Applied Telecommunications

Systems and Technologies

Professor Michael KhaderTel 973-596-6078Office: ITC 2106Office Hours:

Lecture1

Communications Essentials

Overview

Topics

Basic Communications Model Data Communication Networking Protocols and Protocol Architecture Files, text, communication The Public Telephone Network Transmission Media Data Representation and encoding

A Communications Model

Source generates data to be transmitted

Transmitter Converts data into transmittable signals

Transmission System Carries data

Receiver Converts received signal into data

Destination Takes incoming data

Simplified Communications Model - Diagram

Key Communications Tasks Transmission System Utilization Interfacing Signal Generation Synchronization Exchange Management Error detection and correction Addressing and routing Recovery Message formatting Security Network Management

Simplified Data Communications Model

Networking

Point to point communication not usually practical Devices are too far apart Large set of devices would need

impractical number of connections Solution is a communications

network

Simplified Network Model

Wide Area Networks

Large geographical area Crossing public rights of way Rely in part on common carrier

circuits Alternative technologies

Circuit switching Packet switching Frame relay Asynchronous Transfer Mode (ATM)

Circuit Switching

Dedicated communications path established for the duration of the conversation

e.g. telephone network

Packet Switching

Data sent out of sequence Small chunks (packets) of data at a

time Packets passed from node to node

between source and destination Used for terminal to computer and

computer to computer communications

Frame Relay

Packet switching systems have large overheads to compensate for errors

Modern systems are more reliable Errors can be caught in end system Most overhead for error control is

stripped out

Asynchronous Transfer Mode ATM Evolution of frame relay Little overhead for error control Fixed packet (called cell) length Anything from 10Mbps to Gbps Constant data rate using packet

switching technique

Integrated Services Digital Network ISDN Designed to replace public telecom

system Wide variety of services Entirely digital domain

Local Area Networks

Smaller scope Building or small campus

Usually owned by same organization as attached devices

Data rates much higher Usually broadcast systems Now some switched systems and

ATM are being introduced

Protocols

Used for communications between entities in a system

Must speak the same language Entities

User applications e-mail facilities terminals

Systems Computer Terminal Remote sensor

Key Elements of a Protocol

Syntax Data formats Signal levels

Semantics Control information Error handling

Timing Speed matching Sequencing

Protocol Architecture

Task of communication broken up into modules

For example file transfer could use three modules File transfer application Communication service module Network access module

Simplified File Transfer Architecture

A Three Layer Model

Network Access Layer Transport Layer Application Layer

Network Access Layer

Exchange of data between the computer and the network

Sending computer provides address of destination

May invoke levels of service Dependent on type of network

used (LAN, packet switched etc.)

Transport Layer

Reliable data exchange Independent of network being

used Independent of application

Application Layer

Support for different user applications

e.g. e-mail, file transfer

Addressing Requirements

Two levels of addressing required Each computer needs unique

network address Each application on a (multi-

tasking) computer needs a unique address within the computer The service access point or SAP

Protocol Architectures and Networks

Protocols in Simplified Architecture

Protocol Data Units (PDU)

At each layer, protocols are used to communicate

Control information is added to user data at each layer

Transport layer may fragment user data Each fragment has a transport header added

Destination SAP Sequence number Error detection code

This gives a transport protocol data unit

Network PDU

Adds network header network address for destination

computer Facilities requests

Operation of a Protocol Architecture

TCP/IP Protocol Architecture Developed by the US Defense Advanced

Research Project Agency (DARPA) for its packet switched network (ARPANET)

Used by the global Internet No official model but a working one.

Application layer Host to host or transport layer Internet layer Network access layer Physical layer

Physical Layer

Physical interface between data transmission device (e.g. computer) and transmission medium or network

Characteristics of transmission medium

Signal levels Data rates etc.

