The document provides an introduction to computer networks and the Internet. It discusses key concepts like what the Internet is, common network devices like routers and switches, different network topologies, and protocols. It also describes the layered structure of network protocols including physical, link, network, transport and application layers. Packet switching is introduced as the dominant transmission method used by the Internet, compared to circuit switching. The document outlines sources of delay in packet switched networks and how congestion can lead to packet queuing and loss.

1. Introduction to Computer Networks
and Internet
Prof. Chintan Patel
Chintan.patel@marwadieducation.edu.in

2. Motivation
Prof. Chintan Patel

3. Internet
• What is internet ?
– One sentence definition….
• What are nuts & bolts of Internet ?
• Computer Network : Interconnecting hundreds of millions
of computing devices
Prof. Chintan Patel

4. Prof. Chintan Patel

5. Hosts
• TVs , Laptops , Gaming Console , Cell phone , web cams , Automobiles ,
environmental sensing devices……
Prof. Chintan Patel

6. Communication Link
• Transmission medium used for transmission of Data in form of
Packet with particular transmission rate.
Prof. Chintan Patel

7. Router
• A network device which takes the packet from connected
communication link and forward it based on destination.
Prof. Chintan Patel

8. Switch
• Connecting multiple hosts.
Prof. Chintan Patel

9. ISP
• Internet Service Provider
Prof. Chintan Patel

10. Packet – switched Network
• Transportation network of highway.
Prof. Chintan Patel

11. Think about Smart Home !!!!!
Prof. Chintan Patel

12. Protocol
A some set of Rules
• Human Protocols
• Defines the format and order of message exchanged as well
as actions taken on transmission.
• computer network protocol:
• HTTP
• FTP
• SMTP
• etc……..
Prof. Chintan Patel

13. Network structure
• network edge:
• applications and hosts
• Access networks, physical
media:
• wired, wireless
communication links
• network core:
• interconnected routers
• network of networks
Prof. Chintan Patel

14. network edge
• end systems (hosts):
 run application programs
 e.g. Web, email
 at “edge of network”
client/server
peer-peer
• client/server model
 client host requests, receives
service from always-on server
 e.g. Web browser/server;
email client/server
• peer-peer model:
 Both side will work as client and
server
 e.g. Skype, Bit Torrent , TelephonyProf. Chintan Patel

15. Access networks and physical media
Q: How to connect end systems to
edge router?
• residential access nets
• institutional access networks
(school, company)
• mobile access networks
Keep in mind:
• bandwidth (bits per second) of
access network?
• shared or dedicated?
Prof. Chintan Patel

16. telephone
network Internet
home
dial-up
modem
ISP
modem
(e.g., AOL)
home
PC
central
office
 Uses existing telephony infrastructure
 Home is connected to central office
 up to 56Kbps direct access to router (often less)
 Can’t surf and phone at same time: not “always on”
Dial-up Modem
Prof. Chintan Patel

17. Types of Services
• Connection Oriented Service
– Sending a control packet before transmitting
actual data
– 3 way Handshaking
– Reliable , Flow control , Congestion Control
– TCP : HTTP , FTP , TELNET , SMTP
• Connection Less Service
– No handshaking
– Faster Delivery
– UDP : Media streaming , video conferencing
Prof. Chintan Patel
TCP

18. Prof. Chintan Patel
Physical Media
• Bit: propagates between
transmitter/rcvr pairs
• physical link: what lies
between transmitter &
receiver
• guided media:
– signals propagate in solid media:
copper, fiber, coax
• unguided media:
– signals propagate freely, e.g.,
radio
Twisted Pair (TP)
• two insulated copper
wires
– Category 3: traditional
phone wires, 10 Mbps
Ethernet
– Category 5:
100Mbps Ethernet

19. Prof. Chintan Patel
Physical Media: coax, fiber
Coaxial cable:
• two concentric copper
conductors
• bidirectional
• baseband:
– single channel on cable
– legacy Ethernet
• broadband:
– multiple channels on cable
– HFC
Fiber optic cable:
 glass fiber carrying light pulses, each
pulse a bit
 high-speed operation:
 high-speed point-to-point
transmission (e.g., 10’s-100’s
Gps)
 low error rate: repeaters spaced far
apart ; immune to electromagnetic
noise

20. Prof. Chintan Patel
Physical media: radio
• signal carried in
electromagnetic spectrum
• no physical “wire”
• bidirectional
• propagation environment
effects:
– reflection
– obstruction by objects
– interference
Radio link types:
 terrestrial microwave
 e.g. up to 45 Mbps channels
 LAN (e.g., Wifi)
 11Mbps, 54 Mbps
 wide-area (e.g., cellular)
 3G cellular: ~ 1 Mbps
 Satellite
 Kbps to 45Mbps channel (or
multiple smaller channels)
 270 msec end-end delay

21. Protocol Layers and Service Models
Prof. Chintan Patel
Networks are complex!
• many “pieces”:
– hosts
– routers
– links of various
media
– applications
– protocols
– hardware, software
Question:
Is there any hope of
organizing structure of
network?
Or at least our discussion of
networks?

