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CNT5505 DATA/COMUTER COMMUNICATIONS Spring 2010

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CNT5505 DATA/COMUTER COMMUNICATIONS Spring 2010. About myself. Zhenghao Zhang Office: Love 164; Phone: 644-1685 Email: [email protected] URL: http://www.cs.fsu.edu/~zzhang Research area: Wireless networks Network security Peer to peer networks Optical networks. Office Hours.

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slide1

CNT5505

DATA/COMUTER COMMUNICATIONS

Spring 2010

Computer Science, FSU

about myself
About myself
  • Zhenghao Zhang
  • Office: Love 164; Phone: 644-1685
  • Email: [email protected]
  • URL: http://www.cs.fsu.edu/~zzhang
  • Research area:
      • Wireless networks
      • Network security
      • Peer to peer networks
      • Optical networks

Computer Science, FSU

office hours
Office Hours
  • Love 164
  • 3:00pM – 5:00PM, Tuesday, or by appointments through email

Computer Science, FSU

what is cnt5505 about
What is CNT5505 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

Computer Science, FSU

course prerequisites
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
  • Basic understanding of algorithm 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

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

Computer Science, FSU

class information
Class Information
  • Class website
    • http://www.cs.fsu.edu/~zzhang/CNT5505_Spring_2010.htm
    • Go to my website and click teaching
  • Check the Announcements and your email account regularly

Computer Science, FSU

course requirements
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
    • Homework assignments.
    • Projects.
    • One midterm
    • One final

Computer Science, FSU

policies and guidelines
Policies and Guidelines
  • Homework and Assignments usually have two due times.
    • Please work early and make the first due time.
    • 10% penalty for submission by the second due time.
    • Zero if later than the second due time.
  • No make-up exam, no incomplete
    • unless proof of emergency
  • Scholastic behaviors
    • Follow the Academic Honor Code.
    • Acknowledge reference/credits if receive help.
    • You may end up “F” for dishonesty. It is not worth it.

Computer Science, FSU

important dates
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

course project
Course Project
  • There will be several projects.
  • Not coding intensive

Computer Science, FSU

slide12

Questions and Concerns?

Computer Science, FSU

computer communication a motivation example
Computer Communication: A motivation example
  • What happens behind the scene when I click on (on machine diablo)

http://www.google.com?

Computer Science, FSU

step 1 on local host
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

step 2 translating domain name to ip address
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

step 2 getting ip address con t
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.

Computer Science, FSU

step 2 getting ip address cont d
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

step 3 establishing http connection
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

step 4 web page request and retrieval
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

Computer Science, FSU

step 5 web page rendering
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

the above example greatly simplified
The above example greatly simplified

DNS

Browser

(http client)

http server

TCP

TCP/UDP

UDP

IP

IP

IP

Ethernet

Ethernet

Ethernet

Computer Science, FSU

what problems we need to resolve
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

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