TCP Westwood plus
Encyclopedia
TCP Westwood+ is a sender-side only modification of the TCP Reno protocol stack
that optimizes the performance of TCP
congestion control over both wireline and wireless network
s. TCP Westwood+ is based on end-to-end bandwidth
estimation to set congestion window
and slow start threshold after a congestion episode, that is, after three duplicate acknowledgments or a timeout. The bandwidth is estimated by properly low-pass filter
ing the rate of returning acknowledgment packets. The rationale of this strategy is simple: in contrast with TCP Reno, which blindly halves the congestion window after three duplicate ACKs, TCP Westwood+ adaptively sets a slow start threshold and a congestion window which takes into account the bandwidth used at the time congestion is experienced. TCP Westwood+ significantly increases throughput over wireless links and fairness compared to TCP Reno/New Reno in wired networks.
TCP Westwood+ is an evolution of TCP Westwood
. The main idea of Westwood TCP, which is an end-to-end bandwidth estimation for setting control windows after congestion, was proposed by Saverio Mascolo. He came out with the idea after reading the chapter on TCP congestion control in the book Data Networks by Larry Peterson. The first implementation of TCP Westwood in ns2 was done at University of California
at Los Angeles
(UCLA) in 1999. The name "Westwood" was chosen by S. Mascolo as due homage to the UCLA area of Westwood where he was a visiting researcher at that time. Main collaborators were prof. Mario Gerla, Dr. Claudio Casetti and Dr. Medy Senadidi. After that, Saverio Mascolo went back to Italy
and "his evolution of Westwood TCP" was named Westwood+. The main novelty of Westwood+ was the algorithm used to estimate the available bandwidth end-to-end. In fact, it was soon discovered that the Westwood bandwidth estimation algorithm did not work well in the presence of reverse traffic due to ack compression. This phenomenon was explained in terms of aliasing
effects. The new version Westwood+ was implemented for the first time in the kernel of Linux
2.4 by Roberto Ferorelli and in the kernel of Linux 2.6 by Angelo dell'Aera, both working at Politecnico di Bari as undergraduate students in 2003 and 2004.
Protocol stack
The protocol stack is an implementation of a computer networking protocol suite. The terms are often used interchangeably. Strictly speaking, the suite is the definition of the protocols, and the stack is the software implementation of them....
that optimizes the performance of TCP
Transmission Control Protocol
The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...
congestion control over both wireline and wireless network
Wireless network
Wireless network refers to any type of computer network that is not connected by cables of any kind. It is a method by which homes, telecommunications networks and enterprise installations avoid the costly process of introducing cables into a building, or as a connection between various equipment...
s. TCP Westwood+ is based on end-to-end bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
estimation to set congestion window
Congestion window
In Transmission Control Protocol , the congestion window is one of the factors that determines the number of bytes that can be outstanding at any time. This is not to be confused with the TCP window size which is maintained by the receiver. This is a means of stopping the link between two places...
and slow start threshold after a congestion episode, that is, after three duplicate acknowledgments or a timeout. The bandwidth is estimated by properly low-pass filter
Low-pass filter
A low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter...
ing the rate of returning acknowledgment packets. The rationale of this strategy is simple: in contrast with TCP Reno, which blindly halves the congestion window after three duplicate ACKs, TCP Westwood+ adaptively sets a slow start threshold and a congestion window which takes into account the bandwidth used at the time congestion is experienced. TCP Westwood+ significantly increases throughput over wireless links and fairness compared to TCP Reno/New Reno in wired networks.
TCP Westwood+ is an evolution of TCP Westwood
TCP Westwood
TCP Westwood , is a sender-side-only modification to TCP New Reno that is intended to better handle large bandwidth-delay product paths , with potential packet loss due to transmission or other errors , and with dynamic load .TCP Westwood relies on mining the ACK stream for information to help it...
. The main idea of Westwood TCP, which is an end-to-end bandwidth estimation for setting control windows after congestion, was proposed by Saverio Mascolo. He came out with the idea after reading the chapter on TCP congestion control in the book Data Networks by Larry Peterson. The first implementation of TCP Westwood in ns2 was done at University of California
University of California
The University of California is a public university system in the U.S. state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-tier public higher education system, which also includes the California State University...
at Los Angeles
Los Ángeles
Los Ángeles is the capital of the province of Biobío, in the commune of the same name, in Region VIII , in the center-south of Chile. It is located between the Laja and Biobío rivers. The population is 123,445 inhabitants...
(UCLA) in 1999. The name "Westwood" was chosen by S. Mascolo as due homage to the UCLA area of Westwood where he was a visiting researcher at that time. Main collaborators were prof. Mario Gerla, Dr. Claudio Casetti and Dr. Medy Senadidi. After that, Saverio Mascolo went back to Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
and "his evolution of Westwood TCP" was named Westwood+. The main novelty of Westwood+ was the algorithm used to estimate the available bandwidth end-to-end. In fact, it was soon discovered that the Westwood bandwidth estimation algorithm did not work well in the presence of reverse traffic due to ack compression. This phenomenon was explained in terms of aliasing
Aliasing
In signal processing and related disciplines, aliasing refers to an effect that causes different signals to become indistinguishable when sampled...
effects. The new version Westwood+ was implemented for the first time in the kernel of Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
2.4 by Roberto Ferorelli and in the kernel of Linux 2.6 by Angelo dell'Aera, both working at Politecnico di Bari as undergraduate students in 2003 and 2004.
See also
- TCP WestwoodTCP WestwoodTCP Westwood , is a sender-side-only modification to TCP New Reno that is intended to better handle large bandwidth-delay product paths , with potential packet loss due to transmission or other errors , and with dynamic load .TCP Westwood relies on mining the ACK stream for information to help it...
- TCP congestion avoidance algorithmTCP congestion avoidance algorithmTransmission Control Protocol uses a network congestion avoidance algorithm that includes various aspects of an additive increase/multiplicative decrease scheme, with other schemes such as slow-start in order to achieve congestion avoidance....
- Transmission Control Protocol#Development