1. Modeling and Analysis of Computer Networks
Ali Movaghar
Winter 2009

2. Main subjects to be studied
A brief history of computer networks,
Principal concepts being used in computer networking,
Applications of queueing theory to modeling and analysis of computer communication networks
Other mathematical modeling of computer networks,
State of arts in computer networking,

3. Types of networks of particular interest
Mobile ad hoc networks
Wireless sensor networks
Peer-to-peer networks
Overlay networks
Web

4. Textbooks Main Textbook:
D. Bertsekas and R. Gallager, “Data Networks,” 2nd Ed., Prentice-Hall, Inc., 1992.
Secondary Textbooks:
A. Tanenbaum, “Computer Networks,” 4th Ed., Prentice-Hall, Inc., 2003.
J.F. Kurose and K.W. Ross, “Computer Networking: A top-down Approach Featuring the Internet,” Addison-Wesley, 2000.

5. Other references
Recent papers in computer networking which have appeared in renowned national and international conferences or journals.

6. Grading Policy Simulation Tools: 10% Research Papers: 25%
Midterm Exam: 20%
Final Exam: 45%

7. Computer Networks and Distributed Systems
Computer networks: A collection of autonomous computers interconnected by a single technology.
Two computers are interconnected if they are able to exchange information.
Distributed Systems: A collection of independent computers which appears to its users as a single coherent system. It usually has a single model or paradigm that it presents to its users.
Often a layer of software on top of the operating system, called middleware, is responsible for implementing this model.

8. Computer Networks: A Brief History and the Future
Why computer networking?
How was it evolved?
What is the impact of computer networking in our life?
The Internet
Wireless mobile computing

9. A History of Computer Systems
Mainframes (1944-) Minicomputers (1960-) Personal Computers and Workstations (1970-)

10. The 1st Generation: The tube-based mainframe
In 1944 ENIAC (electronic numerical integrator and calculator ) was placed in operation at the Moore School. It had thirty separate units, plus power supply and forced-air cooling, and weighed over thirty tons. It included 19,000 vacuum tubes, 1,500 relays, and hundreds of thousands of resistors, capacitors, and inductors consumed almost 200 kilowatts of electrical power. ENIAC was originally used for ballistics, but played a role in the development of the atomic bomb.

11. The 2nd Generation: Transistor Computer Systems
In 1959 The fully transistorized IBM 7090 computer system delivered. The system had computing speeds up to five times faster than those of its predecessor, the IBM 709. It was both a scientific and business machine.

12. The 3rd Generation computers: Multiprocessing and operating systems make the scene
In 1965 IBM ships the midrange 360 model 40 computer which had COBOL and FORTRAN programming languages available as well as the stock Basic Assembly Language (BAL) assembler.
In 2007 IBM produces the Blue-Gene/P, a system capable of a petaflop (1,000,000 gigaflops or 1,000 teraflops). 
It sports 73,728 processors comprised of four cores each of IBM’s 850MHz PowerPC 450, resulting in 294,912 cores.
The system can be scaled to nearly three times that size, resulting in a 3 petaflop capability and is all hooked up via a high-end optical network.

13. Minicomputers
A minicomputer (colloquially, mini) is a class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems (mainframe computers) and the smallest single-user systems (microcomputers or personal computers).

14. A History of Minicomputers
The term "mini computer" evolved in the 1960s to describe the "small" third generation computers that became possible with the use of transistor and core memory technologies. They usually took up one or a few cabinets the size of a large refrigerator or two, compared with mainframes that would usually fill a room. The first successful minicomputer was IBM’s 16-bit IBM 1130, which cost from US$32,280 upwards when launched February 11, Digital Equipment Corporation’s 12-bit PDP-8, which cost from US$16,000 upwards was launched March 22, 1965.

15. Personal Computers and Workstations
A personal computer (PC) is any computer whose original sales price, size, and capabilities make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator. Throughout the late 1970s and into the 1980s, computers were developed for household use, offering personal productivity, programming and games. Workstations are somewhat larger and more expensive systems (although still low-cost compared with minicomputers and mainframes) were aimed for office and small business use.

