The sender infers segment loss from the absence of an ACK from the receiver.

A TCP receiver must send an acknowledgement for every segment it receives.Group of answer choicesTrue: for the sender to know that the bytes in each segment have been received the receiver must ACK each segment individually.False: TCP uses cumulative acknowledgements, so the receiver need only send an acknowledgment for the bytes in the segment with the largest sequence number that has been successfully received.

TCP sequence numbers and ACKs (2). Suppose that as shown in the figure below, a TCP sender is sending segments with 100 bytes of payload.  The TCP sender sends five segments with sequence numbers 100, 200, 300, 400, and 500.  Suppose that the segment with sequence number 300 is lost.  The TCP receiver will buffer correctly-received but not-yet-in-order segments for later delivery to the application layer (once missing segments are later received). Complete the sentences below ....After receiving segment 100, the receiver responds with an ACK with value: After receiving segment 200, the receiver responds with an ACK with value: After receiving segment 500, the receiver responds with an ACK with value: After receiving the retransmitted segment 300, the receiver responds with an ACK with value:

TCP sequence numbers and ACKs (1). Consider the TCP Telnet scenario below (from Fig. 3.31 in text). Why is it that the receiver sends an ACK that is one larger than the sequence number in the received datagram?Group of answer choicesBecause TCP sequence numbers always increase by 1, with every new segment, and the TCP receiver always send the sequence number of the next expected segmentBecause the send-to receiver segment carries only one byte of data, and after that segment is received, the next expected byte of data is just the next byte (i.e., has an index that is one larger) in the data stream.

Can you identify cases where the receiver is ACKing every other received segment (see Table 3.2 in the text) among these first ten data-carrying segments?Group of answer choicesNo. Each of the first 10 ACKs acknowledges exactly 1448 bytes of payload data.Yes! After the first ACK every remaining ACK acknowledges two segments' worth of payload data.Yes! Every ACK acknowledges two segments' worth of payload data.

Use of ACKs in WiFi. Why are link-layer ACKs used in WiFi (802.11) networks? [Hint: check two of the boxes below].Group of answer choicesWireless links are noisier than wired links, and so bit level errors are more likely to occur, making link-layer error recovery more valuable that in less-noisy wired links.Because of the hidden terminal problem, a node that is transmitting and hears no collisions still doesn’t know if there was a collision at the receiver.The sender can used the differences in the signal strength in an ACK to infer whether the receiver is moving towards, or away from, the senderHearing a receiver ACK, all other stations will stop transmitting.  This reduces collisions.