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Exploring Network Architectures and Communication Protocols in Computer Systems

This course delves into computer networks, from LANs to WANs, addressing types, topologies, congestion control, routing policies, and more. Discusses Ethernet, Infiniband, and ATM networks. Learn about message handling, transmission time, and interconnected systems.

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Exploring Network Architectures and Communication Protocols in Computer Systems

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  1. Δίκτυα Pedro Trancoso Τμήμα Πληροφορικής, Πανεπιστήμιο Κύπρου ΕΠΛ321 – Αρχιτεκτονική Υπολογιστών

  2. Εισαγωγή • Why look at networks? • Shrinking networks => connection between computers, I/O devices, boards, chips, and even modules inside chips • All computers are networked to other devices • Clusters? • Interconnected computers inside room

  3. Είδη Δικτύων • Δίκτυο Ευρείας Περιοχής - Wide area network (WAN) • Thousands of computers, thousands of kilometers • Τοπικό Δίκτυο - Local area network (LAN) • Hundreds of computers, few kilometers • Δίκτυο Αποθήκευσης ή Συστήματος - Storage or system area network (SAN) • Hundreds of nodes, 100 meters

  4. Απλό Δίκτυο • Μηνύματα: Header+Payload+Trailer • Send a Message • (1) Application copies data into OS buffer • (2) OS calculates checksum, includes it in header or trailer and sets timer • (3) OS sends data to network interface • Receive a message • (3), (2), (1) ! • Sender reaction • If gets acknowledgment, releases copy of message • If gets timeout, resends data

  5. Ορισμοί • Bandwidth • Time of flight: time for first bit to arrive • Transmission time: time for message to pass through system excluding time of flight • Transport latency: time of flight + transmission time • Sender overhead: time to inject msg into net • Receiver overhead: time to pull msg from net

  6. Ορισμοί

  7. NFS traffic Μέγεθος των Μηνυμάτων

  8. Καλώδια • Συνεστραμμένο Ζεύγος Καλωδίων -Twisted Pair • Ομοαξονικό Καλώδιο - Coaxial • Τεχνολογία Οπτικών Ινών - Fiber Optics

  9. Καλώδια • Συνεστραμμένο Ζεύγος Καλωδίων - Twisted Pair • 10Mb/s • Ομοαξονικό Καλώδιο - Coaxial Cable • 10Mb/s over kilometer • Τεχνολογία Οπτικών Ινών - Fiber optics • Multimode fiber: inexpensive LED, 62.5-micron, 100m @ 1000Mbps or few Km @ 100Mbps • Single-mode fiber: 8/9-micron, 100s Km @ Gbps

  10. Σύνδεση με περισσότερους από δυο υπολογιστές • Shared versus Switched Media • Carrier sensing and collision detection • Point-to-point communication • Broadcast, multicast • Data switching exchanges, multistage interconnection networks, interface message processors

  11. Σύνδεση με περισσότερους από δυο υπολογιστές • Connection-Oriented versus Connectionless Communication • Frequency-division multiplexing • Δρομολόγηση - Routing: Delivering Messages • Source-based Routing • Virtual Circuit • Destination-based Routing • Πολιτική - Policy • Store-and-forward • Cut-through or wormhole routing

  12. Σύνδεση με περισσότερους από δυο υπολογιστές • Έλεγχος Συμφόρησης - Congestion Control • Packet discarding • Έλεγχο Ροής - Flow control • Backpressure feedback • Credit-based flow control • Choke packets

  13. Τοπολογία Δικτύου • Συγκεντρωτικό Μεταγώγιμο - Centralized Switch • Δίκτυο Διασταύρωσης - Crossbar • Omega Network • Fat tree • Κατανεμημένο Μεταγώγιμο - Distributed Switch • Δίκτυο Δακτυλίου - Ring • Torus • Hypercube

  14. Τοπολογία Δικτύου • Παράδειγμα: • Consider nodes as elements of a 2-D array with nearest neighbor communication (NEWS – North, East, West, South). 8-by-8 array. How long does it take to send one message to northern neighbor and one to eastern neighbor? For Bus, Fully Connected, Ring, 2D Torus, 6-Cube Messages: (64-15)*2+14*1=112 Bus: 112 Fully: 1 Ring: 9 2D Taurus: 2

