CS138-lecture-20210504

LAN cont. #

Switches vs routers #

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VLAN #

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VLAN = virtual local area network

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Data center networks #

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TOR = top of rack

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A day in the life of a web request #

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DHCP (UDP) > ARP (BGP) > DNS > HTTP (TCP)

Summary #

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Review #

  1. What is the difference between network and transport layer? Network is machine to machine, transport is process to process

  2. Differences between TCP and UDP TCP is reliable, UDP is not

  3. What is multiplex at sender? What is demultiplex at sender? View slides

  4. What is different between UDP socket and TCP socket? UDP is SOCK_DGRAM and TCP is SOCK_STREAM, and different respective functions.

  5. What is the usual size of UDP header? 8 bytes

  6. What is the usual size of IPv4 header? 20 bytes

  7. What is the purpose of UDP checksum? Error detection

  8. What is the problem and solution in rdt 2.0, 2.1, 3.0? View slides

  9. For non-pipelined protocols, why does sequence number surface (0,1) suffice? We only send 1 packet at a time

  10. What is the difference between stop-and-wait protocols and pipelined protocols?/ Stop and wait only send 1 packet each time, pipelined send multiple

  11. What is cumulative ACK? Cumulative ACK will confirm success for multiple packets

  12. Why does selective repeat have a dilemma when sequence numbers 0,1,2,3 and window size = 3? View slides

  13. For k-bit sequence number, what is the window size for GBN and selective repeat respectively? GBN is 2^k and selective repeat is 2^(k-1)

  14. Name 5 features TCP has that UDP doesn’t.

    1. Reliability
    2. flow control
    3. Congestion control
    4. handshake
    5. connection management

  15. What is called TCP fast retransmit? If the sender got triple duplicate it will retransmit

  16. Two indicates of data loss. Count down timer, triple duplicate

  17. What is ddefinition of sequence number and ack number for TCP? View slides

  18. Among packet headers, which layer header contains port number?

  19. What is diff between TCP flow control and congestion control? Flow control protects receiver, congestion control protects the network

  20. How does receiver advertise free buffer space in TCP header? View slides.

  21. Why do we need preamble in packet format? synchronization, or recognize start of new packet

  22. 3 costs of congestion

    1. data retranmission due to loss
    2. retransmission due to premature timeout
    3. Network resources allocated to dropped packet

  23. Why does TCP have fairness? Because for all machines involved, each connection will have additive increase multiplicative decrease

  24. What is called longest prefix matching? Selecting the longest matching IP, view slides.

  25. IP: What is subset part and host part? A.B.C.D/X, the a-d is host, x is subnet mask

  26. NAT, why can internal computers use private addresses? The private address is translated on its way out

  27. What is the difference between inter-as and intra-as protocols? Inter is handling tasks between regions, and intra handles only the tasks inside the same region.

  28. What is the functionality of inter-as? Advertise reachability information

  29. Hot potatoe routing is to select which router when multiple choices are present

  30. What is difference between eBGP and iBGP. External and internal

  31. TDMA is time division, FDMA is frequency division

  32. 2 common drawbacks from “taking turns” MAC protocols? Token based has 1 point of failure, also delay

TRUE/FALSE

  1. Multiplexinf occurs at receiver and demultiplexing at sender. FALSE
  2. UDP ssocket is identified by 4 tuple: FALSE
  3. Checksum can be used to detect transmission error 100% correct. FALSE
  4. rdt 3.0 is pipelined: FALSE
  5. Stop and wait protocols are better than pipelined: FALSE
  6. Selective repeat utilizes cumulative ACK: FALSE
  7. GBN has buffers at receivers side: FALSE
  8. Forwarding and routing are independent: FASLE
  9. Forwarding table uses individual IP addresses as indexes, FALSE
  10. Internet is based on datagram network: FALSE
  11. IP address if flat: FALSE
  12. Like TCP and UDP, ICMP is transport layer: FALSE
  13. In tunneling, IPv4 is carried as payload of IPv6: FALSE
  14. For broadcasting, innetwork duplicating is betteer than source duplication: TRUE
  15. What is called reverse path forwarding based controlled flooding.
  16. Data link layer studies logical communication between remote hosts or processes. FALSE
  17. Data link layer studies logical communication between hosts or processes: FALSE
  18. MAC is hierarchical: FALSE