1. CS 352 Internet Technology
Dept. of Computer Science
Rutgers University

2. Administrative Instructor : Richard Martin TA: TBA Textbook
James F. Kurose and Keith W. Ross, Computer Networking, 3rd edition.
Class webpage
Announcements
Lecture notes
Projects
Homeworks
Old exams
CS Fall, 2005

3. Course Goals Understand the basic principles of computer networks
Understand the Internet and its protocols
Understand the key design principles used to build the Internet
Experience building network systems
CS Fall, 2005

4. Course goals (cont.) Course is not about specific skills
E.g. configure a router from company X vs. learn principles of how all routers work
Success means you are confident to tackle a range of network programming, design and maintenance.
CS Fall, 2005

5. Course Approach Lectures: theory behind how networks operate
Tested in exams
See last semesters’ classes for sample problems
Programming assignments:
Real world experience with networks
Program design
Communicating your design
CS Fall, 2005

6. Course Work 2 Mid-terms (15% each) Final (35%) Project (35%)
No electronic devices or notes allowed. No cheat sheets allowed
Final (35%)
You must send the instructor at least 2 weeks before the final if you need to take the makeup!
Project (35%)
Part 1 (10%)
Part 2 (10%)
Part 3 (15%)
CS Fall, 2005

7. Programming assignments
Single long project
Broken into three parts
Can work in a group of 2
Both program and write-up required
Background needed to get started:
Java (112+ level)
Comfortable using data structures(stacks, trees, vector)
Unix (login, handin, permissions, javac)
CS Fall, 2005

8. Programming Assignment
2 Code reviews
10-15 minute oral question and answer period.
TA and instructor will critically review your assignment.
“lost art” of program design.
Make improvements for next level of the assignment.
Grade depends on level of improvement in code quality as well as functionality.
No late handin
Failure to meet the deadline will result in a zero for all team members. No exceptions!
CS Fall, 2005

9. Academic integrity No cheating on projects and exams
Run code similarity detectors on the projects & code review
Scrutinize exams for copying
Department academic integrity policy
Acknowledge your awareness of this policy by the end of September to continue to access department computing facilities
CS Fall, 2005

10. Facilities “Cereal” machines and lab Romulus and remus for general use
~20 UltraSparc machines
~30+ Linux machines
Cardkey Access: student ID card
Romulus and remus for general use
Create your accounts now!
CS Fall, 2005

11. CS352 Fundamentals

12. Why Study Networks? Integral part of society Pervasive
Work, entertainment, community
Pervasive
Home, car, office, school, mall …
Huge impact on people and society
CS Fall, 2005

13. Impact of the Net on People
Anytime access to remote information
HW assignments from my server
Person-to-person and group communication
, blogs, chat
Form and strengthen communities
chat rooms, MUDs, newsgroups
CS Fall, 2005

14. Impact of the Net on Society
Huge impact!
Continuation of technologies that reduce problems of time & space
(e.g. railroads,phone,autos,TV)
Good, bad and ugly
mirror of society
Changes still on the horizon
Commerce, services, entertainment, socializing
CS Fall, 2005

15. Concepts for this week What is the Internet? Network delay analysis
Core and Edge of the Internet
Circuit, message and packet switching
Network delay analysis
Single link
Multi-link
Layering and encapsulation
CS Fall, 2005

16. What is the Internet?

17. What is Internet Technology?
What is an internet?
Network of networks
What is the Internet?
A global internet based on the IP protocol
To what does “Internet technology” refer?
Architecture
Services
Protocols
CS Fall, 2005

18. Architecture-wise Company A Company B
Edge Networks: Companies, organizations with a “default route”
Internet Service Provider 1
ISP 2
Core Networks (ISP tiers)
Tier 1: Biggest ISPs
Tier 2 and 3: Regional and very small.
Network : Collection of interconnected machines
Host: Machine running user application
Media: Physical process used (copper wire, fiber optics, satellite link)
Channel: Logical line of communication
Router: decide where to send data next
CS Fall, 2005

