The document discusses TCP congestion control algorithms. It describes the Additive Increase Multiplicative Decrease (AIMD) approach where the congestion window (cwnd) is increased linearly but reduced by half when packet loss is detected. Slow start is used to quickly ramp up cwnd initially through exponential growth. Fast retransmit detects lost packets using duplicate ACKs to retransmit earlier. Fast recovery then resumes increasing cwnd after a retransmit. The document also examines algorithms for adaptive retransmission timeouts based on mean and variance of measured round-trip times.
Transmission Control Protocol (TCP) is a fundamental protocol of the Internet Protocol Suite. TCP complements the Internet Protocol (IP), therefore it is common to refer to the internet protocol suit as TCP/IP. TCP is used for error detection, detection of packet loss or out of order delivery of data. TCP requests retransmission, rearranges data and helps with network congestion.
Several congestion control algorithms have been developed, over the last years, to improve TCP's performance over various technologies and network conditions.
The purpose of this assignment is to present TCP, network congestion, congestion algorithms and simulate different algorithms in different network conditions to measure their performance. For this assignment's needs, OPNET IT Guru Academic Edition software was used to accomplish the reproduction of projects that have been already published and gave the wanted results.
Computer networks have experienced an explosive growth over the past few years and with
that growth have come severe congestion problems. For example, it is now common to see
internet gateways drop 10% of the incoming packets because of local buffer overflows.
Our investigation of some of these problems has shown that much of the cause lies in
transport protocol implementations (
not
in the protocols themselves): The ‘obvious’ ways
to implement a window-based transport protocol can result in exactly the wrong behavior
in response to network congestion. We give examples of ‘wrong’ behavior and describe
some simple algorithms that can be used to make right things happen. The algorithms are
rooted in the idea of achieving network stability by forcing the transport connection to obey
a ‘packet conservation’ principle. We show how the algorithms derive from this principle
and what effect they have on traffic over congested networks.
In October of ’86, the Internet had the first of what became a series of ‘congestion col-
lapses’. During this period, the data throughput from LBL to UC Berkeley (sites separated
by 400 yards and two IMP hops) dropped from 32 Kbps to 40 bps. We were fascinated by
this sudden factor-of-thousand drop in bandwidth and embarked on an investigation of why
things had gotten so bad. In particular, we wondered if the 4.3
BSD
(Berkeley U
NIX
)
TCP
was mis-behaving or if it could be tuned to work better under abysmal network conditions.
The answer to both of these questions was “yes”.
Transmission Control Protocol (TCP) is a fundamental protocol of the Internet Protocol Suite. TCP complements the Internet Protocol (IP), therefore it is common to refer to the internet protocol suit as TCP/IP. TCP is used for error detection, detection of packet loss or out of order delivery of data. TCP requests retransmission, rearranges data and helps with network congestion.
Several congestion control algorithms have been developed, over the last years, to improve TCP's performance over various technologies and network conditions.
The purpose of this assignment is to present TCP, network congestion, congestion algorithms and simulate different algorithms in different network conditions to measure their performance. For this assignment's needs, OPNET IT Guru Academic Edition software was used to accomplish the reproduction of projects that have been already published and gave the wanted results.
Computer networks have experienced an explosive growth over the past few years and with
that growth have come severe congestion problems. For example, it is now common to see
internet gateways drop 10% of the incoming packets because of local buffer overflows.
Our investigation of some of these problems has shown that much of the cause lies in
transport protocol implementations (
not
in the protocols themselves): The ‘obvious’ ways
to implement a window-based transport protocol can result in exactly the wrong behavior
in response to network congestion. We give examples of ‘wrong’ behavior and describe
some simple algorithms that can be used to make right things happen. The algorithms are
rooted in the idea of achieving network stability by forcing the transport connection to obey
a ‘packet conservation’ principle. We show how the algorithms derive from this principle
and what effect they have on traffic over congested networks.
In October of ’86, the Internet had the first of what became a series of ‘congestion col-
lapses’. During this period, the data throughput from LBL to UC Berkeley (sites separated
by 400 yards and two IMP hops) dropped from 32 Kbps to 40 bps. We were fascinated by
this sudden factor-of-thousand drop in bandwidth and embarked on an investigation of why
things had gotten so bad. In particular, we wondered if the 4.3
BSD
(Berkeley U
NIX
)
TCP
was mis-behaving or if it could be tuned to work better under abysmal network conditions.
The answer to both of these questions was “yes”.
