Computer Networking I
Computer Networking I CS 3251
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This 0 page Class Notes was uploaded by Alayna Veum on Monday November 2, 2015. The Class Notes belongs to CS 3251 at Georgia Institute of Technology - Main Campus taught by Patrick Traynor in Fall. Since its upload, it has received 24 views. For similar materials see /class/234080/cs-3251-georgia-institute-of-technology-main-campus in ComputerScienence at Georgia Institute of Technology - Main Campus.
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Date Created: 11/02/15
13 fjw D wa D D4331 CS 325 Computer Networks IzApplications and EndToEnd Professor Patrick Traynor Lecture 03 32008 Announcements 0 TA will come to class on Thursday gt Learn of ce hours etc 0 Project 2 will be posted tomorrow 0 Homework due on January 22nd gt Start it now It will take time Review 0 In the last two lectures we discussed the fundamentals of networking at a high level a communicate over s a s using J 39 designs use i 7 to provide an abstraction to network devices eg 539quot zquotwhich relay 5 to across the j that makes up the J Ne CWOFk is broken down into f is dif cult we need to think about it at every layer CS 325 Computer Networks Nice to MeetYou CS 325 Computer Networks Nice to MeetYou O Darwin s work signi cantly influenced science gt Students in these elds would be hardpressed to set up a meeting with him today CS 325 Computer Networks Nice to MeetYou O Darwin s work signi cantly influenced science gt Students in these elds would be hardpressed to set up a meeting with him today 0 Computer Science is a very young discipline gt Became an academic discipline in the l9605 gt Many of the founders of our eld are still alive CS 325 Computer Networks System Design 0 EndToEnd Argumean in System Design gt Saltzer Reed Clark Asks the question Where should we place functionality What do we mean by functionality gt eg reliable data transmission 0 What do we mean by where gt Recall the concept of network layers and the devices that interact with the layers Design Principle 0 The Principle The function in question can completely and correctly be implemented only with the knowledge and help of the application standing at the endpoints of the communication systemTherefore providing that questioned function as a feature of the communication system itself is not possible Sometimes an incomplete version of the function provided by the communication system may be useful as a performance enhancementquot Saltzer et a gt What does this mean in layman s terms An Example 0 Reliable data transmission gt Consider a le transferred across a network 0 It is all a matter of context gt What happens to performance if we strictly adhere to the principle 0 Other examples gt guaranteed delivery secure transmission duplicate message suppression inorder delivery gt We will discuss these concepts in more depth in the coming weeks CS 325l Computer Networks l Chapter 2Application layer 0 2 Principles of network applications 22 Web and HTTP 23 FTP ppliantl n 24 Electronic Mall 7 7 7 7 transport gt SMTP POP3 IMAP 25 DNS 26 P2P file sharing physical CS 325 Computer Networks Chapter 2Application Layer Our goals 0 conceptual implementation aspects of network application protocols gt transportlayer service models gt clientserver paradigm gt peertopeer paradigm CS 325 Computer Networks I learn about protocols by examining popular applicationlevel protocols HTTP FTP SMTP POP3 IMAP DNS programming network applications gt socketAPl Some network apps Email Web Instant messaging Remote login P2P le sharing Multiuser network games Streaming stored video clips Internet telephone Realti me video conference Massive parallel computing Creating a network app Write programs that run on different end systems and communicate over a network egWebWeb server software communicates with browser software little software written for devices in network core gt network core devices do not run user application code gt application on end systems allows for rapid app development propagation CS 325 Computer Networks Creating a network app Write programs that applica rion gt run on different end systems and apper da ralink physical gt communicate over a DEtWOFl gt egWebWeb server software communicates with browser software little software written for 0 devices in network core I gt network core devices do not a i ne rwor39k run user application code 39 da rallnk physical gt application on end systems allows for rapid app development propagation CS 325 Computer Networks Chapter 2Appication layer 0 24 Electronic Mail in the Internet 0 21 Prinripieaci i THE o 