Question 1:


a) Consider a network in which packets are delivered reliable across each link. That is, for each pair of adjacent nodes A – B, the datalink layer has an ARQ protocol (such as stop-and-wait) that ensures packets sent by A do arrive at B. In this network, why do you think is necessary for the transport layer to also have its own ARQ protocol and do retransmissions of its packets?

b) For each of the following, identify which OSI layer is responsible for performing the described action:

i) Make sure that a packet is delivered reliably across a single physical link

ii) Describes how a binary tree data structure is to be encoded inside the message

iii) Makes sure that a message is delivered reliably from the source host to the destination host

iv) Coordinates the transmission of multiple flows of data across multiple sources and multiple destinations (for example, a video conference)

v) Defines how the bits are converted into voltages

vi) Decides how a data packet is to be routed from one link to the next.

Question 2 –


a) Assume you have a link that has 50ms of round-trip-time, the transmission rate is 3Mbits/sec, and each packet is 1Kbyte. If we are using the concurrent logical channels protocol, how many logical channels do we need to maintain 100% throughput (assuming no message loss)

b) Assume three of the above (i.e. part (a)) logical channels have lost a message and are stuck waiting for the timeout to occur (assume the timeout value unnecessarily large, way too big). How much is the reduction in throughput?

Question 3


Consider the following sequence of data bits


How would this be translated into physical bits if we use:

a) NRZ

b) NRZI (high value initially)

c) Manchester

d) 4B/5B

Question 4:


a) Consider bit-stuffing (also known as bit-insertion) the way I present it in the slides, NOT the way it is presented in the book. Consider k = 2. If the data bits of the frame to be sent are


what are the actual bits sent by the sender? Please include some idleness bits before and after the frame.

b) Is it possible to have k=1? Why or why not?

Describes how a binary tree data structure is to be encoded inside a message
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