Network Access Layer

Exchange of data between end system and network

Destination address provision Invoking services like priority

Internet Layer (IP)

Systems may be attached to different networks

Routing functions across multiple networks

Implemented in end systems and routers

Transport Layer (TCP)

Reliable delivery of data Ordering of delivery

Application Layer

Support for user applications e.g. http, SMPT

TCP/IP Protocol Architecture Model

OSI Model

Open Systems Interconnection Developed by the International

Organization for Standardization (ISO)

Seven layers A theoretical system delivered too

late! TCP/IP is the de facto standard

OSI Layers

Application Presentation Session Transport Network Data Link Physical

OSI v TCP/IP

Standards Organizations

Internet Society ISO ITU-T (formally CCITT) ATM forum

Types of Communications

Based on directional flow simplex half duplex full duplex

Transmitter Receiver

Simplex: one-way

Transmitter

Receiver Transmitter

Receiver

Full duplex: two-waysimultaneously

Transmitter

Receiver Transmitter

Receiver

or

Half duplex: one at a timeeither transmitting or receiving

Figure 1.3: types of communications, based oninformation flow consideration: simplex, full

duplex, and half duplex.

Communication classification

Based on devices and links configuration point-to-point

A single link with two devices

multipoint Multiple devices on a single link, On may by a

broadcaster and others are receivers.

Point-to-point

Multipoint

(a)

Satellite

Earth Stations

(b)

Figure 1.4: Types of communications,considering the number of devices onlink. (a): point-to-point, and (b): multi-

point.

Relationship between Files, Data, and Signals Files are collection of characters from a

code set (possibly ASCII) When a file to be transmitted:

The characters are translated into 1’s and 0’s An electrical signal representing the 1’s and

0’s is placed on the transmission medium The receiver, converts the incoming

electrical signal into 1’s and 0’s, then into characters that make up the original file.

FILE HAMLET.TXT

USER DATA Yea, from the table of my memoryI'll wipe away all trivial fond records

INTERNALREPRESENTATION

OF USER DATA

y01011001

e01100101

a01100001

,00101100

f01100110

r01110010

o01101111

m01101101

b00100000

b00100000

SIGNAL1 0 0 1 1 0 1 0 1 0 1 0 0 1 1 0

LSB LSB

LSB: Least Significant Bit

Figure 1.5: Files, Data, and Signals

Synchronous & Asynchronous transmission Asynchronous

A character in a message is transmitted as an individual entity, without regard to when the previous character was transmitted

Synchronous All characters in a message are sent contiguously, framing

characters indicate the beginning and end of the entire message

y1 0 0 1 1 0 1 0

e1 0 1 0 0 1 1 0

timeFraming LSB MSB Framing

Asynchronous transmission* Timing of each bit is specified within a character* inter-caharcter time is nonuniform* Each character must be framed

y1 0 0 1 1 0 1 0

e1 0 1 0 0 1 1 0

LSB MSB

Synchronous:* Characters, within a block, aresent contiguously* Each block is framed

Figure 1.6: Asynchronous andsynchronous transmission

In asynchronous transmission: Characters are delineated by a start and a stop bit

In synchronous, framing is for the entire message. Usually a message header and trailer are used

Frame check sequence to protect from transmission errors.

Transmission

SIGNALS Analog and digital signals Analog is equated with continuous Digital is equated with discrete

A telephone set converts the sound waves into an analog signal

The analog signal is digitized when it reaches the telephone network

The digital waveform is converted back into an analog signal and subsequently the sound wave at the receiving end.

Digital Transmission

Digitization of voice signals

Sampling equally spaced discrete values extracted from the

analog signal. The discrete values follow the amplitude of the

analog waveform The result is a PAM signal

quantization Assigning numbers approximate values to the

PAM signal

Bandwidth and Passband of a Communication Channel Bandwidth

A difference between two frequencies : highest and lowest that the channel can handle

Passband The range between the highest and lowest frequencies

CHANNEL A CHANNEL B

8.15 MHz 8.25 MHz 12.8 MHz 12.9 MHz

Bandwidth = 100 KHz

Figure 1.11: PASSBAND AND BANDWIDTHOF A CHANNEL

The Sine and Cosine Waveforms

Periodic signals Characterized by three parameters

Amplitude Frequency (in Hz) Phase shift (in degree or radian)

A

-A

time

PERIOD

PERIOD

SINE WAVE

COSINE WAVE

Figure 1.8: Sine andCosine waveforms

time

A

-A

Fourier Series Expansion

States: almost any periodic signal can be expresses as a sum of sineand cosine waveforms that are harmonically related

usually a sum of DC components and n-harmonic terms first harmonic is the fundamental frequency nthe harmonic is n times the first harmonic

