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Computer Communication Networks. Rajmohan Rajaraman COM1337/3501. Textbook: Computer Networks: A Systems Approach, L. Peterson, B. Davie, Morgan Kaufmann. What is this course about?. Goal Convey the principles and mechanisms that are used to build a computer network that can:

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Computer Communication Networks


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    1. Computer Communication Networks Rajmohan Rajaraman COM1337/3501 Textbook: Computer Networks: A Systems Approach, L. Peterson, B. Davie, Morgan Kaufmann Computer Communication Networks

    2. What is this course about? • Goal • Convey the principles and mechanisms that are used to build a computer network that can: • Grow to global proportion (scalability) • Support diverse applications • Special attention is given to Internet protocols and architecture • Study how protocols work • Explore underlying algorithmic concepts • Understand implementation issues (network programming) Computer Communication Networks

    3. Course Outline • Introduction to networking: principles, architecture, services, implementation issues • Direct link • Internet routing (IP) • Transport protocols (TCP/UDP) • Congestion control • Multicast routing • Internet security • Applications • Selected topics: Content delivery, Caching, Multimedia… Computer Communication Networks

    4. Outline of Lecture 1 • Requirements • Architecture Reading: Chapter 1 of textbook Computer Communication Networks

    5. Requirements • Computer networks are different from classical networks: • General • Not optimized for a specific application • Requirements differ according to the perspective: • Application programmer: services • Network designer: resource efficiency and fairness • Network provider: administration, manageability, accountability Computer Communication Networks

    6. Requirements • Connectivity • Resource Sharing • Support for Common Services • Performance Computer Communication Networks

    7. Connectivity • Goal: allow machines to communicate • Exceptions? • Building blocks: • Nodes: PC, workstations, special-purpose hardware… • hosts • switches • Links: coax cable, optical fiber, wireless… • point-to-point • multiple access (generally limited in size) Computer Communication Networks

    8. Connectivity: Switched Networks • A network can be defined recursively as... • two or more nodes connected by a link, or • two or more networks connected by two or more nodes Computer Communication Networks

    9. Switching Strategies • Circuit switching: carry bit streams • On session establishment a path from source to destination is selected. Resources are allocated over all the links of the path. Route does not change during session life. • Links can be shared by different sessions through mechanisms such time-division multiplexing (TDM) or frequency-division multiplexing (FDM) • Guarantees: rate and packets delivery in order. • Example: original telephone network • Packet switching: store-and-forward messages • Links are shared on a “demand basis” vs. fixed allocation • Packets wait in a queue before being transmitted • E.g., Internet mainly made out of packet switching Computer Communication Networks

    10. Addressing and Routing • Address: byte-string that identifies a node • usually unique • Routing: process of forwarding messages to the destination node based on its address • Types of addresses • unicast: node-specific • broadcast: all nodes on the network • multicast: some subset of nodes on the network Computer Communication Networks

    11. Requirements • Connectivity • Resource Sharing • Support for Common Services • Performance Computer Communication Networks

    12. Resource Sharing • How do hosts that want to communicate share the network resources? • Links • Router queues • Fundamental resource sharing concept: multiplexing Computer Communication Networks

    13. L1 R1 L2 R2 Switch 1 Switch 2 L3 R3 Multiplexing • Time-Division Multiplexing (TDM) • Frequency-Division Multiplexing (FDM) Computer Communication Networks

    14. Statistical Multiplexing • On-demand time-division • Schedule link on a per-packet basis • Packets from different sources interleaved on link • Buffer packets that are contending for the link • Buffer (queue) overflow is called congestion … Computer Communication Networks

    15. Requirements • Connectivity • Resource Sharing • Support for Common Services • Performance Computer Communication Networks

    16. Support for Common Services • A computer network provides more than packet delivery between nodes • We don’t want application developers to rewrite for each application higher layer networking services • The channel is a pipe connecting two applications • How to fill the gap between the underlying network capability and applications requirements? • Problem: identify a set of common services • Delivery guarantees, packet length, delay, security Computer Communication Networks

    17. Communication Patterns:Types of Applications • Interactive terminal and computer sessions: • Small packet length, small delay, high reliability • File transfer: • High packet length, large delay, high reliability • Voice application: • Small packet length, small delay, low reliability, high arrival rate • Video-on-demand: • Variable/high packet length, fixed delay, low reliability • Video-conferencing • Variable/high packet length, small delay, low reliability Computer Communication Networks

    18. Basic Channels • Request/Reply channel: • Guarantees single copy message delivery • Can provide confidentiality and integrity • Used for file transfer and digital library applications • Message Stream channel: • Supports one/two-way traffic, multicast • Parameterized for different delays • Does not need to guarantee message delivery • Guarantees order of delivered messages • Used for video-conferencing, video-on-demand Computer Communication Networks

    19. Reliability:What goes wrong in the network? • Bit-level errors (electrical interference) • 1/10^7 bits on copper, 1/10^12 bits on optical fiber • Packet-level errors (congestion) • Delayed, lost, or received out of order • Link and node failures • Security, Availability: Denial of Service, Integrity, … Computer Communication Networks

    20. Requirements • Connectivity • Resource Sharing • Support for Common Services • Performance Computer Communication Networks

    21. Performance Metrics • Bandwidth (throughput) • data transmitted per time unit • link versus end-to-end • notation • KB = 210 bytes • Mbps = 106 bits per second • Latency (delay) • time to send message from point A to point B • one-way versus round-trip time (RTT) • components Latency = Propagation + Transmit + Queue Propagation = Distance / c Transmit = Size / Bandwidth • Examples of RTT: LAN, Cross-country link, Satellite Computer Communication Networks

    22. Bandwidth versus Latency • Relative importance • 1-byte: 1ms vs 100ms dominates 1Mbps vs 100Mbps • 25MB: 1Mbps vs 100Mbps dominates 1ms vs 100ms • Infinite bandwidth • RTT dominates • Throughput = TransferSize / TransferTime • TransferTime = RTT + TransferSize /Bandwidth • 1-MB file to 1-Gbps link as 1-KB packet to 1-Mbps link Computer Communication Networks

    23. Delay x Bandwidth Product • Amount of data “in flight” or “in the pipe” • Example: 100ms x 45Mbps = 560KB • Why is it important to know Delay x Bandwidth product? Computer Communication Networks