A Computer Network A Computer Network Computer Networks Computer - PDF document

Uni Innsbruck Uni Innsbruck Informatik Informatik - - 1 1 Uni Innsbruck Uni Innsbruck Informatik Informatik - - 2 2 A Computer Network A Computer Network Computer Networks Computer Networks Part 1: Introduction Part 1: Introduction Michael Welzl http://www.welzl.at Michael Welzl http://www.welzl.at DPS NSG Team http://dps.uibk.ac.at/nsg DPS NSG Team http://dps.uibk.ac.at/nsg Institute of Computer Science Institute of Computer Science University of Innsbruck University of Innsbruck Uni Innsbruck Informatik Uni Innsbruck Informatik - - 3 3 Uni Innsbruck Uni Innsbruck Informatik Informatik - - 4 4 Another Computer Network And this is...?! Another Computer Network And this is...?! Distributed System Computer Network Uni Innsbruck Informatik Uni Innsbruck Informatik - - 5 5 Uni Innsbruck Uni Innsbruck Informatik Informatik - - 6 6 Data Communication vs. Data Communication vs. LAN, MAN, WAN: quite different indeed! LAN, MAN, WAN: quite different indeed! Computer Network vs. Distributed System Computer Network vs. Distributed System • Data Communication • Local Area Network (LAN) < 1.5 km – how to transmit data between two connected computers – now: (usually) customer premises – VPNs have no geographic boundaries! • Computer Network • Metropolitan Area Network (MAN) - 2-50 km – several connected nodes, some of which communicate :) – now: (usually) backbone of LANs – how to transmit data from computer 973476 to computer 8762876726 – future: perhaps Ultrawideband / Wireless DSL connections? – some issues: • medium sharing (5 computers, 1 cable?!) 3 different Note the change: • Wide Area Network (WAN) - country • path finding (“routing“) things! From definition – now: (usually) ISP • ensuring reliability and security LAN to industry practice! MAN WAN • Distributed System • Several other areas: car (e.g. Controller Area Network (CAN)), – Implies a certain level of abstraction don‘t care home (e.g. CEBus), body (ubiquitous / wearable computing), – unaware of infrastructure (e.g., GRID) or even notice interplanetary internet, ..

Uni Innsbruck Informatik Uni Innsbruck Informatik - - 7 7 Uni Innsbruck Informatik Uni Innsbruck Informatik - - 8 8 These things are real These things are real Everything is totally heterogeneous Everything is totally heterogeneous • Infrastructure – copper, fibre, infrared, wireless • Devices – PC, notebook, PDA, cell phone, car display, sensor • Services – telephony, web surfing, email, chat, download, distributed computing – location-based / context-aware / ubiquitous services – note: should depend on devices • surf with TV, cell phone: did not work well • i-mode did (in Japan) • video phone: old idea that never really made it • Communication methods http://www.ipnsig.org http://www.media.mit.edu/wearables/ – ad hoc networks, streaming, low-power comm., quantum cryptography, .. funded by DARPA MIT Media Lab – note: should depend on devices and services! NASA JPL involved Uni Innsbruck Informatik Uni Innsbruck Informatik - - 9 9 Uni Innsbruck Informatik Uni Innsbruck Informatik - - 10 10 Example: heterogeneous services More realistic (?) ubicomp example Example: heterogeneous services More realistic (?) ubicomp example • Infrastructure: wireless Hackers will • Device: PDA like this ;-) • Communication Method: ad hoc networking • Service: – Two computer science students meet; they do not know each other. As they pass, Brook‘s PDA sets up an ad hoc network connection with Rich‘s PDA. The two devices exchange some information including a profile; Rich‘s PDA now knows that Brook is bad at maths and that she is generally interested in math related information. The device does not have the storage to permanently carry lecture notes - besides, Rich usually writes them on plain paper - so it queries Rich‘s home database via the Internet about recent places Rich has visited (every once in a while, Rich‘s location is determined via his cell phone and saved in his home database). Rich‘s home server looks for Brook in its own database, where the names of girls like Tailor (who cheated on Rich) are stored. Brook is not in the database, so she might be all right; thus, it queries the university server for rooms and classes that match Rich‘s previous locations / times, and detects that Rich has just been to a Math class. It informs Rich‘s PDA, which provides this information to Brook‘s PDA. Her device now goes through the same process and notices that Rich has visited a class that Brook missed - so it hums softly. Brook smiles and says “hey, have we met before - and are you going to the party tonight?“ Uni Innsbruck Uni Innsbruck Informatik Informatik - - 11 11 Uni Innsbruck Uni Innsbruck Informatik Informatik - - 12 12 Example: Sensor Networks Dealing with heterogeneity Example: Sensor Networks Dealing with heterogeneity • ACM SenSys‘03 - Call for Papers... “topics of interest include the following:“ • Networking – Network protocols for sensor networks – used to be a new / young / fresh discipline – Operating system and middleware for sensor networks – Distributed database processing in sensor networks – now approaching mid-age, but still somewhat immature – Distributed algorithms for sensor networks – Novel sensor node hardware and software platforms • Compare: “computer languages“ / “computer networks“ Classification attempt: – Sensor network planning and deployment Infrastructure – well defined analytical background / plethora of modelling methods – Energy management in sensor networks – Adaptive toplogy management Devices – well structured research area / somewhat disorganized research area – In-network processing and aggregation Services – gone through several phases of maturity / still in infancy? – Data storage in sensor networks Communication methods – Distributed and collaborative signal processing • Problem: constant flux – Distributed Actuation, Control, and Coordination – Localization in time and space – now even with impact on “computer languages“ (.NET ⇒ C#) – Distributed calibration in sensor networks – changing infrastructure, devices, services, communication methods – Simulation and optimization tools – Applications of distributed sensor networks • Long-lasting knowledge / invariants become increasingly important! – Security and Robustness in sensor networks – Sensor network testbed measurements and benchmarks