XPDS13: On Paravirualizing TCP - Congestion Control on Xen VMs - Luwei Cheng,...The Linux Foundation
While datacenters are increasingly adopting VMs to provide elastic cloud services, they still rely on traditional TCP for congestion control. In this talk, I will first show that VM scheduling delays can heavily contaminate RTTs sensed by VM senders, preventing TCP from correctly learning the physical network condition. Focusing on the incast problem, which is commonly seen in large-scale distributed data processing such as MapReduce and web search, I find that the solutions that have been developed for *physical* clusters fall short in a Xen *virtual* cluster. Second, I will provide a concrete understanding of the problem, and reveal that the situations that when the sending VM is preempted versus when the receiving VM is preempted, are different. Third, I will introduce my recent attempts on paravirtualizing TCP to overcome the negative effect caused by VM scheduling delays.
- Áp dụng biểu thức Shannon-Hartley để tính toán kênh
truyền (BT: 1.1- 1.6).
- Biểu diễn các dạng hàm xung tín hiệu cơ bản (BT: 1.7-
1.11).
- Phân biệt truyền thông số nhị phân và truyền thông số đa
mức
Connection Establishment & Flow and Congestion ControlAdeel Rasheed
On these slides i describe all the detail about Connection Establishment & Flow and Congestion Control. For more detail visit: https://chauhantricks.blogspot.com/
XPDS13: On Paravirualizing TCP - Congestion Control on Xen VMs - Luwei Cheng,...The Linux Foundation
While datacenters are increasingly adopting VMs to provide elastic cloud services, they still rely on traditional TCP for congestion control. In this talk, I will first show that VM scheduling delays can heavily contaminate RTTs sensed by VM senders, preventing TCP from correctly learning the physical network condition. Focusing on the incast problem, which is commonly seen in large-scale distributed data processing such as MapReduce and web search, I find that the solutions that have been developed for *physical* clusters fall short in a Xen *virtual* cluster. Second, I will provide a concrete understanding of the problem, and reveal that the situations that when the sending VM is preempted versus when the receiving VM is preempted, are different. Third, I will introduce my recent attempts on paravirtualizing TCP to overcome the negative effect caused by VM scheduling delays.
- Áp dụng biểu thức Shannon-Hartley để tính toán kênh
truyền (BT: 1.1- 1.6).
- Biểu diễn các dạng hàm xung tín hiệu cơ bản (BT: 1.7-
1.11).
- Phân biệt truyền thông số nhị phân và truyền thông số đa
mức
Connection Establishment & Flow and Congestion ControlAdeel Rasheed
On these slides i describe all the detail about Connection Establishment & Flow and Congestion Control. For more detail visit: https://chauhantricks.blogspot.com/
Transport layer is responsible for the overall end-to-end transfer of application data.
Because different applications have different requirements, there are multiple Transport layer protocols.
Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).
TCP and UDP headers.
Port Addressing, socket pair.
Types of port numbers: Well Known Ports (0 to 1023), Registered Ports (1024 to 49151) and Dynamic or Private ‘Ephemeral’ Ports (49152 to 65535).
Netstat command : examines the open connections on a host.
Transport Layer Functions.
TCP Connection Establishment (3-way handshake).
Connection Management - Flow Control through buffering, congestion avoidance, and windowing.
Flow Control – Reducing the window size .
TCP Connection Termination (4-way Handshake).
Abstract - The Transmission Control Protocol (TCP) is
connection oriented, reliable and end-to-end protocol that support
flow and congestion control, with the evolution and rapid growth
of the internet and emergence of internet of things IoT, flow and
congestion have clear impact in the network performance. In this
paper we study congestion control mechanisms Tahoe, Reno,
Newreno, SACK and Vegas, which are introduced to control
network utilization and increase throughput, in the performance
evaluation we evaluate the performance metrics such as
throughput, packets loss, delivery and reveals impact of the cwnd.
Showing that SACK had done better performance in terms of
numbers of packets sent, throughput and delivery ratio than
Newreno, Vegas shows the best performance of all of them.
ER(Entity Relationship) Diagram for online shopping - TAEHimani415946
https://bit.ly/3KACoyV
The ER diagram for the project is the foundation for the building of the database of the project. The properties, datatypes, and attributes are defined by the ER diagram.
1.Wireless Communication System_Wireless communication is a broad term that i...JeyaPerumal1
Wireless communication involves the transmission of information over a distance without the help of wires, cables or any other forms of electrical conductors.
Wireless communication is a broad term that incorporates all procedures and forms of connecting and communicating between two or more devices using a wireless signal through wireless communication technologies and devices.
Features of Wireless Communication
The evolution of wireless technology has brought many advancements with its effective features.
The transmitted distance can be anywhere between a few meters (for example, a television's remote control) and thousands of kilometers (for example, radio communication).
Wireless communication can be used for cellular telephony, wireless access to the internet, wireless home networking, and so on.
