hw3_sols_spring2023
.pdf
keyboard_arrow_up
School
University of California, Berkeley *
*We aren’t endorsed by this school
Course
4119
Subject
Computer Science
Date
Apr 26, 2024
Type
Pages
11
Uploaded by dkpromotional on coursehero.com
© Gil Zussman, Columbia University - Do not upload to external sites
1 CSEE W4119 Computer Networks Homework #3 - Solution Prof. Gil Zussman 1. (16 points)
© Gil Zussman, Columbia University - Do not upload to external sites
2 2. (16 points) Consider the rdt3.0
protocol. Draw a diagram showing that if the network connection between the sender and receiver can reorder messages (that is, that two messages propagating in the medium between the sender and receiver can be reordered), then the alternating-bit protocol will not work correctly (make sure you clearly identify the sender on the left and the receiver on the right, with the time axis running down the page, showing message (M) and acknowledgment (A) message exchange. Make sure you indicate the sequence number associated with any data or acknowledgment segment. T.O. and M0 is retransmitted. 3. (16 points) Consider a scenario in which Host A wants to simultaneously send packets to Hosts B and C. A is connected to B and C via a broadcast channel – a packet sent by A is carried by the channel to both B and C. Suppose that the broadcast channel connecting A, B, and C can independently lose and corrupt packets (and so, for example, a packet sent from A might be correctly received by B, but not by C). Design a stop-and-wait-like error-control protocol for reliably transferring packets from A to B and C, such that A will not get new data from the upper layer until it knows that both B and C have correctly received the current packet. Give FSM descriptions of A and C. (Hint: The FSM for B should be essentially the same for C.)
Also, give a description of the packet format(s) used. This problem is a variation on the simple stop-and-wait protocol (
rdt3.0
). Because the channel may lose messages and because the sender may resend a message that one of the receivers has already received (either because of a premature timeout or because the other receiver has yet to receive the data correctly), sequence numbers are needed. As in rdt3.0
, a 1-
bit sequence number will suffice here. In addition, for detecting packet corruption, a checksum field is needed. M0 M0 M0 M1 M1 A0 A0 A1 A1 old version of M0 accepted!
© Gil Zussman, Columbia University - Do not upload to external sites
3 The FSMs of sender A and receiver B (= receiver C) are shown below. In this problem, the sender state indicates whether the sender has received an ACK from B (only), from C (only) or from neither C nor B. The receiver state indicates which sequence number the receiver is waiting for. To get full credits, it needs to provide a description of the packet format. For example, Source Addr. Destination Addr. Sequence # (0 or 1) ACK (0 or 1) Checksum Data
© Gil Zussman, Columbia University - Do not upload to external sites
4 4. (16 points) Consider the GBN and SR protocols. Suppose the sequence number space is of size k
. What is the largest allowable sender window that will avoid the occurrence of problems such as that in the following figures for each of these protocols? In order to avoid the scenarios above, we want to avoid having the leading edge of the receiver's window (i.e., the one with the “highest” sequence number) wrap around in the sequence number space and overlap with the trailing edge (the one with the "lowest" sequence number in the sender's window). That is, the sequence number space must be large enough to fit the entire receiver window and the entire sender window without this overlap condition. So - we need to determine how large a range of sequence numbers can be covered at any given time by the receiver and sender windows. Suppose that the lowest-sequence number that the receiver is waiting for is packet seq
.
# base
. For the SR protocol, its window is [base,base+N-1]
and it has received (and ACKed) packet seq. # base-1
and the N-1 packets before that, where N is the size of the window. The receiver is not sure that the N ACKs have been received by the sender. If none of those N ACKs have been yet received by the sender, then ACK messages with values of [base-N,base-1]
may still be
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
Related Questions
Both TCP and UDP are separate protocols that may be contrasted with one another. Give us an example of two circumstances in which you, as a software architect, might choose to make use of TCP rather than UDP.
arrow_forward
Both TCP and UDP are separate protocols that may be contrasted with one another. Give us an example of two situations in which you, as a software architect, might choose to make use of TCP rather than UDP.
arrow_forward
Two considerations drive the use of layered protocols.
arrow_forward
Consider an employee using their computer to send and retrieve email at their workplace. Only Ethernet networks are used for physical connectivity, but the mail server is located on a separate network. The employee’s network and the mail server’s network are connected by a single router which also has a connection to the Internet via the workplace’s ISP.
