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CHAPTER 1

INTRODUCTION TO NETWORKINGPrinciples Of Communication

ETHERNET Network (LAN)

Improved by W.N.Wahidah

Dec20131

Department of Information and

Communication Technology

DIPLOMA IN INFORMATION TECHNOLOGY(NETWORKING)

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Data Communications Data communications are the exchange of data between two

devices via some form of transmission medium such as wire

cable.

The effectiveness of data communications system depends on

four fundamental characteristics:

1. Delivery. The system must deliver data to the correct destination.

Data must be received by the intended device or user and only bythat device or user.

2. Accuracy. The system must deliver data accurately. Data that

have been altered in transmission and left uncorrected are

unusable.

3. Timeliness. The system must deliver data in timely manner. Data

delivered late are useless.2

DATA

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COMPONENTS

Messageinformation/data to be communicated. Consist of text,

numbers, pictures, sound or video. Senderdevice that sends the data message. Can be computer,

workstation, telephone, video etc.

Receiverdevice that receives the message. Can be computer,workstation, telephone, video etc.

Mediumphysical path which a message travels from sender to

receiver, wired or wireless. Example of wired medium include : twisted-pair wire, coaxial cable, fiber optic cable, and wireless medium such asra

dio waves.

Protocolset of rules that governs data communication. Representagreement between communicating devices.

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1. Communication devicesi. wired devices eg data terminal equipment (DTE), data circuit-terminating

equipment (DCE);

ii. wireless devices eg 3G, GPRS, mobile phone, laptop, netbook

2. Data elementsi. encapsulationeg frames, packets, datagrams;

ii. addresses; sequence numbers

3. Electronic communication methodsExample: simplex, duplex, half-duplex communication, parallel, universal serial

bus, serial, infra red,

Bluetooth, WiFi, 3G

4. Transmission mediumExample: coaxial, optical fibre, unshielded twisted pair (UTP), shielded twisted pair

(STP), infrared,

radio, microwave, satellite

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emen s o a a ommun ca onSystems

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emen s o a a ommun ca onSystems

Communication devices

wired devices eg data terminal equipment (DTE), data circuit-terminatingequipment (DCE);

wireless devices eg 3G, GPRS, mobile phone, laptop, netbook

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Concepts:

a) Analog and Digital Signaling

Data moves in the form of electromagnetic signals across atransmission medium.

Data can be analog or digital.

Analog data refers to information that is continuous; Example:

Digital data refers to information that has discrete states. Example:

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Analog signal Digital signal

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b) Data modulation

i. Modulation is the technique by which data is turned into an analog

wave or a digital signal.

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A computer with an online or Internet connection that connects over a

regular analogphone line includes a modem. This term is derived by combining

beginning letters from the words modulator and demodulator.

In a modem, the modulation process involves the conversion of the digital computersignals (high and low, or logic 1 and 0 states) to analog audio-frequency (AF)tones.

A mechanism that accepts a sequence of data bits and applies modulation to a

carrier wave according to the bits is called a modulator

A mechanism that accepts a modulated carrier wave and recreates the sequence of

data bits that was used to modulate the carrier is called a demodulator
http://searchcio-midmarket.techtarget.com/definition/analoghttp://searchmobilecomputing.techtarget.com/definition/modemhttp://searchmobilecomputing.techtarget.com/definition/modemhttp://searchcio-midmarket.techtarget.com/definition/analog

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SIMPLEX

The communication

is unidirectional asa one-way street.

HALF-DUPLEX

Each station can both transmit and

receive, but notat the same time.

It is like a one-lane road with trafficallowed in both directions.

Example: the walkie-talkie systems.

c) Simplex, half-duplex, and full-duplex transmission

FULL-DUPLEX

Both stations can transmit and receive data

simultaneously. It is like a two-way street withtraffic flowing in both directions at the same

time.

Example: Telephone network. When two people

are communicating by a telephone line, both

can talk and listen at the same time.

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d) Multiplexing

Multiplexing is the process of transmitting several

different signals or information streams via a single

carrier. The transmissionof all these signals or streams takes

place simultaneously by combining the several signals

into one common signal that will efficiently moves

through the carrier bandwidth.

