into analog signals

Modulation

Frequency modulation (FM)

Amplitude modulation (AM)



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Transmission Direction

Simplex

Half-duplex

Full-duplex

Channel



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Multiplexing

Allows multiple signals to travel simultaneously over one medium

In order to carry multiple signals, the mediums channel is logically

separated into multiple smaller channels, or sub channels

A device that can combine many signals on a channel, amultiplexer (mux), is required at the sending end of the channel

At the receiving end, a demultiplexer (demux) separates thecombined signals and regenerates them in their original form



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Time division multiplexing (TDM)

Wavelength division multiplexing (WDM)

WDM enables one fiber-optic connection to carry multiple light signals

simultaneously

Using WDM, a single fiber can transmit as many as 20 million telephoneconversations at one time

Statistical multiplexing



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Transmission Flaws

Noise is any undesirable influence that may degrade or distort asignal

Crosstalk occurs when a signal traveling on one wire or cable

infringes on the signal traveling over an adjacent wire or cable

Attenuation is the loss of a signals strength as it travels away fromits source



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Media Characteristics

Five characteristics are considered when choosing a datatransfer media:

Throughput

Costs

Size and Scalability

Connectors


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Noise Immunity

The type of media least susceptible to noise is fiber-optic cable

Media Characteristics (continued)


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E1 Transmission

Where does E1 originate ?E1 originates from a telephone where 30 trunk calls to be carried

from that switch to another switch.

A primary multiplexer is used at the originating switch to build theE1 signal.

How does E1 look like physically ?

From the DDF of the switch 4 wires will come out which is the E1.

Out of these 4 wires, 2 wires are for TX and the remaining 2 wiresare for RX.

4 wires can be of two types :

i. Two pairs of twisted copper wires (120 ohms balanced)

ii.Two pairs of co-axial cables (75 ohms unbalanced)


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How we will transport an E1 from obne switch location

to another switch location ?

We can transport the E1 as follows :-By using 4 wire twisted/co-axial line (the distance is limited to

less then about 500mts.)

-By using twisted telephone line and using HDSL modems on bothsides, distance of 3.5kms OR 7kms (by using a repeater)(one

HDSL modem on the switch side and another HDSL modem onthe remote side will be required).

-By using microwave links (this is what we do to connect BTS toBSC in GSM).

-By using optical fiber links.

When we use microwave or optical links of high capacity we willmultiplex n no. of E1s (PDH/SDH) and carry n E1s together.


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Because of its shielding, most coaxial cable has a high resistanceto noise

Coaxial cable is more expensive than twisted-pair cable because itrequires significantly more raw materials to manufacture

The significant differences between the cable types lie in thematerials used for their center cores, which in turn influence theirimpedance

Twisted-pair cable consists of color-coded pairs of insulated copperwires

Every two wires are twisted around each other to form pairs and all

the pairs are encased in a plastic sheath The number of pairs in a cable varies, depending on the cable type The more twists per inch in a pair of wires, the more resistant the

pair will be to all forms of noise

The number of twists per meter or foot is known as the twist ratio

Coaxial Cable


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Twisted-pair cable is the most common form of cabling found onDDF, MDF and LAN today

It is relatively inexpensive, flexible, and easy to install, and it canspan a significant distance before requiring a repeater (though not

as far as coax)

Twisted-Pair Cable (continued)


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All twisted-pair cable falls into one of two categories: shieldedtwisted-pair (STP) or unshielded twisted-pair (UTP)

Unshielded twisted-pair (UTP) Consists of one or more insulated wire pairs encased in a plastic

sheath

Twisted-Pair Cable (continued)


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Fiber-Optic Cable

Contains one or several glass or plastic fibers at its center,or core

Data is transmitted via pulsing light sent from a laser or

light-emitting diode (LED) through the central fibers

Surrounding the fibers is a layer of glass or plastic calledcladding


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Fiber cable variations fall into two categories: Single-mode

Multimode

Fiber-Optic Cable (continued)


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Single-mode fiber

Uses a narrow core (less than 10 microns in diameter) through which lightgenerated by a laser travels over one path, reflecting very little

Allows high bandwidths and long distances (without requiring repeaters)

Costs too much to be considered for use on typical data networks



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Multimode fiber

Contains a core with a diameter between 50 and 115 microns in diameter;the most common size is 62.5 microns over which many pulses of light

generated by a laser or LED travel at different angles

It is commonly found on cables that connect a router to a switch or a serveron the backbone of a network



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Wireless Transmission (continued)

Signal Propagation

Line-of-sight (LOS)

Signal Degradation

Wireless signals also experience attenuation

Wireless signals are also susceptible to noise (often called

interference)


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Choosing The Right Transmission Medium

Most environments will contain a combination of these factors;you must therefore weigh the significance of each

Areas of high EMI Distance Security Existing infrastructure Growth


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Multiplexing Hierarchies and Transport

Technologies


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PDH=Plesiochronous Digital Hierarchy

Plesiochronous(in greek) = Almost-Synchronous

PDH is a transmission standard to carry digital telephone signal betweenTelephone Exchanges. Each PDH signal carries many voice calls.