  15. Πρακτικά Ζητήματα για Εμπορικά Δίκτυα - Practical Issues for Commercial Interconnection Networks • Συνεκτικότητα - Connectivity • Connecting the Network to the Computer • Standardization: Cross-Company Interoperability • Message Failure Tolerance • Node Failure Tolerance

  16. Ethernet: Το Τοπικό Δίκτυο • Γέφυρα Δικτύων (Bridges); Δρομολογητής Δικτύων (Routers)ήΠύλη Δικτύων (Gateways)

  17. Infiniband: Δίκτυο Αποθήκευσης • Clock 2.5GHz, Peak speed 2000Mbps • Packet switched, connectionless network • Cut-through routing, destination-based addressing • Backpressure storage control • Very light protocol! (e.g. no security)

  18. ATM: Δίκτυο Ευρείας Περιοχής • 155Mbps, 620Mbps, 2480Mbps, … • Fiber optics • Virtual channel • Store-and-forward routing • Small fixed-sized packets (48-byte payload) -> quality-of-service • Simple switches but large and complex protocol stack

  19. Διασύνδεση Δικτύων - Internetworking • TCP/IP • Open Systems Interconnect (OSI)

  20. Ζητήματα Δικτύων - Crosscutting Issues for Interconnection Networks • Density-Optimized Processors versus SPEC-Optimized Processors • Smart Switches versus Smart Interface Cards • Protection and User Access to the Network • Efficient Interface to Memory Hierarchy versus Interconnection Network • Compute-Optimized Processors versus Receiver Overhead

  21. Συμπλέγματα - Clusters • Performance Challenges • Dependability and Scalability Advantage • Pros and Cons of Cost • Shooting for the Best of Both Worlds • Popularity • Amazon, AOL, Google, Hotmail, Inktomi, WebTV, and Yahoo

  22. Σχεδίαση ενός Συμπλέγματος - Designing a Cluster • 32 CPU Cluster, Cost of ownership for 3-year

  23. Το Σύμπλεγμα Υπολογιστών • Number of pages on the web grew by a factor of 1000 between 1994 and 1997 • People want top 10 answers only! • In December 2000, Google indexed 1327 million pages, had 70 million queries-per-day • Requirements: • Reliability: continuously available • Small latency: 0.5s • High bandwidth: • 1000 queries per second • Crawling the Web

  24. Το Σύμπλεγμα Υπολογιστών • December 2000: • More than 6000 processors, 12.000 disks (1 petabyte storage) • No RAID, redundant sites! • Performance • Bandwidth: Query 26Mbps, Crawl 53Mbps, Replication 132Mbps! • Cost • Best cost-performance CPU not latest model! • Large energy demands • Reliability • Software: 20 reboot per day • Hardware: 2-3% PC replacement per year (disk, DRAM failures)

  25. Το Σύμπλεγμα Υπολογιστών

  26. Μέσα από ένα Κινητό Τηλέφωνο • Wireless networks • Cells • Cell phone = mobile computer acting as a radio! • I/O devices: keyboard and LCD display, etc. • Protocol to find cell

  27. Μέσα από ένα Κινητό Τηλέφωνο • Standards: • CDMA • AMPS • TDMA • GSM

  28. Πλάνες και Παγίδες (Fallacies and Pitfalls) • Pitfall: Using bandwidth as the only measure of network performance • Pitfall: Ignoring software overhead when determining performance • Intel Paragon: HW 0.2us – SW 250us! … 25us • Pitfall: Trying to provide features only within the network versus end to end • Pitfall: Relying on TCP/IP for all networks, regardless of latency, bandwidth, or software requirements

  29. Συμπεράσματα • Internet and WWW revolutionize information access: TCP/IP makes it practical • Switches is a growing technology • Network Processors • Networking at all levels: within chip, across chips, across boards, etc. • Disks connected with a SAN • Clusters of small computers connected with LAN • Performance grows

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