The document discusses various approaches to improving TCP for mobile networks. It begins by describing traditional TCP and its mechanisms for congestion control and reliable data transmission. However, TCP was designed for fixed networks and faces challenges in mobile environments due to higher error rates, mobility-induced packet loss, and inefficient slow start behavior after losses. Several TCP improvements are then outlined, including Indirect TCP which segments connections and uses a proxy at the access point to isolate the wireless portion. This allows specialized TCP variants to be used for the wireless link without changing the fixed network. Finally, socket migration during handover is discussed to maintain connections as the mobile host moves.
A THROUGHPUT ANALYSIS OF TCP IN ADHOC NETWORKScsandit
This document analyzes the throughput of TCP in mobile ad hoc networks through simulations. It finds that TCP throughput decreases initially as the number of hops increases, then stabilizes at higher hop counts. This is due to hidden terminal problems at low hops. The number of retransmissions increases with payloads and flows due to buffering and congestion. TCP performance degrades in wireless networks because it cannot differentiate between congestion and non-congestion packet losses. Mobility, interference, and dynamic topology changes specific to wireless networks cause unnecessary triggering of TCP congestion control mechanisms.
T/TCP is a protocol that aims to reduce the number of packets needed for transaction-style applications by allowing a client to open a connection, send data, and close the connection in a single packet. It utilizes a mechanism called TCP Accelerated Open (TAO) to bypass the standard 3-way TCP handshake. Testing showed T/TCP saved an average of 5 packets per transaction compared to TCP. However, the percentage savings decreased with larger data transfers as T/TCP is most beneficial for small transactions. While improving performance, T/TCP also introduced some security and operational issues that needed to be addressed for broader adoption.
This document discusses various transport layer protocols for mobile networks. It begins by describing TCP and its mechanisms for congestion avoidance, flow control, slow start, and retransmission. It then covers several TCP variants including Tahoe, Reno, and Vegas. It also discusses indirect TCP, Snoop TCP, and Mobile TCP which aim to optimize TCP for wireless networks by handling retransmissions locally or splitting the connection. The document provides details on the algorithms and functioning of these different protocols.
The document discusses various transport layer protocols for mobile networks, including traditional TCP, Indirect TCP, Snooping TCP, and Mobile TCP. Traditional TCP was designed for fixed networks and experiences issues in mobile networks due to factors like packet loss from handoffs. Indirect TCP splits the TCP connection at the access point to isolate the wireless link. Snooping TCP has the access point buffer packets and detect losses to enable local retransmissions. Mobile TCP uses a supervisory host to handle disconnections and restart the connection when needed. Each approach aims to improve TCP performance over mobile networks while maintaining compatibility with traditional TCP.
This document discusses various transport layer protocols for mobile networks. It begins with an overview of TCP and UDP, and then describes several strategies for improving TCP performance over mobile networks, including indirect TCP (I-TCP), snooping TCP, and Mobile TCP. It also discusses congestion control strategies like slow start and fast retransmit. Overall, the document analyzes how TCP can be optimized through techniques like connection splitting, buffering, and selective retransmission to better accommodate the characteristics of wireless networks.
The document discusses various approaches to improving TCP performance over mobile networks. Indirect TCP splits the TCP connection at the foreign agent to isolate the wireless link. Snooping TCP has the foreign agent buffer packets and retransmit lost packets locally. Mobile TCP uses a supervisory host to monitor connections and choke the sender window during disconnections. Other techniques discussed include fast retransmit/recovery after handovers, freezing TCP states during interruptions, selective retransmission of only lost packets, and transaction-oriented TCP to reduce overhead of short messages. Each approach has advantages but also disadvantages related to compatibility, transparency, and complexity.
The transport layer provides end-to-end communication over a network by providing services such as connection-oriented communication, reliability, flow control, and multiplexing. It links the application layer to the network layer and performs functions like segmenting messages and establishing connections between endpoints. Common transport protocols are TCP, which provides connection-oriented and reliable data transfer, and UDP, which provides connectionless datagram delivery.
The document discusses various approaches to modifying TCP for use in mobile networks. Indirect TCP splits the TCP connection at the foreign agent, keeping the fixed network unchanged but losing end-to-end semantics. Snooping TCP has the foreign agent snoop packets and retransmit lost packets locally without changing TCP. Mobile TCP uses a supervisory host to monitor disconnections and choke senders. Other approaches include forced fast retransmit after handovers, freezing TCP timers during disconnects, selective retransmission of only lost packets, and transaction-oriented TCP to combine connection setup in fewer packets. Each approach has advantages like efficiency or compatibility but also disadvantages like overhead or non-transparency.
A THROUGHPUT ANALYSIS OF TCP IN ADHOC NETWORKScsandit
This document analyzes the throughput of TCP in mobile ad hoc networks through simulations. It finds that TCP throughput decreases initially as the number of hops increases, then stabilizes at higher hop counts. This is due to hidden terminal problems at low hops. The number of retransmissions increases with payloads and flows due to buffering and congestion. TCP performance degrades in wireless networks because it cannot differentiate between congestion and non-congestion packet losses. Mobility, interference, and dynamic topology changes specific to wireless networks cause unnecessary triggering of TCP congestion control mechanisms.
