unit 3 Flashcards
_______________ is the physical layer protocol that is most commonly used over the wide-area optical fiber links that make up the backbone of communications networks, including the telephone system.
sonet
Explain how a sliding window protocol works.
a sliding window is a technique for someone to be able to send multiple frames at one time. During the sliding window, the sender mainstains a set of sequence numbers that corresponds to frames that it is permitted to send. The receiver also maintains a receiving window that corresponds to a set of frames.
When this protocol is used, a bad frame that is received is discarded, but any good frames received after it are accepted and buffered. When the sender times out, only the oldest unacknowledged frame is retransmitted. If that frame arrives correctly, the receiver can deliver to the network layer, in sequence, all the frames it has buffered. What is this protocol called?
selective repeat
The data link layer uses the services of the physical layer to send and receive bits over communication channels. What is NOT a service on the data link layer?
Assigning an identifier for each frame.
The data link layer takes the packets it gets from the network layer and encapsulates them into frames for transmission. Each frame contains three fields. What is NOT a field contained by each frame?
preamble
The sender’s data link layer inserts a special escape byte (ESC) just before each accidental flag byte in the data. A framing flag byte can be distinguished from one in the data by the absence or presence of an escape byte before it. The data link layer on the receiving end removes the escape bytes before giving the data to the network layer. What is this technique called?
byte stuffing
What is NOT an error-detecting code?
Hamming codes
What is NOT an error-correcting code?
checksums
The physical layer process and some of the data link layer process run on dedicated hardware. What is this hardware called?
network interface card
This strategy is for the receiver simply to discard all subsequent frames, sending no acknowledgements for the discarded frames. It corresponds to a receive window of size 1. In other words, the data link layer refuses to accept any frame except the next one it must give to the network layer. If the sender’s window fills up before the timer runs out, the pipeline will begin to empty. Eventually, the sender will time out and retransmit all unacknowledged frames in order, starting with the damaged or lost one. What is this strategy called?
go-back-n
