7.3-1. Overlapping 802.11 wireless networks, with ACKs (d)Overlapping wireless senders with ACKs. Now suppose we are again in the wireless scenario, and that for every data message sent from source to destination, the destination will send an ACK message back to the source (e.g., as in TCP). Also suppose that each ACK message takes up one slot. What is the maximum rate at which data messages can be transferred from C to A, given that there are no other messages between any other source/destination pairs? [Note that successful ACKs do not count towards data message throughput].Group of answer choices1 message/slot.0.25 messages/slot (i.e., one message every four slots).0.5 messages/slot (i.e., 1 message every two slots).2 messages/slot.

7.3-1. Overlapping 802.11 wireless networks (c)Suppose now that A sends messages to B, and C sends messages to D. What is the combined maximum rate at which data messages can flow from A to B and from C to D?Group of answer choices2 messages/slot.1 message/slot.0.5 messages/slot (i.e., 1 message every two slots).0.25 messages/slot (i.e., one message every four slots).

Why are link-layer ACKs used in WiFi (802.11) networks? [Hint: check two of the boxes below].Group of answer choicesBecause 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.Hearing a receiver ACK, all other stations will stop transmitting.  This reduces collisions.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 senderWireless 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.

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.

How many Ack[i] signals can be 1 at the same time?A1B2CNSUBMIT

7.3-1. Overlapping 802.11 wireless networks (a)Consider the scenario shown below in which there are four wireless nodes, A, B, C, and D. The radio coverage of the four nodes is shown via the shaded ovals; all nodes share the same frequency. When A transmits, it can only be heard/received by B; when B transmits, both A and C can hear/receive from B; when C transmits, both B and D can hear/receive from C; when D transmits, only C can hear/receive from D. If a node hears two simultaneous transmissions at a time, the messages interfere at that receiver, even through they may not interfere at other receivers, where only one of the messages is heard.[Make sure you understand this paragraph.]Suppose now that each node has an infinite supply of messages that it wants to send to each of the other nodes. If a message’s destination is not an immediate neighbor, then the message must be relayed. For example, if A wants to send to D, a message from A must first be sent to B, which then sends the message to C, which then sends the message to D. Time is slotted, with a message transmission time taking exactly one time slot, e.g., as in slotted Aloha. During a slot, a node can do one of the following: (i) send a message (ii) receive a message (if exactly one message is being sent to it), (iii) remain silent. As always, if a node hears two or more simultaneous transmissions, a collision occurs and none of the transmitted messages are received successfully.You can assume here that there are no bit-level errors, and thus if exactly one message is heard at a receiver, it will be received correctly at that receiver.Suppose now that an omniscient controller (e.g., a controller that knows the state of every node in the network) can command each node to do whatever it (the omniscient controller) wishes, that is, to send a message, to receive a message, or to remain silent. Given this omniscient controller, what is the maximum rate at which messages can be transferred from C to A, given that there are no other messages between any other source/destination pairs?Group of answer choices0.5 messages/slot (i.e., 1 message every two slots).1 message/slot.2 messages/slot.0.25 messages/slot (i.e., one message every four slots).