22. Example 1
Prof. Chintan Patel
Organization of air travel
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing

23. Prof. Chintan Patel
Layering of airline functionality

24. Example 2
Postal System
• Hostel communication
Components:
• Hostel
• Students
• Letters
• Office Boy
• Postmen
• Vehicles/ Tracks/ Roads
Functionality:
• Generate letters
• Multiplex/de-multiplex letters
• End-to-end path determination
• Hop-to-hop transfer
• Physical transfer
Prof. Chintan Patel

25. Challenges
• Large Reach (international, national, villages)
• Need to be scalable (many users)
• Many user requirements (reliable, express, cheap)
• Heterogeneous Technology (airplanes, trucks, trains,
bullock-carts)
Prof. Chintan Patel

26. Internet
• Computer communication
• Components:
• Hostel -------> Computing Device
• Students -----> Application Processes
• Letters -------> Messages/Packets
• Office Boy ---> Transport Software
• Postmen ------> Routers/Switches
• Vehicles/ Tracks/ Roads ---> Hardware/Cables
Prof. Chintan Patel

27. Challenges
• Complex System
–Many users (Billions)
–World-wide reach
–Many user requirements
•reliable, express, cheap, interactive (real-time), multicast
–Heterogeneous Technology
•Ethernet, Wireless, Bluetooth, WiFi, Cellular
Prof. Chintan Patel

28. Prof. Chintan Patel
Internet protocol stack
• Application:
• Supports application processes which generate messages
• Email, Web, File-transfer FTP, SMTP, HTTP
• Transport:
• Supervises process to process communication (multiplexing/de-
multiplexing messages, reliability)
•TCP, UDP
• network:
• End to End routing of data grams from source to destination
• IP, routing protocols
• link:
• Hop to Hop data transfer between neighboring network
elements
• Ethernet , 802.11
• physical:
• Enables bit transmissions on media (wire/air)
• 10Base-T, OFDM
application
transport
network
Link
physical

29. Advantages of Layering
• Modular design ----------> less complex
–Explicit structure allows identification, relationship of complex system’s
pieces
• Software reuse ---> upper layers can share lower layer functionality
–E.g. Web, email both make use of TCP
• Abstraction of implementation
• –Allows extensibility, new technologies
– Can change specific parts of implementation as long as interface kept
same
•Add new physical layer (technology) without having to change network
or transport layer
Prof. Chintan Patel

30. Prof. Chintan Patel
ISO/OSI reference model
• presentation: allow applications to interpret
meaning of data, e.g., encryption,
compression, machine-specific conventions
• session: synchronization, check pointing,
recovery of data exchange
• Internet stack “missing” these layers!
– these services, if needed, must be
implemented in application
– needed?
application
presentation
session
transport
network
link
physical

31. Prof. Chintan Patel
Protocols of Each Layer

32. Prof. Chintan Patel
source
application
transport
network
link
physical
HtHn M
segment Ht
datagram
destination
application
transport
network
link
physical
HtHnHl M
HtHn M
Ht M
M
network
link
physical
link
physical
HtHnHl M
HtHn M
HtHn M
HtHnHl M
router
switch
Encapsulationmessage M
Ht M
Hn
frame

33. The Network Core
Prof. Chintan Patel
• Switching
• Need of Switching
• Types of Switching

34. Prof. Chintan Patel
Switching
• “Moving the information between two different Network or
Between various network segments in the form of Packet is
called Switching”
• Example :
– Students class rotation to maintain time table or to smooth class
allocation.
– Establishment of telephone call for to provide dedicated link

35. Prof. Chintan Patel
Need of Switching Techniques
• Mesh topology : Most reliable topology in Computer Network
• But…………………..its fine for network in which limited no. of devices are
there for large network its use less.

