CS204: Week 4

What mechanism do proxy servers use to check for obsolete cached HTML objects? 

• RTT

• Cookies

• Conditional GET

• TTL

Consider sending over HTTP/2 a web page that consists of 1 video clip, and 2 images. Suppose that the video clip is transported as 100 frames, and each image has 4 frames. Which of the following statements are true? 

• If all the video frames are sent first without interleaving, 108 frame times are needed until the two images are sent. 

• If frames are interleaved, 12 frame times are needed until the two images are sent. 

• Suppose the two images are given priority over the video clip, and that the first image is given priority over the second image. 8 frame times are needed until the second image is sent. 

• The total frame times to send all the objects (the video clip and the two images) do not change with the given priority.

If the local DNS server stops caching DNS information, it will _________________

• start receiving more DNS requests if iterated DNS query is used.

• start sending more DNS requests if iterated DNS query is used. 

• start receiving more DNS requests if recursive DNS query is used.

• start sending more DNS requests if recursive DNS query is used. 

The checksum value for two 8-bit words: 1100 0111 and 1010 1100 is _______________

• 0111 0011

• 1000 1100

• 0111 0100

• 1000 1011

If an application uses UDP as the transport layer, it can still achieve reliable data transfer. The statement is:

• True

• False

Host A and B are directly connected via two separate parallel links of the same type. Removing one link will _____________________

• halve the propagation delay from A to B.

• double the propagation delay from A to B. 

• halve the average throughput from A to B. 

• double the average throughput from A to B. 

In the scenario below, the left and right clients communicate with a server using UDP sockets.

What is the source & destination port # for packet D?

• (7072, 5143)

• (7315, 5143)

• (5143, 7072)

• (5143, 7072)

Select all the statements that are true:

• UDP sockets needs to be identified using <source IP, destination IP, source port, destination port>

• TCP sockets needs to be identified using <source IP, destination IP, source port, destination port>

• It is possible for two UDP segments to be sent from the same socket with source port 3524 at a server to two different clients

• When multiple TCP clients send TCP segments to the same destination port # at a receiving host, those segments from different senders will be directed to the same socket.

Select the statements that are FALSE

• Go-Back-N (GBN) uses cumulative ACK

• In GBN, the receiver buffers the packets received out-of-order

• Selective Repeat (SR) uses cumulative ACK

• In SR, the receiver discards the packets that are received out-of-order

• 
  In SR, each individual received packet is acknowledged

In RDT 2.1, how does the sender know about the garbled acknowledgment?

• Using checksum in the ACK packet sent by the receiver

• Using the checksum in the data packet sent by the sender

• Using the sequence number

• Using timeout