Lecture05 - Tuesday, April 15 Lab #2 Sessions run through...

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Tuesday, April 15 Lab #2 Sessions run through Wednesday TA Office hours Thursday and Friday Due Friday by midnight Program #1 Definition is posted Due by midnight Friday, May 2 Accepted until midnight Sunday, May 4, with a 10% penalty
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Today’s topics More network applications FTP (file transfer) SMTP (mail) DNS (domain name services) Program #1
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Addressing processes to receive messages, process must have identifier Receiving host device has unique IP address Q: does IP address of host on which process runs suffice to identify the process? identifier consists of: IP address (host) port numbers (process) 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 on this soon … A: No, many processes can be running on same host
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Application Layer Protocols An application 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
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Application Layer Protocols Public-domain protocols: defined in RFCs allow for interoperability e.g., HTTP, SMTP, etc. Proprietary protocols: e.g., Skype
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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 Timing some apps (e.g., Internet telephony, interactive games) require low delay to be “effective” Bandwidth some apps (e.g., multimedia) require a certain amount of bandwidth to be “effective” other apps (“elastic apps”) make use of whatever bandwidth they get Security How big a problem is this?
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Transport service requirements of common apps Application file transfer e-mail Web documents real-time audio/video stored audio/video interactive games instant messaging Data loss no loss no loss no loss loss-tolerant loss-tolerant loss-tolerant no loss Bandwidth elastic elastic elastic audio: 5kbps-1Mbps video:10kbps-5Mbps same as above few kbps up elastic Time Sensitive no no no yes, 100’s msec yes, few secs yes, 100’s msec yes and no
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What services do Internet transport protocols provide? TCP 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 UDP service: 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?
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Internet apps: application, transport protocols Application e-mail remote terminal access Web file transfer
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This note was uploaded on 06/28/2009 for the course CS 372 taught by Professor Leviet during the Fall '07 term at Oregon State.

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Lecture05 - Tuesday, April 15 Lab #2 Sessions run through...

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