Δίκτυα Pedro Trancoso Τμήμα Πληροφορικής, Πανεπιστήμιο Κύπρου ΕΠΛ321 – 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 Clusters? Interconnected computers inside room

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

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

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

Ορισμοί

Μέγεθος των Μηνυμάτων NFS traffic

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

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, 1000Mbps or few 100Mbps Single-mode fiber: 8/9-micron, 100s Gbps

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

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

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

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

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

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

Ethernet: Το Τοπικό Δίκτυο Γέφυρα Δικτύων (Bridges); Δρομολογητής Δικτύων (Routers) ή Πύλη Δικτύων (Gateways)

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)

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

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

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

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

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

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

December 2000: More than 6000 processors, 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

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

Μέσα από ένα Κινητό Τηλέφωνο Standards: CDMA AMPS TDMA GSM

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

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