)cossin()(1

0 tnbtnaatf nn

n

Noise

Types of Noise Thermal: heat dissipation in electronic

devices. Crosstalk: Occurs on adjacent

channels, conversation from one channel can be heard on another

Interference: Caused by many stimulus; power lines, Auto ignition, …. etc

The Concept of signal to noise ratio

TRANSMITTED LEVEL(K) SIGNAL

NOISE

TIME

TIME

(K)

(K + 1)

* To reduce effect of noise:A. Increase separation between levelsB. Slow rate of transmissionC. Add error-correction information

Result: Decrease the effective datatransfer rate

Figure 1.12: The concept of signal-to-noise-ratio

RECEIVED SIGNAL PLUSNOISE

Transmission Media

Guided media Twisted pair Optical fibers Coaxial cables

Unguided media Microwave Wireless

Twisted Pair

One of the oldest media At one point AT&T owned 80% of world

copper Typical use: subscriber’s loop, T1 carrier,

and moderate to low speed analog transmission.

Amplification every 5 to 6 km for analog signals

Repeaters every 2 to 3 km for digital signals

Twisted Pair

Figure 1.13: Twisted Pair

Coaxial Cables

the cable Workhorse of industry Used for both digital and analog

transmission Other use: Local Area Networks (Token

rings) Less susceptible to crosstalk and

interference

Coaxial Cables

Solid Cylinder

Stiff Wire

Insulating Bead

Polythylene filler

WireBraided

outerconductor

Figure 1.14: Coaxial Cable

Optical Fibers

Significant breakthrough in telecommunication

Enormous bandwidth Billion bits/sec (Gpbs) Low attenuation rate, 1 bit in error

ever 100 billion or more bits Immune from electrical interference

Optical Fibers

Based on rules of physics Incident angle between different

media Two types:

Single mode multi-mode

Optical FibersB1 B2 B3

a1 a2 a3

AIR/SILICABOUNDARY

SILICA

(a)

Total internalreflection

Light source(b)

Figure 1.15: (a) Three examples of a light ray from inside asilica fiber impinging on the air/silica boundary at different

angles, (b) Light trapped by total internal reflection.

Terrestrial Microwave

Towers operation use line-of-sight transmission. Line-of-site refers to the geographical

arrangement of the transmitting antennas and the receiving tower such that the wave travels in straight line from the transmitter to the receiver.

Since microwaves travel in straight line, if the towers are too far apart, the earth will get in the way .

The higher the towers are, the further apart they can be. For 100-m high tower, repeaters can be spaced 80 km apart (assuming there are no large hills in between).

Radio Tower

Satellite dish

STUDIO

BRO ADCAST RADIATIO NTO A 25 TO 75 M ILE

RADIUS

A n exam p le o f a m ic row avecon figu ra tion

Terrestrial Microwave - Continue

Microwaves do not pass through buildings well. In addition, even though the beam may be well focused at

the transmitter, there is still some divergence in space. Multipath Fading is caused when some waves may be

refracted off low-lying atmospheric layers and may take slightly longer to arrive than direct waves.

The delayed wave may arrive out of phase. The most common type of microwave antenna is a rigidly

fixed parabolic dish-shaped antenna of approximately ten feet diameter, Common frequencies used for microwave transmission are in the rang of 2 GHz to 40 GHz. The higher the frequency employed, the higher the bandwidth and data rate.

Satellite Microwave

A communication satellite is essentially a microwave relay station.

It links two or more ground-based transmitters/receivers called earth stations.

The satellite receives the analog or digital signals transmitted by an earth station on one frequency band called the uplink

It then repeats or amplifies the signal on another frequency band known as the downlink.

A single satellite can operate on a number of frequency bands called a transponder.

To ensure that the satellite is in the line-of-site of earth, it is made to rotate at a period equal of that of the earth. This is possible when the satellite is at a distance of approximately 35,800 km.

Satellite

Satellite dish

Sat

ellit

e di

sh

(a)

Satellite

Transmitter

Satellite dish

Satellite dish

Sat

ellit

e di

sh

Sat

ellit

e di

sh

S ate llite M ic row ave : (a ) po in t-to -po in t, (b ) B roadcas t (m u lti-rece ive rs

(b)

The Public Telephone Network--- History and Evolution --

Alexander Graham Bell invented the telephone Around 1890

Simple networks connected telephones by manually operated switches.