Multi-cluster Kubernetes Networking- Patterns, Projects and GuidelinesSanjeev Rampal
Talk presented at Kubernetes Community Day, New York, May 2024.
Technical summary of Multi-Cluster Kubernetes Networking architectures with focus on 4 key topics.
1) Key patterns for Multi-cluster architectures
2) Architectural comparison of several OSS/ CNCF projects to address these patterns
3) Evolution trends for the APIs of these projects
4) Some design recommendations & guidelines for adopting/ deploying these solutions.
This 7-second Brain Wave Ritual Attracts Money To You.!nirahealhty
Discover the power of a simple 7-second brain wave ritual that can attract wealth and abundance into your life. By tapping into specific brain frequencies, this technique helps you manifest financial success effortlessly. Ready to transform your financial future? Try this powerful ritual and start attracting money today!
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Tcp congestion control (1)
1. Computer Networks: TCP 1
TCPTCP
Congestion ControlCongestion Control
Lecture material taken from
“Computer Networks A Systems Approach”,
Third Ed.,Peterson and Davie,
Morgan Kaufmann, 2003.
2. Computer Networks: TCP 2
TCP Congestion ControlTCP Congestion Control
• Essential strategy :: The TCP host sends
packets into the network without a reservation
and then the host reacts to observable events.
• Originally TCP assumed FIFO queuing.
• Basic idea :: each source determines how
much capacity is available to a given flow in the
network.
• ACKs are used to ‘pace’ the transmission of
packets such that TCP is “self-clocking”.
3. Computer Networks: TCP 3
AIMDAIMD
(Additive Increase / Multiplicative(Additive Increase / Multiplicative
Decrease)Decrease)
• CongestionWindow (cwnd) is a variable held by
the TCP source for each connection.
• cwnd is set based on the perceived level of
congestion. The Host receives implicit (packet
drop) or explicit (packet mark) indications of
internal congestion.
MaxWindow :: min (CongestionWindow , AdvertisedWindow)
EffectiveWindow = MaxWindow – (LastByteSent -LastByteAcked)
4. Computer Networks: TCP 4
Additive IncreaseAdditive Increase
• Additive Increase is a reaction to perceived
available capacity.
• Linear Increase basic idea:: For each “cwnd’s
worth” of packets sent, increase cwnd by 1
packet.
• In practice, cwnd is incremented fractionally for
each arriving ACK.
increment = MSS x (MSS /cwnd)
cwnd = cwnd + increment
5. Computer Networks: TCP 5
Figure 6.8 Additive IncreaseFigure 6.8 Additive Increase
Source Destination
Add one packet
each RTT
6. Computer Networks: TCP 6
Multiplicative DecreaseMultiplicative Decrease
* The key assumption is that a dropped packet and the
resultant timeout are due to congestion at a router or
a switch.
Multiplicate Decrease:: TCP reacts to a timeout by
halving cwnd.
• Although cwnd is defined in bytes, the literature often
discusses congestion control in terms of packets (or
more formally in MSS == Maximum Segment Size).
• cwnd is not allowed below the size of a single packet.
7. Computer Networks: TCP 7
AIMDAIMD
(Additive Increase / Multiplicative(Additive Increase / Multiplicative
Decrease)Decrease)
• It has been shown that AIMD is a necessary
condition for TCP congestion control to be stable.
• Because the simple CC mechanism involves
timeouts that cause retransmissions, it is important
that hosts have an accurate timeout mechanism.
• Timeouts set as a function of average RTT and
standard deviation of RTT.
• However, TCP hosts only sample round-trip time
once per RTT using coarse-grained clock.
9. Computer Networks: TCP 9
Slow StartSlow Start
• Linear additive increase takes too long to
ramp up a new TCP connection from cold
start.
• Beginning with TCP Tahoe, the slow start
mechanism was added to provide an initial
exponential increase in the size of cwnd.
Remember mechanism by: slow start
prevents a slow start. Moreover, slow start
is slower than sending a full advertised
window’s worth of packets all at once.
10. Computer Networks: TCP 10
SloSloww StartStart
• The source starts with cwnd = 1.
• Every time an ACK arrives, cwnd is
incremented.
cwnd is effectively doubled per RTT “epoch”.
• Two slow start situations:
At the very beginning of a connection {cold start}.
When the connection goes dead waiting for a
timeout to occur (i.e, the advertized window goes
to zero!)
12. Computer Networks: TCP 12
Slow StartSlow Start
• However, in the second case the source
has more information. The current value
of cwnd can be saved as a congestion
threshold.
• This is also known as the “slow start
threshold” ssthresh.
