1. CS4470 Computer Networking Protocols
5/5/2019
CS4470 Computer Networking Protocols
Final Review
Huiping Guo
Department of Computer Science
California State University, Los Angeles

2. Final Time Closed book, closed note You may need scratch paper
3:40pm – 5:40pm , Tuesday 12/05
No office hours in the finals week
Closed book, closed note
You may need scratch paper
You may need to bring your calculator
You can bring two pages of cheat sheet (letter size, back and front)
Final Review

3. Outline
Network layer
Transport layer
Application layer
Final Review

4. Network layer Routing algorithms Routing protocols Link State
Distance Vector
Routing protocols
Internet routing
Intro-AS Routing
RIP
OSPF
Inter-AS Routing
BGP
Final Review

5. Transport layer ICMP Network Address Translation (NAT) DHCP
What is ICMP for?
How to transmit an ICMP message?
How to avoid infinite loop?
Network Address Translation (NAT)
Why NAT
How it works
DHCP
What is DHCP for?
How it works?
Final Review

6. User Datagram Protocol (UDP)
Services UDP provides
The applications that use UDP
UDP header
Some important fields
Compute the checksum
Final Review

7. Principles of reliable transfer
Errors
A segment is corrupted
A segment is lost
Automatic retransmission request (ARQ)
When errors occur, the receiver sends a message to the sender asking for retransmission
Types of ARQ
Stop and wait
Sliding window (Go back N)
Final Review

8. Pros and Cons of Stop-and-wait
Stop-and-wait is a complete reliable transfer protocol
It’s very simple
Cons
Inefficient
While the sender is waiting for an ACK, it doesn’t do anything.
Why not the sender sends multiple segments at a time?
Need more than 1 bits for the sequence number.
Final Review

9. Go-Back-N Based on a sliding window
Use window to control number of segments to send
Number of segments that the sender can send
N-(nextseqnum – send_base)
Final Review

10. Go-Back-N Cumulative ACKs
ACK (n): ACKs all segments up to, including seq # n - 1
Timer
Only one timer is used.
The timer is for the oldest transmitted, yet un-acked segment
Final Review

11. TCP What services TCP provides The TCP connection TCP header format
TCP reliable transfer
TCP vs. GBN Vs. SR
How TCP detects data lost?
How to calculate the timeout value?
TCP flow control
How it works
Flow control vs. congestion control
Final Review

12. TCP header format Some most important fields SYN, FIN Seq, ACK
Receive Window
Final Review

13. TCP connection management
Connection establishment
Three-way handshake
In each step, what the send and the receiver do?
Connection teardown
The steps
Final Review

14. TCP congestion control
Slow start
When the phase starts and ends
Congestion avoidance
Timeout
How to adjust the two variables
3 duplicate ACKs
Final Review

15. HTTP The service it uses Stateless HTTP connections Cookies
Non-persistent
Persistent
Cookies
How do cookies work?
Final Review

16. FTP What is FTP for? How it works?
Two connections: control connection, data connection
Which connection is for transferring which kinds of data?
Final Review

17. Email Components Send an email Receive an email user agents
mail servers
SMTP
Send an
SMTP is used
Between Sender’s agent and sender’s mail server
Sender’s mail server and receiver’s mail server
Receive an
POP3 or IMAP is used
Between receiver’s mail server and receiver’s agent
Differences between POP3 and IMAP
Final Review