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Δίκτυα

Δίκτυα. Pedro Trancoso Τμήμα Πληροφορικής, Πανεπιστήμιο Κύπρου ΕΠΛ 321 – Αρχιτεκτονική Υπολογιστών. 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

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Δίκτυα

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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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