36. Prof. Chintan Patel
• A better alternative is to use switched Network or Switching
technique.
• switching mechanism : Controlling information transmission

37. • Key features of switched Network :-
– There is no fix topology to follow
– We can use FDM or TDM for node-to-node
communication.
– Multiple path exists from source to destination for better
network reliability.
– Switching node are not concerned with contents of data.
– Node provides a switching facility that will move data
from node to node Until they reach to destination
Prof. Chintan Patel

38. Types of Switching
• Circuit switching
– Reserved resources for communication
• Packet switching
– Resources are not reserved
Prof. Chintan Patel

39. Circuit Switching
Prof. Chintan Patel

40. • Circuit : Established connection between sender and receiver
• Reserved bandwidth between sender and receiver provides
guaranteed constant rate between sender and receiver
• TDM and FDM Circuit switching :
– FDM : Each established circuit continuously gets a fraction of the
bandwidth
– TDM : Each circuit gets all bandwidth periodically during brief interval
of time
Prof. Chintan Patel

41. Frequency Division Multiplexing(FDM)
& Time Division Multiplexing(TDM)
Prof. Chintan Patel

42. Prof. Chintan Patel
Example -1
• How long does it take to send a file of 640,000 bits from host A
to host B over a circuit-switched network?
– All links are 1.536 Mbps
– Each link uses TDM with 24 slots/sec
– 500 msec to establish end-to-end circuit
Let’s work it out!
Solutions :
1.536 Mbps means per second 1536 Kb ,
Per second 24 slots so for one slot 1536 kb / 24 = 64Kbps
So 640000 bits / 64 kbps = 10 second for transmission
Total time = 10 second + 0.5 second = 10.5 second

43. Circuit switching
Prof. Chintan Patel
• Communication via circuit switching involves three phases:
– Circuit Establishment :-
• path must be established before data transmission begins
– Data Transfer :-
• Transfer data is from the source to the destination.
• The data may be analog or digital, depending on the nature of the
network.
• The connection is generally full-duplex
– Circuit Disconnect: -
• Terminate connection at the end of data transfer.
• Signals must be propagated to deallocate the dedicated resources
• Silent period is a disadvantage in circuit switching

44. What is store-and-Forward transmission ?
Prof. Chintan Patel
• Message is sent to nearest directly connected switching
node.
– Node stores the message
– Check for the errors.
– Select best path from available paths.
– Forward message to next intermediate node
• Queuing Delay

45. Packet switching
Prof. Chintan Patel
• It is also based on the same ‘store-and-forward’ approach.
• To overcome the limitations of message switching, messages
are divided into subsets of equal length called packets.
• This approach was developed for long-distance data
communication (1970)

46. Prof. Chintan Patel
Packet Switching: Statistical Multiplexing
Sequence of A & B packets does not have fixed pattern, bandwidth
shared on demand  statistical multiplexing.
TDM: each host gets same slot in revolving TDM frame.

47. Prof. Chintan Patel
Packet switching versus circuit switching
• Packet switching is great for bursty data
– resource sharing
– simpler, no call setup
• excessive congestion: packet delay and loss
– protocols needed for reliable data transfer, congestion
control

48. Prof. Chintan Patel
Internet structure: network of networks
• roughly hierarchical
• at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and
Wireless), national/international coverage
– treat each other as equals
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-1
providers
interconnect
(peer)
privately

49. Prof. Chintan Patel
Internet structure: network of networks
• “Tier-2” ISPs: smaller (often regional) ISPs
– Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
Tier-2 ISP pays
tier-1 ISP for
connectivity to
rest of Internet
 tier-2 ISP is
customer of
tier-1 provider
Tier-2 ISPs
also peer
privately with
each other.

50. Prof. Chintan Patel
Internet structure: network of networks
• “Tier-3” ISPs and local ISPs
– last hop (“access”) network (closest to end systems)
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
local
ISP
local
ISP
local
ISP
local
ISP
local
ISP Tier 3
ISP
local
ISP
local
ISP
local
ISP
Local and tier-
3 ISPs are
customers of
higher tier
ISPs
connecting
them to rest
of Internet

51. Prof. Chintan Patel
Internet structure: network of networks
• a packet passes through many networks!
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
local
ISP
local
ISP
local
ISP
local
ISP
local
ISP Tier 3
ISP
local
ISP
local
ISP
local
ISP

52. Prof. Chintan Patel
How do loss and delay occur?
 packets queue in router buffers
• packet arrival rate to link exceeds output link capacity
• packets queue, wait for turn

53. Prof. Chintan Patel
Four sources of packet delay
 1. nodal processing:
 check bit errors
 determine output link
 2. queuing
 time waiting at output link
for transmission
 depends on congestion
level of router

54. Prof. Chintan Patel
Delay in packet-switched networks
3. Transmission delay:
• R=link bandwidth (bps)
• L=packet length (bits)
• time to send bits into link
= L/R
4. Propagation delay:
• d = length of physical link
• s = propagation speed in
medium (~2x108 m/sec)
• propagation delay = d/s
Note: s and R are very different
quantities!