16. Time Sharing of Mainframes and Minicomputers
Time-sharing refers to sharing a computing resource among many users by multitasking. Because computers in interactive use often spend much of their time idly waiting for user input, it was suggested that multiple users could share a machine by allocating one user's idle time to service other users. Similarly, small slices of time spent waiting for disk, tape, or network input could be granted to other users.

17. History of Time Sharing
The concept was first described publicly in early 1957 by Bob Bemer as part of an article in Automatic Control Magazine. The first project to implement a time-sharing system was initiated by John McCarthy in late 1957, on a modified IBM 704, and later an additionally modified IBM 7090 computer. It influenced the design of other early timesharing systems developed by Hewlett Packard, Control Data Corporation, UNIVAC and others (in addition to introducing the BASIC programming language).

18. Computer Networks
Computer networks: A collection of autonomous computers interconnected by a single technology.
Two computers are interconnected if they are able to exchange information.

19. Network Hardware
Network hardware has two important aspects: transmission technology and Scale.
There are two types of transmission technologies: broadcast and point to point (switched).

20. Broadcast Networks
Broadcast networks have a single communication channel that is shared by all the machines in the network.
Multicasting: a mode of broadcasting that supports transmission only to a subset of machines.

21. Point-to-Point (Switched) Computer Networks
Point-to-point (Switched) computer networks consist of many connections between individual pairs of machines. To go from the source to the destination, a packet must have to visit one or more intermediate machines.

22. Classification of Computer Networks by Scale
Example
Processors located in same
Inter-processor distance
PAN
Square meter
1 m
LAN
Room
10 m
Building
100 m
Campus
1 km
MAN
City
10 km
WAN
Country
100 km
Continent
1000 km
The Internet
Planet
10000 km

23. Local Area Networks (LANs)
They are distinguished by their transmission technology and their topology.
Traditional LANs run at speeds 10Mbps and 100 Mbps, have low delay (microseconds or nanoseconds), and make few errors.
Newer LANs operate at up to 10 Gbps.

24. Local Area Networks (LANs)
Various topologies are possible for broadcast LANs: Bus and Ring.
Examples: Ethernet (IEEE 802.3), token ring (IEEE 802.5), FDDI, Wireless LAN (IEEE ).
Bus
Ring

25. Metropolitan Area Networks (MANs)
Examples: Cable television networks, DQDB, Wireless MAN (IEEE )

26. Metropolitan Area Networks
A metropolitan area network based on cable TV.

27. Wide Area Networks
Wide Area Networks or WANs consist of hosts and communication subnet.
A communication subnet consists of transmission lines and switching elements.

28. A Taxonomy of Computer Networks
Computer networks can be classified based on the way in which the nodes exchange information
Computer Networks
Switched Computer Networks
Broadcast Computer Networks
Packet-Switched Computer Networks
Circuit-Switched Computer Networks
Datagram Networks
Virtual Circuit Networks

29. Broadcast vs. Switched Computer Networks
Broadcast computer networks
information transmitted by any node is received by every other node in the network
examples: usually in LANs (Ethernet, Wavelan)
Problem: coordinate the access of all nodes to the shared communication medium (Multiple Access Problem)
Switched computer networks
information is transmitted to a sub-set of designated nodes
examples: WANs (Telephony Network, Internet)
Problem: how to forward information to intended node(s)
this is done by special nodes (e.g., routers, switches) running routing protocols

30. Circuit Switching Three phases If circuit not available: “Busy signal”
circuit establishment
data transfer
circuit termination
If circuit not available: “Busy signal”
Examples
Telephone networks
ISDN (Integrated Services Digital Networks)

31. Timing in Circuit Switching
Host 1
Host 2
Node 1
Node 2
DATA
processing delay at Node 1
propagation delay
between Host 1
and Node 1
Circuit Establishment
Data Transmission
Circuit Termination
propagation delay
between Host 2
and Host 1

32. Circuit Switching A node (switch) in a circuit switching network
incoming links
Node
outgoing links

33. Packet Switching
Data are sent as formatted bit-sequences, so-called packets.
Packets have the following structure:
Header and Trailer carry control information (e.g., destination address, checksum)
Each packet is passed through the network from node to node along some path (Routing)
At each node the entire packet is received, stored briefly, and then forwarded to the next node (Store-and-Forward Networks)
Typically no capacity is allocated for packets
Header
Data
Trailer

