QUESTION 25 Why does it make sense to have error detection codes at the link layer in addition to the checksums at the t

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Question 25 Why Does It Make Sense To Have Error Detection Codes At The Link Layer In Addition To The Checksums At The T 1 (71.58 KiB) Viewed 71 times

QUESTION 25 Why does it make sense to have error detection codes at the link layer in addition to the checksums at the transport layer? Link layer error detection codes, can themselves have bit errors, and having a second layer of bit error checking can help lessen the impact of this. Link layer error detection codes capture bit errors in the data payload whereas transport layer checksums only cover the TCP/UDP header fields. Link layer bit errors can be corrected faster via a retranmission across the previous link edge whereas a TCP retransmission would have to be from source host to destination. It does not make sense. In fact, this is a redundancy that should always be removed (either check for bit errors in the link layer or in the transport layer, but no need for both). QUESTION 26 In the 802.11 wifi protocol, what is the purpose of the CTS(X) and ACK(X) signals transmitted by the access point? These are broadcasts that are used to let nearby hosts know about the AP's presense. These act as collision avoiding locks by telling all stations when it expects X to transmit and when it is done receiving from X X These are signals that are used to tell different hosts to immediately start their backoff procedures These are signals that are broadcasted when the AP detects a collision has begin and when it has finished. QUESTION 27 Suppose you own a wireless transmission station and you find that the surrounding noise has increased, which in turn has decreased your effective signal to noise ratio. Further suppose that you are unable to increase the power of your transmission to neutralize the SNR. What else can you do to reduce bit errors? Reduce your data transmission rate. There is nothing else you can really do as only increasing power or eliminating the noise will help with the SNR, and therefore, the bit error rate. O Transmit a signal that destructively interferes with the noise. O Switch to a more advanced data modulation scheme where you can transmit 16 or even 256 bits at a time instead of 1. QUESTION 28 What is the purpose of the SIM card on a smart phone? To store the phone's permanent MAC address for link layer connectivity O It contains extensive, detailed logs of your usage so that your home network can bill you correctly. To store the phone's permanent IP address needed to connect to the data network? O To store subscriber identification data that is used to associate the device with the subscriber's home network. QUESTION 29 What does it mean when a number of wireless hosts are operating in ad hoc mode? They are not connected to any other devices (it is a synonym for airplane mode) They are effectively forming a network and routing data among themselves without the support of a base station. They are communicating via UDP instead of TCP for faster performance. They are actively sending broadcasts in the blind to identify nearby base stations. QUESTION 30 Which of the following is not a benefit of 5G data networks over 4G data networks? 5G networks achieve higher data throughput O 5G antenna systems are directional, which means more energy can be propagated in directions having a higher density of subscribers. O 5G supports transmissions over longer distances, which means that fewer cell towers are needed. 5G networks can handle significantly more hosts at the same time.