1. CS470 Computer Networking Protocols
4/26/2017
CS470 Computer Networking Protocols
Final Review
Huiping Guo
Department of Computer Science
California State University, Los Angeles

2. Final Time Open book, open note
8:00 am – 10:30am , Wed. 03/21
Open book, open note
No web surfing (except for the class webpage)
No s
Bring your own scratch paper
There are no spaces for your answers on the exam paper
Write down your answers (in order) on your own scratch paper
Write down your name on each paper
Final Review

3. Outline
Transport layer
Application layer
Final Review

4. 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

5. User Datagram Protocol (UDP)
Services UDP provides
The applications that use UDP
UDP header
Some important fields
Final Review

6. 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

7. 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

8. 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

9. 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

10. TCP What services TCP provides The TCP connection TCP header format
TCP reliable transfer
TCP vs. GBN
How TCP detects data lost?
TCP flow control
How it works
Flow control vs. congestion control
Final Review

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

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

13. 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

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

15. 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

16. 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

17. DNS The service it uses Distributed hierarchical databases
Root DNS servers
TLD servers
Authoritative DNS servers
Local DNS servers
Types of DNS queries
Recursive
Iterative
Final Review

18. DNS DNS caching DNS records Where and why? RR format RR types
Final Review