T/TCP is a protocol that aims to reduce the number of packets needed for transaction-style applications by allowing a client to open a connection, send data, and close the connection in a single packet. It utilizes a mechanism called TCP Accelerated Open (TAO) to bypass the standard 3-way TCP handshake. Testing showed T/TCP saved an average of 5 packets per transaction compared to TCP. However, the percentage savings decreased with larger data transfers as T/TCP is most beneficial for small transactions. While improving performance, T/TCP also introduced some security and operational issues that needed to be addressed for broader adoption.
This document discusses various transport layer protocols for mobile networks. It begins by describing TCP and its mechanisms for congestion avoidance, flow control, slow start, and retransmission. It then covers several TCP variants including Tahoe, Reno, and Vegas. It also discusses indirect TCP, Snoop TCP, and Mobile TCP which aim to optimize TCP for wireless networks by handling retransmissions locally or splitting the connection. The document provides details on the algorithms and functioning of these different protocols.
The document discusses various transport layer protocols for mobile networks, including traditional TCP, Indirect TCP, Snooping TCP, and Mobile TCP. Traditional TCP was designed for fixed networks and experiences issues in mobile networks due to factors like packet loss from handoffs. Indirect TCP splits the TCP connection at the access point to isolate the wireless link. Snooping TCP has the access point buffer packets and detect losses to enable local retransmissions. Mobile TCP uses a supervisory host to handle disconnections and restart the connection when needed. Each approach aims to improve TCP performance over mobile networks while maintaining compatibility with traditional TCP.
This document discusses various transport layer protocols for mobile networks. It begins with an overview of TCP and UDP, and then describes several strategies for improving TCP performance over mobile networks, including indirect TCP (I-TCP), snooping TCP, and Mobile TCP. It also discusses congestion control strategies like slow start and fast retransmit. Overall, the document analyzes how TCP can be optimized through techniques like connection splitting, buffering, and selective retransmission to better accommodate the characteristics of wireless networks.
The document discusses various approaches to improving TCP performance over mobile networks. Indirect TCP splits the TCP connection at the foreign agent to isolate the wireless link. Snooping TCP has the foreign agent buffer packets and retransmit lost packets locally. Mobile TCP uses a supervisory host to monitor connections and choke the sender window during disconnections. Other techniques discussed include fast retransmit/recovery after handovers, freezing TCP states during interruptions, selective retransmission of only lost packets, and transaction-oriented TCP to reduce overhead of short messages. Each approach has advantages but also disadvantages related to compatibility, transparency, and complexity.
The transport layer provides end-to-end communication over a network by providing services such as connection-oriented communication, reliability, flow control, and multiplexing. It links the application layer to the network layer and performs functions like segmenting messages and establishing connections between endpoints. Common transport protocols are TCP, which provides connection-oriented and reliable data transfer, and UDP, which provides connectionless datagram delivery.
The document discusses various approaches to modifying TCP for use in mobile networks. Indirect TCP splits the TCP connection at the foreign agent, keeping the fixed network unchanged but losing end-to-end semantics. Snooping TCP has the foreign agent snoop packets and retransmit lost packets locally without changing TCP. Mobile TCP uses a supervisory host to monitor disconnections and choke senders. Other approaches include forced fast retransmit after handovers, freezing TCP timers during disconnects, selective retransmission of only lost packets, and transaction-oriented TCP to combine connection setup in fewer packets. Each approach has advantages like efficiency or compatibility but also disadvantages like overhead or non-transparency.
Overview of transport protocols.
The transport layer (OSI layer 4) is the interface between the network and application (network API).
The transport layer provides data transport service and some level of quality of service (QoS) to the application.
While all transport protocols offer data transport services, they have varying levels of quality of service in terms of error detection and correction, packet ordering and packet delay.
Simple transport protocols like UDP are often connectionless while connection-oriented transport protocols like TCP provide many quality of service properties.
Indirect TCP suggests splitting the TCP layer into two sub-layers: a TCPM connection between the mobile node and base transceiver, and a TCP connection between fixed nodes. The TCPM sends and receives packets to/from the mobile node via the base transceiver and to/from a TCPF layer at a fixed node. Selective repeat protocol modifies indirect TCP by using UDP for selective retransmission of data between the mobile node and base transceiver, while still using TCPM and TCP between network endpoints. Mobile-end transport protocol further modifies this by guaranteeing in-order delivery between the mobile node and base transceiver like TCP instead of UDP.
The document provides an overview of transport layer protocols including UDP, TCP, and SCTP. It discusses the services each protocol provides such as reliable vs unreliable data delivery. For TCP, it describes connection establishment and termination, segments, flow and error control using mechanisms like acknowledgments and retransmissions. It also discusses TCP timers used for retransmission timeouts and congestion control algorithms like slow start and congestion avoidance.
The document summarizes key aspects of the transport layer and two main Internet transport protocols: TCP and UDP. It describes how the transport layer provides logical communication between application processes on different hosts by breaking messages into segments and reassembling them. TCP provides reliable, in-order delivery using congestion control with additive increase/multiplicative decrease, while UDP provides unreliable delivery. The document also discusses causes of network congestion and how TCP detects and responds to packet loss.