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http://www.wisegeek.org/what-is-a-transmission.htmhttp://www.wisegeek.org/what-is-bandwidth.htmhttp://www.wisegeek.org/what-is-bandwidth.htmhttp://www.wisegeek.org/what-is-a-transmission.htm

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e) Point-to-point transmission

f) Broadcast transmissionIn broadcasting communication, the relationship between the

source and the destination is ONE-TO-ALL. There is only one

source but all the other hosts are the destinations.

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Point-to-point provides a dedicated link between two devices. The

entire capacity of the link is reserved for transmission between

those two devices.

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g) Bluetooth and 3G Bluetooth technology is a short-range wireless

communications technology intended to replace

the cables connecting many different types of

devices, from mobile phones and headsets toheart monitors and medical equipment.

The key features of Bluetooth technology are

robustness, low power, and low cost. The Bluetooth

Specification defines a uniform structure for a wide

range of devices to connect and communicate with

each other. When two Bluetooth enabled devices connect to

each other, this is called pairing. The structure and

the global acceptance of Bluetooth technology means

any Bluetooth enabled device, almost everywhere in

the world, can connect to other Bluetooth enabled

devices located in proximity to one another.

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3G, short for third Generation, is the third generation of mobile

telecommunications technology.

3G technologygenerally refers to the standard of accessibility and speed of

mobile devices. It was first used in Japan in the year 2001. The standards of

the technology were set by the International Telecommunication Union (ITU).

This technology enables use of various services like GPS (Global Positioning

System), mobile television and video conferencing. It not only enables them to

be used worldwide, but also provides with better bandwidth and increasedspeed. 4G ?
http://www.engineersgarage.com/articles/what-is-3g-technology-specificationshttp://www.engineersgarage.com/articles/global-positioning-system-gpshttp://www.engineersgarage.com/articles/global-positioning-system-gpshttp://www.engineersgarage.com/articles/video-conferencinghttp://www.engineersgarage.com/articles/video-conferencinghttp://www.engineersgarage.com/articles/global-positioning-system-gpshttp://www.engineersgarage.com/articles/global-positioning-system-gpshttp://www.engineersgarage.com/articles/what-is-3g-technology-specifications

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h) ThroughputNetwork Throughput refers to the volume of data that can flow

through a network. Network Throughput is constrained by

factors such as the network protocols used, the capabilities of

routers and switches, and the type of cabling, such asEthernet and fiber optic, used to create a network.

In communication networks, such as Ethernet or packet radio,

throughput or network throughput is the average rate of

successful message delivery over a communication

channel.This data may be delivered over a physical or

logical link, or pass through a certain network node. The

throughput is usually measured in bits per second (bit/s or

bps), and sometimes in data packets per second or data

packets per time slot.

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i) BandwidthBandwidth describes the maximum data transfer rateof

a networkor Internetconnection. It measures how

much data can be sent over a specific connection in

a given amount of time.

For example, a gigabit Ethernetconnection has abandwidth of 1,000 Mbps, (125 megabytes per

second). An Internet connection via cable

modemmay provide 25 Mbps of bandwidth.

A link may have a bandwidth of B bps, but we can only

send T bps through this link with T always less than B.(T

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Transmission Flaws

Signals travel through transmission media, whichare not perfect. The signal at the beginning of the

medium is not the same as the signal at the end of

the medium. The causes of the flaws or impairment

are: NOISE and ATTENUATION

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NOISE

There are several types of noise, such as

thermal noise, induced noise, crosstalk,

and impulse noise which, may corrupt the

signal.

1. Thermal noise : The random motion ofelectrons in a wire which creates an extra

signal not originally sent by the

transmitter.

2. Induced noise : It comes from sourcessuch as motors and appliances. These

devices act as a sending antenna, andthe transmission medium acts as a

receiving antenna.

3. Crosstalk: It is the effect of one wire onthe other. One wire acts as a sending

antenna and the other as the receiving

antenna.4. Impulse noise : It is a spike (a signal

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Noise can be defined as an unwanted signal that interferes with the communication or

measurement of another signal. A noise itself is a signal that conveys information regarding

the source of the noise. For example, the noise from a car engine conveys informationregarding the state of the engine.