Uni Innsbruck Uni Innsbruck Informatik Informatik - - 13 13 Uni Innsbruck Informatik Uni Innsbruck Informatik - - 14 14 What invariants are there? What invariants are there? • (Roughly) ordered according to longevity: Some Invariants Some Invariants – General knowledge: rules / guidelines (KISS, ..) (“Theory“) (“Theory“) e.g. languages: – Models (Graph Theory, Queuing Theory, FSM, ..) (E)BNF - Logo – Algorithms (Dijkstra shortest path first, ..) ISO/OSI model, protocol, Message Sequence Charts, FSMs, connectionless vs. connection-oriented service, confirmed service – How things are designed (how guidelines, models, algorithms are applied) functions, switching, routing, the Internet, DoD model, scalability, End2end Argument, Client-Server vs. Peer-to-Peer, IP hourglass – How things are deployed (standardization) – Certain technology that is difficult to change (TCP/IP, your TV, ..) – Human interaction with technology + economics (cell phones, ubicomp, ..) Uni Innsbruck Uni Innsbruck Informatik Informatik - - 15 15 Uni Innsbruck Uni Innsbruck Informatik Informatik - - 16 16 Most Important CN Invariant: Abstraction Abstraction Logical communication flow Most Important CN Invariant: Logical communication flow • Programming Languages: – Machine code – Assembler draw a green rectangle – Low level languages – High level languages (special purposes), OO Design, .. • Simplification by abstraction • Same for networks: Network Layer Models – ISO/OSI model – DoD model Uni Innsbruck Uni Innsbruck Informatik Informatik - - 17 17 Uni Innsbruck Uni Innsbruck Informatik Informatik - - 18 18 Physical communication flow ISO/OSI Reference Model Physical communication flow ISO/OSI Reference Model UK US • THE famous layer model S please send 5 pairs of black suspenders language (protocol) Layer 2 O • 7 layers draw a green rectangle A letter content request to secy.: delivered • precise terminology, huge write order letter amount of theoretical work H Layer 1 service to higher layer according to “protocol” translation translation • layer provides service to upper C Network layers Choose a path request: letter (“Internet Cloud“) transmit delivered, check for logical errors → opened, letter processed • strict rules (layers must not be Layer 0 check for bit errors skipped, but they are letter transport interchangeable) 010010101111010100101011101000101011000011110100010111001011