Mobile Transport Layer protocols aim to address challenges with TCP over mobile networks. Traditional TCP uses congestion control like slow start and fast retransmit/recovery that can reduce performance over mobile. Indirect TCP splits the connection at the access point to avoid wireless errors affecting the wired segment. Snooping TCP buffers packets at the access point and performs local retransmissions on errors. Mobile TCP splits the connection and uses an optimized TCP between the supervisory host and mobile host, choking the sender when the mobile is disconnected to avoid buffering large amounts of undelivered data.
IMPACT OF CONTENTION WINDOW ON CONGESTION CONTROL ALGORITHMS FOR WIRELESS ADH...cscpconf
TCP congestion control mechanism is highly dependent on MAC layer Backoff algorithms that
predict the optimal Contention Window size to increase the TCP performance in wireless adhoc
network. This paper critically examines the impact of Contention Window in TCP congestion
control approaches. The modified TCP congestion control method gives the stability of
congestion window which provides higher throughput and shorter delay than the traditional TCP. Various Backoff algorithms that are used to adjust Contention Window are simulatedusing NS2 along with modified TCP and their performance are analyzed to depict the influence of Contention Window in TCP performance considering the metrics such as throughput, delay, packet loss and end-to-end delay
This document summarizes key aspects of the transport layer:
- The transport layer provides logical communication between application processes running on different hosts and handles reliable data transfer.
- It provides both connection-oriented and connectionless services to the application layer. Quality of service parameters like throughput and delay can be negotiated.
- Transport layer protocols like TCP and UDP are described. TCP provides reliable byte-stream delivery using connections while UDP provides best-effort unreliable datagram delivery.
Mobile transport layer - traditional TCPVishal Tandel
This document summarizes several mechanisms proposed to improve TCP performance in wireless networks. It discusses approaches like indirect TCP, snooping TCP, and mobile TCP that split the TCP connection to isolate the wireless link. It also covers fast retransmit/recovery techniques, transmission freezing, and selective retransmission to more efficiently handle packet losses due to mobility. While each approach aims to address TCP issues in wireless networks, they often do so by mixing layers or requiring changes to the basic TCP protocol stack.
This document discusses a proposed congestion control mechanism called Network Border Protocol (NBP) that aims to prevent congestion collapse and unfairness in networks. NBP works by having edge routers monitor and control the ingress rates of individual flows to prevent packets from entering the network faster than they can leave. It uses feedback exchanged between ingress and egress routers to inform them of flow rates. While adding complexity to edge routers, NBP's approach aims to isolate this within the network borders and not require changes to end systems or transport protocols. The key components of NBP include its rate control algorithm, use of leaky bucket algorithms at ingress routers, and feedback control between edge routers.
This document summarizes key concepts about the transport layer in computer networks. It discusses:
1. The transport layer is responsible for process-to-process delivery of data across a network. This involves delivering packets from one process to another, often using a client-server model.
2. There are two main transport layer protocols - UDP, which is a connectionless and unreliable protocol, and TCP, which establishes connections and provides reliable data delivery.
3. TCP and UDP use port numbers along with IP addresses to uniquely identify processes. TCP also implements flow and error control to ensure reliable data transfer.
THIS DESCRIBES VARIOUS ELEMENTS OF TRANSPORT PROTOCOL IN TRANSPORT LAYER OF COMPUTER NETWORKS
THERE ARE SIX ELEMENTS OF TRANSPORT PROTOCOL NAMELY
1. ADDRESSING
2. CONNECTION ESTABLISHMENT
3.CONNECTION REFUSE
4.FLOW CONTROL AND BUFFERS
5.MULTIPLEXING
6.CRASH RECOVERY
This document discusses the use and copyright of slides from the textbook "Computer Networking: A Top Down Approach" by Jim Kurose and Keith Ross. It states that the slides are being made freely available for educational use provided that the source is cited and the copyright is acknowledged if posted online. The document asks users to mention the source of the slides if used in a class and to note the authors' copyright if posted on a website.
The document discusses congestion control in computer networks. It defines congestion as occurring when the load on a network is greater than the network's capacity. Congestion control aims to control congestion and keep the load below capacity. The document outlines two categories of congestion control: open-loop control, which aims to prevent congestion; and closed-loop control, which detects congestion and takes corrective action using feedback from the network. Specific open-loop techniques discussed include admission control, traffic shaping using leaky bucket and token bucket algorithms, and traffic scheduling.
TCP guarantees reliable delivery of data packets in the correct order, while UDP does not provide these guarantees. TCP is commonly used for applications that require reliable data transfer like HTTP and FTP. UDP is used for applications that prioritize speed over reliability, such as media streaming, VoIP, and online games. While TCP ensures error-free transmission, it introduces more overhead and latency than UDP. The choice between TCP and UDP depends on an application's requirements for reliability versus speed.
The document provides an overview of the transport layer in computer networks. It discusses the key services provided by the transport layer, including reliable data transmission and isolating applications from the underlying network technology. It introduces some common transport layer protocols like TCP and UDP, and describes important transport layer concepts such as connection-oriented vs. connectionless services, transport service primitives, and elements that transport protocols must address like error control and flow control.