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ATTENUATIONAttenuation is a loss of signal strength measured

in decibels (dB). It also means a loss of energy.

When a signal travels through a medium, it loses

some of its energy in overcoming the resistance

of the medium. That is why a wire carrying

electric signals gets warm after a while.

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http://compnetworking.about.com/od/wireless80211/g/decibel_db.htmhttp://compnetworking.about.com/od/wireless80211/g/decibel_db.htm

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RULES OF COMMUNICATION In any conversation between two people, there are

many rules, or protocols, that the two must follow inorder for the message to be successfully deliveredand understood.

Among the protocols for successful humancommunication are: Identification of sender and receiver

Agreed-upon medium or channel (face-to-face,telephone, letter, photograph)

Appropriate communication mode (spoken, written,illustrated, interactive or one-way)

Common language

Grammar and sentence structure

Speed and timing of delivery

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RULES OF COMMUNICATION

Protocols are specific to the characteristics of the source,

channel and destination of the message. The rules used to communicate over one medium, like a

telephone call, are not necessarily the same ascommunication using another medium, such as a letter.

Protocols define the details of how the message istransmitted, and delivered. This includes issues of:

Message format

Message size

Timing

Encapsulation Encoding

Standard message pattern

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RULES OF COMMUNICATION(1) Message Encoding

Encoding - process of converting thoughts into the language,symbols, or sounds, for transmission.

Decoding - reverses this process in order to interpret the thought.

Encoding between hosts must be in an appropriate form for the

medium.

Messages sent across the network are first converted into bits bythe sending host.

Each bit is encoded into a pattern of sounds, light waves, or

electrical impulses depending on the network media over which

the bits are transmitted.

The destination host receives and decodes the signals in order tointerpret the message.

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RULES OF COMMUNICATION(2) Message Formatting

Depend on the type of message and the channel that is usedto deliver the message.

Each computer message is encapsulated in a specific format,called a frame, before it is sent over the network.

Frame - provides the address of the intended destination andthe address of the source host.

The format and contents of a frame are determined by thetype of message being sent and the channel over which it iscommunicated.

Messages that are not correctly formatted are notsuccessfully delivered to or processed by the destinationhost.

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(2) Message Formatting

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- ACTIVITY(2) Message Formatting

Place the components of the following voice message into

the proper location within a frame. Mizi calls his friend

Yanti and leaves her a voice message about their

homework assignment.

Yanti tel no: 012 345 6789

Mizi tel no: 012 987 6543

Voice message: Hi Yanti. Can you help me on question

number 2? Thank you.

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(3) Message Size When a long message is sent from one host to another

over a network, it is necessary to break the message

into smaller pieces.

The rules that govern the size of the pieces, or frames,

communicated across the network are very strict.

They can also be different, depending on the channel

used.

Frames that are too long or too short are not delivered.

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(3) Message Size The size restrictions of frames require the source host to

break a long message into individual pieces that meet

both the minimum and maximum size requirements.

Each piece is encapsulated in a separate frame with the

address information, and is sent over the network.

At the receiving host, the messages are de-

encapsulated and put back together to be processed

and interpreted.

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(4) Message TimingAccess method

Determines when is able to send a message.

Based on the environment.

Hosts on a network need an access method to know when to

begin sending messages and how to respond when errors occur.

Flow control

How much information can be sent and the speed that it can be

delivered.

A sending host can transmit messages at a faster rate than thedestination host can receive and process.

Source and destination hosts use flow control to negotiate correct

timing for successful communication.

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(4) Message Timing Response timeout

Hosts on the network also have rules that specify how long to

wait for responses and what action to take if a response timeout

occurs.

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(5) Message Patterns Unicast

A one-to-one message pattern.

There is only a single destination for the message.

Multicast

A host needs to send messages using a one-to-many pattern.

Delivery of the same message to a group of host destinations

simultaneously.

Broadcast

All hosts on the network need to receive the message at thesame time.

Represents a one-to-all message pattern.

Hosts have requirements for acknowledged versus

unacknowledged messages.

