Chapter 2 Application Layer A note on the use of these ppt slides We re making these slides freely available to all faculty students readers They re in PowerPoint form so you can add modify and delete slides including this one and slide content to suit your needs They obviously represent a lot of work on our part In return for use we only ask the following If you use these slides e g in a class in substantially unaltered form that you mention their source after all we d like people to use our book If you post any slides in substantially unaltered form on a www site that you note that they are adapted from or perhaps identical to our slides and note our copyright of this material Thanks and enjoy JFK KWR All material copyright 1996 2007 J F Kurose and K W Ross All Rights Reserved 1 CS118 Spring 2014 Lecture 2A Chapter 2 Application layer 2 1 Principles of network applications 2 2 Web and HTTP 2 3 FTP 2 4 Electronic Mail SMTP POP3 IMAP 2 6 P2P Applications 2 7 Socket programming with TCP 2 8 Socket programming with UDP 2 5 DNS 2 Application Layer 3 Chapter 2 Application Layer Our goals conceptual implementation aspects of network application protocols transport layer service models client server paradigm peer to peer paradigm learn about protocols by examining popular application level protocols HTTP FTP SMTP POP3 IMAP DNS programming network applications socket API 2 Application Layer 4 Some network apps e mail web instant messaging remote login P2P file sharing multi user network games streaming stored video clips voice over IP real time video conferencing grid computing 2 Application Layer 5 Creating a network app write programs that run on different end systems communicate over network e g web server software communicates with browser software little software written for devices in network core network core devices do not run user applications applications on end systems allows for rapid app development propagation applicatio n transport network data link physical applicatio n transport network data link physical applicatio n transport network data link physical 2 Application Layer 6 Chapter 2 Application layer 2 1 Principles of network applications 2 2 Web and HTTP 2 3 FTP 2 4 Electronic Mail SMTP POP3 IMAP 2 5 DNS 2 6 P2P file sharing 2 7 Socket programming with TCP 2 8 Socket programming with UDP 2 9 Building a Web server 2 Application Layer 7 Application architectures Client server Peer to peer P2P Hybrid of client server and P2P 2 Application Layer 8 Client server architecture client server server always on host permanent IP address server farms for scaling clients communicate with server may be intermittently connected may have dynamic IP addresses 2 Application Layer do not communicate 9 Pure P2P architecture No such thing as always on server arbitrary end systems peer peer directly communicate peers are intermittently connected and change IP addresses example Gnutella Highly scalable but difficult to manage 2 Application Layer 10 Hybrid of client server and P2P Skype voice over IP P2P application centralized server finding address of remote party client client connection direct not through server Instant messaging chatting between two users is P2P centralized service client presence detection location user registers its IP address with central server when it comes online user contacts central server to find IP addresses of buddies 2 Application Layer 11 Processes communicating Process program running within a host within same host two processes communicate using inter process communication defined by OS processes in different hosts communicate by exchanging messages Client process process that initiates communication Server process process that waits to be contacted Note applications with P2P architectures have client processes server processes 2 Application Layer 12 Sockets process sends receives messages to from its socket socket analogous to door sending process shoves message out door transport infrastructure delivers message to receiving process host or server host or server process controlled by app developer process socket socket TCP with buffers variables Internet TCP with buffers variables controlled by OS API 1 choice of transport protocol 2 ability to fix a few parameters lots more on this later 2 Application Layer 13 Addressing processes to receive messages process must have identifier host device has unique 32 bit IP address Q is host IP address sufficient to identify process 2 Application Layer 14 Addressing processes to receive messages process must have identifier host device has unique 32 bit IP address Q is host IP address sufficient to identify process A No many processes can be running on same host identifier includes both IP address and port numbers associated with process on host Example port numbers HTTP server 80 Mail server 25 to send HTTP message to gaia cs umass edu web server IP address 128 119 245 12 Port number 80 more shortly 2 Application Layer 15 App layer protocol defines Types of messages exchanged e g request response Message syntax what fields in messages how fields are delineated Message semantics meaning of information in fields Rules for when and how processes send respond to messages Public domain protocols defined in RFCs allows for interoperability e g HTTP SMTP Proprietary protocols e g Skype 2 Application Layer 16 What transport service does an app need Data loss some apps e g audio can tolerate some loss other apps e g file transfer telnet require 100 reliable data transfer Delay some apps e g Internet telephony interactive games require low delay to be effective Bandwidth some apps e g multimedia require minimum amount of bandwidth to be effective other apps elastic apps make use of whatever bandwidth they get 2 Application Layer 17 Internet transport protocols services TCP service UDP service connection oriented setup required between client and server processes reliable transport between sending and receiving process flow control sender won t overwhelm receiver congestion control throttle sender when network overloaded does not provide timing minimum bandwidth guarantees unreliable data transfer between sending and receiving process does not provide connection setup reliability flow control congestion control timing or bandwidth guarantee Q why bother Why is there a UDP 2 Application Layer 18 Transport service requirements of common apps Application Data loss file transfer e mail Web documents real time audio video no
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