MainlineNet Holdings owns Extreme TCP, a new technology that improves upon the standard TCP congestion avoidance algorithm used on the internet. Extreme TCP uses complex router and network models to transmit data at higher speeds while avoiding congestion events that slow transmission. Testing showed transmission speed improvements of 400-1000% for some connections and up to 1400% for longer connections. While Extreme TCP can be applied as a software patch, its benefits are only seen on the device that has it installed, not requiring widespread adoption. It has the potential to significantly increase transmission speeds for most internet communications that use TCP.
The document discusses the differences between packets and frames, and provides details on the transport layer. It explains that the transport layer is responsible for process-to-process delivery and uses port numbers for addressing. Connection-oriented protocols like TCP use three-way handshaking for connection establishment and termination, and implement flow and error control using mechanisms like sliding windows. Connectionless protocols like UDP are simpler but unreliable, treating each packet independently.
Iaetsd an effective approach to eliminate tcp incastIaetsd Iaetsd
This document proposes an Incast Congestion Control for TCP (ICTCP) scheme to eliminate TCP incast collapse in datacenter environments. TCP incast collapse occurs when multiple synchronized servers send data to the same receiver in parallel, overwhelming the switch buffer and causing packet loss. ICTCP is a receiver-side approach that proactively adjusts the TCP receive window size of connections to control their aggregate burstiness and prevent switch buffer overflow before packet loss occurs. It estimates available bandwidth and uses this as a quota to coordinate receive window increases. For each connection, the receive window is adjusted based on the ratio of the difference between measured and expected throughput. This allows adaptive tuning of receive windows to meet sender throughput needs while avoiding congest
International Journal of Engineering Research and Applications (IJERA) is a team of researchers not publication services or private publications running the journals for monetary benefits, we are association of scientists and academia who focus only on supporting authors who want to publish their work. The articles published in our journal can be accessed online, all the articles will be archived for real time access.
Our journal system primarily aims to bring out the research talent and the works done by sciaentists, academia, engineers, practitioners, scholars, post graduate students of engineering and science. This journal aims to cover the scientific research in a broader sense and not publishing a niche area of research facilitating researchers from various verticals to publish their papers. It is also aimed to provide a platform for the researchers to publish in a shorter of time, enabling them to continue further All articles published are freely available to scientific researchers in the Government agencies,educators and the general public. We are taking serious efforts to promote our journal across the globe in various ways, we are sure that our journal will act as a scientific platform for all researchers to publish their works online.
LinkedIn is very much so like an always-accessible resume on the net. It can be your outlet to help you meet new professional contacts, potential clients and reconnect with former friends and co-workers.
XML is a flexible data format that allows users to define their own tags to structure information in a way that makes it readable by both humans and machines. It allows sharing of data across different systems on the internet or intranets. XML uses tags to mark up content with semantic meaning, which facilitates parsing and allows the same information to be rendered in multiple formats.
This document summarizes key aspects of Java servlets including:
- The servlet lifecycle which includes initialization, service, and destruction phases.
- How servlets handle HTTP requests through methods like doGet() and doPost().
- How servlets can communicate with other components using various protocols beyond just HTTP.
- How servlet contexts allow servlets to share information and resources.
- How servlets can create, read, and modify cookies to maintain state across requests.
Overview of transport protocols.
The transport layer (OSI layer 4) is the interface between the network and application (network API).
The transport layer provides data transport service and some level of quality of service (QoS) to the application.
While all transport protocols offer data transport services, they have varying levels of quality of service in terms of error detection and correction, packet ordering and packet delay.
Simple transport protocols like UDP are often connectionless while connection-oriented transport protocols like TCP provide many quality of service properties.
Indirect TCP suggests splitting the TCP layer into two sub-layers: a TCPM connection between the mobile node and base transceiver, and a TCP connection between fixed nodes. The TCPM sends and receives packets to/from the mobile node via the base transceiver and to/from a TCPF layer at a fixed node. Selective repeat protocol modifies indirect TCP by using UDP for selective retransmission of data between the mobile node and base transceiver, while still using TCPM and TCP between network endpoints. Mobile-end transport protocol further modifies this by guaranteeing in-order delivery between the mobile node and base transceiver like TCP instead of UDP.
The document provides an overview of transport layer protocols including UDP, TCP, and SCTP. It discusses the services each protocol provides such as reliable vs unreliable data delivery. For TCP, it describes connection establishment and termination, segments, flow and error control using mechanisms like acknowledgments and retransmissions. It also discusses TCP timers used for retransmission timeouts and congestion control algorithms like slow start and congestion avoidance.
The document summarizes key aspects of the transport layer and two main Internet transport protocols: TCP and UDP. It describes how the transport layer provides logical communication between application processes on different hosts by breaking messages into segments and reassembling them. TCP provides reliable, in-order delivery using congestion control with additive increase/multiplicative decrease, while UDP provides unreliable delivery. The document also discusses causes of network congestion and how TCP detects and responds to packet loss.
Mobile Transport Layer protocols aim to address challenges with TCP over mobile networks. Traditional TCP uses congestion control like slow start and fast retransmit/recovery that can reduce performance over mobile. Indirect TCP splits the connection at the access point to avoid wireless errors affecting the wired segment. Snooping TCP buffers packets at the access point and performs local retransmissions on errors. Mobile TCP splits the connection and uses an optimized TCP between the supervisory host and mobile host, choking the sender when the mobile is disconnected to avoid buffering large amounts of undelivered data.