34. Packet Switching A node in a packet switching network incoming links
outgoing links
Memory

35. Datagram Packet Switching
Each packet is independently switched
each packet header contains destination address
No resources are pre-allocated (reserved) in advance
Example: IP networks

36. Timing of Datagram Packet Switching
Host 1
Host 2
Node 1
Node 2
propagation
delay between
Host 1 and
Node 2
processing & queueing delay of Packet 1 at Node 2
transmission
time of Packet 1
at Host 1
Packet 1
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3

37. Datagram Packet Switching
Host C
Host D
Host A
Node 1
Node 2
Node 3
Node 5
Host B
Host E
Node 7
Node 6
Node 4

38. Virtual-Circuit Packet Switching
Hybrid of circuit switching and packet switching
data is transmitted as packets
all packets from one packet stream are sent along a pre-established path (=virtual circuit)
Guarantees in-sequence delivery of packets
However: Packets from different virtual circuits may be interleaved
Example: ATM networks

39. Virtual-Circuit Packet Switching
Communication with virtual circuits takes place in three phases
VC establishment
data transfer
VC disconnect
Note: packet headers don’t need to contain the full destination address of the packet

40. Timing of Virtual Circuit Packet Switching
Host 1
Host 2
Node 1
Node 2
propagation delay
between Host 1
and Node 1 VC
establishment
Packet 1
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3
Data
transfer
Packet 1
Packet 2
Packet 3 VC
termination

41. Virtual Circuit Packet Switching
Host C
Host D
Host A
Node 1
Node 2
Node 3
Node 5
Host B
Host E
Node 7
Node 6
Node 4

42. Packet-Switching vs. Circuit-Switching
Most important advantage of packet-switching over circuit switching: Ability to exploit statistical multiplexing:
efficient bandwidth usage; ratio between peek and average rate is 3:1 for audio, and 15:1 for data traffic
However, packet-switching needs to deal with congestion:
more complex routers
harder to provide good network services (e.g., delay and bandwidth guarantees)
In practice they are combined:
IP over SONET, IP over Frame Relay

43. Network Software Network Architecture Protocol Hierarchy Layering
The number of layers
The protocols defined in each layer

44. What is Layering?
A technique to organize a network system into a succession of logically distinct entities, such that the service provided by one entity is solely based on the service provided by the previous (lower level) entity.

45. Why Layering?
HTTP
Application
Telnet
FTP
NFS
Coaxial
cable
Fiber
optic
Packet
radio
Transmission
Media
No layering: each new application has to be re-implemented for every network technology!

46. Why Layering?
Solution: introduce an intermediate layer that provides a unique abstraction for various network technologies
Application
Telnet
FTP
NFS
HTTP
Intermediate
layer
Coaxial
cable
Fiber
optic
Packet
radio
Transmission
Media

47. Layering Advantages: Disadvantages:
Modularity – protocols easier to manage and maintain
Abstract functionality –lower layers can be changed without affecting the upper layers
Reuse – upper layers can reuse the functionality provided by lower layers
Disadvantages:
Information hiding – inefficient implementations

48. ISO OSI Reference Model
ISO – International Standard Organization
OSI – Open System Interconnection
Started in 1978; first standard in 1979
ARPANET started in 1969; TCP/IP protocols ready by 1974
Goal: a general open standard
Allow vendors to enter the market by using their own implementation and protocols

49. ISO OSI Reference Model
Seven layers
Lower three layers are peer-to-peer
Next four layers are end-to-end
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Network
Network
Network
Datalink
Datalink
Datalink
Physical
Physical
Physical
Physical medium

50. Data Transmission
A layer can use only the service provided by the layer immediate below it
Each layer may change and add a header to data packet
data
data
data
data
data
data
data
data

51. Summary: Layering
Key technique to implement communication protocols; provides
Modularity
Abstraction
Reuse
Key design decision: what functionality to put in each layer?