13. Computer Networks: TCP 13
Figure 6.11 Behavior of TCPFigure 6.11 Behavior of TCP
Congestion ControlCongestion Control
60
20
1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
Time (seconds)
70
30
40
50
10
14. Computer Networks: TCP 14
Fast RetransmitFast Retransmit
• Coarse timeouts remained a problem, and Fast
retransmit was added with TCP Tahoe.
• Since the receiver responds every time a packet
arrives, this implies the sender will see duplicate
ACKs.
Basic Idea:: use duplicate ACKs to signal lost packet.
Fast Retransmit
Upon receipt of three duplicate ACKs, the TCP Sender
retransmits the lost packet.
15. Computer Networks: TCP 15
Fast RetransmitFast Retransmit
• Generally, fast retransmit eliminates about half
the coarse-grain timeouts.
• This yields roughly a 20% improvement in
throughput.
• Note – fast retransmit does not eliminate all
the timeouts due to small window sizes at the
source.
16. Computer Networks: TCP 16
Figure 6.12 Fast RetransmitFigure 6.12 Fast Retransmit
Packet 1
Packet 2
Packet 3
Packet 4
Packet 5
Packet 6
Retransmit
packet 3
ACK 1
ACK 2
ACK 2
ACK 2
ACK 6
ACK 2
Sender Receiver
Fast Retransmit
Based on three
duplicate ACKs
19. Computer Networks: TCP 19
Fast RecoveryFast Recovery
• Fast recovery was added with TCP Reno.
• Basic idea:: When fast retransmit detects
three duplicate ACKs, start the recovery
process from congestion avoidance region
and use ACKs in the pipe to pace the
sending of packets.
Fast Recovery
After Fast Retransmit, half cwnd and commence
recovery from this point using linear additive increase
‘primed’ by left over ACKs in pipe.
20. Computer Networks: TCP 20
ModifiedModified Slow StartSlow Start
• With fast recovery, slow start only
occurs:
–At cold start
–After a coarse-grain timeout
• This is the difference between
TCP Tahoe and TCP Reno!!
22. Computer Networks: TCP 22
Adaptive RetransmissionsAdaptive Retransmissions
RTT:: Round Trip Time between a pair of
hosts on the Internet.
• How to set the TimeOut value?
– The timeout value is set as a function of
the expected RTT.
– Consequences of a bad choice?
23. Computer Networks: TCP 23
Original AlgorithmOriginal Algorithm
• Keep a running average of RTT and
compute TimeOut as a function of this
RTT.
– Send packet and keep timestamp ts .
– When ACK arrives, record timestamp ta .
SampleRTT = ta - ts
24. Computer Networks: TCP 24
Original AlgorithmOriginal Algorithm
Compute a weighted average:
EstimatedRTT =EstimatedRTT = αα xx EstimatedRTT +EstimatedRTT +
((1-1- αα) x SampleRTT) x SampleRTT
Original TCP spec: αα in range (0.8,0.9)in range (0.8,0.9)
TimeOut = 2 xTimeOut = 2 x EstimatedRTTEstimatedRTT
25. Computer Networks: TCP 25
Karn/Partidge AlgorithmKarn/Partidge Algorithm
An obvious flaw in the original algorithm:
Whenever there is a retransmission it is
impossible to know whether to associate
the ACK with the original packet or the
retransmitted packet.
26. Computer Networks: TCP 26
Figure 5.10Figure 5.10
Associating the ACK?Associating the ACK?
Sender Receiver
Original transmission
ACK
Retransmission
Sender Receiver
Original transmission
ACK
Retransmission
(a) (b)
27. Computer Networks: TCP 27
Karn/Partidge AlgorithmKarn/Partidge Algorithm
1. Do not measure SampleRTTSampleRTT when
sending packet more than once.
2. For each retransmission, set TimeOutTimeOut
to double the last TimeOutTimeOut.
{ Note – this is a form of exponential
backoff based on the believe that the
lost packet is due to congestion.}
28. Computer Networks: TCP 28
Jaconson/Karels AlgorithmJaconson/Karels Algorithm
The problem with the original algorithm is that it did not
take into account the variance of SampleRTT.
Difference = SampleRTT – EstimatedRTTDifference = SampleRTT – EstimatedRTT
EstimatedRTT = EstimatedRTT +EstimatedRTT = EstimatedRTT +
((δδ x Difference)x Difference)
Deviation =Deviation = δδ (|Difference| - Deviation)(|Difference| - Deviation)
where δδ is a fraction between 0 and 1.
29. Computer Networks: TCP 29
Jaconson/Karels AlgorithmJaconson/Karels Algorithm
TCP computes timeout using both the mean
and variance of RTT
TimeOut =TimeOut = µµ x EstimatedRTTx EstimatedRTT
++ ΦΦ x Deviationx Deviation
where based on experience µ = 1µ = 1 and ΦΦ = 4= 4.