IMPACT OF CONTENTION WINDOW ON CONGESTION CONTROL ALGORITHMS FOR WIRELESS ADH...cscpconf
TCP congestion control mechanism is highly dependent on MAC layer Backoff algorithms that
predict the optimal Contention Window size to increase the TCP performance in wireless adhoc
network. This paper critically examines the impact of Contention Window in TCP congestion
control approaches. The modified TCP congestion control method gives the stability of
congestion window which provides higher throughput and shorter delay than the traditional TCP. Various Backoff algorithms that are used to adjust Contention Window are simulatedusing NS2 along with modified TCP and their performance are analyzed to depict the influence of Contention Window in TCP performance considering the metrics such as throughput, delay, packet loss and end-to-end delay
This document summarizes key aspects of the transport layer:
- The transport layer provides logical communication between application processes running on different hosts and handles reliable data transfer.
- It provides both connection-oriented and connectionless services to the application layer. Quality of service parameters like throughput and delay can be negotiated.
- Transport layer protocols like TCP and UDP are described. TCP provides reliable byte-stream delivery using connections while UDP provides best-effort unreliable datagram delivery.
Mobile transport layer - traditional TCPVishal Tandel
This document summarizes several mechanisms proposed to improve TCP performance in wireless networks. It discusses approaches like indirect TCP, snooping TCP, and mobile TCP that split the TCP connection to isolate the wireless link. It also covers fast retransmit/recovery techniques, transmission freezing, and selective retransmission to more efficiently handle packet losses due to mobility. While each approach aims to address TCP issues in wireless networks, they often do so by mixing layers or requiring changes to the basic TCP protocol stack.
This document discusses a proposed congestion control mechanism called Network Border Protocol (NBP) that aims to prevent congestion collapse and unfairness in networks. NBP works by having edge routers monitor and control the ingress rates of individual flows to prevent packets from entering the network faster than they can leave. It uses feedback exchanged between ingress and egress routers to inform them of flow rates. While adding complexity to edge routers, NBP's approach aims to isolate this within the network borders and not require changes to end systems or transport protocols. The key components of NBP include its rate control algorithm, use of leaky bucket algorithms at ingress routers, and feedback control between edge routers.
This document summarizes key concepts about the transport layer in computer networks. It discusses:
1. The transport layer is responsible for process-to-process delivery of data across a network. This involves delivering packets from one process to another, often using a client-server model.
2. There are two main transport layer protocols - UDP, which is a connectionless and unreliable protocol, and TCP, which establishes connections and provides reliable data delivery.
3. TCP and UDP use port numbers along with IP addresses to uniquely identify processes. TCP also implements flow and error control to ensure reliable data transfer.
THIS DESCRIBES VARIOUS ELEMENTS OF TRANSPORT PROTOCOL IN TRANSPORT LAYER OF COMPUTER NETWORKS
THERE ARE SIX ELEMENTS OF TRANSPORT PROTOCOL NAMELY
1. ADDRESSING
2. CONNECTION ESTABLISHMENT
3.CONNECTION REFUSE
4.FLOW CONTROL AND BUFFERS
5.MULTIPLEXING
6.CRASH RECOVERY
This document discusses the use and copyright of slides from the textbook "Computer Networking: A Top Down Approach" by Jim Kurose and Keith Ross. It states that the slides are being made freely available for educational use provided that the source is cited and the copyright is acknowledged if posted online. The document asks users to mention the source of the slides if used in a class and to note the authors' copyright if posted on a website.
The document discusses congestion control in computer networks. It defines congestion as occurring when the load on a network is greater than the network's capacity. Congestion control aims to control congestion and keep the load below capacity. The document outlines two categories of congestion control: open-loop control, which aims to prevent congestion; and closed-loop control, which detects congestion and takes corrective action using feedback from the network. Specific open-loop techniques discussed include admission control, traffic shaping using leaky bucket and token bucket algorithms, and traffic scheduling.
TCP guarantees reliable delivery of data packets in the correct order, while UDP does not provide these guarantees. TCP is commonly used for applications that require reliable data transfer like HTTP and FTP. UDP is used for applications that prioritize speed over reliability, such as media streaming, VoIP, and online games. While TCP ensures error-free transmission, it introduces more overhead and latency than UDP. The choice between TCP and UDP depends on an application's requirements for reliability versus speed.
The document provides an overview of the transport layer in computer networks. It discusses the key services provided by the transport layer, including reliable data transmission and isolating applications from the underlying network technology. It introduces some common transport layer protocols like TCP and UDP, and describes important transport layer concepts such as connection-oriented vs. connectionless services, transport service primitives, and elements that transport protocols must address like error control and flow control.
MainlineNet Holdings owns Extreme TCP, a new technology that improves upon the standard TCP congestion avoidance algorithm used on the internet. Extreme TCP uses complex router and network models to transmit data at higher speeds while avoiding congestion events that slow transmission. Testing showed transmission speed improvements of 400-1000% for some connections and up to 1400% for longer connections. While Extreme TCP can be applied as a software patch, its benefits are only seen on the device that has it installed, not requiring widespread adoption. It has the potential to significantly increase transmission speeds for most internet communications that use TCP.