52. Reference Models The OSI Reference Model The TCP/IP Reference Model
A Comparison of OSI and TCP/IP

53. OSI Model Concepts Service – says what a layer does
Interface – says how to access the service
Protocol – says how is the service implemented
A set of rules and formats that govern the communication between two peers

54. Physical Layer (1)
Service: move the information between two systems connected by a physical link
Interface: specifies how to send a bit
Protocol: coding scheme used to represent a bit, voltage levels, duration of a bit
Examples: coaxial cable, optical fiber links; transmitters, receivers

55. Data link Layer (2) Service:
Framing, i.e., attach frames separator
Send data frames between peers attached to the same physical media
Others (optional):
Arbitrate the access to common physical media
Ensure reliable transmission
Provide flow control
Interface: send a data unit (packet) to a machine connected to the same physical media
Protocol: layer addresses, implement Medium Access Control (MAC) (e.g., CSMA/CD)…

56. Network Layer (3) Service:
Deliver a packet to specified destination
Perform segmentation/reassemble (fragmentation/defragmentation)
Others:
Packet scheduling
Interface: send a packet to a specified destination
Protocol: define global unique addresses; construct routing tables
Buffer management

57. Data and Control Planes
Data plane: concerned with
Packet forwarding
Buffer management
Packet scheduling
Control Plane: concerned with installing and maintaining state for data plane

58. Example: Routing Data plane: use Forwarding Table to forward packets
Control plane: construct and maintain Forwarding Tables (e.g., Distance Vector, Link State protocols)
Fwd table
Fwd table
H2 R6
H2 R4 … … H1 H2 R4 R1 R3 R6 R2 R5

59. Transport Layer (4) Service:
Provide an error-free and flow-controlled end-to-end connection
Multiplex multiple transport connections to one network connection
Split one transport connection in multiple network connections
Interface: send a packet to specify destination
Protocol: implement reliability and flow control
Examples: TCP and UDP

60. Session Layer (5) Service: Interface: depends on service
Full-duplex
Access management, e.g., token control
Synchronization, e.g., provide check points for long transfers
Interface: depends on service
Protocols: token management; insert checkpoints, implement roll-back functions

61. Presentation Layer (6)
Service: convert data between various representations
Interface: depends on service
Protocol: define data formats, and rules to convert from one format to another

62. Application Layer (7) Service: any service provided to the end user
Interface: depends on the application
Protocol: depends on the application
Examples: FTP, Telnet, WWW browser

63. Summary: Layering
Key technique to implement communication protocols; provides
Modularity
Abstraction
Reuse
Key design decision: what functionality to put in each layer?

64. Design Issues for the Layers
Addressing
Error Control
Flow Control
Multiplexing
Routing

65. Connection-Oriented and Connectionless Services
Six different types of service.

66. Service Primitives
Five service primitives for implementing a simple connection-oriented service.

67. Service Primitives (2)
Packets sent in a simple client-server interaction on a connection-oriented network.

68. Services to Protocols Relationship
The relationship between a service and a protocol.

69. The TCP/IP reference model.
Reference Models (2)
The TCP/IP reference model.

70. Protocols and networks in the TCP/IP model initially.
Reference Models (3)
Protocols and networks in the TCP/IP model initially.

71. Comparing OSI and TCP/IP Models
Concepts central to the OSI model
Services
Interfaces
Protocols

72. A Critique of the OSI Model and Protocols
Why OSI did not take over the world
Bad timing
Bad technology
Bad implementations
Bad politics

73. The apocalypse of the two elephants.
Bad Timing
The apocalypse of the two elephants.

74. A Critique of the TCP/IP Reference Model
Problems:
Service, interface, and protocol not distinguished
Not a general model
Host-to-network “layer” not really a layer
No mention of physical and data link layers
Minor protocols deeply entrenched, hard to replace

75. The hybrid reference model to be used in this book.
Hybrid Model
The hybrid reference model to be used in this book.

76. Example Networks The Internet
Connection-Oriented Networks: X.25, Frame Relay, and ATM
Ethernet
Wireless LANs: 802:11

77. The ARPANET (a) Structure of the telephone system.
(b) Baran’s proposed distributed switching system.

78. The original ARPANET design.
The ARPANET
The original ARPANET design.

79. The ARPANET Growth of the ARPANET (a) December 1969. (b) July 1970.
(c) March (d) April (e) September 1972.

80. NSFNET
The NSFNET backbone in 1988.

81. Traditional Internet Usage (1970-1990)
News
Remote login
File transfer

82. Services Provided by the Internet
Shared access to computing resources
Telnet (1970’s)
Shared access to data/files
FTP, NFS, AFS (1980’s)
Communication medium over which people interact
(1980’s), on-line chat rooms, instant messaging (1990’s)
Audio, video (1990’s)
Replacing telephone network?
A medium for information dissemination
USENET (1980’s)
WWW (1990’s)
Replacing newspaper, magazine?
Audio, video (2000’s)
Replacing radio, CD, TV?

