1. Midterm Exam Review Time: Knowledge questions
Oct. 15 (Thursday, in class, close book)
Knowledge questions
True or false statement (explain why)
Protocols
Calculations

2. Knowledge Question Examples
Difference between TCP and UDP?
Why UDP is better than TCP in some applications?
How many layers in computer networking?
What’s usage of TTL field in DNS record? IP packet?
Why asymmetric speed in DSL and Cable Modem?
What service port used by DNS, HTTP, SMTP, SSH, POP3,etc?
Why use window in TCP packet transmission?
What service provided by DNS?
TCP or UDP used in which applications (HTTP, SMTP, DNS, VOIP, etc)?

3. Knowledge Question Examples
What is HTTP cookie used for?
TCP socket programming:
the basic socket APIs and their orders
(Page 13, Chapter2-part3.ppt)
TCP/UDP header fields, header size
(Page 3, Chapter3-part3.ppt)
User agent uses the same protocol for sending/receiving ?
Why with an attachment sent out is much bigger than the attachment?
What is a torrent file? A tracker in BitTorrent?
Ethernet switch checks what layer’s header? Router?

4. Protocol Problem Examples
Show what sender/receiver reacts when a specific incident (bit-error, lose, timeout) happens
Use graph to show reactions for TCP’s SR or GBN
Example (P.16, 20 in Chapter3-part2.ppt)
Show for rdt3.0 (no test on rdt1.x to rdt2.x)
Example (P. 7,8 in Chapter3-part2.ppt)
TCP syn/ack number changes in a connection
Example (P. 5, Chapter3-part3.ppt)
Draw packet transmission time-line scenario
Example (P. 14, 15, Chapter3-part3.ppt)
TCP three-way connection setup procedure
SYN, SYN/ACK, ACK and changes of seq/ack number
Example (P.25, chapter3-part3.ppt)

5. Protocol Problem Examples
Why TCP delays its ACK “Wait up to 500ms for next segment. If no next segment, send ACK”?
DNS RR entries setup for an /Web server in a company (HW1, problem 4)
TCP AIMD (HW2, problem 6)
SMTP command and manual send spam
HTTP protocol
TCP congestion window low-pass filter (estimate RTT)

6. Calculation Problem Examples
Proxy impact (access time)
HW1, problem 5
UDP checksum calculation
Packet switching advantage
HW1, problem 1
TCP window usage
HW2, problem 7

7. Try to go over homework problems
Try to go over my lecture notes

8. What’s wrong? Socket programming: Char *welcomStr=“welcome”, *recvStr;….
If ( new_fd = accept(sockfd, (sockaddr *)&remote_addr, &sizeof(sockaddr)) == -1){
perror(“accept error\n”); exit(1); }
send(new_fd, welcomeStr, strlen(welcomeStr), 0);
recvNumByte=recv(new_fd, recvStr, MAXDATASIZE-1, 0);
printf(“%s\n”, recvStr);