19. Service-wise (applications)
Electronic mail
Remote terminal
File transfer
Newsgroups
File sharing
Resource distribution
World Wide Web
Video conferencing
Games
CS Fall, 2005

20. Protocols Protocol Architecture  Service Rules of communication … FTP
HTTP
RTP
TFTP
TCP
UDP IP
Ethernet
802.11
PPP
CAT-5
Single-Mode
Fiber
RS-232
CS Fall, 2005

21. Core Network Switching Schemes
How much “state” about the connection between two hosts does each node/router along a path through the network maintain?
CS Fall, 2005

22. Switching Schemes Circuit Switching
Message Switching (Store-and-Forward)
Packet Switching (Store-and-Forward)
CS Fall, 2005

23. Circuit Switching
Provides service by setting up the total path of connected lines hop-by-hop from the origin to the destination
Example: Telephone network
CS Fall, 2005

24. Circuit Switching (cont’d)
1. Control message sets up a path from origin to destination
2. Return signal informs source that data transmission may proceed
3. Data transmission begins
4. Entire path remains allocated to the transmission (whether used or not)
5. When transmission is complete, source releases the circuit
CS Fall, 2005

25. Circuit Switching (cont’d)
Call request signal
Propagation Delay
Transmission
Delay
Time
Call accept signal
Data
Transmission
Time
Data A B C D
Routers/Switches
CS Fall, 2005

26. Message Switching Each message is addressed to a destination
When the entire message is received at a router, the next step in its journey is selected; if this selected channel is busy, the message waits in a queue until the channel becomes free
Thus, the message “hops” from node to node through a network while allocating only one channel at a time
Analogy: Postal service
CS Fall, 2005

27. Message Switching (cont’d)
Msg
Header
Transmission
Delay
Time
Msg
Queueing
Delay
Msg A B C D
Routers/switches
CS Fall, 2005

28. Packet Switching Messages are split into smaller pieces called packets
These packets are numbered and addressed and sent through the network one at a time
Allows Pipelining
Overlap sending and receiving of packets on multiple links
CS Fall, 2005

29. Packet Switching (cont’d)
Pkt 1
Pkt 2
Pkt 3
Header
Pkt 1
Pkt 2
Pkt 3
Time
Transmission
Delay
Pkt 1
Pkt 2
Pkt 3
Pipelining A B C D
CS Fall, 2005

30. Comparisons (1) Header Overhead Circuit < Message < Packet
(2) Transmission Delay
Short Bursty Messages:
Packet < Message < Circuit
Long Continuous Messages:
CS Fall, 2005

31. Network delay analysis

32. Why Study Network Performance
Networks cost $
OC-3 line ~= $10,000/month
Cable modem: $40/month
Are you getting your $/worth?
Why is the network “slow”?
Approach:
Build abstract models of network performance
Observe where real networks deviate from model
Simple Models: Tells us average/best/worse cases->useful, practical
Complex Models: Hard to understand -> useless
CS Fall, 2005

33. Units
Bits are the units used to describe an amount of data in a network
1 kilobit (Kbit) = 1 x 103 bits = 1,000 bits
1 megabit (Mbit) = 1 x 106 bits = 1,000,000 bits
1 gigabit (Gbit) = 1 x 109 bits = 1,000,000,000 bits
Seconds are the units used to measure time
1 millisecond (msec) = 1 x 10-3 seconds = seconds
1 microsecond (msec) = 1 x 10-6 seconds = seconds
1 nanosecond (nsec) = 1 x 10-9 seconds = seconds
Bits per second are the units used to measure channel capacity/bandwidth and throughput
bit per second (bps)
kilobits per second (Kbps)
megabits per second (Mbps)
CS Fall, 2005

34. Types of Delay Processing Queuing Transmission Propagation
Time to execute protocol code
Queuing
Time waiting in queue to be processed
Transmission
Time to “get bits on wires”
Propagation
Time for bits to “move across wires”
CS Fall, 2005

