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- 1. Computer Networks Module 1: Introduction Computer Networks, Andrew Tanenbaum 4e Dr. Vikram Shete Symbiosis Institute of Technology
- 2. Why Study Computer Networks? ● Age of information ● Ever evolving ● Created jobs (both, Steve and paid!) ● Society has been affected by it
- 3. What is this course about? ● Fundamental concepts of networking ● Types of networks ● Features of networks ● Design issues involved in networking ● Will develop concepts which are at core of networking
- 4. What is this course NOT about? ● Not about a specific device or company ● May not be sufficient to get a job in itself
- 5. Syllabus
- 6. Administrative Trivia ● Copying ○ From each other ○ From the web ○ From text book ● Paraphrase in your own words and cite the original sources ○ Unless you have developed significant theory independently
- 7. Administrative Trivia ● Penalty if found copying/cheating on assignments, labs and exams ○ 0 marks on that deliverable ○ Take great care of what you submit ● Meet me if you need help
- 8. Administrative Trivia ● Books ○ Data Communications & Networking ■ Behrouz Forouzan ○ Computer Networks ■ Andrew Tanenbaum & David Wetherall ○ Computer Networks: A top down approach ■ James Kurose & Keith Ross
- 11. 1869
- 12. 1901
- 13. Origins 1960
- 15. Origins ARPANET ‘68 (Advanced Research Projects Agency Network)
- 18. ENIAC
- 20. 1984: Cisco Leonard Bosack Sandy Lerner
- 21. Historical Perspective ● December 23, 1947 ○ William Shockley ○ Walter Brattain ○ John Bardeen Source: http://www.computerhistory.org/
- 22. Historical Perspective Source: Wikimedia Commons: http://en.wikipedia.org/wiki/File:Wafer_2_Zoll_bis_8_Zoll_2.jpg
- 23. 2016 Produced with permission from Chris Harrison- Carnegie Mellon University
- 24. 2021
- 25. India in 2022 ● Over 800 million use internet (~60% Indians) ● 2 billion interconnected devices ● Cheap access to internet ● 5.6% of GDP in 2016-16 ○ 16% in 2020
- 26. Social Issues ● Ideas move beyond country boundaries ● Countries have different cultural and legal structures ● Technical issues are not problematic ● Issues escalate when people discuss ○ Politics ○ Sex ○ Religion
- 27. Social Issues ● Censorship ○ Internet operators similar to phone operators ○ Cannot control what users say or do online ○ Can censor but defies freedom of expression ● Government censorship ○ Patriot Act of USA ○ PIPA and SOPA? ● Internet provides true freedom but ○ Brings forth many other unsolved issues
- 29. Introduction ● Network Applications: ○ Business ○ Home ○ Mobile ○ Social Payroll System Updates Email System Information Company wide broadcasts Training Recruitment Taxes Data centers E-Commerce Collaborative work
- 30. Business Applications of Networks (Tanenbaum) A network with two clients and one server.
- 31. Network Applications (Tanenbaum) ● Some forms of e-commerce.
- 32. Introduction ● Network Applications: ○ Business ○ Home ○ Mobile ○ Social Access to remote information Person-to-person communication Interactive entertainment Electronic commerce “There is no reason for any individual to have a computer in his home” ~ Ken Olsen – President, Digital Equipment Corporation (# 2 computer vendor after IBM)
- 33. Home Network Applications ● In peer-to-peer system there are no fixed clients and servers. (eg: Napster)
- 34. Network Hardware
- 35. Network Hardware ● Technology ● Scale • Broadcast links • Point-to-Point links • Different from P2P networks
- 36. Network Hardware ● Technology ● Scale • Broadcast links • Point-to-Point links • Different from P2P networks PAN LAN MAN WAN
- 42. Mesh Topology
- 43. Star Topology
- 44. Tree Topology
- 45. Bus Topology
- 46. Ring Topology
- 47. Hybrid Topology
- 49. Simplex
- 50. Half-Duplex
- 51. Full-Duplex
- 52. Network Hardware ● Technology ● Scale • Broadcast links • Point-to-Point links • Different from P2P networks PAN LAN MAN WAN
- 56. Network Hardware (LAN) ● Local Area Networks (LAN) ○ Widely used for private network within ■ Building, factory, campus etc. ■ Share common resources (printers, database etc) ○ Small in size ■ Worst case transmission times known apriori ■ Tailor made designs are possible
- 57. Network Hardware (LAN) ○ Wired LANs ■ Use cables, high speeds and low delays with no errors ■ Traditional LANs operate at 10 Mbps to 100 Mbps ■ Newer ones can go upto 1Gbps
- 58. Network Hardware (LAN) ○ LAN topologies ■ Bus ● At most one computer can transmit at a time ● Rest must remain quiet ● An arbitration method is required to resolve conflicts ● IEEE 802.3 a.k.a Ethernet is a bus based broadcast network. Operates at 10Mbps to 10Gbps ■ Ring ● IEEE 802.5, the IBM Token Ring protocol. Operates at 4 and 16 Mbps ● Fiber Distributed Data Interface (FDDI) ring network
- 59. Local Area Networks ● Two broadcast networks ● (a) Bus ● (b) Ring
- 61. Metropolitan Area Networks ● A metropolitan area network based on cable TV.