22Web and HTTP D i s 7 F J 2 0 23 File Transfer FTP 39 x 39 0 25 DNS Internet Directory Service 0 26 P2PAppIications 0 2728 Socket Programming Application architectures 0 Clientserver 0 Peertopeer P2P 0 Hybrid of clientserver and P2P Clientserver architecture server gt alwayson host gt permanenth address gt server farms for scaling clients gt communicate with server gt may be intermittently connected gt may have dynamic IP addresses gt do not communicate directly with each other CS 325 Computer Networks Hybrid of clientserver and P2P gt Internet telephony app gt Finding address of remote party centralized servers gt Clientclient connection is direct not through server gt Chatting between two users is P2P gt Presence detectionlocation centralized 0 User registers its IP address with central server when it comes online 0 User contacts central server to nd IP addresses of buddies Processes communicating W Client Process program running within a host within same host tWO Server process Processes communicate using i tintii l l 7 m w 739 i s 1 Tl d e ned by Note applications with P2P architectures have client processes amp server processes 0 processes in different hosts communicate by exc hanging t u 25 CS 325 Computer Networks Sockets 0 process sendsreceives messages tofrom its socket host or host or server server 0 socket analogous to door controlled by gt sending process shoves message aPP developer out door gt sending process relies on transport infrastructure on other side of door which brings message to socket at receiving process Internet controlled by OS APl I choice of transport protocol 2 ability to x a few parameters lots more on this later CS 325 Computer Networks Addressing processes 0 to receive messages process must have identi er 0 host device has unique 32bit IP address 0 39 V does IP address of host on which process runs suf ce for identifying the process CS 325 Computer Networks Addressing processes 0 to receive messages process must have iden er host device has unique 32bit IP address Q does IP address of host on which process runs suffice for identifying the process gt Answer NO many processes can be running on same host CS 325 Computer Networks Addressing processes to receive messages identi er includes both IP process must have address and port numbers identifier associated with process on host host deVIce has unique 32bit P address Example port numbers gt HTTP server 80 d IP dd f Q 095 a resso gt Mail server25 host on which process runs suffice for identifying to send HTTP message to the process wwwcsepsuedu web server gt IP address 3020342 gt Answer NO many processes gt Port number 80 can be running on same host more shortly CS 325 Computer Networks Applayer protocol de nes TYPes 0f messages Publicdomain protocols eXChanged de ned in RFCs 39 eSv request response allows for interoperability 0 Message syntax 39 eg HTTP SMTP gt what elds in messages amp how Proprietary PrOtOCOlS fields are delineated eg Skype 0 Message semantics gt meaning of information in fields 0 Rules for when and how processes send amp respond to messages I E T F CS 325 Computer Networks What transport service does an app need Bandwidth some apps eg multimedia require minimum amount of 0 other apps eg le transfer bandwidth to be effective telnet require 00 reliable data transfer Data loss 0 some apps eg audio can tolerate some loss other apps elastic apps make use of whatever bandwidth they get Tlmmg Security some apps eg Internet telephony interactive games require low delay to be effective Encryption integrity CS 325l Computer Network I Transport service requirements of common apps Application Data loss Bandwidth Time Sensitive file transfer no loss elastic no email no loss elastic no Web documents no loss elastic no realtime audiovideo losstolerant audio 5kbps1Mbps yes 100 s msec video10kbps5Mbps stored audiovideo losstolerant same as above yes few secs interactive games losstolerant few kbps up yes 100 s msec instant messaging no loss elastic yes and no CS 325 Computer Networks Internet transport protocols services a 0 connectionorientedsetup 39 unrel39able data tranSfer required between client and between sending and receiving server processes Process does not provide connection 39 reliable transport between setup reliability flow control sending and receiving process congestion control timing or bandwidth guarantee 0 flow control sender won t Why bother overwhelm receiver L 39 Why is there a UDP 0 congestion control throttle sender when network overloaded 0 does not providetiming minimum bandwidth guarantees CS 325 Computer Networks l
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