35. Transmission vs. Prop. delay
A single transmission link as a water pipe
The thicker the pipe, the more water it can carry from one end to the other in each unit time
Water is carried from one end of the pipe to the other at constant speed, no matter how thick the pipe is
Water = Data bits
Thickness of the pipe = Channel capacity
Speed of water through the pipe = Propagation speed
CS Fall, 2005

36. Transmission vs. Prop. Delay (cont)
pipe
Propagation delay is how long takes to cross the pipe, irrespective of volume
Transmission (bandwidth delay) is related to how much water can be pushed in through the opening per unit time
CS Fall, 2005

37. Transmission Time Another way to ask this question:
How long does it take A to transmit an entire packet onto the link?
Relevant information: packet length = 1500 bytes
channel capacity = 100 Mbps
Another way to ask this question:
If the link can transmit 10 million bits in a second, how many seconds does it take to transmit 1500 bytes (8x1500 bits)?
Solving for t…
t = sec (or 120 msec)
100 Mbits
1500 x 8 bits =
1 sec t
CS Fall, 2005

38. Propagation Delay Another way to ask this question:
How long does it take a single bit to travel on the link from A to B?
Relevant information: link distance = 500 m
prop. delay factor = 5 msec/km
Another way to ask this question:
If it takes a signal 5 msec to travel 1 kilometer, then how long does it take a signal to travel 500 meters?
5 msec t
Solving for t…
t = 2.5 msec =
1000 m
500 m
CS Fall, 2005

39. Processing Delay Stylized format required to send data
Analogy: adding and removing envelopes to letters
Application
Layer
Transport
Network
Host-to-
Net Layer
Host
Application
Layer
Transport
Network
Host-to-
Net Layer
Host
How long does it take to execute all these layers?
Why is this time important?
Network
Layer
Host-to-
Net Layer
Router
CS Fall, 2005

40. Example How long to format the data?B
500 m
Protocol Processing Time = 40 msec
packet length = 1500 bytes
channel capacity = 100 Mbps
propagation delay factor = 5 msec/km
How long to format the data?
How long does it take a single bit to travel on the link from A to B?
How long does it take A to transmit an entire packet onto the link?
CS Fall, 2005

41. Timeline Method Host A Host B Protocol Delay 40 2.5 Propagation delay
1st bit
2.5
Propagation delay
Time
120
Transmission time
last bit 40
Protocol Delay
Total time: = msec
CS Fall, 2005

42. Queuing Delay
Network
Layer
Host-to-
Net Layer
Router
Packets waiting processing at input ports 3 2 1
Packets waiting transmission at output ports
Router 1 2 2 3
Packets arriving faster than processing or transmission delay
=> queuing (I.e. waiting in line)
CS Fall, 2005

43. Analytic Comparison of multi-link network
Given choice of 2 switching schemes, how would you compare their performance?
What would you need to know?
What are the independent variables?
What is the dependent variable?
Could you come up with a closed form expression based on your choices?
CS Fall, 2005

44. Example: Circuit Switching vs. Packet Switching
Goal: Determine which is faster
Formal definition: Least time to move a fixed amount of data
Approach:
Compute time where circuit switching and packet switching are equal based on all possible factors
A factor moving in one direction or the other will tip the balance in favor of one or the other
We’ll ignore wire-line propagation delay in this example
CS Fall, 2005

45. Factors: Number of bytes in the message: N Time to set up circuit: c
Per-link bandwidth: B
Size of the packet: p
Size of the header: h
Number of switches: s
CS Fall, 2005

46. Circuit Switching Time
Time to send N bytes using circuit switching
= Set-up cost + bandwidth delay
CS Fall, 2005

47. Pipelining “Parallelogram” for packet switching
Host A
Switch 1
Switch 2
Host B
Packet 1
Propagation
Delay
Packet 2
Packet 3
Time
Packet 4
Bandwidth
Delay
CS Fall, 2005