In this network, as shown on next slide, the signal is analog

To call another telephone, a customer first rings the operator and provides the phone number of the party.

The operator then determines the line that goes either directly to the other party or to another operator along a path to the other party.

The Public Telephone Network -- History and Evolution --

The parties remain connected for the duration of the conversation and are disconnected by the operator at the end of the call.

Paths are established by means of circuit switching “circuit” refers to the capability of transmitting one

telephone conversation along one link. To set up a call, a set of circuits has to be connected,

joining the two telephone sets. By modifying the connection, the operators can switch

the circuits. Circuit switching occurs at the beginning of a telephone call. Operators were later replaced by mechanical switches and, eventually, by electronic

switches.

Telephone

Telephone

Telephone

Telephone

A

A

A

The telephone network as existed around1890 (the telephone however looks like

today's telephone, I'm looking for atemplate for an antique telephone

A = Analog

The Public Telephone Network-- History and Evolution --

A major development in the Public Telephone Network is the digital transmission, as shown on the next slide.

An electronic interface in the switch converts the analog signal traveling on the link from the telephone set to the switch into a digital signal, and from digital to analog in the opposite direction.

The switches themselves are computers, which makes them very flexible.

This flexibility allows the Telephone Company to modify connections by sending specific instructions to the computer.

common channel signaling (CCS) – another major development CCS is a data communication network that the switches use to

exchange control information among themselves. This “conversation” between switches serves the same function as the conversation that took place between operators in the manual network.

Telephone

Telephone

Telephone

Telephone

A

D

D

CCS

Telephone network around 1988.The transmissions are analog (A)

or digital (D). The switches areelectronic and exchange control

information by using a datanetwork called common channel

signaling (CCS).

Current Telephone Network Structure Currently, The telephone system is organized as a highly

redundant, multilevel hierarchy. The present configuration, simplified:

From each telephone comes a pair of wires that goes directly to the telephone company’s nearest end office which is also called the local central office.

The two-wire connection between each subscriber’s telephone and the end office is known as the local loop.

In the United States alone there are about 20,000 local central offices. The concentration of the area code and the first three digits of the telephone number uniquely specify a local central office, which is why the rate structure uses this information.

If a subscriber, attached to a particular end office calls a subscriber attached to the same end office, the switching mechanism within the office sets up a direct electrical connection between the two local loops. This connection remains intact for the duration of the call.

The current Telephone Network Structure

If the called telephone is attached to another end office, a different procedure has to be used.

Each end office (local switch) has a number of outgoing lines to one or more nearby switching centers, called toll offices (or if they are within the same local area, tandem switches).

These lines are called toll-connecting trunks. If both the calling party and the called party end offices happen to have a toll connecting trunk to the same toll office (a likely occurrence if they are close by), the connection may be established within the toll office.

If the calling party and the called party do not have a toll office in common, the path will have to be established somewhere higher up in the hierarchy.

Telephone

End office

Toll office

Intermediat switches

offices

Toll office

End officeTelephone

Very high bandwidth inter-toll trunks

Toll connecting trunks

Typical circuit rout for a call of a mediumdistance

OFF-HOOK

Switch connects DTMF receiver

Dial Tone

Start DialingTelephone Number Switch Starts to Collect Digits (one

by one using DTMF circuit)

Select path

Send ringing signal if called partyis not busy

Ring-backtone

OFF-HOOKSwitch disconnects ringing signal

from callee and remove ringbacktone from caller

Removering-back

Connection Path between callerand callee

ON-HOOK (HANG up)Connection path is removed andresources are freed for another

call

Stop dial tone

Ringing signal

Removeringingsignal

A local telephone call scenario

Table 1.1: The telephone system hierarchy as it exists today

Order Name Comments

Class 1 Regional center Top of the hierarchy

Class 2 Sectional Center

Class 3 Primary Center

Class 4 Toll center Now “point of presence” (POP) where local

exchange meets IEX

Class 5 End Office In the local exchange carrier (LEC) area

Standards

Required to allow for interoperability between equipment

Advantages Ensures a large market for equipment and

software Allows products from different vendors to

communicate Disadvantages

Freeze technology May be multiple standards for the same thing

Five components of data communication

Components of data communications

Message: The information to be communicated – text, sound, video, or a combination

Sender: The device that sends the message – computer, telephone, TV, and so on.

