Questions tagged [congestion]

For questions about network congestion, where a network node or link is carrying more data than it can handle. For instance, you are troubleshooting or trying to find a bottleneck in your network topology.

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What stategy use TCP Cubic in Fast Recovery?

I want to do some simulations with different TCP algorithms I was reading one of the earliest papers for TCP CUBIC and I don't see explicitly the strategy of Fast Recovery after a loss of the packet. ...
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2 answers
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Differences between TCP congestion and TCP flow control

From my understanding, flow control essentially how much the receiver can process. Suppose I can send packets at 100mb/s but the receiver can only process information at 10mb/s, flow control would ...
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"Expected" packet loss under heavy network load in TCP cubic

context We have two machines that receive a lot of data, and mirror each other's content with rsync. When monitoring these boxes via ICMP echo requests (using the mtr tool), we see up to a couple % of ...
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Why does TCP sender drop rate 50% on lost-packets?

Why is the standard TCP sender response to packet-loss (congestion), to drop 50% of the sending rate and then start working back up ? If packet-loss was 20%, why not just drop 20% or maybe 25% to be ...
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1 answer
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In what situation would normal choke packet be preferred over hop-by-hop choke packets?

When the host is far away, it makes sense to use hop-by-hop choke packets to resolve congestion. But is there situations where normal choke packet is more appropriate? And by the 'source' we mean a ...
1 vote
2 answers
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How is congestion avoided when using UDP?

I understand how TCP goes about this - through various methods such as Congestion Window (CWND), Sliding Window, Slow Start and Fast Recovery - it's basically built into the protocol. I understand ...
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0 answers
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why is the length same with the MSS value? [duplicate]

I have read this I have issue with MSS and window size and what is difference between MSS and Window Size? I'm confused. I have a setup like this: my host machine (Macbook) and a virtual machine (...
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1 answer
64 views

Why does congestion happen

Imagine a network full of routers . The job of a router is to be able to receive multiple packets from multiple sources then send the packets 1 at a time in each of its outputs.If the routers are able ...
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2 answers
140 views

Does window size in tcp header include tcp header size?

Let's say a TCP segments has in the field of "window size" = 1400 bytes. Does that mean that we can send 1400 bytes counted in tcp segments = TCP headers + data or it does specify only ...
-1 votes
1 answer
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Latency between a churn and congestion event triggered in the TCP code

I am analyzing the time it takes between a churn occurring in the network (e.x. that causes packet drops or delays) and when the congestion event handling codes are triggered in the TCP kernel in the ...
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-1 votes
1 answer
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Why sender window or congestion window size becomes 2^n mss after nRTT in slow start mechanism?

I seen everywhere in slow start mechanism if initial sender size denoted by cwnd= 1mss , then after 1 RTT cwnd becomes = 2 mss, and after 2 RTT cwnd becomes = 4 mss and so on. My question is why ...
2 votes
2 answers
210 views

Congestion control behaviour of TCP Reno

Which behaviour of TCP Reno after 3 DUP ACK is correct: The one described in the Italian Wikipedia (https://it.wikipedia.org/wiki/Controllo_della_congestione_in_TCP#TCP_Reno). It says the new cwnd is:...
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Why large queueing delays are experienced as a packet arrival rate nears the link's capacity? [duplicate]

From the book "Computer Networks A top Down Approach": It says if hosts A and B both are sending at rate R/2 and router's outgoing link has a capacity of R. There will be delays experienced ...
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Does UDP's lack of congestion control clog up the Internet?

I'm reading Computer Networking: A Top-Down Approach, and from what I understand, UDP has no widely adopted mechanism for congestion control like TCP does. Isn't this a problem for the Internet as a ...
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Difficulty in understanding the concept of "artificial inflate" and "deflate" in the fast recovery phase of TCP

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 ...
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1 answer
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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 ...
1 vote
1 answer
35 views

tcp how the receiver behaves if it received an incomplete window

Suppose, for example, that the window has a size of 5 MSS, the sender sends 5 segments to the network, the fifth is lost. Actually the question: how does the recipient behave? It just doesn't ...
-1 votes
1 answer
31 views

Would a bidirectional exchange of data between two hosts, one using TCP Reno and the other using TCP Tahoe, be possible?