Explain how the employees email client sends and receives emails using the email server, indicating any protocols involved and where any encapsulation/decapsulation occurs as data travels between the client, local mail server, and remote mail servers.
arrow_forward
The use of layered protocols is driven by two different concerns.
arrow_forward
Computer Networks - Internet Architecture & Application Layer
Please answer the question
Someone suggested to use a local file called hosts.txt on each machine instead of DNS. Discuss the advantages (at least 2) and disadvantages (at least 2) of such suggestion. What is ‘saw-tooth’ behavior in TCP, and what is causing it?
arrow_forward
To what extent do each of the following contribute to the benefits of layered protocols? Explain what you mean by providing some examples.
arrow_forward
For NAT Network Address Translation Scenario: Jenny Bello is a small business owner selling and making customized computer peripherals. She has been finding it difficult to track her sales and inventories, however recently after an expert's advice, she adopted a Point of Sale (PoS) server. So, she can now track her sales and inventories at the store. However, she ran into another issue, the server can only be accessed within the store, because it has been assigned a private IPv4 address, it is not publicly accessible via the Internet.
a) Why is not having the PoS server accessible over the Internet a problem for the business?
b) What caused this problem?
c) Propose a solution for the problem and explain how the solution works.
arrow_forward
Two distinct protocols that may be contrasted are TCP and UDP. Give two examples of situations when you, as a software architect, might choose TCP over UDP.
arrow_forward
The tunneling process entails what steps, exactly? Can you name the three protocols used for tunneling?
arrow_forward
Chose the appropriate terminology which expresses the following concepts:
(Flow control, A token-ring Network, RTT, star topology, non-persistent HTTP, persistent HTTP,
Network layer, Persistent, Interconnection, bus topology, Transport services, DNS).
NO
Terminology
Description
1
Is a deterministic network, meaning each station connected to the
network is assured access for transmission of its messages at regular
or fixed time intervals.
2
Multiple objects can be sent over single TCP connection between
client, server.
3
Allows users to exchange information (data) with other network
members.
All LAN data traffic is carried over a common coaxial cable link.
Value used for error checking.
Response time=2RTT+ file transmission time.
10
5
6
arrow_forward
Non-Repudiation and Anonymity ProtocolsFor the Zhou-Gollman non-repudiation protocol discussed in the lecture on “Non-Repudiation and Anonymity Protocols”, which one of the following statements is false:a) At time point 4, both A and B can produce evidence to prove that they received Kb) At time point 2, both A and B can produce evidence to prove that they received a signed message from the other partyc) At time point 0, S cannot prove anythingd) At time point 3, B cannot produce evidence to prove that A has access to key Ke) At time point 1, A can prove that B is alivef) At time point 4, S can prove that A is aliveg) At time point 3, S can produce evidence that that A has access to key Kh) At time point 0, A is not alivei) At time point 2, A can produce evidence to prove that B is alivej) At time point 4, the protocol terminatesExplain your answer below:
arrow_forward
The usage of layered protocols is motivated by two factors.
arrow_forward
What two of the following arguments are strongest in support of layered protocols?
arrow_forward
The most common uses of layered protocols are security and performance.
arrow_forward
Provide an overview of the four abstraction layers that make up TCP/IP. ii) Speculate on a scenario where two computers are transferring a video file via an unencrypted ftp connection using a weak TCP three-way handshake.
arrow_forward
There are two main reasons why layered protocols are used.
arrow_forward
Kerberos is a protocol that is based around Needham-Schroeder protocol for many to
many authentications. Now answer the following questions. (Use necessary diagrams
to justify your answers)
i) Explain why the password of the user is not sent over the network and instead
session keys are generated and shared in the Kerberos protocol.
ii) The information in a TGT (Ticket Granting Ticket) is encrypted so the client
cannot access the information in the TGT. However, all information in the
ticket is already known to the client. Why is it still necessary to encrypt it?
iii) Describe the working mechanism of how a ticket is generated between the
client and server by the TGS (Ticket Granting Server) and how it is used for
client-server communication.
arrow_forward
The use of layered protocols is supported by two main arguments. You must provide evidence for your claims.
arrow_forward
- 3 -
(b) The Internet Protocol (IP) can sometimes surprise with its flexibility.
Since the overall design is close enough to the principles of the
OSI Protocol Model, IP is independent of the Data Link and
Physical network layers.
And some Norwegians indeed showed successful IP network
transmission is possible with carrier pigeons.
(i)
If we would want to attempt to use carrier pigeons to
establish a TCP connection between Canterbury and
London, how long would it take to successfully establish the
transmission under perfect conditions? (Assume the
pigeons are perfectly reliable.) Explain how you come to
your result.
For the experiment, let's assume that the concrete distance
between Canterbury and London is 60miles (or ca. 100km) and our
pigeons fly with a speed of 60 miles per hour (or ca. 100km/h).
(ii)
With current technology and considering the weight a
pigeon can carry, we are able to send 2TB of data on an
USB stick with a pigeon. On a 4G mobile network, we can
likely send about…
arrow_forward
DNS makes use of UDP rather than TCP. If a DNS packet is dropped, there is no way to recover automatically. Is this a problem, and if so, how does one go about resolving it?
arrow_forward
IPv4’s ARP and IPv6’s Neighbor Solicitation both map an address from one space to another. In this respect they are similar. However, there are several differences. In what major ways do they differ?
arrow_forward
A frame containing http request is sent from Computer (A) [in whichever subnet it is now, make sure to show it in your figure], to the access point it is associated with. Draw the address fields (1, 2, and 3) of the frame travelling from Computer A to AP and the source and destination addresses of the frame travelling from AP to R1.