The Plesiochronous Digital Hierarchy (PDH) is a technology used intelecommunications networks to transport large quantities of data over digitaltransport equipment such as fibre optic and microwave radio systems.

The term plesiochronous is derived from Greek plesio, meaning near, andchronos, time, and refers to the fact that PDH networks run in a state wheredifferent parts of the network are almost, but not quite perfectly,synchronised.

PDH is now being replaced by Synchronous Digital Hierarchy (SDH) equipmentin most telecommunications networks.

PDH allows transmission of data streams that are nominally running at thesame rate, but allowing some variation on the speed around a nominal rate.

By analogy, any two watches are nominally running at the same rate, clockingup 60 seconds every minute. However, there is no link between watches toguarantee they run at exactly the same rate, and it is highly likely that one isrunning slightly faster than the other.


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2.048 Mbit/s FRAME STRUCTURE(32 Time slots)This signal is also called as E1 signal

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

FAW

Call1

Call2

Call3

Call4

Call5

Call6

Call7

Call8

Call9

Call10

Call11

Call12

Call13

Call14

Call15

Signallin

g

Call16

Call17

Call18

Call19

Call20

Call21

Call22

Call23

Call24

Call25

Call26

Call27

Call28

Call29

Call30

SignallingFrame Alignment Word

125us

256bits

1 Frame


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2.048MBPS SIGNAL

1 Bit Rate 2.048Mbps+-50ppm

2 Input Signal 64 kbps

3 No. of Channels 30+2

4 Bit duration 488ns

5 No. of bits per Time Slots 8

6 Time Slot duration 3.9us

7 No. of TS per frame 32

8 Frame duration 125us

9 No. of frames per multi frame 16

10 MF duration 2ms

11 Frame alignment B0011011s use n

international networks

otherwise 0


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Line coding

1. Line coding in clock recovery in receiver. Since we do nottransmit the clock along with data in the case of E1,E2,E3,E4,line coding becomes essential.

2. Line coding makes capacitive coupling possible in the receiver(as it ensures almost equal number of positive and negative

pulses in the transmission, and removes the DC in the linecoded signal). No need of DC coupling means, the gain of theAC coupled receiver can be kept as high as needed (withoutworrying about DC offset voltages). Higher receiver gainmeans longer transmission distances.

3. Violations in the coding rules in the receiver can be counted asbit errors and approximate bit error can be estimated in thereceiver.


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Line coding in PDH systems

PDH Signal Line coding used as per standards

64kbps AMI (Alternate Mark Inversion)

2.048Mbps HDB3 (High Density Block 3)

8.448 Mbps HDB3 (High Density Block 3)

34.368 Mbps HDB3 (High Density Block 3)

139.364 Mbps CMI (Code Mark Inversion )


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PDH bit rates

PDH is a technique to transport digital signals. There are three different

standards, for Europe (E), Japan (J) and North America (T). All thesestandards use a frame of 125s.

The first order in PDH in Europe consists of 32 time slots of 8 bits,the first time slot (TS0) is used for frame synchronization and the16th (TS16) for signaling. The remaining 30 TS are used fortraffic with a bit rate of 64 kbit/s each. This first order is called E1

with a total capacity of 2048 kbit/s (2 Mbit/s) where 1920 kbit/s isfor traffic. The 16th TS could also be used for user traffic, thengiving total bit rate of 1984 kbit/s.

The first order in North America is called T1 and consists offrames with 24 TS of 8 bits and one bit for frame alignment. Thetotal capacity is 1544 kbit/s (1.5Mbit/s) where 1536 kbit/s is usedfor traffic.

Japan uses the same basic frame as North America but it differsfrom the third level of multiplexing. The basic rate is called J1.


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Plesiochronous Digital Hierarchy

PDH Hierarchy:

1 64Kbps PCM 1 voice channel

2 2.048Mbps E1 30 voice channels

3 8.448Mbps E2 120 voice channels

4 34.3687Mbps E3 480 voice channels5 139.264Mbps E4 1920 voice channels


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FIG here shows the different rates for these standards.

