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Computer Networks - Exam #2 Questions and Answers
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Computer Networks - Exam #2 Questions and Answers
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Computer Networks - Exam #2Questions and Answers
logical communication - Answer-letting app processes talk to each other as if they
weren't separated by a great distance
segments - Answer-the fancy name for transport layer messages
network layer - Answer-an abstraction allowing logical communication between hosts
transport layer - Answer-an abstraction allowing logical communication between
processes
TCP - Answer-protocol providing reliable, in-order delivery with congestion control, flow
control, and connection setupd
UDP - Answer-protocol providing nothing
limitations of transport-layer protocols - Answer-unable to provide delay and bandwidth
guarantees
multiplexing - Answer-handling data from multiple sockets and assigning the appropriate
transport header
demultiplexing - Answer-using header info to deliver received segments to the correct
socket
checksum - Answer-detects 1-bit errors by summing the segment data and inverting
and comparing
ACK - Answer-receiver explicitly tells sender that a packet was received OK
NAK - Answer-receiver explicitly tells sender that a packet has errors in it
stop and wait - Answer-sender sends a packet and then waits for a response from the
receiver
timeout - Answer-because of underlying channel unreliability, the sender considers a
certain amount of time to be a NAK
sequence number - Answer-ID field for packets sent
pipelining - Answer-the sender allows multiple, yet-to-be-acknowledged packets
, utilization - Answer-the fraction of time the sender is busy sending
(L/R) / (RTT + L/R) * number of packets in pipeline
window size - Answer-the number of unacknowledged packets in the pipeline
Go-Back-N - Answer-- sender can have N unacked packets in the pipeline and has
timers set for the older unacked packet
- receiver send a cumulative ack
Selective Repeat - Answer-- sender can have N unacked packets in the pipeline and
maintains timers for each unacked packet
- receiver sends individual acks for each packet
TCP - sequence numbers - Answer-byte stream number of the first byte in the
segment's data
TCP - ACK number - Answer-the sequence number of the next byte expected
(cumulative ACK)
TCP - EstimatedRTT - Answer-exponential weighted moving average
(1 - a)*EstimatedRTT + a*SampleRTT
a is usually 0.125
TCP - DevRTT - Answer-(1-b)*DevRTT + B*|SampleRTT - EstimatedRTT|
b is usally 0.25
TCP - TimeoutInterval - Answer-EstimatedRTT + 4*DevRTT
TCP - fast retransmit - Answer-if sender receives 4 ACKs for same data (triple duplicate
ACKs) resend unacked segment with smallest sequence number
TCP - flow control - Answer-receiver controls the sender so sender won't overflow
receiver's buffer by transmitting too much, too fast
receiver tells the sender how much room he has left in his buffer
TCP - handshake - Answer-3-way handshake where A sends SYN and Seq X, B sends
SYN, Seq Y, ACK X+1, and A sends ACK Y+1
congestion - Answer-too many sources sending too much data too fast for the network
to handle
end-end congestion control - Answer-- no feedback from network
- congestion inferred from end-system observed loss, delay
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