I know Reno and Tahoe are TCP congestion control algorithms and one recovers much faster than the other when a packet is lost, but would they affect how data are exchanged between the hosts? ...
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2 answers
131 views

Congestion control in transport and network layers in TCP/IP

Why do we need congestion control in BOTH the transport layer and network layer in TCP/IP model. Cant we be good enough with control in just one of the layers only? And how do they differ?
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2 votes
1 answer
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TCP Congestion Control, Sender window = minimum ( Congestion window, Receiver window)

When can the congestion window size be greater than the receiver window size? An example of a scenario will be helpful. I know that the congestion window is used by the sender to gauge the network ...
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1 answer
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Does higher retransmission time imply lesser chances of congestion?

I believe that with higher retransmission time value, the frequency at which retransmissions occur will reduce. And with less frequent retransmissions, the traffic will decrease. So with that logic, I ...
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1 vote
1 answer
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TCP flow control active waiting

To perform flow control between a sender and a receiver during a TCP connection, the receiver includes in each packet to the sender, the size of available space ‘rwnd’ in its receiving buffer. This is ...
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1 answer
90 views

Effect of block size on network congestion?

I am interested in comparing TCP/IP network congestion under two scenarios: Scenario 1: A large number of senders send messages to a group of receivers Scenario 2: Same as above except that the ...
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Reason for congestion in CSMA based networks

A typical channel with SNR 10dB and BW 10 MHz will have a channel capacity of something around 150 Mbps. In CSMA, at any given time, only 1 user is allowed to transmit and in 802.11p, the default ...
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1 answer
2k views

TCP cwnd is increasing when congestion occur

I am a newbie network engineer. I did a small experiment with iperf3. But I run into a small problem. (1) My question. I think TCP flow do not act properly despite of its congestion control. The flow ...
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Response time of TCP congestion control

I would like to know about the overall latency of the TCP congestion control for adapting to varying network conditions. Specifically, my questions are: How fast can the system react after a change ...
1 vote
1 answer
350 views

Routers and output buffers: Why can two devices interfere with each other and cause latency?

I apologize if this question has been asked already because I couldn't find anything related. I'm a beginner in networking and am reading through Computer Networking: A Top-Down Approach, as well as ...
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1 answer
103 views

What does the speed of Network Switch actually mean?

Network switches usually come in speeds of 10/100/1000 Mbps, and that's all fine and dandy, then I got thinking.. Suppose I have an 8 port 1000 Mbps switch, each port connected to a client. If a ...
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1 answer
249 views

Initial TCP congestion window sizes

I have tried to look for this information on Google, but I haven't been able to find a good source for this information. So, I am interested in what are the initial TCP congestion windows on ...
1 vote
0 answers
306 views

Simple Token Bucket - Policing - Terms - CIR, CBS

I have gone through token bucket algorithm. However, I am struggling to apply this knowledge into the real devices like CISCO, etc. So, for QoS policing, interface meter. I am trying to understand ...
5 votes
2 answers
1k views

QoS shaper, shapes traffic without dropping packets?

I have a problem with my QoS policy, or I should better say, I have a problem understanding how my policy manages to achieve what ask of it without dropping a packet! Here is the scenario: We have ...
3 votes
1 answer
2k views

Relationship between TCP window size and TCP congestion control

Am I correct that TCP receive window(which is a send window for the sender) has nothing to do with TCP CUBIC congestion control? TCP receive window is solely a property of TCP flow control?
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2 votes
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What is congestion collapse?