Receiver: The device that receives the message – computer, telephone, TV, and so on.

Medium: A path by which the a message travels from sender to receiver – twisted pair, coaxial cables, fiber optic cable, or radio waves (terrestrial or satellite microwave)

Protocol: Rules that governs communications among devices

Data representation Text: represented by a bit pattern of 0s and 1s, the

number of bits in a pattern depends on the number of symbols in the language – English uses 26 symbols (a, b, …) and 26 for (A, B, ..) and 10 symbols for (0, 1, 2, ..)

ASCII: American Standard Code for Information Exchange: uses 7 bit pattern (128 symbols)

Extended ASCII: 8-bit patterns – ASCII is a subset of it by adding a 0 to the left

Unicode: 65,536 symbols because it uses a 16 bit code Images: also represented by bit patterns,

however the mechanism is different.. In its simplest form an image is divided into a matrix of pixels, where each pixel is a small dot

Data Representation

Audio: is a representation of sound, it is by nature different from text, numbers, or images. It is continuous, not discrete.

Video: Can be produced as a continuous entity, (by a TV camera), or it can be a combination of images, each a discrete entity arranged to convey the idea of motion.

Encoding Techniques

Digital data, digital signal Analog data, digital signal Digital data, analog signal Analog data, analog signal

Digital Data, Digital Signal

Digital signal Discrete, discontinuous voltage

pulses Each pulse is a signal element Binary data encoded into signal

elements

Terms (1)

Unipolar All signal elements have same sign

Polar One logic state represented by positive

voltage the other by negative voltage Data rate

Rate of data transmission in bits per second Duration or length of a bit

Time taken for transmitter to emit the bit

Terms (2)

Modulation rate Rate at which the signal level

changes Measured in baud = signal elements

per second Mark and Space

Binary 1 and Binary 0 respectively

Interpreting Signals

Need to know Timing of bits - when they start and

end Signal levels

Factors affecting successful interpreting of signals Signal to noise ratio Data rate Bandwidth

Comparison of Encoding Schemes (1) Signal Spectrum

Lack of high frequencies reduces required bandwidth

Lack of dc component allows ac coupling via transformer, providing isolation

Concentrate power in the middle of the bandwidth

Clocking Synchronizing transmitter and receiver External clock Sync mechanism based on signal

Comparison of Encoding Schemes (2) Error detection

Can be built in to signal encoding Signal interference and noise immunity

Some codes are better than others Cost and complexity

Higher signal rate (& thus data rate) lead to higher costs

Some codes require signal rate greater than data rate

Encoding Schemes

Nonreturn to Zero-Level (NRZ-L) Nonreturn to Zero Inverted (NRZI) Bipolar -AMI Pseudoternary Manchester Differential Manchester B8ZS HDB3

Nonreturn to Zero-Level (NRZ-L) Two different voltages for 0 and 1 bits Voltage constant during bit interval

no transition I.e. no return to zero voltage e.g. Absence of voltage for zero,

constant positive voltage for one More often, negative voltage for one

value and positive for the other This is NRZ-L

Nonreturn to Zero Inverted

Nonreturn to zero inverted on ones Constant voltage pulse for duration of bit Data encoded as presence or absence of

signal transition at beginning of bit time Transition (low to high or high to low)

denotes a binary 1 No transition denotes binary 0 An example of differential encoding

NRZ

Differential Encoding

Data represented by changes rather than levels

More reliable detection of transition rather than level

In complex transmission layouts it is easy to lose sense of polarity

NRZ pros and cons

Pros Easy to engineer Make good use of bandwidth

Cons dc component Lack of synchronization capability

Used for magnetic recording Not often used for signal

transmission

Multilevel Binary

Use more than two levels Bipolar-AMI

zero represented by no line signal one represented by positive or negative pulse one pulses alternate in polarity No loss of sync if a long string of ones (zeros

still a problem) No net dc component Lower bandwidth Easy error detection

Pseudoternary

One represented by absence of line signal

Zero represented by alternating positive and negative

No advantage or disadvantage over bipolar-AMI

Bipolar-AMI and Pseudoternary

Trade Off for Multilevel Binary Not as efficient as NRZ

Each signal element only represents one bit In a 3 level system could represent log23 =

