# Questions tagged [computer-networks]

Questions about problems that arise when you connect multiple computers to form a network.

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### Exercise: Sliding window protocol: Bits for sequence number

This is a task in a lecture on computer networks: "Suppose you are designing a sliding window protocol for a 1-Mbps point-to-point link to the moon, which has a one-way latency of 1.25 seconds. ...
2k views

### Finding the optimal packet size

I have recently started reading the book Computer Networking: A Top-down Approach in hopes to get introduced to computer networks. When attempting one of the questions from the book for practice, I ...
1 vote
227 views

### How does non-DMA transfers really work?

I recently discussed DMA and non-DMA with my OS professor. Here is my current understanding: disk controller has its own CPU, maybe own ISA, tiny program that simply handles reading from the disk (...
1 vote
154 views

### Two Generals' Problem - Thought Experiment

After reading the Two Generals' Problem, I am wondering as to why there isn't any solution and please correct me if I am missing something. What if, the generals decide that they will attack if they ...
1 vote
2k views

### Small doubt in vulnerable time of CSMA/CD and pure aloha

I understand that vulnerable time is the time when collision is possible. In CSMA/CD, the vulnerable time is Tp because it takes Tp time for bit to travel from source to destination and collision ...
205 views

### 'Half-Close' figure of Data Communications and Networking, 5/e

In the Figure 24.13 of Data Communications and Networking, 5/e the first ACK message from the server holds y-1 in it's Sequence no. field. Note that the first FIN ...
50 views

### RPI cluster performance related to network performance

I'm writing my thesis and i have built a RPI cluster, containing 10 nodes which consists of RPI model 3b. I've them connected to two gigabit switches. I don't know the CAT of the cables. They are not ...
354 views

### Finding maximal and average number of time slots in an Adaptive tree walk protocol

Tried to research here and on other sites with no luck regarding finding the maximal and average number of time slots in an Adaptive tree walk protocol. i'll explain what i mean here: In a simple(...
1 vote
513 views

### Wifi throughput calculation

I have a problem which i don't know how to calculate or more specifically what am I missing. The subject is about 802.11 (wifi) The selected PHY rate is 54Mbit/s, that is whenever DATA is being sent ...
1 vote
7k views

### Calculating the end-to-end delay of a message sent over a network

This is a problem from a MOOC on computer networking: We wish to send a message of size $150,000$ bytes over the network. There are four hops, each of length $20$ km and running at $100$ Mb/s. ...
1 vote
15 views

### what kind of resources do microservices use when they communicate each other within a same machine?

Assume microservices are in the same machine and they exchange their data via RESTapi calls, what kind of resources (ex:CPU,memory) do microservices use when they communicate each other within a same ...
10 views

### Why is the bandwidth of the pre-established reserved link divided on multiple new connections?

I am reading Kurose Computer Networking book 8e, on page number 57, under 1.3.2 Circuit Switching Because it link has $4$ circuits, for each link used by the end-to-end connection, the connection ...
136 views

### Window slider difference between GoBackN vs Selective Repeat

I am trying to learn about GoBackN and Selective Repeat ARQ. And I have the following practice question: Consider sender A and receiver B which communicate using an ARQ protocol. The current window ...
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### Understanding the differences between link and channel

While reading computer networking, I am confused between link and channel and seen people using this interchangeably (which often bugs me). Language written in books and forums A link refers to the ...
624 views

### Introductory books on Computer Networks

While I have come to learn some computer science, I find that I have next to no knowledge on computer networks. Are there any good books at a basic level that cover some of the fundamental topics? ...
2k views

### Difference between DNS Spoofing and DNS Hijacking?

DNS Spoofing and DNS Hijacking, both of them basically are type of attacks where the request is redirected to some other malicious website or some other web page. But I did not find some concrete ...
1 vote
3k views

### Go-Back-N ARQ Protocol Throughput Question

I am an undergraduate studying Data Coms and Networking and this question about go-back-N ARQ popped up that I am struggling to get my head around and cant find anything similar online. Any help at ...
13 views

### Networking - RDT 2.0 - How can this FSM transition occur?

I attempted this question and I do not understand why the last option is necessary in order to get the right answer. My logic/thought-process: In this question, only two scenarios can occur: Scenario ...
1 vote
464 views

### Tearing down the FSM description of congestion control

I was going through the text Computer Networking- A Top-Down Approach by Kurose and Ross, there I found subtleties with the TCP congestion control FSM which is shown below: Mainly I am having ...
58 views

### Computer Networking - Basic Circuit Switching - Calculate Max Number of Connections

I don't understand how to solve this problem. I understand the concept of bottleneck links but I can't seem to solve this specific question type. For Question 3, I know the answer is 31 and that is ...
939 views

### Two Generals Problems - What's wrong with my approach?

Some time ago, I've come across the Two Generals Problem and that it cannot be resolved. Now, recently, I've had an idea how to approach it. IMHO, it is a very obvious way to handle it but I haven't ...
25 views

### How does waiting 7ms and atomic clock help GCP spanner create external consistency?

My understanding why distributed transaction need synchronized clock is the following Assume NTP max drift is 250ms ...
5k views

### Why is TCP known as reliable protocol?

Is it because it uses 3 way handshaking, it is reliable? Or is it due to other reasons? Like due to congestion control, flow control and error control in TCP? Why do we call TCP as reliable?
1 vote
1k views

