MODULE 1 21CS52 INTRO + Physical Layer.pdf

VISVESVARAYA TECHNOLOGICAL UNIVERSITY, V SEMESTER, COMPUTER SCIENCE AND ENGINEERING, Computer Networks, Andrew S Tenenbaum, VTU SUBJECT CODE: 21CS52

1. Module 1

2. Types of transmission technology
•Broadcast links
•Point-to-point links
•Unicasting
•Multicasting
•Broadcasting
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3. Classification of interconnected processors
by scale.
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4. •Personal Area Networks
•Local Area Networks
•Metropolitan Area Networks
•Wide Area Networks
•Internetworks
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5. PANs (Personal Area Networks) let devices
communicate over the range of a person.
Eg : Personal Computer connected with peripherals
devices.
Inthesimplestform,Bluetoothnetworksuse
themaster-slaveparadigm.Thesystemunit
(thePC)isnormallythemaster,talkingtothe
mouse,keyboard,etc.,asslaves.
Themastertellstheslaveswhataddressesto
use,whentheycanbroadcast,howlongthey
cantransmit,whatfrequenciestheycanuse,
andsoon..
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9. •Computers (desktop PC, PDA, shared peripherals
•Entertainment (TV, DVD, VCR, camera, stereo,
MP3)
•Telecomm (telephone, cell phone, intercom, fax)
•Appliances (microwave, fridge, clock, furnace,
airco)
•Telemetry (utility meter, burglar alarm, babycam).
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10. Must be easy to install..
The network and devices must be foolproof.
Low price..
Sufficient capacity –scalable
Start out with one or more devices.
Security and reliability..
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11. Two broadcast networks
(a)Bus
(b)Ring
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12. A metropolitan area network based on cable
TV.
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13. AWAN(WideAreaNetwork)spansalarge
geographicalarea,oftenacountryor
continent.
Wewillfollowtraditionalusageandcall
thesemachineshosts.
Therestofthenetworkthatconnectsthese
hostsisthencalledthecommunication
subnet,orjustsubnetforshort.
thesubnetconsistsoftwodistinct
components:transmissionlinesand
switchingelements.
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14. Usually in a WAN, the hosts and subnet are
owned and operated by different people.
A second difference is that the routers will
usually connect different kinds of networking
technology.
A final difference is in what is connected to
the subnet. This could be individual
computers, as was the case for connecting to
LANs, or it could be entire LANs.
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18. A stream of packets from sender to receiver.
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19. •Protocol Hierarchies
•Design Issues for the Layers
•Connection-Oriented and Connectionless Services
•Service Primitives
•The Relationship of Services to Protocols
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20. Subnet
Networks
Internetworks
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Subnet : Collection of
routers and
communication lines
with context to WAN
Network : the combination
of a subnet and its hosts
Internetworks: Distinct
networks are interconnected

21. What is a protocol..?
Acommunication protocolis a system of rules that
allow two or more entities of acommunication
systemto communicate between them to transmit
informationvia any kind of variation of aphysical
quantity.
These are the rules or standard that defines
thesyntax,semanticsandsynchronizationof
communicationand possible error recovery methods.
Protocols may be implemented byhardware,software,
or a combination of both.
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22. Layers, protocols, and interfaces, Network
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Protocol Stack

23. The philosopher-translator-secretary architecture.
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24. Example information flow supporting virtual
communication in layer 5.
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25. •Error Control
•Routing
•Protocol Layering..(wct new networks)
•Addressing
•Internetworking
•Flow Control
•Statistical Multiplexing
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26. Six different types of service.
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27. Six service primitives for implementing a simple
connection-oriented service.
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29. A service is a set of primitives (operations)
that a layer provides to the layer above it.
The service defines what operations the
layer is prepared to perform on behalf of its
users, but it says nothing at all about how
these operations are implemented.
A service relates to an interface between
two layers, with the lower layer being the
service provider and the upper layer being
the service user.
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30. A protocol, in contrast, is a set of rules
governing the format and meaning of the
packets, or messages that are exchanged by
the peer entities within a layer.
Entities use protocols to implement their
service definitions.
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A service is like
an abstract data type or an object
in an object-oriented language.
In contrast, a protocol
relates to the
implementation of the
service
and as such is not visible
to the user of the service