1.58 bits Receiver must distinguish between three

levels (+A, -A, 0)

Requires approx. 3dB more signal power for same probability of bit error

Biphase

Manchester Transition in middle of each bit period Transition serves as clock and data Low to high represents one High to low represents zero Used by IEEE 802.3

Differential Manchester Midbit transition is clocking only Transition at start of a bit period represents zero No transition at start of a bit period represents one Note: this is a differential encoding scheme Used by IEEE 802.5

Manchester Encoding

Differential Manchester Encoding

Biphase Pros and Cons

Con At least one transition per bit time and

possibly two Maximum modulation rate is twice NRZ Requires more bandwidth

Pros Synchronization on mid bit transition (self

clocking) No dc component Error detection

Absence of expected transition

Modulation Rate

Scrambling

Use scrambling to replace sequences that would produce constant voltage

Filling sequence Must produce enough transitions to sync Must be recognized by receiver and replace with

original Same length as original

No dc component No long sequences of zero level line signal No reduction in data rate Error detection capability

B8ZS

Bipolar With 8 Zeros Substitution Based on bipolar-AMI If octet of all zeros and last voltage pulse

preceding was positive encode as 000+-0-+ If octet of all zeros and last voltage pulse

preceding was negative encode as 000-+0+- Causes two violations of AMI code Unlikely to occur as a result of noise Receiver detects and interprets as octet of

all zeros

HDB3

High Density Bipolar 3 Zeros Based on bipolar-AMI String of four zeros replaced with

one or two pulses

B8ZS and HDB3

Digital Data, Analog Signal

Public telephone system 300Hz to 3400Hz Use modem (modulator-demodulator)

Amplitude shift keying (ASK) Frequency shift keying (FSK) Phase shift keying (PK)

Modulation Techniques

Amplitude Shift Keying

Values represented by different amplitudes of carrier

Usually, one amplitude is zero i.e. presence and absence of carrier is

used Susceptible to sudden gain changes Inefficient Up to 1200bps on voice grade lines Used over optical fiber

Binary Frequency Shift Keying Most common form is binary FSK (BFSK) Two binary values represented by two

different frequencies (near carrier) Less susceptible to error than ASK Up to 1200bps on voice grade lines High frequency radio Even higher frequency on LANs using

co-ax

Multiple FSK

More than two frequencies used More bandwidth efficient More prone to error Each signalling element represents

more than one bit

FSK on Voice Grade Line

Phase Shift Keying

Phase of carrier signal is shifted to represent data

Binary PSK Two phases represent two binary digits

Differential PSK Phase shifted relative to previous

transmission rather than some reference signal

Differential PSK

Quadrature PSK

More efficient use by each signal element representing more than one bit e.g. shifts of /2 (90o) Each element represents two bits Can use 8 phase angles and have more than

one amplitude 9600bps modem use 12 angles , four of

which have two amplitudes Offset QPSK (orthogonal QPSK)

Delay in Q stream

QPSK and OQPSK Modulators

Examples of QPSF and OQPSK Waveforms

Performance of Digital to Analog Modulation Schemes Bandwidth

ASK and PSK bandwidth directly related to bit rate

FSK bandwidth related to data rate for lower frequencies, but to offset of modulated frequency from carrier at high frequencies

(See Stallings for math) In the presence of noise, bit error rate of

PSK and QPSK are about 3dB superior to ASK and FSK

Quadrature Amplitude Modulation QAM used on asymmetric digital subscriber

line (ADSL) and some wireless Combination of ASK and PSK Logical extension of QPSK Send two different signals simultaneously on

same carrier frequency Use two copies of carrier, one shifted 90°

Each carrier is ASK modulated Two independent signals over same medium Demodulate and combine for original binary

output

QAM Modulator

QAM Levels

Two level ASK Each of two streams in one of two states Four state system Essentially QPSK