48. Note on Pipelining The above analysis is very general:
Packets in a computer network
Messages/packets are the unit of work.
Instructions in a processor
Instructions are the unit of work.
Jobs through a batch Q in an operating system.
Processes are the unit of work.
Pipelining speeds up work over time.
How?
CS Fall, 2005

49. Packet Switching Time Delay = Transmission + “Propagation” delays
Time for a single packet to cross
- not really prop. delay in the traditional sense
+ Transmission delay (also bandwidth delay):
Time to push all the packets into the network
CS Fall, 2005

50. Packet Switching Time Transmission delay “Propagation” delay
Number of packets
Number of links/hops
Time for each packet to go through each link
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51. Equilibrium Point Assuming all other factors equal, solve for C
Q: Can you add link propagation delay to this example?
CS Fall, 2005

52. Homework Questions
If we use message switching, how does the time increase as we scale s?
How does packet switching reduce the impact of increasing s?
Show, using an equation, how reducing the packet size and packet switching reduces the impact of increasing s.
Where does the approach of reducing packet size fail to give any benefit?
CS Fall, 2005

53. Layering and Encapsulation

54. Why Layering? Network communication is very complex
Separation of concerns
Different vendors and organizations responsible for different layers
Testing and maintenance is simplified
Easy to replace a single layer with a different version
CS Fall, 2005

55. Protocol Hierarchy Use layers to hide complexity Interface
Each layer implements a service
Layer N uses service provided by layer N-1
layer N-1 provides a service to layer N
Protocols
Each layer communicates with its peer by a set of rules
Interface
A layers interface specifies the operations
CS Fall, 2005

56. Protocol Hierarchy (cont’d)
Host A
Host B
Layer 7
Layer 7 Protocol
Layer 7
Layer 6 Protocol
Layer 6
Layer 6
Layer 5 Protocol
Layer 5
Layer 5
Layer 4 Protocol
Layer 4
Layer 4
Layer 3 Protocol
Layer 3
Layer 3
Layer 2 Protocol
Layer 2
Layer 2
Layer 1 Protocol
Layer 1
Layer 1
CS Fall, 2005
Physical Medium

57. Different Layering Architectures
ISO OSI 7-Layer Architecture
TCP/IP 4-Layer Architecture
+ application layer = 5 layers in Kurose
Novell NetWare IPX/SPX 4-Layer Architecture
CS Fall, 2005

58. Standards Making Organizations
ISO = International Standards Organization
ITU = International Telecommunication Union (formerly CCITT)
ANSI = American National Standards Institute
IEEE = Institute of Electrical and Electronic Engineers
IETF = Internet Engineering Task Force
ATM Forum = ATM standards-making body
...and many more
CS Fall, 2005

59. Why So Many Standards Organizations?
Multiple technologies
Different areas of emphasis and history
Telecommunications/telephones
ITU,ISO,ATM
Local area networking/computers
IETF, IEEE
System area networks/storage
ANSI
CS Fall, 2005

60. ISO OSI Layering Architecture
Host A
Host B
Application
Layer
Application Protocol
Application
Layer
Presentation Protocol
Presentation
Layer
Presentation
Layer
Session Protocol
Session
Layer
Session
Layer
Transport Protocol
Transport
Layer
Transport
Layer
Network
Layer
Network
Layer
Network
Layer
Network
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Physical
Layer
Physical
Layer
Physical
Layer
Physical
Layer
CS Fall, 2005
Router
Router

61. ISO’s Design Principles
A layer should be created where a different level of abstraction is needed
Each layer should perform a well-defined function
The layer boundaries should be chosen to minimize 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 become unwieldy
CS Fall, 2005

62. Layer 1: Physical Layer Functions: Issues:
Transmission of a raw bit stream
Forms the physical interface between devices
Issues:
Which modulation technique (bits to pulse)?
How long will a bit last?
Bit-serial or parallel transmission?
Half- or Full-duplex transmission?
How many pins does the network connector have?
How is a connection set up or torn down?
CS Fall, 2005

