1 Introduction Basic concepts Basic concepts Terminology Terminology

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  • 1 Introduction Basic concepts Basic concepts Terminology Terminology
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  • 2 Ubiquitous Computing Computers everywhere. Computers everywhere. Also means ubiquitous communication Also means ubiquitous communication Users connected anywhere/anytime. PC (laptop, palmtop) equivalent to cell phone. Networking computers together is critical! Networking computers together is critical!
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  • 3 Computer Network Provide access to local and remote resources. Provide access to local and remote resources. Collection of interconnected end systems: Collection of interconnected end systems: Computing devices (mainframes, workstations, PCs, palm tops) Peripherals (printers, scanners, terminals). Applications: location transparency. Applications: location transparency.
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  • 4 Computer Networks (contd) Components: Components: End systems (or hosts), Routers/switches/bridges, and Links (twisted pair, coaxial cable, fiber, radio, etc.).
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  • 5 Communication Model Network SourceDestination
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  • 6 Example PTN Source Destination Modem Source System Destination System PTN: Public Telephone Network
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  • 7 Connecting End Systems Dedicated link Multiple access / shared medium
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  • 8 Connecting End Systems (contd) Router Switched network Router: switching element; a.k.a., IMPs (Interface Message Processors) in ARPAnets terminology.
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  • 9 Shared Communication Infrastructure Shared medium: Shared medium: Examples: ethernet, radio. How to acquire channel: medium access control protocols. Switched networks: Switched networks: Shared infrastructure consisting of point-to- point links. Circuit- versus packet-switching.
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  • 10 Circuit Switching Establish dedicated path (circuit) between source and destination. Example: telephone network. +s: dedicated resources(stream-oriented). -s: lower resource utilization (e.g.,bursts).
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  • 11 Packet Switching Data split into transmission units, or packets. Routers: store packets briefly store packets and forward them: store-and-forward. Efficient resource use: statistical multiplexing. Ability to accommodate bursts. S1 D1 S2 D2
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  • 12 (Switched) Network Topologies Star Ring Tree Irregular
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  • 13 Protocol Set of rules that allow peering entities to communicate. Set of rules that allow peering entities to communicate. Example: 2 friends talking on the phone. Peering entities or peers: user application programs, file transfer services, e-mail services, etc.
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  • 14 Network Architecture Protocol layers: reduce design complexity. Protocol layers: reduce design complexity. Main idea: each layer uses the services from lower layer and provide services to upper layer. Main idea: each layer uses the services from lower layer and provide services to upper layer. Higher layer shielded from the implementation details of lower layers. Interface between layers must be clearly defined: services provided to upper layer.
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  • 15 Example 1: ISO OSI Model ISO: International Standards Organization ISO: International Standards Organization OSI: Open Systems Interconnection. OSI: Open Systems Interconnection. Physical Data link Network Transport Session Presentation Application
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  • 16 OSI ISO 7-Layer Model Physical layer: transmission of bits. Physical layer: transmission of bits. Data link layer: reliable transmission over physical medium; synchronization, error control, flow control; media access in shared medium. Data link layer: reliable transmission over physical medium; synchronization, error control, flow control; media access in shared medium. Network layer: routing and forwarding; congestion control; internetworking. Network layer: routing and forwarding; congestion control; internetworking.
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  • 17 OSI ISO 7-Layer Model (contd) Transport layer: error, flow, and congestion control end-to-end. Transport layer: error, flow, and congestion control end-to-end. Session layer: manages connections (sessions) between end points. Session layer: manages connections (sessions) between end points. Presentation layer: data representation. Presentation layer: data representation. Application layer: provides users with access to the underlying communication infrastructure. Application layer: provides users with access to the underlying communication infrastructure.
