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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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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61 views

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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Difficulty in understanding the action “transmit new segment(s), as allowed” in TCP 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 ...
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67 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 ...
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29 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 ...
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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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83 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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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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21 views

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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83 views

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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75 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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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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124 views

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 ...
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184 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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67 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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160 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 ...
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251 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 ...
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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 ...
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1k 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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2k views

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?
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399 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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3k views

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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338 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 ...
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80 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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2k views

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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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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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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413 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 ...
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525 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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281 views

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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986 views

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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47 views

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 ...
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2k views

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 ...
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1answer
117 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?
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1answer
474 views

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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1answer
189 views

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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207 views

What is the maximum value that a receiver can set in its advertising window

I know an advertising window is set by the receiver to inform the sender not to send more than what is advertised in the receiver's window to avoid packet loss due to overflow of packets at receiver(...
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153 views

Why does throughput (consumed BW) increase when the packet error rate is increased in the TCP?

I was simulating TCP used by dailymotion.com, and I noticed that when I increased packet error rate, the consumed BW was increased. How?
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1answer
2k views

Using StreamSocket() mrthod of Scapy to send ECN enabled TCP packets

I am trying to understand how ECN flag affects TCP congestion window of sender (snd_cwnd parameter in linux). To do so, I used scapy to generate the desired packet on HostA directed to HostB as sr(...
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684 views

How can a TCP Flow with smaller congestion window have higher throughput?

It might be a stupid question, but as far as I understood the CNWD dictates the rate of a TCP flow. I created a "load-balancer" that split single packets on two paths of 10Mb/s. This introduces some ...
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1answer
384 views

Latency in P2P Circuit

I have one P2P Circuit from our HQ to a secondary office. the distance between them is approx 2kms. Earlier when the Circuit was delivered at that time we were having an RTT of 3-4ms. It is a 10Mbps ...
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804 views

In TCP Congestion Avoidance Phase, are cwnd and CongWin the same thing?

I'm trying to understand TCP Congestion Avoidance Phase. According to pages 82-83 of the slide below, cwnd equals CongWin. According to pages 84-85, they are different. The writer did not bother to ...
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why token bucket algorithm is better than leak bucket algorithm? [closed]

I am trying to clear up concept here. This is regarding shaper using Token bucket algorithm. Let’s assume that the bucket depth is 1500 bytes. And assume that the data rate is 2Bps (very slow one). ...
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4k views

How exactly does TCP react to a retransmission timeout?

Hi! Could someone explain to me what happens at the time-out? Then the window size completely drops. I thought that at time-out the same thing as in 3 duplicate ACKs would happen; half the cwnd and go ...
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141 views

How do I configure bandwidth throttling for all HTTP? [closed]

I configured bandwidth throttling for HTTP and ftp FTP using following commands: sudo /sbin/tc qdisc add dev eth0 root handle 1:0 htb default 1 sudo /sbin/tc class add dev eth0 parent 1:0 classid 1:1 ...
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6k views

What is a token in token bucket?

I believe, tokens are nothing but packets, but my question is, weather these tokens are fixed size? If yes, why fixed packets? Can anyone explain the algorithm clearly with examples. Thanks.
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186 views

Small office networking via powerline [closed]

We're moving to a new office that has no cables installed and we're wondering if using a powerline solution would be adequate. It's a small office with 5 users, 1 server, and some additional devices (...