4

3

2

1

0

Level Europe North America Japan

139,264 kbit/s139,264 kbit/s 139,264 kbit/s139,264 kbit/s 97,728 kbit /s97,728 kbit /s

34,368 kbit/s34,368 kbit/s 44,736 kbit/s44,736 kbit/s 32,064 kbit/s32,064 kbit/s

8,448 kbit/s8,448 kbit/s 6,312 kbit/s6,312 kbit/s

2,048 kbit/s2,048 kbit/s

64 kbit/s64 kbit/s

1,544 kbit/s1,544 kbit/s

64 kbit/s64 kbit/s

x 4

x 4

x 4

x 32

. . .

x 3 x 3

x 7 x 5

x 4

. . .

x 24


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SDH/SONET

SDH and SONET are both gradually replacing the higher order of PDHsystems. The advantages of higher bandwidth, greater flexibility andscalability make these standards ideal for ATM networks.

SONET and SDH are almost equal, but they differ mainly in some parts of theoverhead. The basic rate in SONET is the STS-1(OC-1) at 52 Mbit/s. While forSDH the basic rate is the STM-1 at 155 Mbit/s. Lately ITU-T G.707 and G.708have regulated the STM-0, with 52 Mbit/s and which is 1/3 of the basic STM-1. It can allocate one VC3 corresponding to 21 VC12 or 21 VC11 or 7 VC2.Both standards can be used with optical or electrical interfaces.

The bit rates defined for SDH are:

1) 155.52 Mbps SDH Level 1 STM 1



4) 9953.28 Mbps SDH level 64 STM 64

These hierarchy levels are Synchronous.

If we have 4 level 1 signals, we simply byte-interleave these signals in asynchronous to get the level 4 signal.

So multiplexing/de-multiplexing is easier in SDH


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For STM-N (STS-3N) the frame format is shown in Figure below..

MSOH

RSOH

AU pointer

Payload

1

3

5

9

9 rows

N 9 N 261

N 270 columns

SOH: Section OverheadAU: Administration Unit RSOH: Repeater Section Overhea

MSOH:Multiplexer Section Overhea


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Figure: Standardized SDH/SONET bit rates.

2 Mbit/s

140 Mbit/s

34 Mbit/s

8 Mbit/s

1.5 Mbit/s

6 Mbit/s

45 Mbit/s

STS-1 (OC-1) 52 Mbit/s

STM-1 STS-3 (OC-3) 155 Mbit/s

STM-64 STS-192 (OC-192) 10 Gbit/s

STM-16 STS-48 (OC-48) 2.5 Gbit/s

STM-4 STS-12 (OC-12) 622 Mbit/s

PDH ETSI

PDH USA

SONET USA

SDH ITU-T

STM-0 52 Mbit/s


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SDH Mapping


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The following combination of PDH signals can be carried within an STM-1(STS-3) frame:

European standard.

1 x 140 Mbit/s

3 x 34 Mbit/s

63 x 2 Mbit/s

1 x 34 Mbit/s + 42 x 2 Mbit/s

2x 34 Mbit/s + 21 x 2 Mbit/s

American standard.

3 x STS-1

3x 45 Mbit/s

63 x 1.5 Mbit/s

1 x 45 Mbit/s + 42 x 1.5 Mbit/s

2 x 45 Mbit/s + 21 x 1.5 Mbit/s

The main feature when introducing SDH, is the controllability of the transport

network. The most important changes are: centralised remote control of thenetwork elements, increased utilisation of the physical transport network andshorter delivery time for leased lines. The SDH technology also reduces themultiplexing process.


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Why SDH ?

The main feature when introducing SDH, is the controllability of the transportnetwork. The most important changes are: centralised remote control of the networkelements, increased utilisation of the physical transport network and shorter deliverytime for leased lines. The SDH technology also reduces the multiplexing process.

SONET/SDH development was originally driven by the need to transport multiple PDHsignals like DS1, E1, DS3 and E3 along with other groups of multiplexed 64 kbit/spulse-code modulated voice traffic. The ability to transport ATM traffic was another

early application. In order to support large ATM bandwidths, the technique ofconcatenation was developed, whereby smaller SONET multiplexing containers (eg,STS-1) are inversely multiplexed to build up a larger container (eg, STS-3c) tosupport large data-oriented pipes. SONET/SDH is therefore able to transport bothvoice and data simultaneously.