83. Architecture of the Internet
Overview of the Internet.

84. The Internet
Global scale, general purpose, heterogeneous-technologies, public, computer network
Internet Protocol
Open standard: Internet Engineering Task Force (IETF) as standard body
Technical basis for other types of networks
Intranet: enterprise IP network
Developed by the research community

85. History of the Internet
70’s: started as a research project, 56 kbps, < 100 computers
80-83: ARPANET and MILNET split,
85-86: NSF builds NSFNET as backbone, links 6 Supercomputer centers, 1.5 Mbps, 10,000 computers
87-90: link regional networks, NSI (NASA), ESNet(DOE), DARTnet, TWBNet (DARPA), 100,000 computers
90-92: NSFNET moves to 45 Mbps, 16 mid-level networks
94: NSF backbone dismantled, multiple private backbones
Today: backbones run at 10 Gbps, 10s millions computers in 150 countries

86. Time Line of the Internet
Source: Internet Society

87. Growth of the Internet Number of Hosts on the Internet: Aug. 1981 213
Oct ,024
Dec ,174
Oct ,000
Oct ,056,000
Apr ,706,000
Jul ,540,000
Jul ,218,000
Jul ,888,197
Jul ,128,493

88. Recent Growth ( )

89. Internet Users

90. Internet Users

91. Recent Growth ( )

92. Internet Physical Infrastructure
Backbone
ISP
ISP
Campus network
Ethernet, ATM
Internet Service Providers
access, regional, backbone
Point of Presence (POP)
Network Access Point (NAP)
Residential Access
Modem
DSL
Cable modem
Satellite
Enterprise/ISP access,
Backbone transmission
T1/T3, DS-1 DS-3
OC-3, OC-12
ATM vs. SONET, vs. WDM

93. Who is Who in the Internet ?
Internet Engineering Task Force (IETF): The IETF is the protocol engineering and development arm of the Internet. Subdivided into many working groups, which specify Request For Comments or RFCs.
IRTF (Internet Research Task Force): The Internet Research Task Force is a composed of a number of focused, long-term and small Research Groups.
Internet Architecture Board (IAB): The IAB is responsible for defining the overall architecture of the Internet, providing guidance and broad direction to the IETF.
The Internet Engineering Steering Group (IESG): The IESG is responsible for technical management of IETF activities and the Internet standards process. Standards. Composed of the Area Directors of the IETF working groups.

94. Internet Standardization Process
All standards of the Internet are published as RFC (Request for Comments). But not all RFCs are Internet Standards !
available:
A typical (but not only) way of standardization is:
Internet Drafts
RFC
Proposed Standard
Draft Standard (requires 2 working implementation)
Internet Standard (declared by IAB)
David Clark, MIT, 1992: "We reject: kings, presidents, and voting. We believe in: rough consensus and running code.”

98. ATM Virtual Circuits
A virtual circuit.

99. ATM Virtual Circuits (2)
An ATM cell.

100. The ATM Reference Model

101. The ATM Reference Model (2)
The ATM layers and sublayers and their functions.

102. Architecture of the original Ethernet.

103. Wireless LANs (a) Wireless networking with a base station.
(b) Ad hoc networking.

104. The range of a single radio may not cover the entire system.
Wireless LANs (2)
The range of a single radio may not cover the entire system.

105. Wireless LANs (3)
A multicell network.

106. Network Standardization
Who’s Who in the Telecommunications World
Who’s Who in the International Standards World
Who’s Who in the Internet Standards World

107. ITU Main sectors Classes of Members Radio communications
Tele-communications Standardization
Development
Classes of Members
National governments
Sector members
Associate members
Regulatory agencies

108. IEEE 802 Standards
The 802 working groups. The important ones are marked with *. The ones marked with  are hibernating. The one marked with † gave up.

109. The principal metric prefixes.
Metric Units
The principal metric prefixes.