The document discusses the differences between packets and frames, and provides details on the transport layer. It explains that the transport layer is responsible for process-to-process delivery and uses port numbers for addressing. Connection-oriented protocols like TCP use three-way handshaking for connection establishment and termination, and implement flow and error control using mechanisms like sliding windows. Connectionless protocols like UDP are simpler but unreliable, treating each packet independently.
Iaetsd an effective approach to eliminate tcp incastIaetsd Iaetsd
This document proposes an Incast Congestion Control for TCP (ICTCP) scheme to eliminate TCP incast collapse in datacenter environments. TCP incast collapse occurs when multiple synchronized servers send data to the same receiver in parallel, overwhelming the switch buffer and causing packet loss. ICTCP is a receiver-side approach that proactively adjusts the TCP receive window size of connections to control their aggregate burstiness and prevent switch buffer overflow before packet loss occurs. It estimates available bandwidth and uses this as a quota to coordinate receive window increases. For each connection, the receive window is adjusted based on the ratio of the difference between measured and expected throughput. This allows adaptive tuning of receive windows to meet sender throughput needs while avoiding congest
International Journal of Engineering Research and Applications (IJERA) is a team of researchers not publication services or private publications running the journals for monetary benefits, we are association of scientists and academia who focus only on supporting authors who want to publish their work. The articles published in our journal can be accessed online, all the articles will be archived for real time access.
Our journal system primarily aims to bring out the research talent and the works done by sciaentists, academia, engineers, practitioners, scholars, post graduate students of engineering and science. This journal aims to cover the scientific research in a broader sense and not publishing a niche area of research facilitating researchers from various verticals to publish their papers. It is also aimed to provide a platform for the researchers to publish in a shorter of time, enabling them to continue further All articles published are freely available to scientific researchers in the Government agencies,educators and the general public. We are taking serious efforts to promote our journal across the globe in various ways, we are sure that our journal will act as a scientific platform for all researchers to publish their works online.
LinkedIn is very much so like an always-accessible resume on the net. It can be your outlet to help you meet new professional contacts, potential clients and reconnect with former friends and co-workers.
XML is a flexible data format that allows users to define their own tags to structure information in a way that makes it readable by both humans and machines. It allows sharing of data across different systems on the internet or intranets. XML uses tags to mark up content with semantic meaning, which facilitates parsing and allows the same information to be rendered in multiple formats.
This document summarizes key aspects of Java servlets including:
- The servlet lifecycle which includes initialization, service, and destruction phases.
- How servlets handle HTTP requests through methods like doGet() and doPost().
- How servlets can communicate with other components using various protocols beyond just HTTP.
- How servlet contexts allow servlets to share information and resources.
- How servlets can create, read, and modify cookies to maintain state across requests.
- XML and HTML are both markup languages but have different purposes
- XML is used to store and transport data, HTML is used to display web pages
- XML focuses on describing data, HTML focuses on both structure and appearance
- XML allows users to define their own elements while HTML uses a fixed set of predefined tags
JavaScript is used to add interactivity to web pages. It can validate forms, detect browsers, create cookies, and more. JavaScript is the most popular scripting language on the internet and works in all major browsers. JavaScript is an interpreted language that is usually embedded directly into HTML pages. It is commonly used to dynamically update content and validate user input. Java and JavaScript are two completely different languages - Java is more complex and powerful while JavaScript is lightweight.
Java script es un lenguaje de programación utilizado para crear efectos interactivos en páginas web. Fue creado en 1995 para mejorar las capacidades de HTML y permitir el desarrollo de aplicaciones web dinámicas. Java script se ejecuta en el navegador del usuario y puede modificar el contenido HTML, reaccionar a eventos como clics del mouse, y validar datos ingresados en formularios.
The document contains four exam papers for the subject of Mobile Computing. Each paper contains 8 questions with sub-questions focusing on various topics related to mobile computing including GSM architecture, CDMA, mobile IP, TCP for mobility, ad-hoc networks, and wireless protocols. The papers are from Jawaharlal Nehru Technological University and include questions ranging from basic concepts to detailed explanations and examples.
This document discusses several approaches to improving TCP performance over mobile networks:
Traditional TCP uses slow start and congestion control mechanisms that reduce efficiency over mobile networks. Indirect TCP segments connections and uses a proxy to improve performance. Snooping TCP buffers packets to enable fast retransmissions without changing endpoints. Mobile TCP freezes the sender's window on disconnection to avoid unnecessary retransmissions. These methods aim to isolate wireless losses from congestion responses and enable fast recovery from errors and handovers.
This document discusses various approaches to improving TCP performance over mobile networks. It describes Indirect TCP, Snooping TCP, Mobile TCP, optimizations like fast retransmit/recovery and transmission freezing, and transaction-oriented TCP. Each approach is summarized in terms of its key mechanisms, advantages, and disadvantages. Overall, the document evaluates different ways TCP has been adapted to better support mobility and address challenges like frequent disconnections, packet losses during handovers, and high bit error rates over wireless links.
The document discusses several mechanisms used in TCP for mobile computing. It describes:
1) TCP congestion control mechanisms like slow-start and fast retransmit/fast recovery which are designed to address packet loss. However, these can be inappropriate for wireless networks where packet loss is often due to errors rather than congestion.
