Lec15_distributed

Lec15_distributed - What is a Distributed System? CSE120...

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1 CSE120 Principles of Operating Systems Prof Yuanyuan (YY) Zhou Lecture 15: Distributed Systems Nov 18, 2010 What is a Distributed System? Cooperating processes in a computer network Degree of integration Loose: Internet applications, email, web browsing Medium: remote execution, remote file systems Tight: distributed file systems 11/17/2010 CSE 120 2 Benefits Performance: parallelism across multiple nodes Google file systems, BigTable, MapReduce, hadoop, etc Reliability and fault tolerance Redundancy E.g.: Google search engine Scalability by adding more nodes 11/17/2010 CSE 120 3 CSE 120 4 Clients and Servers The prevalent model for structuring distributed computation is the client/server paradigm A server is a program (or collection of programs) that provide a service (file server, name service, etc.) The server may exist on one or more nodes Often the node is called the server, too, which is confusing A client is a program that uses the service A client first binds to the server (locates it and establishes a connection to it) A client then sends requests , with data, to perform actions , and the servers sends responses , also with data 11/17/2010
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2 Issues Naming Communication Fault tolerance Consistency Each one can update data independently 11/17/2010 CSE 120 5 11/17/2010 CSE 120 6 Naming Name systems in network often hierarchical name. cs.ucsd.edu is ``domain'' Network Address (Internet IP address) 192.17.4.131 -- 192.17.4.** 128.174.240.** Physical Network Address Ethernet address or Token Ring Address Address processes/ports within system (host, id) pair Domain name service (DNS) specifies naming structure of hosts and provides resolution of names to network address Communication Socket (TCP/IP) Remote Procedure Call (RPC) /Remote Method Invocation(RMI) 11/17/2010 CSE 120 7 11/17/2010 CSE 120 8 TCP/IP (Socket) Transport Protocols User Datagram Protocol (UDP) UDP/IP is an unreliable , connectionless transport protocol, which uses IP to transport IP datagrams but adds error correction and a protocol port address to specify the process on the remote system for which the packet is destined. Transmission Control Protocol (TCP). TCP/IP is a reliable stream protocol for communicating information between two processes
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3 11/17/2010 CSE 120 9 TCP/IP Protocol Layers END USER APPLICATION IEEE802.X/X.25 IP TCP UDP FTP, TELNET, SMTP, NSP, SNMP LAN/WAN Layers 5-7 Layers 1-3 Layers 4 http://www.webopedia.com/ quick_ref/OSI_Layers.asp 11/17/2010 CSE 120 10 TCP Sockets Communication endpoint (IP address, Port number) Client-server server listens to a port Telnet Port 23, ftp port 21, web server port 80 11/17/2010 CSE 120 11 TCP/IP Ports Ports < 1024, standard Ports > 1024, user created All connections unique (161.25.19.8:20) IP Address: 161.25.19.8 TCP/IP Port: 20 (ftpdata)
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Lec15_distributed - What is a Distributed System? CSE120...

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