The MAC addresses of AP1, AP2, and AP3 are M1, M2, and M3 respectively, and the Router R1’s MAC address connected to this Switch/AP is MRA. IP address values are already given, and the port addresses could also be used as given. The Router’s MAC address facing WAN side is MRW.
arrow_forward
What are the primary rationales behind the implementation of layered protocols?
arrow_forward
I need The Answer
Pure Aloha in Multiple Access Protocols should be described in three to four lines, without plagiarizing.
arrow_forward
SEE MORE QUESTIONS
Recommended textbooks for you
Principles of Information Security (MindTap Cours...
Computer Science
ISBN:9781337102063
Author:Michael E. Whitman, Herbert J. Mattord
Publisher:Cengage Learning
Systems Architecture
Computer Science
ISBN:9781305080195
Author:Stephen D. Burd
Publisher:Cengage Learning
Related Questions
- Both TCP and UDP are separate protocols that may be contrasted with one another. Give us an example of two circumstances in which you, as a software architect, might choose to make use of TCP rather than UDP.arrow_forwardBoth TCP and UDP are separate protocols that may be contrasted with one another. Give us an example of two situations in which you, as a software architect, might choose to make use of TCP rather than UDP.arrow_forwardTwo considerations drive the use of layered protocols.arrow_forward
- Consider an employee using their computer to send and retrieve email at their workplace. Only Ethernet networks are used for physical connectivity, but the mail server is located on a separate network. The employee’s network and the mail server’s network are connected by a single router which also has a connection to the Internet via the workplace’s ISP. Explain how the employees email client sends and receives emails using the email server, indicating any protocols involved and where any encapsulation/decapsulation occurs as data travels between the client, local mail server, and remote mail servers.arrow_forwardThe use of layered protocols is driven by two different concerns.arrow_forwardComputer Networks - Internet Architecture & Application Layer Please answer the question Someone suggested to use a local file called hosts.txt on each machine instead of DNS. Discuss the advantages (at least 2) and disadvantages (at least 2) of such suggestion. What is ‘saw-tooth’ behavior in TCP, and what is causing it?arrow_forward
- To what extent do each of the following contribute to the benefits of layered protocols? Explain what you mean by providing some examples.arrow_forwardFor NAT Network Address Translation Scenario: Jenny Bello is a small business owner selling and making customized computer peripherals. She has been finding it difficult to track her sales and inventories, however recently after an expert's advice, she adopted a Point of Sale (PoS) server. So, she can now track her sales and inventories at the store. However, she ran into another issue, the server can only be accessed within the store, because it has been assigned a private IPv4 address, it is not publicly accessible via the Internet. a) Why is not having the PoS server accessible over the Internet a problem for the business? b) What caused this problem? c) Propose a solution for the problem and explain how the solution works.arrow_forwardTwo distinct protocols that may be contrasted are TCP and UDP. Give two examples of situations when you, as a software architect, might choose TCP over UDP.arrow_forward
- The tunneling process entails what steps, exactly? Can you name the three protocols used for tunneling?arrow_forwardChose the appropriate terminology which expresses the following concepts: (Flow control, A token-ring Network, RTT, star topology, non-persistent HTTP, persistent HTTP, Network layer, Persistent, Interconnection, bus topology, Transport services, DNS). NO Terminology Description 1 Is a deterministic network, meaning each station connected to the network is assured access for transmission of its messages at regular or fixed time intervals. 2 Multiple objects can be sent over single TCP connection between client, server. 3 Allows users to exchange information (data) with other network members. All LAN data traffic is carried over a common coaxial cable link. Value used for error checking. Response time=2RTT+ file transmission time. 10 5 6arrow_forwardNon-Repudiation and Anonymity ProtocolsFor the Zhou-Gollman non-repudiation protocol discussed in the lecture on “Non-Repudiation and Anonymity Protocols”, which one of the following statements is false:a) At time point 4, both A and B can produce evidence to prove that they received Kb) At time point 2, both A and B can produce evidence to prove that they received a signed message from the other partyc) At time point 0, S cannot prove anythingd) At time point 3, B cannot produce evidence to prove that A has access to key Ke) At time point 1, A can prove that B is alivef) At time point 4, S can prove that A is aliveg) At time point 3, S can produce evidence that that A has access to key Kh) At time point 0, A is not alivei) At time point 2, A can produce evidence to prove that B is alivej) At time point 4, the protocol terminatesExplain your answer below:arrow_forward
arrow_back_ios
SEE MORE QUESTIONS
arrow_forward_ios
Recommended textbooks for you
- Principles of Information Security (MindTap Cours...Computer ScienceISBN:9781337102063Author:Michael E. Whitman, Herbert J. MattordPublisher:Cengage LearningSystems ArchitectureComputer ScienceISBN:9781305080195Author:Stephen D. BurdPublisher:Cengage Learning
Principles of Information Security (MindTap Cours...
Computer Science
ISBN:9781337102063
Author:Michael E. Whitman, Herbert J. Mattord
Publisher:Cengage Learning
Systems Architecture
Computer Science
ISBN:9781305080195
Author:Stephen D. Burd
Publisher:Cengage Learning