2) Approaches like Indirect TCP, Snooping TCP, and Mobile TCP which modify TCP for mobile networks by splitting connections or having a supervisory host monitor the connection to enable local retransmissions and avoid unnecessary window reductions when the mobile host disconnects.
3) Other TCP optimizations for mobile like forced fast retransmit after handovers and transmission timeout freezing to avoid slow-start
The document discusses TCP and its mechanisms for reliable data transfer over networks. TCP uses congestion control mechanisms like slow start and congestion avoidance to gradually increase transmission rates and avoid overwhelming network capacity. It also uses fast retransmit and fast recovery to address packet losses without causing unnecessary slow starts. However, TCP faces challenges in wireless environments like mobile networks due to factors such as packet losses and handoffs.
The document discusses various transport layer protocols for mobile computing environments:
- Traditional TCP faces problems with high error rates and mobility-induced packet losses in wireless networks. It can lead to severe performance degradation.
- Indirect TCP segments the TCP connection and uses a specialized TCP for the wireless link, isolating wireless errors. But it loses end-to-end semantics.
- Snooping TCP buffers packets near the mobile host and performs local retransmissions transparently. But wireless errors can still propagate to the server.
- Mobile TCP splits the connection and uses different mechanisms on each segment. It chokes the sender window during disconnections to avoid retransmissions and slow starts. This maintains throughput during
This document discusses several proposals to modify TCP for use in mobile environments:
1. Indirect TCP splits the TCP connection to isolate the wireless link but loses end-to-end semantics.
2. Snooping TCP allows local retransmissions through buffering and "snooping" but does not fully isolate the wireless link.
3. Mobile TCP handles disconnections through a supervisory host but does not isolate wireless link losses.
4. Fast retransmit/recovery avoids the slow start algorithm after handovers but mixes network layers.
The approaches vary in their ability to isolate the wireless link, efficiency, and amount of modification required to TCP.
NetWork Design Question2.) How does TCP prevent Congestion Dicuss.pdfoptokunal1
NetWork Design Question
2.) How does TCP prevent Congestion? Dicuss the information identifying congestion in the
network as well as the mechanism for reducing congestion?
Solution
Congestion is a problem that occurs on shared networks when multiple users contend for access
to the same resources (bandwidth, buffers, and queues).
Transmission Control Protocol (TCP) uses a network congestion-avoidance algorithm that
includes various aspects of an additive increase/multiplicative decrease (AIMD) scheme, with
other schemes such as slow-start to achieve congestion avoidance.
The TCP congestion-avoidance algorithm is the primary basis for congestion control in the
Internet.
Congestion typically occurs where multiple links feed into a single link, such as where internal
LANs are connected to WAN links. Congestion also occurs at routers in core networks where
nodes are subjected to more traffic than they are designed to handle.
TCP/IP networks such as the Internet are especially susceptible to congestion because of their
basic connection- less nature. There are no virtual circuits with guaranteed bandwidth. Packets
are injected by any host at any time, and those packets are variable in size, which make
predicting traffic patterns and providing guaranteed service impossible. While connectionless
networks have advantages, quality of service is not one of them.
Shared LANs such as Ethernet have their own congestion control mechanisms in the form of
access controls that prevent multiple nodes from transmitting at the same time.
Identifying:
Congestion is primarily reflected by a conventional user feeling-- slowness. This statement
reflects the change in the network effective flow, that is the time required to transmit an entire
data from one point to another. The effective flow doenot exist as such, it consists in reality of
three seperate indicators:
*Latency:the effective flow is inversely proportional to the latency.
*Jitter:it is latency variation over time, impacts by influencing the flow latency
*Loss Rate:the theoritical bandwidth is inversely proportional to the square root of the loss rate
These Congestion symtoms allow us to rely on objective indicators to characterize it.
Mechanism to reduce congestion:
The standard fare in TCP implementations today has four standard congestion control algorithms
that are now in common use. Their usefulness has passed the test of time.
The four algorithms, Slow Start, Congestion Avoidance, Fast Retransmit and Fast Recovery are
described below. (a) Slow Start
Slow Start, a requirement for TCP software implementations is a mechanism used by the sender
to control the transmission rate, otherwise known as sender-based flow control. This is
accomplished through the return rate of acknowledgements from the receiver. In other words, the
rate of acknowledgements returned by the receiver determine the rate at which the sender can
transmit data. When a TCP connection first begins, the Slow Start algorithm initializes a
.
The document summarizes key aspects of the transport layer, including the transport service it provides to upper layers, connection-oriented and connectionless transport services, and transport service primitives. It discusses transport layer protocols like TCP and UDP, explaining how TCP uses a three-way handshake to establish connections and addressing challenges like congestion control, delayed packet delivery, and host crashes.