My understanding is that it involves multiple copies of the same packet existing in the network. But how does that situation end up happening? And why is it so harmful?
2 votes
2 answers
440 views

AIMD: Total number of packets sent

While answering to the quizz 4-3 of the great Introduction to Computer Networking (Stanford Lagunita), I found myself unable to explain the answer of one of the questions: Consider a long flow being ...
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1 answer
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Calculating average size of congestion window

In the computer networking book (James F. Kurose, Keith W. Ross), it is written that we need 83,333 in-flight segments(window size) in order to reach 10 Gbps throughput. (We have 1500 byte segments &...
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388 views

BGP: Route congestion

Using a BGP Multihoming design, is it possible redirect or modify any metric to determinate destination? Example: I detected that the most of users are having problem to access a webserver: high ...
1 vote
1 answer
88 views

congestion control

Suppose , a sender sends a packet and it does not receive an acknowledgement . The timer at the sender side runs out . In which cases the sender resends the packets and in which cases it does not ? ...
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2 answers
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When should TCP send a cumulative acknowledgement?

I am simulating TCP and I don't know when it should send the Acknowledgment. For example as soon as a segment dropped should we send the Acknowledgment or should we take some time, maybe the segment ...
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2 answers
1k views

Ethernet Flow Control vs Quality of Service

What are the trade-offs/major differences of Ethernet Flow Control vs Quality of Service? How to know when to choose one over the other? They seem to both be a solution for congestion. The obvious ...
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2 votes
1 answer
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Congestion control,flow control, MTU and MSS, Rwnd-Cwnd and slow-start

OK, so basically I'm getting confused with all the terms, and if some are related to others or not. I'll explain myself: From what I understand, flow control depends on the receiver side buffer ...
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1 vote
1 answer
468 views

Can tcp throughput be equal to bandwidth?

I have a conceptual question which I cannot understand. Can the TCP throughput be equal to the bandwidth and why? The throughput from what I have learned so far is (3/4)*congwing/RTT. Is is fair to ...
1 vote
2 answers
653 views

If, and why torrent traffic is creating greater congestion on a link, than regular traffic of the same size?

For simplicity let's assume that we have very simple LAN. There is some router with uplink to the internet. To this router there is connected some basic 24 ports switch, and from that switch there are ...
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How to choose the right congestion control algorithm

In my simulation platform, I noticed three new parameters to me: Hierarchical Token Bucket (TBF scheduling). Explicit Congestion Notification (ECN) Random Early Detection (RED) When I googled them, ...
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2 answers
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The difference between simple ACK and ACK aggregation improvement in TCP

I came across a new term in TCP ACK aggregation which is a bit new to me. I tried finding a good resource online that precisely explains this concept in a clear but unfortunately all of them are very ...
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1 answer
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LSA Weighted Fair Queuing Algorithm

In weighted round robin (weighted fair queuing) scheduling, suppose I have 3 queues (weights):- A (4), B (3) and C (2). I have packets of equal lengths on the 3 queues. Now will the packet output ...
2 votes
1 answer
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If we have Fast Retransmit does it mean we have Fast Recovery?

My question is, in which cases is the Fast Recovery activarted ? Like we have done a Fast Retransmit does it mean that Fast Recovery must be used as well ? For example, we lose a segment and send it ...
2 votes
1 answer
142 views

WiFi signal drops and difficulty connecting... too many clients?

I am a volunteer network engineer working in a building housing refugees in Greece. It's an old school and is extremely densely populated (multiple families in each classroom). Many people have phones ...
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Why only after 3-duplicate ACK retransmission takes place in TCP?

Is there any reason of choosing "3" only for retransmission. why not 2 or 4 or any other number?
2 votes
1 answer
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TCP Traceroute with actual TCP session [closed]

Has anyone ever found a tool that performs a TCP traceroute with an actual established TCP session? I can launch a server/client on each end, if required. tcptraceroute & mtr aren't candidates ...
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Tuning TCP Reno parameters to reduce delay experienced by short flows of size 20KB ?

I am trying to tune TCP reno parameters in order to reproduce fig 21 here. The author uses TCP New Reno as congestion control algorithm. I am tuning the parameters as : rto_min = 10ms Set sender ...
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