- 62. Figure 2-18 WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998 Wide Area Network
- 63. Wide Area Networks ● Relation between hosts on LANs and the subnet.
- 65. Network Hardware (Summary) ● Technology ● Scale • Broadcast links • Point-to-Point links • Different from P2P networks
- 66. Network Software ● The start was hardware ● Networks evolved ● Network software is more structured now than ever before ● Layered architecture of network
- 67. Network Software ● Layered architecture ○ Reduces complexity ○ Organized as a stack of layers ○ Each layer has responsibilities and tasks ○ Layers interact with the ones above and below
- 68. Network Software ● Layered Architecture ○ Each layer provides a service to the layer above ○ Layer to layer communication in different devices ○ The rules of communication are called protocols
- 69. Network Software ● Set of layers and protocols together is called the network architecture ● Each layer uses a protocol ● A set of protocols used by layers is called a protocol suite/stack
- 71. Network Software • Example information flow supporting virtual communication in layer 5.
- 72. Design Issues for Layers • Addressing – Layers need to identify sources & destinations – Computers can have multiple processes • Data transfer – Unidirectional flow – Bidirectional flow – Prioritized bidirectional flow
- 73. Design Issues for Layers • Error Control – Physical connections are noisy – Common standard between receiver and transmitter – Means to communicate errors have occurred • Order of Data Received – Order may not preserved – Mechanism to detect out of order pieces – Mechanism to put those in order
- 74. Design Issues for Layers • Flow Control – A sender may swamp the network with data – Feedback to reduce data transmission • Length of Messages – Too long • Disassemble, transmit and reassemble – Too short • Assemble, transmit and disassemble
- 75. Design Issues for Layers • Multiplexing-Demultiplexing – Inefficient to setup channels for each processes – Layers will multiplex data streams from different processes • Routing – Choosing a right path based on various parameters • Privacy laws, costs involved, infrastructure etc.
- 76. Design Issues for Layers ARE DATA FOrM ● Addressing ● Routing ● Error Control ● Data Transfer Mode ● Flow Control ● Order of Data Received ● Mux-Demux
- 77. Types of Services Offered by Layers to Layers Above Them
- 79. Reference Models for Layers
- 80. Open Systems Interconnection ● OSI Reference Model ○ First introduced in 1970 by International Standards Organization (ISO-OSI reference model) ○ Aimed at enabling communication between two different systems ○ No need to changed underlying hardware and technology
- 81. Open Systems Interconnection ● OSI Reference Model ○ An open system is a set of protocols ○ OSI model is not a protocol ○ Model allows designing a network architecture which is: ■ Flexible ■ Robust ■ Interoperable
- 82. Open Systems Interconnection ● OSI Reference Model ○ Architecture is very general ○ Earlier protocols are rarely used today ○ Consists of 7 separate but related layers ○ Each layer defines a part of process in moving data forward ○ Each layer is a group of closely related functions ○ Each group is distinct from the other
- 83. OSI Layers (Forouzan) Interface 7/6 Interface 6/5 Interface 5/4 Interface 4/3 Interface 3/2 Interface 2/1 Interface 7/6 Interface 6/5 Interface 5/4 Interface 4/3 Interface 3/2 Interface 2/1 Peer-to-Peer Protocol 7th Layer 7 6 5 4 3 2 1 7 6 5 4 3 2 1 Application Presentation Session Transport Network Data Link Physical Application Presentation Session Transport Network Data Link Physical Network Da.Li Physical Network Da.Li Physical
- 84. OSI Layers ● Layers belong to 3 subgroups ○ Network Support Layers (Layers 1,2,3) ■ Electrical properties, physical connections, physical and logical addressing, transport timing and reliability ○ User Support Layers (Layers 5,6,7) ■ Allow interoperability between unrelated software systems ○ Link (Layer 4) ■ Ensures seamless communication between above 2 groups
- 85. OSI Layers ● Upper layers are always implemented in software ● Lower layers are a combination of hardware and software ● The physical layers is almost always hardware
- 86. An Exchange Using the OSI Model Header Header + Data from Previous layer Encapsulation
