Welcome to

1
Welcome to
CEN5515 Data and Computer Communications
Time 335AM-450AM, MW Location Love 103 Fall
2007, 3 credits
2
About myself

• Zhenghao Zhang
• Office Love 164 Phone [phone]
• Email zzhang_at_cs.fsu.edu
• URL http//www.cs.fsu.edu/zzhang
• Research area
• Computer networks
• Network security
• Peer to peer networks
• Optical networks
• Wireless networks

3
Office Hours

• Love 164
• 200pM 300PM, MW, or by appointments
• You can send me email regarding this course
  (Subject CEN5515)

4
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

5
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

6
Course Materials

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

7
Class Information

• Class website
• http//www.cs.fsu.edu/zzhang/CEN5515.htm
• Go to my website and click teaching
• Announcement page
• Check regularly

8
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

9
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.

10
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

11
Grading Policies
A 90-100
A- 85-89
B 80-84
B 70-79
B- 65-69
C 60-64
D 55-59
E 50-54
F lt50
12
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

13
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

14
Questions and Concerns?
15
Computer Communication A motivation example

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

16
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

17
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)

18
Step 2 Getting IP address (Cont)

• 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 0030482A29FD
• IP asks Ethernet to send an Ethernet frame to
  0030482A29FD.
• 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.

19
Step 2 Getting IP address (Contd)

• 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

20
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.

21
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

22
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

23
The above example greatly simplified
DNS
Browser (http client)
http server
TCP
TCP/UDP
UDP
IP
IP
IP
Ethernet
Ethernet
Ethernet
24
What problems we need to resolve?

• Naming, addressing
• fragmentation/reassembly
• multiplexing/demultiplexing
• routing
• resolve contention
• Speed mismatch between sender/receiver
• error control
• ...