63. Layer 2: Data Link Layer Functions:
Provides reliable transfer of information between two adjacent nodes
Creates frames from bits and vice versa
Provides frame-level error control
Provides flow control
In summary, the data link layer provides the network layer with what appears to be an error-free link for packets
CS Fall, 2005

64. Layer 3: Network Layer Functions: Responsible for routing decisions
Dynamic routing
Fixed routing
Performs congestion control
CS Fall, 2005

65. Layer 4: Transport Layer
Functions:
Hide the details of the network from the session layer
Example: If we want replace a point-to-point link with a satellite link, this change should not affect the behavior of the upper layers
Provides reliable end-to-end communication
CS Fall, 2005

66. Transport Layer (cont’d)
Host A
Host B
Application
Layer
Application Protocol
Application
Layer
first
end-to-end
layer
Presentation Protocol
Presentation
Layer
Presentation
Layer
Session Protocol
Session
Layer
Session
Layer
Transport Protocol
Transport
Layer
Transport
Layer
Network
Layer
Network
Layer
Network
Layer
Network
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Physical
Layer
Physical
Layer
Physical
Layer
Physical
Layer
CS Fall, 2005
Router
Router

67. Transport Layer (cont’d)
Functions (cont’d):
Perform end-to-end flow control
Perform packet retransmission when packets are lost by the network
CS Fall, 2005

68. Layer 5: Session Layer
May perform synchronization between several communicating applications or logical transmissions
Groups several user-level connections into a single “session”
Examples:
Banking session
Network meetings
CS Fall, 2005

69. Layer 6: Presentation Layer
Performs specific functions that are requested regularly by applications
Examples:
encryption
ASCII to Unicode, Unicode to ASCII
LSB-first representations to MSB-first representations
CS Fall, 2005

70. Layer 7: Application Layer
Application layer protocols are application-dependent
Implements communication between two applications of the same type
Examples:
FTP
HTTP
SMTP ( )
CS Fall, 2005

71. Encapsulation
Treat the neighboring layer’s information as a “black box”, can’t look inside or break message
Sending: add information needed by the current layer “around” the higher layers’ data
headers in front
trailers in back
Receiving: Strip off headers and trailers before handing up the stack
CS Fall, 2005

72. Encapsulation Headers Trailer Data Application Layer Data AH
Presentation
Layer PH
Data
Session
Layer
Data SH
Transport
Layer
Data TH
Network
Layer NH
Data
Data Link
Layer DH
Data DT
Physical
Layer PH
Data
CS Fall, 2005

73. Internet “Hourglass” Architecture
Defined by Internet Engineering Task Force (IETF)
“Hourglass” Design …
FTP
HTTP
RTP
TFTP
TCP
UDP IP
Ethernet
802.11
PPP
CAT-5
Single-Mode
Fiber
RS-232
CS Fall, 2005

74. Internet Design Principles
Scale
Protocols should work in networks of all sizes and distances
Incremental deployment
New protocols need to be deployed gradually
Heterogeneity
Different technologies, autonomous organizations
End-to-end argument
Some functions can only be correctly implemented at the end hosts; the network should not provided these.
CS Fall, 2005

75. TCP/IP Layering Architecture
A simplified model
The network layer
Hosts drop packets into this layer, layer routes towards destination- only promise- try my best
The transport layer
reliable byte-oriented stream
Application
Transport
Internet/Network
Host-to-Net
CS Fall, 2005

76. TCP/IP Layering Architecture (cont’d)
Application
Layer
Transport
Network
Host-to-
Net Layer
Host A
Host B
Application Protocol
Application
Layer
Transport Protocol (TCP)
Transport
Layer IP IP IP
Network
Layer
Network
Layer
Network
Layer
Host-to-
Net Layer
Host-to-
Net Layer
Host-to-
Net Layer
CS Fall, 2005