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RULES OF COMMUNICATION(6) Message Patterns

Protocol use in communication

All communication, both human and computer, is governed by

pre-established rules, or protocols.

These protocols are determined by the characteristics of the

source, channel and destination. Based on the source, channel and destination, the protocols

define the details for the issues of message format, message

size, timing, encapsulation, encoding and standard message

pattern.

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- ACTIVITY Determine if the communication problem described

deals with message format, timing, message pattern

or message size.

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IMPORTANCE OF PROTOCOLS

Computers use rules, or protocols, in order tocommunicate.

In a wired environment, a local network is defined

as an area where all hosts must "speak the same

language" or in computer terms "share a commonprotocol".

If devices in a local network did not use the same

protocols they would not be able to communicate.

Ethernet - The most common set of protocols

used on local wired networks.

The Ethernet protocol defines many aspects of

communication over the local network, including:30

STANDARDIZATION OF

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STANDARDIZATION OF

PROTOCOL

As networks became more widespread,standards were developed that defined rules by

which network equipment from different vendors

operated.

Standards are beneficial to networking in manyways:

Facilitate design

Simplify product development

Promote competition

Provide consistent interconnections

Facilitate training

Provide more vendor choices for customers31

STANDARDIZATION OF

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STANDARDIZATION OF

PROTOCOL

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STANDARDIZATION OF

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STANDARDIZATION OF

PROTOCOL

IEEE The Institute of Electrical and Electronic Engineers

Maintains the networking standards, including

Ethernet and wireless standards.

Responsible for approving and maintaining thestandards for connections, media requirements and

communications protocols.

Each technology standard is assigned a number

that refers to the committee that is responsible forapproving and maintaining the standard.

Eg:

Ethernet standards is 802.3.

100BASE-T33

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Local Area Network (LAN)

ETHERNET Network

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PHYSICAL ADDRESSING

For identifying source and destination hosts. Every Ethernet network interface has a physical

address assigned to it - Media Access Control

(MAC) address.

The MAC address identifies each source and

destination host on the network.

Ethernet network

Are cable based, meaning that a copper or fiberoptic cable connects hosts and networking devices.

This is the channel used for communications

between the hosts.

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PHYSICAL ADDRESSING

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ETHERNET COMMUNICATION

When messages are sent between hosts on anEthernet network, the hosts format the messages

into the frame layout that is specified by the

standards.

Frames, also referred to as Protocol Data Units(PDUs).

The format for Ethernet frames specifies the

location of the destination and source MAC

addresses, and additional information including:

Preamble for sequencing and timing

Start of frame delimiter / Frame Header Section

Length and type of frame / Data Section

Frame Check Se uence FCS to detect37

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Preamble Defined pattern of alternating 1 and 0 bits used to

synchronize timing.

Frame Header Section

Marks the end of the timing information and start ofthe frame.

Destination MAC Address

Contains the destination MAC address (receiver).

Can be unicast, multicast or broadcast.38

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Source MAC Address Contains the source MAC address (sender).

This is the unicast address of the Ethernet node

that transmitted the frame.

Length / Type Support two different uses.

Type - indicates which protocol will receive the data.

Length - indicates the number of bytes of data that

follows this field.39

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Encapsulated Data Contains the packet of information being sent.

Ethernet requires each frame to be between 64 and

1518 bytes.

Frame Check Sequence Contains 4-byte value that is created by the device

that sends data and is recalculated by the

destination device to check for damaged frames.

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Build a standard IEEE 802.3 Ethernet frame baseon the source and the destination device.

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HIERARCHICAL ETHERNET

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HIERARCHICAL ETHERNET

NETWORK DESIGN

Access layer Distribution layer

Core layer

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LOGICAL ADDRESS

Physical address It is physically assigned to the host NIC

MAC address does not change

IP address/network address

Also known as logical address

Assigned to each host by a network administrator

based on the local network, where the host is

located.

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LOGICAL ADDRESS

IP addresses contain two parts:(1) Identifies the local network.

The network portion of the IP address will be the same for

all hosts connected to the same local network.

(2) Identifies the individual host. Within the same local network, the host portion of the IP

address is unique to each host.

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