ACO330_HW_03
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School
Arizona State University *
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Course
330
Subject
Mathematics
Date
Apr 3, 2024
Type
docx
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3
Uploaded by MagistrateFogViper29
Arizona State University
School of Mathematical and Natural Sciences
ACO-330: Computer Networks
Homework-03
100 Points Total
[8 points] Question 1: HTTP Streaming and DASH
Consider a DASH system for which there are
N
video versions (at
N
different rates and qualities)
and
N
audio versions (at
N
different rates and qualities). Suppose we want to allow the player to choose at any time any of the
N
video versions and any of the
N
audio versions.
a)
If we create files so that the audio is mixed in with the video, so server sends only one media stream at given time, how many files will the server need to store (each a different URL)?
b)
If the server instead sends the audio and video streams separately and has the client synchronize the streams, how many files will the server need to store?
[12 points] Question 2: Relationship Between Transport Layer and Network Layer
Suppose the network layer provides the following service. The network layer in the source host
accepts a segment of maximum size 1,200 bytes and a destination host address from the transport
layer. The network layer then guarantees to deliver the segment to the transport layer at the
destination host. Suppose many network application processes can be running at the destination
host.
a)
Design the simplest possible transport-layer protocol that will get application data to the
desired process at the destination host. Assume the operating system in the destination
host has assigned a 4-byte port number to each running application process.
b)
Modify this protocol so that it provides a “return address” to the destination process.
c)
In your protocols, does the transport layer “have to do anything” in the core of the
computer network?
[8 points] Question 3: Relationship Between Transport Layer and Network Layer
Consider a planet where everyone belongs to a family of six, every family lives in its own house,
each house has a unique address, and each person in a given house has a unique name. Suppose
this planet has a mail service that delivers letters from source house to destination house. The
mail service requires that (1) the letter be in an envelope, and that (2) the address of the
destination house (and nothing more) be clearly written on the envelope. Suppose each family
has a delegate family member who collects and distributes letters for the other family members.
The letters do not necessarily provide any indication of the recipients of the letters.
1
a)
Describe a protocol that the delegates can use to deliver letters from a sending family
member to a receiving family member.
b)
In your protocol, does the mail service ever have to open the envelope and examine the
letter in order to provide its service?
[5 points] Question 4: TCP Protocol
Consider a TCP connection between Host A and Host B. Suppose that the TCP segments traveling from Host A to Host B have source port number
x
and destination port number
y
. What is the source and destination port numbers for the segments traveling from Host B to Host A?
[5 points] Question 5: TCP VS. UDP Protocol Describe why an application developer might choose to run an application over UDP rather than
TCP.
[5 points] Question 6: TCP VS. UDP Protocol
Why is it that voice and video traffic is often sent over TCP rather than UDP in today’s Internet?
(Hint: The answer we are looking for has nothing to do with TCP’s congestion-control
mechanism.)
[5 points] Question 7: Reliable Data Transfer
Is it possible for an application to enjoy reliable data transfer even when the application runs
over UDP? If so, how?
[8 points] Question 8: UDP Protocol
Suppose a process in Host C has a UDP socket with port number 6789. Suppose both Host A and
Host B each send a UDP segment to Host C with destination port number 6789.
a)
Will both of these segments be directed to the same socket at Host C?
b)
If so, how will the process at Host C know that these two segments originated from two
different hosts?
[8 points] Question 9: Web Server TCP Connection Suppose that a Web server runs in Host C on port 80. Suppose this Web server uses persistent connections, and is currently receiving requests from two different Hosts, A and B. a)
Are all of the requests being sent through the same socket at Host C?
b)
If they are being passed through different sockets, do both of the sockets have port 80? Discuss and explain.
[18 points] Question 10: Transport-layer multiplexing and demultiplexing
Suppose Client A initiates a Telnet session with Server S. At about the same time, Client B also initiates a Telnet session with Server S. Provide possible source and destination port numbers for
a.
The segment sent from A to S.
2
b.
The segment sent from B to S.
c.
The segment sent from S to A.
d.
The segment sent from S to B.
e.
If A and B are different hosts, is it possible that the source port number in the segment from A to S is the same as that from B to S?
f.
How about if they are the same hosts?
[18 points] Question 11: Transport-layer multiplexing and demultiplexing
Consider Figure 3.5 in your textbook. What are the source and destination port values in the segment flowing from the server back to clients’ processes? What are the IP addresses in the network-layer datagrams carrying the transport-layer segments? Use letters a, b and c to represent IP addresses for A, B and C hosts, respectively. 3
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