CS162 Operating Systems and Systems Programming Lecture 25 ReviewNew CS162New vs. Old CS162Example: Accessing AmazonUniversal Resource Locator (URL)Domain Name Service (DNS) ResolutionDNS ResolutionHow Does Client Communicates with DNS Server?Transport Layer (cont’d)How does UDP packets Get to Destination?Network (IP) Layer (cont’d)IP Packet RoutingSlide 13Packet ForwardingPacket Forwarding TimingSlide 16Slide 17Slide 18Packet Forwarding Timing: Packets of Different LengthsDatalink LayerSlide 21Physical LayerThe Internet HourglassImplications of Hourglass & LayeringApplication Layer: DNS ResolutionDNS: Separating Naming and AddressingDomain Name System (DNS)Distributed Hierarchical DatabaseExampleHTTP (HyperText Transport Protocol)HTTP RequestSlide 32HTTP over TCPTCP Open Connection: 3-Way HandshakingTCP Flow Control & ReliabilityHow do You Secure your Credit Card?Administrivia5min BreakSymmetric KeysPublic Key / Asymmetric EncryptionSymmetric vs. Asymmetric CryptographyIntegrityOperation of Hashing for IntegrityDigital CertificatesHTTPSHTTPS Connection (SSL/TLS), con’tInside the Server’s CertificateValidating Amazon’s IdentityCertificate ValidationSlide 50Two Key ConceptsStatistical MultiplexingExample: One FlowExample: Two FlowsExample: 50 FlowsStatistical Multiplexing (cont’d)Lookup/Directory ServicesExamples: Lookup/Directory ServicesDNS PropertiesService Discovery: RPC BindingExample of RPC BindingPropertiesPeer-to-Peer SystemsNapsterNapster: ExampleNapster PropertiesGnutellaGnutella: ExampleGnutella PropertiesChord Lookup ServiceIdentifier to Node Mapping Example (Consistent hashing)Achieving Efficiency: finger tablesSlide 73Not Cover in This ReviewCS162Operating Systems andSystems ProgrammingLecture 25ReviewApril 27, 2011Ion Stoicahttp://inst.eecs.berkeley.edu/~cs162Lec 25.24/27 Ion Stoica CS162 ©UCB Spring 2011New CS162•Gateway system class to give students a broad view on how today’s systems and services–Better prepare students to design and develop such services•Teach students how to develop large projects in teams•Enable department to create a new core OS class (which will be offered in Spring 2012)–Will use a real OS for projects (likely Android)•Enable other system classes (for which cs 162 will be prerequisite) to go deeper in their specific material and have more sophisticated projectsLec 25.34/27 Ion Stoica CS162 ©UCB Spring 2011New vs. Old CS162•Curriculum: 70% overlap−File systems, queueing theory, slightly fewer lectures on concurrency, caching, and distributed systems+More networking, database transactions, p2p, and cloud computing•Different project: emphasize on how a system works end-to-end rather than focusing on implementing OS concepts in Nachos•What if you want to do an OS project?–CS 163 (?) in Spring 2012–CS 262 graduate System class (you’ll need instructor approval)–CS295 Cloud computing Seminar (you’ll need my approval)Lec 25.44/27 Ion Stoica CS162 ©UCB Spring 2011Example: Accessing Amazon•Complex interaction of multiple components in multiple administrative domainsDatacenterLoadbalancerAd ServerDNS ServersUser AccountDBDNSrequestcreateresultpageProductDBLec 25.54/27 Ion Stoica CS162 ©UCB Spring 2011Universal Resource Locator (URL)protocol://host-name:port/directory-path/resource•This is what you enter in the browser!•Example: http://www.amazon.com = http://www.amazon.com:80/index.html–protocol = http –host-name = www.amazon.com »Name of an Amazon’s web server–port = 80 (default HTTP port)–directory-path = “” »Path relative to web directory at server (e.g., public_html)–resource = index.html (default file)»Contains HTML home page of AmazonLec 25.64/27 Ion Stoica CS162 ©UCB Spring 2011Domain Name Service (DNS) Resolution•Resolve www.amazon.com to the IP address of an Amazon HTTP serverDatacenterLoadbalancerAd ServerDNS ServersUser AccountDBDNSrequestcreateresultpageProductDBLec 25.74/27 Ion Stoica CS162 ©UCB Spring 2011DNS Resolution•Resolve www.amazon.com to the IP address of an Amazon HTTP server•How does client know DNS server–Client configured with the address of the local DNS server DNS request: www.amazon.comDNSserverDNS response:72.21.211.176Lec 25.84/27 Ion Stoica CS162 ©UCB Spring 2011How Does Client Communicates with DNS Server?•A: Via transport protocol (e.g., UDP)•Transport protocol in a nutshell:–Allow two application end-points to communicate»Each application identified by a port number on the machine it runs–Multiplexes/demultiplexes packets from/to different processes using port numbers–Can provide reliability, flow control, congestion control•Two main transport protocols in the Internet–User datagram protocol (UDP): just provide multiplexing/demultiplexing, no reliability–Transport Control Protocol (TCP): provide reliability, flow control, congestion controlLec 25.94/27 Ion Stoica CS162 ©UCB Spring 2011InternetTransport Layer (cont’d)•DNS server runs at a specific port number, i.e., 53–Most popular DNS server: BIND (Berkeley Internet Name Domain)–Assume client (browser) port number 1234TransportFirefox(port 1234)BIND(port 53)TransportDNS ReqDNS Req1234 53DNS ReqDNS Req1234 53Lec 25.104/27 Ion Stoica CS162 ©UCB Spring 2011How does UDP packets Get to Destination?•A: Via network layer, i.e., Internet Protocol (IP)•Implements datagram packet switching–Enable two end-hosts to exchange packets»Each end-host is identified by an IP address»Each packets contains destination IP address»Independently routes each packet to its destination–Best effort service»No deliver guarantees»No in-order delivery guaranteesLec 25.114/27 Ion Stoica CS162 ©UCB Spring 2011Network (IP) Layer (cont’d)•Assume DNS server runs on machine 128.15.11.12–Client configured with DNS server IP address•Client runs on machine 16.25.31.10TransportBIND(port 53)TransportDNS ReqDNS Req1234 5316.25.31.10128.15.11.12NetworkNetworkDNS Req1234 5316.25.31.10 128.15.11.12DNS Req1234 5316.25.31.10 128.15.11.12DNS ReqDNS Req1234 53Firefox(port 1234)Lec 25.124/27 Ion Stoica CS162 ©UCB Spring 2011IP Packet RoutingHost AHost BHost EHost DHost CRouter 1Router 2Router 3Router 4Router 5Router 6Router 7•Each packet is individually routedLec 25.134/27 Ion Stoica CS162 ©UCB Spring 2011IP Packet RoutingHost AHost BHost EHost DHost CRouter 1Router 2Router 3Router 4Router 5Router 6Router 7•Each packet is individually routedLec 25.144/27 Ion Stoica CS162 ©UCB
View Full Document
Unlocking...