31. The relationship between a service and a
protocol.
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32. •The OSI Reference Model
•The TCP/IP Reference Model
•A Comparison of OSI and TCP/IP
•A Critique of the OSI Model and Protocols
•A Critique of the TCP/IP Reference Model
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33. The OSI
reference
model.
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34. Principles applied to arrive at these seven
layers
A layer should be created where a different
abstraction is needed.
Each layer should perform a well-defined
function.
The function of each layer should be chosen
with an eye toward defining internationally
standardized protocols
The layer boundaries should be chosen to
minimize the information flow across the
interfaces.
The number of layers should be large enough
that distinct functions need not be thrown
together in the same layer out of necessity and
small enough that the architecture does not
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35. The physical layer is concerned with
transmitting raw bits over a communication
channel.
making sure that when one side sends a 1 bit
it is received by the other side as a 1 bit, not
as a 0 bit.
what electrical signals should be used to
represent a 1 and a 0.?
How many nanoseconds a bit lasts..?
Transmission Direction..? Two way / one way
initial connection, torn down, how many pins
the network connector has..?
These design issues largely deal with
mechanical, electrical, and timing interfaces
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36. To transform a raw transmission facility into a line
that appears free of undetected transmission
errors.
It accomplishes this task by having the sender break
up the input data into data frames.
If the service is reliable, the receiver confirms
correct receipt of each frame by sending back an
acknowledgement frame.
how to keep a fast transmitter from drowning a
slow receiver in data.?
medium access control sublayer. how to control
access to the shared channel…?
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37. The network layer controls the operation of the
subnet.
how packets are routed from source to
destination.?
Handling congestion is also a responsibility of the
network layer, in conjunction with higher layers
that adapt the load.
Routing from one network to another..?
The addressing used by the second network may be
different from that used by the first one.
The second one may not accept the packet at all
because it is too large.
It is up to the network layer to overcome all
these problems to allow heterogeneous
networks to be interconnected.Saturday, December 30, 2023Aslam B Nandyal 37

38. The basic function of the transport layer is to
accept data from above it, split it up into smaller
units if need be, pass these to the network layer,
and ensure that the pieces all arrive correctly at
the other end.
The transport layer also determines what type of
service to provide to the session layer, and,
ultimately, to the users of the network.
error-free point-to-point channel that delivers messages
or bytes in the order in which they were sent.
transporting of isolated messages with no guarantee
about the order of delivery,
broadcasting of messages to multiple destinations.
The transport layer is a true end-to-end layer.
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39. The session layer allows users on different
machines to establish sessions between them.
Session Services
Dialog control (whose turn to transmit)
Token management (simultaneous critical Operation)
Synchronization (checkpoint to pick from where they
left)
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40. Unlike the lower layers, which are mostly
concerned with moving bits around, the
presentation layer is concerned with the syntax
and semantics of the information transmitted.
In order to make it possible for computers with
different internal data representations to
communicate, the data structures to be exchanged
can be defined in an abstract way, along with a
standard encoding to be used ‘‘on the wire.’’
The presentation layer manages these abstract data
structures and allows higher-level data structures
(e.g., banking records) to be defined and
exchanged.
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41. The application layer contains a variety of
protocols that are commonly needed by users.
One widely used application protocol is HTTP
(HyperText Transfer Protocol), which is the basis
for the World Wide Web.
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42. Model used in ARPANET..(the grandparent of
all wide area computer networks).
TCP/IP Reference Model, after its two
primary protocols. It was first described by
Cerf and Kahn (1974), and later refined and
defined as a standard in the Internet
community (Braden, 1989). The design
philosophy behind the model is discussed by
Clark (1988).
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43. The TCP/IP reference model.
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44. Protocols and networks in the TCP/IP model
initially.
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45. Requirement of DOD led to choice of a
packet-switching network based on a
connectionless layer that runs across
different networks.
The lowest layer in the model, the link layer
describes what links such as serial lines and
classic Ethernet must do to meet the needs
of this connectionless internet layer.
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46. The internet layer is the linchpin that holds the whole
architecture together
Its job is to permit hosts to inject packets into any
network and have them travel independently to the
destination.
They may even arrive in a completely different order
than they were sent, in which case it is the job of
higher layers to rearrange them, if in-order delivery is
desired.
The internet layer defines an official packet format
and protocol called IP (Internet Protocol).
ICMP (Internet Control Message Protocol) that helps
it function.
Packet routing is clearly a major issue here, as is
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47. Two end-to-end transport protocols have been
defined here.
TCP -(Transmission Control Protocol),
is a reliable connection-oriented protocol that allows
a byte stream originating on one machine to be
delivered without error on any other machine in the
internet.
TCP also handles flow control to make sure a fast
sender cannot swamp a slow receiver with more
messages than it can handle.
UDP –(User Datagram Protocol),
is an unreliable, connectionless protocol for
applications that do not want TCP’s sequencing or
flow control and wish to provide their own.
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48. The TCP/IP model does not have session or
presentation layers. No need for them was
perceived. Instead, applications simply include any
session and presentation functions that they
require.
On top of the transport layer is the application
layer. It contains all the higher-level protocols.
The early ones included virtual terminal (TELNET),
file transfer (FTP), and electronic mail (SMTP).
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49. Magnetic Media
Twisted Pairs
Coaxial Cable
Power Lines
Fiber Optics
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50. An industry-standard Ultrium tape can hold
800 gigabytes.
A box 60 ×60 ×60 cm can hold about 1000 of
these tapes, for a total capacity of 800
terabytes, or 6400 terabits (6.4 petabits).
The cost of an Ultrium tape is around $40
when bought in bulk and we have a cost of
roughly $5000 to ship around 800 TB.
Never underestimate the bandwidth of a
station wagon full of tapes hurtling down
the highway.
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CAT 3
CAT 5
CAT 6
CAT 7
Full duplex
Half duplex
Simplex