Both SONET and SDH can be used to encapsulate earlier digital transmissionstandards, such as the PDH standard, or used directly to support either ATM or so-

called Packet over SONET/SDH (POS) networking. As such, it is inaccurate to think ofSDH or SONET as communications protocols in and of themselves, but rather asgeneric and all-purpose transport containers for moving both voice and data. Thebasic format of an SDH signal allows it to carry many different services in its VirtualContainer (VC) because it is bandwidth-flexible.


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High transmission rates

Transmission rates up to 10Gbit/s can be achieved in modern SDH systems. SDH is thereforethe most suitable technology for backbones, which can be considered as being the super

highways in todays telecommunications networks. Simplified add & drop function

Compared with the older PDH systems, it is much easier to extract and insert low-bit ratechannels from or into the high-speed bit streams in SDH. It is no longer necessary todemultiplex and then remultiplex the plesiochronous structure, a complex and costlyprocedure at the best of the times.

High availability and capacity matching

With SDH, network providers can react quickly and easily to the requirements of their

customers. For example, leased lines can be switched in a matter of minutes. The networkprovider can use standardized network elements that can be controlled and monitored fromthe central location by means of a telecommunication network management (TMN) system.

Reliability

Modern SDH networks include various automatic back-up and repair mechanisms to copewith system faults. Failure of a link or an network element does not lead to failure of theentire network which could be a financial disaster for the network provider.

These back-up circuits are also monitored by a management system.

Future-proof platform for new services Right now, SDH is the ideal platform for services ranging from POTS, ISDN and mobile radiothrough to data communications (LAN, WAN, etc.), and it is able to handle the very latestservices, such as video on demand and digital video broadcasting via ATM that are graduallyestablished

Interconnection

SDH makes it much easier to setup gateways between different network providers and toSONET systems. The SDH interfaces are globally standardized, making it possible tocombine network elements from different manufacturers into a network. The result is a

reduction in equipment costs as compared with PDH.


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ATM

Asynchronous Transfer Mode (ATM) is a cell switching protocol (53-byte celllength).

ATM provides QoS guarantees. This means that a certain network nodenotifies ATM that the data or service requested requires a certain level ofpriority. Figure shows an ATM cell layout.

PayloadHeader

5 bytes 48 bytes

53 bytes


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Three types of ATM services exist: Permanent Virtual Circuits (PVC), SwitchedVirtual Circuits (SVC) and connectionless service (which are similar to SMDS,Switched Multimegabit Digital Service).

PVC allows direct connectivity between sites, which guarantee availability of aconnection with no call set up procedures.

An SVC is created and released dynamically and remains in use only as long asdata are being transferred. It provides more flexibility but use signallingprocedures.

There are three different types of switching: Virtual Path Cross Connect (VPCC), Virtual Channel Cross Connect (VC CC) and AAL2 switching. VC and VPswitching is shown in below.


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IP

IP (Internet Protocol) is a connectionless protocol that is primarily responsiblefor addressing and routing packets between network devices.

The packets can be as small as 20 bytes and as large as 64 Kbytes.

Fragment OffsetIdentification Flags

Total lengthType of ServiceIHLVersion

Options (variable) Padding

Header CkecksumTime to Live Protocol

DATA (VARIABLE)

Destination Address

Source Address

4 Bytes

Addresses are 4 bytes long in version 4 and in version 6 they are 16 byteslong. If IP is used with the higher protocol TCP (Transmission Control Protocol) thesmallest packet is 40 bytes long because it has to transmit both headers


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ATM over PDH

The ATM cells are mapped onto primary PDH frames as shown in Figure

PDHFramen

PDHFramen+1

PDHFramen+2

PDHFramen+3

ATMCelln ATMCelln+1

The available capacity for ATM traffic in a primary PDH frame (E1) is 30 timeslots, which is equal to 30 bytes. The length of the ATM cell is 53 bytes, thus in anE1 bitstream the maximum ATM cell rate is approximately 4500 cells/s and in one T1bitstream only a rate of 3600 cells/s can be achieved.


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When mapping ATM cells directly onto an SDH frame, one VC4 is used. SeeFigure.


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The next table shows the different cell rates for different SDH/SONETbit rates.

STM STS (OC) Bit Rate Cell Rate

- STS-1 (OC-1) 52 Mbit/s 117 kcell/s

STM-1 STS-3 (OC-3) 155 Mbit/s 350 kcell/sSTM-4 STS-12 (OC-12) 622 Mbit/s 1.4 Mcell/s

STM-16 STS-48 (OC-48) 2.5 Gbit/s 564 Mcell/s

STM-64 STS-192 (OC-192) 10 Gbit/s 2.25 Gcell/s


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IP over ATM

Methods for running IP over ATM are: Classical IP over ATM (also called CLIP). This is the method

used in UTRAN.