### Bit times and propagation delay

Nodes A and B are accessing a shared medium using CSMA/CD, with a propagation delay of 245-bit times between them (i.e., propagation delay equals the amount of time to transmit 245 bits). The minimum ...
75 views

### How do you tell whether a binary number is positive or negative?

Consider the figure in Exercise 2. If the current machine code that executes is 0x214bfffd and the values of the registers in the processor are as shown below, what is then the value of the input WD3 ?...
1 vote
237 views

### Do all computers use parity checking? When does it happen?

I know that parity checking is testing for accurate data transmission between nodes in a communication network. When does this parity checking happen on a computer? Does it happen every time data is ...
10k views

### Clock synchronization in a network with asymmetric delays

Assume a computer has a precise clock which is not initialized. That is, the time on the computer's clock is the real time plus some constant offset. The computer has a network connection and we want ...
22 views

### Do I need to consider the header size to calculate the original datagram?

The following question is related to finding the size of the original datagram. The formula for original datagram size is: Data length of first packet + (Total length of subsequent packets * no. of ...
15k views

### What is the difference between transmission delay, queuing delay, and processing delay?

My book defines queuing delay as the time the packet waits to be transmitted onto the link. It defines transmission delay as the amount of time required to push all of the packet's bits onto the link. ...
33 views

### Would the computers be able to communicate if all of them had same name hardcoded in their OS? Why not?

The name of a computer should never be bound into an operating system at compile time. Explain why. I don't see a reason why this should not be allowed? Say we have couple of computers all with the ...
13k views

### Link utilization of sliding window protocol

Before I ask my doubt I would like to state that problem which led me to my doubt. It can also serve as a good example scenario. A $20\ Kbps$ satellite link has a propagation delay of $400\ ms$. ...
2k views

### How is this example sequentially consistent but not linearizable?

Background information that I know(But not understand with examples, I will be glad if you could explain it to me with examples) A replicated service is said to be linearizable if for any executin ...
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### A mathematical question on error detection

For a bit of context, I was going through the previous year questions of my college computer networks course and found this in one of the papers. I don't even know how to go about solving this problem,...
45 views

### What is practical implication of Bandwidth delay product?

It's given that the bandwidth-delay product defines the number of bits that can fill the link; while the sender can send (1+(2 * Bandwidth * Delay)) units before getting acknowledged for the first ...
32 views

### Question on vulnerable time of pure aloha, and why it does include propagation time

I have read that pure Aloha's vulnerable time is 2*transmission time. But shouldn't it also include propagation time? What if a frame is propagating in media and gets collided with another frame (...
1 vote
1k views

### What is the actual formula for the efficiency in CSMA/CD?

Let there are $n$ devices in the setup. Let each device sends data with a probability $p$. Successful transmission for a slot (hence of the setup in general) occurs when only one device communicates. ...
1 vote
100 views

### Throughput and response time

I have read that a decrease in response time does not necessarily entail an increase in throughput, but I'm struggling to understand the exact way that this can happen. What I'm imagining is a server ...
1 vote
27 views

### Current research in TCP congestion control?

Question: What are the current main challenges in TCP congestion control algorithms? Are there any foundational trade offs that algorithms need to make? E.g. minimizing router buffer sizes while ...
1 vote
106 views

### How does OSI model and TCP/IP work?

If I go into google browser and type in the name of a website, this is the application layer of the OSI. HTTP protocol is being used and is a request-response, so when exactly does my computer send ...
107 views

### Minimum spanning tree with dynamic edge cost based on degrees

I have a problem that I'm struggling to solve or even name, I'd really appreciate any help or pointer to potential existing solutions. Suppose there is a connected graph $G$ and we are trying to find ...
1 vote
55 views

### distribution choice for network latency

Consider this situation. A few clients are connected to a server over the internet. I define network latency as the time between request leaving the client and reaching the server. What distributions (...
19 views

### k-compact vectored I/O

I have a practical programming problem that I am struggling to find an optimal algorithm for, in part because I don't know what to call it. The problem concerns vectored I/O (scatter/gather). Consider ...
175 views

### Is it possible to transmit bits digitally?

I have learnt that all data transmission is analog. Is there any mediums that could transmit bits digitally?
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### How to understand CSMA/CD algorithm from this graph?

I am currently studying Computer Network, and I have some problems when encountered CSMA/CD, I can understand how it works, but I am struggling in understanding this graph, anyone can give me some ...
156 views

In S/Kademlia two crypto puzzles is used, one static and dynamic. The static is used to generate a key pair that makes an eclipse attack difficult to achieve, the dynamic to make Sybil attacks harder. ...
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### Find connected components in a graph of computer network with parallel pairwise tests

I have N nodes, a node might have an undirected edge to other nodes, resulting in K connected components (K<=N, K unknown). I can test if a given pair is connected. In each step in time, I can run ...
11k views

### What happens when an internet connection is faster than the storage write speed?

If one attempted to download a file at a speed of 800 Mb/s (100 MB/s) onto a hard drive with a write speed of 500 Mb/s (62.5 MB/s), what would happen? Would the system cap the download speed?
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### How to resolv this NAT problem?

I am taking my first network class and I came across a question I just cant wrap my head around. We have an external machine that has a public IP address from using NAT, the external machine want to ...