Four level ASK Combined stream in one of 16 states

64 and 256 state systems have been implemented

Improved data rate for given bandwidth Increased potential error rate

Analog Data, Digital Signal

Digitization Conversion of analog data into digital data Digital data can then be transmitted using

NRZ-L Digital data can then be transmitted using code

other than NRZ-L Digital data can then be converted to analog

signal Analog to digital conversion done using a codec Pulse code modulation Delta modulation

Digitizing Analog Data

Pulse Code Modulation(PCM) (1) If a signal is sampled at regular intervals

at a rate higher than twice the highest signal frequency, the samples contain all the information of the original signal (Proof - Stallings appendix 4A)

Voice data limited to below 4000Hz Require 8000 sample per second Analog samples (Pulse Amplitude

Modulation, PAM) Each sample assigned digital value

Pulse Code Modulation(PCM) (2) 4 bit system gives 16 levels Quantized

Quantizing error or noise Approximations mean it is impossible to

recover original exactly 8 bit sample gives 256 levels Quality comparable with analog

transmission 8000 samples per second of 8 bits each

gives 64kbps

Direction of Data Flow

Simplex: the communication is Unidirectional as on a one-way street. Only one device can transmit and the other can receive. Keyboards and traditional monitors are examples

Half-Duplex: Each station can transmit and receive but not at the same time – one lane bridge with bi-directional traffic. Walkie-talkies and CB (citizen band) radio

Full Duplex: also called duplex, both stations can transmit and receive at the same time

Simplex

Half-duplex

Full-duplex

Networks

Distributed Processing --tasks are divide among multiple computers

Network Criteria most important reliability, security, and performance

Physical Structures – how devices are connected: point-to-point, and multipoint, and network topology

Categories of Networks – LAN, MAN, WAN, …

Point-to-point connection

Multipoint connection

Categories of topology

Fully connected mesh topology (for five devices)

Star topology

Bus topology

Ring topology

Categories of networks

LAN

LAN (Continued)

MAN

WAN

The InternetThe Internet

A Brief History

The Internet Today

The Internet – a Brief History

ARPANET: the advance research project agency (ARPA) in the department of defense – DOD

1973: the idea of transmission control protocol (TCP) came about which included concepts as datagrame, and encapsulations.

Shortly after TCP was split into two protocols: TCP and IP (TCP/IP)

Internet today

Terms

ISP: International Service Providers NSPs: National Service Providers Regional ISPs: smaller ISPs that are

connected to one or more NSP Local Internet Service Providers:

provide direct service to the end user. It can be connected to regional ISPs or directly to NSPs

Protocols and StandardsProtocols and Standards

Protocols key elements are syntax

semantics and timing StandardsStandards Organizations ISO. ITU-T, CCITT ANSI, and IEEE, EIA

Internet Standards

Layered Tasks

Sender, Receiver, and Carrier

Hierarchy

Services

Internet Model

Peer-to-Peer Processes

Functions of Layers

Summary of Layers

Internet layers

Peer-to-peer processes

An exchange using the Internet model

Physical layer

The physical layer is responsible for transmitting individual bits from one

node to the next.

Note:Note:

Data link layer

The data link layer is responsible for transmitting frames from

one node to the next.

Note:Note:

Node-to-node delivery

Example 1Example 1

A node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level. The trailer usually contains extra bits needed for error detection

Example 1

Network layer

The network layer is responsible for the delivery of packets from the

original source to the final destination.

Note:Note:

Source-to-destination delivery

Example 2Example 2

We want to send data from a node with network address A and physical address 10, located on one LAN, to a node with a network address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use physical addresses only; the physical addresses only have local jurisdiction. What we need here are universal addresses that can pass through the LAN boundaries. The network (logical) addresses have this characteristic.

Example 2

Transport layer

The transport layer is responsible for delivery of a message from one process

to another.

Note:Note:

Reliable process-to-process delivery of a message

Example 3Example 3

This is an example of transport layer communication. Data coming from the upper layers have port addresses j and k (j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each packet retaining the port addresses (j and k). Then in the network layer, network addresses (A and P) are added to each packet.

Example 3

Application layer

The application layer is responsible for providing services to the user.

Note:Note:

Summary of duties

OSI ModelOSI Model

A comparison

OSI model

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