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53. 50-ohm -digital transmission from start
75-ohm cable, is commonly used for analog
transmission and cable television.
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MULTI MODE SINGLE MODE

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58. The Electromagnetic Spectrum
Radio Transmission
Microwave Transmission
Infrared Transmission
Light Transmission
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59. When electrons move, they create
electromagnetic waves that can propagate
through space (even in a vacuum).
These waves were predicted by the British
physicist James Clerk Maxwell in 1865 and first
observed by the German physicist Heinrich
Hertz in 1887.
The number of oscillations per second of a wave
is called its frequency, f, and is measured in
Hz.
The distance between two consecutive maxima
(or minima) is called the wavelength, which is
universally designated by the Greek letter λ
(lambda).
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60. Inavacuum,allelectromagneticwaves
travelatthesamespeed,nomatterwhat
theirfrequency.
Thisspeedisspeedoflight,c,is
approximately3×10
8
m/sec,orabout1foot
(30cm)pernanosecond.
Thefundamentalrelationbetweenf,λ,and
c(inavacuum)isλf=c
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62. Thetransmitterhopsfromfrequencyto
frequencyhundredsoftimespersecond.
Itispopularformilitarycommunication
becauseitmakestransmissionshardto
detectandnexttoimpossibletojam.
Italsooffersgoodresistancetomultipath
fadingandnarrowbandinterferencebecause
thereceiverwillnotbestuckonanimpaired
frequencyforlongenoughtoshutdown
communication.
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63. uses a code sequence to spread the data
signal over a wider frequency band..
It is widely used commercially as a spectrally
efficient way to let multiple signals share the
same frequency band.
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64. A third method of communication with a
wider band is UWB (Ultra-WideBand)
communication.
UWB sends a series of rapid pulses, varying
their positions to communicate information.
The rapid transitions lead to a signal that is
spread thinly over a very wide frequency
band.
UWB is defined as signals that have a
bandwidth of at least 500 MHz or at least 20%
of the center frequency of their frequency
band.
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65. Radio frequency (RF) waves are easy to
generate, can travel long distances, and can
penetrate buildings easily, so they are widely
used for communication.
Radio waves also are omnidirectional,
meaning that they travel in all directions
from the source, so the transmitter and
receiver do not have to be carefully aligned
physically. both indoors and outdoors
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67. Above 100 MHz, the waves travel in nearly
straight lines and can therefore be narrowly
focused..
Concentrating all the energy into a small
beam by means of a parabolic antenna (like
the familiar satellite TV dish) gives a much
higher signal to-noise ratio,
but the transmitting and receiving antennas
must be accurately aligned with each other.
Before fiber optics, for decades these
microwaves formed the heart of the long-
distance telephone transmission system.
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68. Unguided infrared waves are widely used for
short-range communication.
The remote controls used for televisions,
VCRs, and stereos all use infrared
communication.
They are relatively directional, cheap, and
easy to build but have a major drawback:
they do not pass through solid objects.
On the other hand, controlling your
neighbor’s television with your remote
control is not possible.
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