- 88. Physical Layer
- 89. Physical Layer ● Physical characteristics of interfaces and medium ● Representation of bits ○ electrical/optical encoding ● Data rate ○ Define duration of bit ● Bit synchronization ○ Clock synchronization between sender and receiver ● Line configuration ○ Point to point or multipoint ● Physical topology ○ Mesh, star etc ● Transmission mode ○ Simplex, half duplex or full duplex
- 90. Data Link Layer
- 91. Data Link Layer ● Transforms a raw transmission facility into a reliable service ● Physical layer appears error free to the network layer
- 92. Data Link Layer ● Broadly responsible for moving frames from one node to another ● Other functions include ○ Framing ○ Physical addressing ○ Flow control ○ Error control ○ Access control
- 93. Data Link Layer ● Framing ○ Divide stream of bits from network layer into manageable units called frames ● Physical addressing ○ Sender’s and receiver’s address of the frame within the network ○ If outside the network then to default gateway
- 94. Data Link Layer ● Flow control ○ Imposes flow control mechanism at the sender’s end to avoid overwhelming the receiver ● Error control ○ Detect and retransmit damaged or lost frames ○ Recognize duplicate frames ● Access control ○ When 2 or more devices connect to same link, data link layer protocols select the controlling device
- 95. Data Link Layer
- 96. Network Layer
- 97. Network Layer ● Logical addressing ○ Enables communication across networks ● Routing ○ Enable moving of packets over the network
- 99. Transport Layer
- 100. Transport Layer ● Responsible for Process to Process delivery
- 101. Transport Layer ● Other functions ○ Service-point addressing ○ Segmentation and reassembly ○ Connection control ○ Flow control ○ Error control
- 102. Transport Layer (Other Functions) ● Service-point addressing ○ Transport layer header contains the port address ○ Network layer gets each packet to the correct computer ○ Transport layer delivers it to the correct process
- 103. Transport Layer (Other Functions) ● Segmentation and reassembly ○ Message is divided into segments each with a sequence number ○ Sequence numbers allow reassembly ● Connection control ○ In connectionless each segment is treated independently and delivered ○ In connection oriented service, a connection is first setup and then segment is delivered
- 104. Transport Layer (Other Functions) ● Flow Control ○ Flow control is end to end and not link to link like in data link layer ● Error Control ○ Control is performed process to process and not on a link to link basis ○ Correction is achieved through retransmission
- 105. Transport Layer
- 106. Self Study ● Session ● Presentation ● Application
- 107. Summary of Layers
- 109. TCP/IP Protocol Suite ● TCP/IP was designed to have 4 layers ● Compared to OSI it can be said to have 5 layers ● Some of the functions in OSI are bundled in TCP/IP
- 111. TCP/IP Protocol Suite ● 4 levels of addressing are used in internet using TCP/IP
- 113. TCP/IP v/s OSI
- 114. Comparison of OSI & TCP/IP ● Concepts central to OSI model ○ Services: Tells what a layer does ○ Interfaces: How to access services? ○ Protocols: Layers internal business to get the job done ● Analogous to objects in OOP ● TCP/IP does not clearly differentiate between the above three
- 115. Comparison of OSI & TCP/IP ● Consequently protocols are well hidden in OSI compared to TCP/IP ○ Protocols can be changed as and when technology changes ○ This is primary reason for a layered structure
- 116. Comparison of OSI & TCP/IP ● OSI model was before protocols ○ Hence is not protocol biased ○ Designers were inexperienced and did not know “what functionality belonged to which layer” ● TCP/IP came after protocols ○ Model fits the existing protocols very well ○ Unsuitable for non-TCP/IP networks
- 117. Comparison of OSI & TCP/IP ● OSI model has 7 layers ○ Uneven distribution of functionalities ○ Very little in upper layers and transport and network layers are overcrowded ● TCP/IP has 4 layers
- 118. Comparison of OSI & TCP/IP ● OSI supports connection oriented and connectionless in the network layer ○ Only connection oriented in the transport layer ○ Transport layers services visible to user ● TCP/IP supports connectionless in network layer ○ But both in transport layer ○ Users get to choose between either