Midterm Exam Review

1
Midterm Exam Review

• Time
• Oct. 11 (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?
• Whats 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 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 layers header?
  Router? Firewall?
• What is SYN flooding attack? Why it is hard to
  defend?

4
Protocol Problem Examples

• Show what sender/receiver reacts when a specific
  incident (bit-error, lose, timeout) happens
• Use graph to show reactions for TCPs 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 Email/Web server in a
  company (HW1, problem 6)
• TCP AIMD (HW2, problem 6)
• Email SMTP command and manual send spam
• HTTP protocol (HW1, problem 4)
• TCP congestion window low-pass filter (Quiz 1)

6
Calculation Problem Examples

• Proxy impact (access time)
• HW1, problem 7
• M/M/1 queue (formula given to you)
• Example, P. 9, MM1-queue.ppt
• 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
Whats wrong?

• Socket programming
• If ( new_fd accept(sockfd, (sockaddr
  )remote_addr, sizeof(sockaddr)) -1)
• perror(accept error\n) exit(1)
• send(new_fd, welcomeStr, strlen(welcomeStr), 0)
• recvNumByterecv(new_fd, recvStr, MAXDATASIZE-1,
  0)
• printf(s\n, recvStr)
• Low-pass filter programming
• void main(void)
• alpha 0.125
• for (int i0 iltNi)
• EstimateRTTi EstimateRTTi-1
  alphaSampleRTTi