Local Area Network Emulation (also called LANE or LAN-Emulation).

Multiprotocol over ATM (also called MPOA).

Multiprotocol Label Switching (Also called MPLS).


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Optical Fibers basics


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Content

Basics of optical fiber transmission Fiber Types

Optical Fiber Impairments

Fiber standards

Advantages of fiber optic

transmission


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Basics of optical fiber transmission I

What is an opticalfiber?

A glass or plastic fiberthat has the ability to

guide light along itsaxis.

A fiber cable consistsof three layers:

core,

cladding,

jacket.


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Basics of optical fiber transmission II

Total Internal Reflection: whenthen the light is totally reflected in the core, whererefractive index of the core and claddingrespectively.

1(1sin nn

c

10,nn


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Fiber Types

Multi-Mode: supportshundreds paths for light.

Single-Mode: supports asingle path for light


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Multi-Mode vs Single-Mode

Multi-Mode Single-Mode

Modes of light Many One

Distance Short Long

Bandwidth Low High

Typical

Application

Access Metro, Core


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Attenuation

It is the reduction of light power over the length of the fiber.

Its mainly caused by scattering.

It depends on the transmission frequency.

Its measured in dB/km ( )

(log1010 ioutPdB


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Multimode Dispersion

Light rays are transmitted from the source ata variety of angles and arrive at the receiverat different times.

Source www.cisco.com


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Chromatic Dispersion (CD)

Light from lasers consists of a range of wavelengths,each of which travels at a slightly different speed.This results to light pulse spreading over time.

Its measured in psec/nm/km.

The chromatic dispersion effects increase for highrates.

Source www.teraxion.com


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Polarization Mode Dispersion (PMD)

Single-mode fibers support two orthogonalpolarizations of the transmitted signal. Polarizationmodes travel with different speeds resulting indispersion.

Its measured in

This phenomenon is evident at bit rates of 10Gbpsor more

kmps


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Transmission Bands

Band Wavelength (nm)

O 12601360

E 13601460

S 1460

1530

C 15301565

L 15651625

U 16251675

Optical transmission is conducted inwavelength regions, called bands.

Commercial DWDM systems typically transmitat the C-band

Mainly because of the Erbium-Doped FiberAmplifiers (EDFA).

Commercial CWDM systems typically transmitat the S, C and L bands.

ITU-T has defined the wavelength grid forxWDM transmission

G.694.1 recommendation for DWDMtransmission, covering S, C and L bands.

G.694.2 recommendation for CWDMtransmission, covering O, E, S, C and L bands.


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Single Mode Fiber Standards I

ITU-T G.652 standard Single Mode Fiber (SMF) or Non Dispersion ShiftedFiber (NDSF).

The most commonly deployed fiber (95% of worldwide deployments).

Water Peak Region: it is the wavelength region of approximately 80nanometers (nm) centered on 1383 nm with high attenuation.


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Single Mode Fiber Standards II

ITU-T G.652c - Low Water Peak NonDispersion Shifted Fiber.

Source www.corning.com


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Single Mode Fiber Standards III

ITU-T G.653 Dispersion Shifted Fiber (DSF) It shifts the zero dispersion value within the C-band.

Channels allocated at the C-band are seriously affected bynoise due to nonlinear effects (Four Wave Mixing).


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Single Mode Fiber Standards IV

ITU-T G.655 Non Zero DispersionShifted Fiber (NZDSF)

Small amount of chromatic dispersion at

C-band: minimization of nonlinear effects Optimized for DWDM transmission (C

and L bands)


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Single Mode Fiber Standards V

ITU-T

Standard

Name Typical

Attenuation

value (C-

band)

Typical CD

value

(C-band)

Applicability

G.652 standard

Single Mode

Fiber

0.25dB/km 17 ps/nm-

km

OK for xWDM

G.652c Low Water

Peak SMF

0.25dB/km 17 ps/nm-

km Good for CWDM

G.653 Dispersion-

Shifted Fiber

(DSF)

0.25dB/km 0 ps/nm-km Bad for xWDM

G.655 Non-ZeroDispersion-

Shifted Fiber

(NZDSF)

0.25dB/km 4.5 ps/nm-km Good for DWDM


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Fiber optic transmission advantages

Really broadband medium.

The fiber is immune to virtually all kinds of interference.

A fiber optic cable is much smaller and lighter in weight than awire or coaxial cable with similar information carrying capacity.

Fiber optic cable is ideal for secure communications.

Low production cost (~euro/km)

ch-2 transmission basics

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