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  • 18 Example 2: TCP/IP Model Model employed by the Internet. Model employed by the Internet. Physical Data link Network Transport Session Presentation Application Transport Internet Network Access Physical TCP/IP ISO OSI
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  • 19 TCP/IP Protocol Suite: Physical layer: same as OSI ISO model. Physical layer: same as OSI ISO model. Network access layer: medium access and routing over single network. Network access layer: medium access and routing over single network. Internet layer: routing across multiple networks, or, an internet. Internet layer: routing across multiple networks, or, an internet. Transport layer: end-to-end error, congestion, flow control functions. Transport layer: end-to-end error, congestion, flow control functions. Application layer: same as OSI ISO model. Application layer: same as OSI ISO model.
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  • 20 The Internet: Some History Late 1970s/ early 1980s: the ARPANET (funded by ARPA). Late 1970s/ early 1980s: the ARPANET (funded by ARPA). Connecting university, research labs and some government agencies. Main applications: e-mail and file transfer. Features: Features: Decentralized, non-regulated system. No centralized authority. No structure. Network of networks.
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  • 21 The Internet (contd) Early 1990s, the Web caused the Internet revolution: the Internets killer app! Early 1990s, the Web caused the Internet revolution: the Internets killer app! Today: Today: Almost 60 million hosts as of 01.99. Doubles every year.
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  • 22 Topics for Further Reading Some Internet governing entities: Some Internet governing entities: IAB IETF IRTF The Internets standardization process. The Internets standardization process. Other network standardization bodies. Other network standardization bodies. Other networks (Bitnet, SNA, etc). Other networks (Bitnet, SNA, etc).
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  • 23 Physical Layer Sending raw bits across the wire. Sending raw bits across the wire. Issues: Issues: Whats being transmitted. Transmission medium.
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  • 24 Basic Concepts Signal: electro-magnetic wave carrying information. Signal: electro-magnetic wave carrying information. Time domain: signal as a function of time. Time domain: signal as a function of time. Analog signal: signals amplitude varies continuously over time, ie, no discontinuities. Digital signal: data represented by sequence of 0s and 1s (e.g., square wave).
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  • 25 Time Domain Periodic signals: Periodic signals: Same signal pattern repeats over time. Example: sine wave Amplitude (A) Period (or frequency) (T = 1/f) Phase
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  • 26 Frequency Domain Signal consists of components of different frequencies. Signal consists of components of different frequencies. Spectrum of signal: range of frequencies signal contains. Spectrum of signal: range of frequencies signal contains. Absolute bandwidth: width of signals spectrum. Absolute bandwidth: width of signals spectrum.
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  • 27 Example: Spectrum of S(f) extends from f 1 to 3f 1. Bandwidth is 2f 1. S(f) f 1 2 3
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  • 28 Bandwidth and Data Rate Data rate: rate at which data is transmitted; unit is bits/sec or bps (applies to digital signal). Data rate: rate at which data is transmitted; unit is bits/sec or bps (applies to digital signal). Example: 2Mbits/sec, or 2Mbps. Digital signal has infinite frequency components, thus infinite bandwidth. Digital signal has infinite frequency components, thus infinite bandwidth. If data rate of signal is W bps, good representation achieved with 2W Hz bandwidth. If data rate of signal is W bps, good representation achieved with 2W Hz bandwidth.
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  • 29 Baud versus Data Rate Baud rate: number of times per second signal changes its value (voltage). Baud rate: number of times per second signal changes its value (voltage). Each value might carry more than 1 bit. Each value might carry more than 1 bit. Example: 8 values of voltage (0..7); each value conveys 3 bits, ie, number of bits = log 2 V. Thus, bit rate = log 2 V * baud rate. Thus, bit rate = log 2 V * baud rate. For 2 levels, bit rate = baud rate. For 2 levels, bit rate = baud rate.
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  • 30 Data Transmission 1 Analog and digital transmission. Analog and digital transmission. Example of analog data: voice and video. Example of digital data: character strings Use of codes to represent characters as sequence of bits (e.g., ASCII). Historically, communication infrastructure for analog transmission. Historically, communication infrastructure for analog transmission. Digital data needed to be converted: modems (modulator-demodulator).
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  • 31 Digital Transmission Current trend: digital transmission.