55. Prof. Chintan Patel
Nodal delay
• dproc = processing delay
– typically a few microsecs or less
• dqueue = queuing delay
– depends on congestion
• dtrans = transmission delay
– = L/R, significant for low-speed links
• dprop = propagation delay
– a few microsecs to hundreds of msecs
proptransqueueprocnodal ddddd 

56. Queuing Delay and Packet loss
• Queuing delay can very from packet to packet
• a = packets/sec (Packet arriving rate)
• R = bits / sec (Transmission rate)
• L = bits (Packet size)
• Avg. Rate at which bits arrive at queue = La bits/sec
• La/R = Traffic intensity
• If La/R > 1 average rate at which bits arrive at the queue exceeds the
rate at which the bits can be transmitted from the queue.
• La/R ≤ 1. Here, the nature of the arriving traffic impacts the queuing
delay
Prof. Chintan Patel

57. Example
• If a = 2 , L = 2 , R = 4 what will be Queuing delay.
• If a = 5 , L = 50 , R = 25 what will be Queuing Delay.
“ Queuing delay depends on traffic intensity “
• Task : Surf website which provide animated
environment on queuing delay and set packet arrival
rate high….Enjoy.!!!!!!!
Prof. Chintan Patel

58. Prof. Chintan Patel
Packet loss
• queue preceding link in buffer has finite capacity
• packet arriving to full queue dropped .
• lost packet may be retransmitted by previous node, by source
end system, or not at all

59. Throughput
• “ rate of successful message delivery over a communication
channel “
• Unit of throughput = bits/time or bits/timeslot
• Instantaneous throughput : Rate at which host is receiving a file
at any instant of time.
• Average throughput : Rate over longer period of time.
– Throughput = F/T bits/sec. where F = no of bits transferred and T = time
taken for transmission.
Prof. Chintan Patel
server, with
file of F bits
to send to clients
link capacity
Rs bits/sec
link capacity
Rc bits/sec
pipe that can carry
fluid at rate
Rs bits/sec)
pipe that can carry
fluid at rate
Rc bits/sec)
server sends bits
(fluid) into pipe

60. bottleneck link
Prof. Chintan Patel
• Rs < Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
• Rs > Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
link on end-end path having throughput = min (Rs, Rc)

61. Prof. Chintan Patel
10 connections (fairly) share
backbone bottleneck link R bits/sec
Rs
Rs
Rs
Rc
Rc
Rc
R
Throughput: Internet scenario
• per-connection end-
end throughput:
min(Rc ,Rs ,R /10)
• in practice: Rc or Rs is
often bottleneck

62. Example
• If Rs = 2 Mbps , Rc = 1 Mbps , R = 5 Mbps ,
Assume there are 10 client to download. What
will be throughput ?
Prof. Chintan Patel

63. History Of Internet
Prof. Chintan Patel

64. Prehistoric
• Smoke signals :
• Talking Drums :
– Message can be delivered
100 mules in 1 hour
Prof. Chintan Patel

65. Before Common Era (BCE)
• Pigeons
• Hydraulic Semaphore
Prof. Chintan Patel

66. Prof. Chintan Patel
• 1790’s :
Semaphore
lines
• 1830’s : Electric Telegraph
• 1870’s: Telephone

67. • 1890’s: Radio
• 1920’s: Television
• 1960’s: Satellite
Prof. Chintan Patel

68. Computer Network beginning
• 1960’s:
–Fiber Optics
–Packet switching by Kleinrock
•1969: Four nodes (UCLA, Stanford, UCSB
and Univ. of Utah) connected by 50kbps links
• ARPANET (Advanced Research Projects Agency)
•1972: ARPANET connected 15 nodes, Email was introduced
Prof. Chintan Patel

69. • The 1970’s
•Different networks emerged
– ALOHANet (microwave)
– DARPA Satellite
– BBN Commercial
• 1976: Ethernet by Metcalfe
•Internetwork these networks (Internet)
End of 1970s: TCP/IP by Kahn and Cerf
•1981: 213 hosts on ARPANET
Prof. Chintan Patel

70. 1980’s
• 1982: TCP/IP formalized
• 1982: SMTP (Email)
• 1983: Domain Name System (DNS)
• 1986: Internet Engineering Task Force
• 1988 – OSI Reference Model released
• 1989 – Routing Protocols: BGP, RIP
Prof. Chintan Patel

71. Prof. Chintan Patel

72. 1990’s
• The 1990’s
• Early 1990’s: Commercialization of Internet
(ISPs)
• 1991: World Wide Web (WWW)
• 1995’s: Many new applications
–Instant Messaging, P2P, e-commerce (eBay,
Amazon)
• 1998: Google Search
• 1999: WiFi (wireless)
Prof. Chintan Patel

73. 2000’s
• 2003: Skype
• 2004: Facebook
• 2005: YouTube
• 2006: Twitter
• 2008: Cloud based services (E.g. Dropbox)
• 2010: Instagram (Photosharing)
• 2011: Google+
Prof. Chintan Patel

74. References
• PPT of Kurose and Ross
• Computer network , Bodhi tree , IIT Bombay
Prof. Chintan Patel

75. Prof. Chintan Patel