Computer Science, FSU1 Welcome to CEN5515 Data and Computer Communications Time: 3:35AM-4:50AM, MW...

Computer Science, FSU 1

Welcome to

CEN5515Data and Computer Communications

Time: 3:35AM-4:50AM, MWLocation: Love 103Fall 2007, 3 credits


About myselfZhenghao ZhangOffice: Love 164; Phone: 644-1685Email: [email protected]: http://www.cs.fsu.edu/~zzhang

Research area: • Computer networks • Network security• Peer to peer networks• Optical networks• Wireless networks


Office Hours

• Love 164

• 2:00pM – 3:00PM, MW, or by appointments

• You can send me email regarding this course (Subject: CEN5515)


What is CEN5515 about?• General purpose computer networks

– Not specialized networks (e.g., telephone or cable)

• Fundamental principles– Not survey of existing protocol standards

• Focus on network software architecture– Only discuss some relevant network hardware

• Designing and building network systems– Not queuing theory– CIS5930 Modeling and Performance Analysis


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


Course Materials• Required textbook

– “Computer Networks,'' by Andrew S. Tanenbaum, Prentice Hall, 4th edition, 2003

• Class notes, other assigned readings • Materials on the Internet


Class Information

• Class website– http://www.cs.fsu.edu/~zzhang/CEN5515.htm– Go to my website and click teaching

• Announcement page– Check regularly

http://www.cs.fsu.edu/~zzhang/CEN5515.htm


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%


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.

http://www.cs.berkeley.edu/~aiken/moss


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


Grading PoliciesA 90-100

A- 85-89

B+ 80-84

B 70-79

B- 65-69

C 60-64

D 55-59

E 50-54

F <50


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-to-peer content distribution network

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



Questions and Concerns?


Computer Communication: A motivation example

• What happens behind the scene when I click on (on machine diablo)http://www.google.com?


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


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)


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: 00:30:48:2A:29:FD

• IP asks Ethernet to send an Ethernet frame to 00:30:48:2A: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.


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


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.


Step 4: Web page request and retrieval

• Use TCP to send strings (following the HTTP protocol): “get / HTTP/1.1\nHost: diablo.cs.fsu.edu\n\n”

– TCP entity calls IP to send a datagram– …..– www.google.com responses with the

content of index.html


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– …


The above example greatly simplified

DNS Browser(http client)

http server

TCP/UDP

IP

Ethernet

TCPUDP

IPIP

EthernetEthernet


What problems we need to resolve?

• Naming, addressing• fragmentation/reassembly• multiplexing/demultiplexing• routing• resolve contention• Speed mismatch between

sender/receiver• error control• …...

Computer Science, FSU1 Welcome to CEN5515 Data and Computer Communications Time: 3:35AM-4:50AM, MW...

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