Computer Science, FSU1 CNT5505 DATA/COMUTER COMMUNICATIONS Fall 2010.

Computer Science, FSU 1

CNT5505DATA/COMUTER COMMUNICATIONS

Fall 2010


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

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


Office Hours

• Love 164• 3:30pM – 5:30PM, Thursday, or by

appointments through email


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


Course Prerequisites• A rudimentary understanding of computer

architecture, and operating systems would be helpful

• 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

• Basic probability theory may be needed to understand some performance analysis


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/CNT5505_Fall_2010.htm

– Go to my website and click teaching• Check the Announcements and your email

account regularly

http://www.cs.fsu.edu/~zzhang/CNT5505_Fall_2008.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– Homework assignments.– Projects.– One midterm– One final


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.


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

Course Project• There will be several projects.• 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• …...

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Computer Science, FSU1 CNT5505 DATA/COMUTER COMMUNICATIONS Fall 2010.

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