Computer Network Software
Budget $10-30 USD
Answer with work for questions 1 (a-c) and question 2 (a-h)
1. Calculate the latency (from the first bit sent to the last bit received) for the following:
(a) 10-Mbps Ethernet with a single store-and-forward switch in the path,
and a packet size of 5000 bits. Assume that each link introduces a propagation delay
of 10 µs and that the switch begins retransmitting immediately after it has finished
receiving the packet.
(b) Same as (a) but with three switches.
(c) Same as (a) but assume the switch implements “cut-through”
switching: It is able to begin transmitting the packet after the first 200 bits have been
2. Consider two hosts, A and B, directly connected by a link of 40,000 Km,
propagation speed 2.5*108 m/s, and transmission rate R=5 Mbps. Assume zero
(a) How long does it take to move a packet of length 1000 bytes from one
A to B?
(b) Generally, how long does it take to move a packet of length L over a
link of distance d, propagation speed s, and transmission rate R bps?
(c) Assume the transmission time of the packet is dtrans and the
propagation delay dprop. Suppose that host A begins to transmit a packet at time t=0.
At time t= dtrans where is the last bit of the packet?
(d) Suppose dprop is greater than dtrans. At time t= dtrans, where is the
first bit of the packet?
(e) Suppose dprop is less than dtrans. At time t= dtrans, where is the first
bit of the packet?
(f) Calculate the bandwidth-delay product R* dprop.
(g) Consider sending a file of 1,200,000 bits from host A to host B.
Suppose the file is sent continuously as a large message. What is the maximum
number of bits that will be in the link at any time? (Hint: the answer shall be the
smaller value of bandwidth-delay product and packet size)
(h) What is the width (in meters) of a bit in the link? (Hint: the width of a
bit = length of link / bandwidth-delay product)
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