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ΔημοσίευσεCatherine Golias Τροποποιήθηκε πριν 9 χρόνια
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Δίκτυα Pedro Trancoso Τμήμα Πληροφορικής, Πανεπιστήμιο Κύπρου ΕΠΛ321 – Αρχιτεκτονική Υπολογιστών
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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
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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
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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
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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
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Ορισμοί
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Μέγεθος των Μηνυμάτων NFS traffic
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Καλώδια Συνεστραμμένο Ζεύγος Καλωδίων -Twisted Pair Ομοαξονικό Καλώδιο - Coaxial Τεχνολογία Οπτικών Ινών - Fiber Optics
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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
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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
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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
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Σύνδεση με περισσότερους από δυο υπολογιστές Έλεγχος Συμφόρησης - Congestion Control Packet discarding Έλεγχο Ροής - Flow control Backpressure feedback Credit-based flow control Choke packets
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Τοπολογία Δικτύου Συγκεντρωτικό Μεταγώγιμο - Centralized Switch Δίκτυο Διασταύρωσης - Crossbar Omega Network Fat tree Κατανεμημένο Μεταγώγιμο - Distributed Switch Δίκτυο Δακτυλίου - Ring Torus Hypercube
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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
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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
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Ethernet: Το Τοπικό Δίκτυο Γέφυρα Δικτύων (Bridges); Δρομολογητής Δικτύων (Routers) ή Πύλη Δικτύων (Gateways)
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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)
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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
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Διασύνδεση Δικτύων - Internetworking TCP/IP Open Systems Interconnect (OSI)
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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
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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
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Σχεδίαση ενός Συμπλέγματος - Designing a Cluster 32 CPU Cluster, Cost of ownership for 3-year
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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
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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) Το Σύμπλεγμα Υπολογιστών
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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
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Μέσα από ένα Κινητό Τηλέφωνο Standards: CDMA AMPS TDMA GSM
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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
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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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