• Release questions via webcourse “assignment” around
10:30am, Thur. Oct. 20 th , due via webcourse at 10:30am next day
• Submit format:
– Word file, PDF file
– Scanned answer sheets
• Make sure your writing is large and readable
– Photos of your answer sheets if you have no scanner
• Make sure it is readable
• You can resubmit, so submit first version early!
• From 10:30am to 1pm, you can call me for any questions related to exam problems
– Office number: 407-823-5015 (HEC 335)

– Knowledge questions
– True or false statement (explain why)
– Protocols
– Calculations

• 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)?

• 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 email agent uses the same protocol for sending/receiving email?
• Why email 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?

– Show what sender/receiver reacts when a specific incident (bit-error, lose, timeout) happens
• Use graph to show interactions 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)

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

– Proxy impact (access time)
• HW1, problem 5
– UDP checksum calculation
– Packet switching advantage
• HW1, problem 1
– TCP window usage
• HW2, problem 7

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);