Welcome to CEN 5515 Data and Computer Communications

Welcome to CEN 5515 Data and Computer Communications Time: 3: 35 AM-4: 50 AM, MW Location: Love 103 Fall 2007, 3 credits Computer Science, FSU 1

About myself Zhenghao Zhang Office: Love 164; Phone: 644 -1685 Email: zzhang@cs. fsu. edu URL: http: //www. cs. fsu. edu/~zzhang Research area: • Computer networks • Network security • Peer to peer networks • Optical networks • Wireless networks Computer Science, FSU 2

Office Hours • Love 164 • 2: 00 p. M – 3: 00 PM, MW, or by appointments • You can send me email regarding this course (Subject: CEN 5515) Computer Science, FSU 3

What is CEN 5515 about? • General purpose computer networks – • Fundamental principles – • Not survey of existing protocol standards Focus on network software architecture – • Not specialized networks (e. g. , telephone or cable) Only discuss some relevant network hardware Designing and building network systems – – Not queuing theory CIS 5930 Modeling and Performance Analysis Computer Science, FSU 4

Course Prerequisites • A rudimentary understanding of computer architecture, and operating systems would be helpful • Basic probability theory may be needed to understand some performance analysis • C/C++ or Java programming is required – Socket programming – Unix programming • Event multiplexing, timer • Provided executable code and template of project in C/C++ – You can develop the project in Java Computer Science, FSU 5

Course Materials • Required textbook – “Computer Networks, '' by Andrew S. Tanenbaum, Prentice Hall, 4 th edition, 2003 • Class notes, other assigned readings • Materials on the Internet Computer Science, FSU 6

Class Information • Class website – http: //www. cs. fsu. edu/~zzhang/CEN 5515. htm – Go to my website and click teaching • Announcement page – Check regularly Computer Science, FSU 7

Course Requirements • Do assigned readings – Be prepared; read textbook/lectures before class • Attend and participate in class activities – Please ask and answer questions in (and out of) class – Attendance will be considered in the final letter grade • Workload – – 4 homework assignments: 20% One course project: 30% One midterm: 20% One final: 30% Computer Science, FSU 8

Policies and Guidelines • No late homework – Please work on homework assignments early and hand in on time – 20% penalty for homework no late than 2 days – Zero for homework more than 2 days late. • No make-up exam, no incomplete – unless proof of emergency • Scholastic behaviors – Encouraged to study in groups but do your work independently – Acknowledge reference/credits if receive help – Academic Honor Code enforced • Stanford Moss will be used to detect plagiarism – You may end up “F” for dishonesty – It is not worth it. Computer Science, FSU 9

Important dates • Check the course website • For homework assignments – Hand in hard-copy in class on due dates – Preferably typed instead of handwritten • For course project – Submit by email – Midnight on the due dates – Demo time will be announced later Computer Science, FSU 10

Grading Policies A AB+ B BC D E F 90 -100 85 -89 80 -84 70 -79 65 -69 60 -64 55 -59 50 -54 <50 Computer Science, FSU 11

Course project • The page for the course project – go to the course website and click link to project • About building a Bit-torrent like peer-topeer content distribution network Computer Science, FSU 12

Course Project • Will be divided into four smaller projects. First two really easy, third most difficult, fourth interesting • 30% of the final grade • Not coding intensive Computer Science, FSU 13

Questions and Concerns? Computer Science, FSU 14

Computer Communication: A motivation example • What happens behind the scene when I click on (on machine diablo) http: //www. google. com? Computer Science, FSU 15

Step 1: on local host • Browser figures out what to do with the URL: http: //www. google. com/ – Three components in URL • Where: www. google. com • What: (retrieving file index. html) • How: through HTTP protocol – Talk to http daemon on www. google. com to get file index. html through HTTP protocol Computer Science, FSU 16

Step 2: translating domain name to IP address • Each machine on the Internet identified by one or more IP address • Browser translating domain name (www. google. com) to corresponding IP address using domain name server (DNS) – DNS in CS department: 128. 186. 120. 179 • How does browser know IP address of DNS server? – Hard-coded (/etc/resolv. conf) Computer Science, FSU 17

Step 2: Getting IP address (Con’t) • Call its UDP protocol entity to talk to 128. 186. 120. 179 port 53 • UDP protocol calls IP to send a datagram to 128. 186. 120. 179. • Turns out that 128. 186. 120. 179 and 128. 186. 120. 2 (diablo) are on the same Ethernet domain, can send directly via the Ethernet. • Needs to find out the Ethernet address of 128. 186. 120. 179. • uses ARP protocol, sends an ARP packet over the network What is the address of 128. 186. 120. 179? result: 00: 30: 48: 2 A: 29: FD • IP asks Ethernet to send an Ethernet frame to 00: 30: 48: 2 A: 29: FD. • Ethernet on 128. 186. 120. 179 receives an Ethernet frame, turns out to be an IP packet, pass it to the IP module. • IP module finds out it is a UDP packet and passes it to UDP module. • UDP realizes that a process is listening to port 53, notifies the process. Computer Science, FSU 18

Step 2: Getting IP address (Cont’d) • Browser calls UDP protocol entity to send a message to 128. 186. 120. 179/53 • The UDP message to the DNS server is “What is the IP address of www. google. com? ” • The DNS server sends a message back: 64. 233. 161. 99 – Actually situation is complicated than this – www. google. com is associated with multiple IP addresses Computer Science, FSU 19

Step 3: establishing HTTP connection • Calls TCP entity to set up a connection to 64. 233. 161. 99 /80 • TCP protocol calls IP to send a datagram to 64. 233. 161. 99 – turns out that www. google. com and diablo are not directly connected. – need to forward to the first-hop router (128. 186. 120. 1) – find the Ethernet address of first-hop router using arp – forward packet to first-hop router – (second router, third router) …. . . – www. google. com receives a packet. Computer Science, FSU 20

Step 4: Web page request and retrieval • Use TCP to send strings (following the HTTP protocol): “get / HTTP/1. 1n. Host: diablo. cs. fsu. edunn” – TCP entity calls IP to send a datagram – …. . – www. google. com responses with the content of index. html Computer Science, FSU 21

Step 5: web page rendering • Browser displays the content of the web page • This example was greatly simplified – We did not discuss routing in detail – We did not discuss rate-control – We did not discuss error-control –… Computer Science, FSU 22

The above example greatly simplified DNS UDP IP Ethernet Browser (http client) http server TCP/UDP TCP IP IP Ethernet Computer Science, FSU 23

What problems we need to resolve? • • • Naming, addressing fragmentation/reassembly multiplexing/demultiplexing routing resolve contention Speed mismatch between sender/receiver • error control • …. . . Computer Science, FSU 24