1. Data and Computer Communications
CNT 5505
Data and Computer Communications
9:30AM –10:45AM, M & W
Fall 2017

2. Instructor Xin Yuan (xyuan@cs.fsu.edu) Office: Love 259 Office hours:
1:00PM – 2:30PM, Monday & Wednesday
Or by appointments (
Class website
Use blackboard

3. Teaching Assistant TA: Mehran Sadeghi Lahijani
Office: TBA
Office hour: TBA

4. What is this class about?
General purpose computer networks (Internet)
Not specialized networks (e.g., telephone or cable TV)
Fundamental principles
Not survey of existing protocol standards
Focus on network software architecture
Only discuss some relevant network hardware
Designing, evaluating, building network systems
Not queuing theory
CIS5930 Modeling and Performance Analysis
After taking this class, you should be able to
Describe the overall Internet architecture
Describe the design issues in each layer of the architecture
Describe, analyze, apply, and code the key techniques and protocols in each layer

5. Course Prerequisites Official CDA 3101 (Computer Org II),
COP 4610 (Operating Systems)
Unofficial notes
A student can pass this course without much required background knowledge if he or she is motivated enough
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++ programming is required

6. Course Materials Required textbook Recommended reference textbooks
“Computer Networks,'' by Andrew S. Tanenbaum, Prentice Hall, 5th edition, 2011
Recommended reference textbooks
“Computer Networking: A Top-Down Approach,'' by Jim Kurose and Keith Ross, Addison-Wesley.
“Advanced Programming in the Unix Environment,” by W. Richard Stevens, Addison-Wesley
“Unix Network Programming, the Socket Networking API,” Volume 1, 3rd Edition, by W. Richard Stevens, et al. Addison-Wesley
Lecture notes, other assigned readings
Materials on the Internet

7. Workload and Grading Policies
3-5 homework assignments: 10% - equally weighted
4 course projects (single and/or group): 30% - equally weighted
1 midterm exam: 25%
1 final exam: 35%

8. Tentative Grading Policies
[90-100] A-
[87-90) B+
[84-87) B
[80-84) B-
[76-80) C+
[73-76) C
[69-72) C-
[66-69) D
[56-66) F
< 56

9. Important dates Check blackboard on important dates
Subject to change
Changes will be announced in the blackboard
For homework assignments
Hand in hard-copy in class on due dates
Preferably typed instead of handwritten
For course projects
Submit through the online submission page
Midnight on the due dates
Demo time will be announced later

10. Accounts Computer Science account (<yourid>@cs.fsu.edu)
For doing projects
FSU account
For receiving class announcements
For submitting assignments
For getting your grades
Access to blackboard
For class materials, discussion board, grades etc.
Through your FSU account

11. Policies and Guidelines
Willing to consider your special situation of ANY kind if you let me know 48 hours before the event. Show proof of extenuating situation after that.
No late homework/projects
Please work on homework assignments/projects early and hand in on time
10% penalty no late than 24 hours
20% penalty no late than 48 hours
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 be strictly enforced
Moss will be used to detect plagiarism
Please read detailed course policies in the syllabus.

12. Honors Code Violation Follow university academic honor policy at
Step 1 agreement:
The student will receive a score of zero on the concerned assignment.
The final letter grade will be lowered by one level (for example, B+ will become C+).
Do not copy from anywhere (e.g from the Internet)
Do not give your solution/code to others, at any time.
I will not negotiate with the accused violator and will not listen to explanations (it is the job for the honor court judges).

13. Questions and Concerns?

14. questions What will you be learning in this class?
Will you learn how Cable networks work?
How many exams will be there in this class?
If you are under weather for a few days, which will prevent from completing an assignment on time, what can you do?
If you are wrongfully accused of honor code violation and would like to defend yourself, what can you do?

15. Computer Communication: An overview example
What happens behind the scene when I click on the following link in a browser on diablo.cs.fsu.edu
Don’t be overwhelmed by the example; we will study all aspects involved in this semester

16. Layered Internet Protocol Architecture
Application layer
HTTP, SMTP, FTP
Transport layer
TCP, UDP
Network layer IP
Data link layer + Physical layer
Ethernet
Application
Transport
Network
Data Link
Physical

17. Step 1: on local host
Browser (an HTTP client) figures out what to do with the URL:
Three components
Where:
What: (retrieving default file under root path / -- index.html)
How: through HTTP protocol
Talk to http server daemon on to get file index.html through HTTP protocol
Most Internet application level protocols are text-based. Try the following on a machine:
<diablo> Telnet 80 …
GET /index.html HTTP/1.0

18. Step 2: translating domain name to IP address
Each machine on the Internet identified by one or more IP address
Browser translating domain name ( to corresponding IP address using the domain name server (DNS) system
DNS in CS department:
Try ‘nslookup
How does browser know IP address of DNS server?
Hard-coded (/etc/resolv.conf)
DHCP auto-configured system.

19. Step 2: Getting IP address (Con’t)
Call its UDP API routine (a transport layer API routing) to talk to port 53
UDP routine calls an IP routine (a network layer API routine) to send a datagram to
Turns out that and (diablo) are on the same Ethernet domain, can send directly via the Ethernet.
Needs to find out the Ethernet address of
uses ARP protocol, sends an ARP packet over the network
What is the physical (Ethernet) address of ?
result: 00:0C:29:DD:BB:2F
IP asks Ethernet to send an Ethernet frame to 00:0C:29:DD:BB:2F.
Ethernet on 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.
Port number for different applications: /etc/services
Showing ARP cache: /sbin/arp

20. Step 2: Getting IP address (Cont’d)
Browser calls UDP protocol entity to send a message to /53
The UDP message to the DNS server is “What is the IP address of
The DNS server sends a message back:
Actually situation is complicated than this
is associated with multiple IP addresses
Commands mapping name and IP: host, nslookup, dig

21. Step 3: establishing HTTP connection
Calls TCP entity to set up a connection to /80
TCP protocol calls IP to send a datagram to
turns out that and diablo are not directly connected.
need to forward to the first-hop router ( )
find the Ethernet address of first-hop router using ARP
forward packet to first-hop router
The first-hop router sends to the second router, the second hop router sends to the third router, …...
receives a packet.
Showing routing table: netstat –r, or /sbin/route
Showing “complete” path: traceroute

22. 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
…..
responses with the content of index.html

23. 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 …

24. The above example greatly simplified
DNS
Browser
(http client)
http server
TCP
UDP
TCP/UDP IP IP IP
Ethernet
Ethernet
Ethernet

25. Some problems we need to resolve in the Internet
Naming, addressing
routing
Speed mismatch between sender/receiver
error control
resolve contention
fragmentation/reassembly
multiplexing/demultiplexing
…...

26. Reading
Chapter 1