A throughput analysis of tcp in adhoc networkscsandit
Transmission Control Protocol (TCP) is a connection oriented end-end reliable byte stream
transport layer protocol. It is widely used in the Internet.TCP is fine tuned to perform well in
wired networks. However the performance degrades in mobile ad hoc networks. This is due to
the characteristics specific to wireless networks, such as signal fading, mobility, unavailability
of routes. This leads to loss of packets which may arise either from congestion or due to other
non-congestion events. However TCP assumes every loss as loss due to congestion and invokes
the congestion control procedures. TCP reduces congestion window in response, causing unnecessary
degradation in throughput. In mobile ad hoc networks multi-hop path forwarding further
worsens the packet loss and throughput. To understand the TCP behavior and improve the
TCP performance over mobile ad hoc networks considerable research has been carried out. As
the research is still active in this area a comprehensive and in-depth study on the TCP throughput
and the various parameters that degrade the performance of TCP have been analyzed. The
analysis is done using simulations in Qualnet 5.0
1) Standard TCP performs poorly over wireless networks due to packet loss from errors and mobility rather than congestion. This causes unnecessary slow starts and window reductions.
2) Early approaches like Indirect TCP, Snooping TCP, and Mobile TCP split or modify the TCP connection to isolate the wireless link but lose end-to-end semantics or require changes.
3) Later techniques like forced fast retransmit and selective acknowledgements improve efficiency without changing TCP but require cooperation between layers. Overall no single solution is optimal due to the need to maintain compatibility with fixed networks.
Improving Performance of TCP in Wireless Environment using TCP-PIDES Editor
Improving the performance of the transmission
control protocol (TCP) in wireless environment has been an
active research area. Main reason behind performance
degradation of TCP is not having ability to detect actual reason
of packet losses in wireless environment. In this paper, we are
providing a simulation results for TCP-P (TCP-Performance).
TCP-P is intelligent protocol in wireless environment which
is able to distinguish actual reasons for packet losses and
applies an appropriate solution to packet loss.
TCP-P deals with main three issues, Congestion in
network, Disconnection in network and random packet losses.
TCP-P consists of Congestion avoidance algorithm and
Disconnection detection algorithm with some changes in TCP
header part. If congestion is occurring in network then
congestion avoidance algorithm is applied. In congestion
avoidance algorithm, TCP-P calculates number of sending
packets and receiving acknowledgements and accordingly set
a sending buffer value, so that it can prevent system from
happening congestion. In disconnection detection algorithm,
TCP-P senses medium continuously to detect a happening
disconnection in network. TCP-P modifies header of TCP
packet so that loss packet can itself notify sender that it is
lost.This paper describes the design of TCP-P, and presents
results from experiments using the NS-2 network simulator.
Results from simulations show that TCP-P is 4% more
efficient than TCP-Tahoe, 5% more efficient than TCP-Vegas,
7% more efficient than TCP-Sack and equally efficient in
performance as of TCP-Reno and TCP-New Reno. But we can
say TCP-P is more efficient than TCP-Reno and TCP-New
Reno since it is able to solve more issues of TCP in wireless
environment.
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.
Comparative Analysis of Different TCP Variants in Mobile Ad-Hoc Network partha pratim deb
The document analyzes the performance of different TCP variants (New Reno, Reno, Tahoe) with MANET routing protocols (AODV, DSR, TORA) through simulation. It finds that in scenarios with 3 and 5 nodes, AODV has better throughput than DSR and TORA for all TCP variants. Throughput decreases for all variants as node count increases. New Reno provides multiple packet loss recovery and is the best choice for AODV in MANETs due to its consistent performance with changes in node count. Further analysis of additional protocols and TCP variants is recommended.
TCP provides several services to applications including process-to-process communication using port numbers, reliable stream delivery of data between processes, and full-duplex communication where data can flow in both directions simultaneously. TCP uses buffers, segments, checksums, acknowledgments, timeouts, and retransmissions to provide reliable data transmission. It establishes connections between processes, delivers data in-order as a stream, and ensures all data is received correctly through error control mechanisms.
The document discusses various protocols and approaches for improving the performance of TCP over wireless networks. It notes that wireless networks have higher bit error rates, lower bandwidth, and mobility issues compared to wired networks. Several protocols are described that aim to distinguish wireless losses from congestion losses to avoid unnecessary TCP reactions:
- Indirect TCP splits the connection and handles losses locally at the base station. Snoop caches packets at the base station for retransmission.
- Mobile TCP further splits the connection and has the base station defer acknowledgments. It can also inform the sender about handoffs versus interface switches.
- Multiple acknowledgments uses two types of ACKs to isolate the wireless and wired portions of the network.
-
WIRELESS NETWORKS _ BABU M_ unit 3 ,4 & 5 PPT
EC 6802 WIRELESS NETWORKS PPT
POWER POINT PRESENTAION ON WIRELESS NETWORKS
BABU M
ASST PROFESSOR/ ELECTRONICS AND COMMUNICATION ENGINEERING,
RMK COLLEGE OF ENGINEERING AND TECHNOLOGY
CHENNAI, THIRUVALLUR DISTRICT
Ctcp a cross layer information based tcp for manetijasuc
Traditional TCP cannot detect link contention losses and route failure losses which occur in MANET and
considers every packet loss as congestion. This results in severe degradation of TCP performance. In this
research work, we modified the operations of TCP to adapt to network states. The cross-layer notifications
are used for adapting the congestion window and achieving better performance. We propose Cross-layer
information based Transmission Control Protocol (CTCP) which consists of four network states.
Decelerate state to recover from contention losses, Cautionary state to deal with route failures, Congested
state to handle network congestion and Normal state to be compatible with traditional TCP. Decelerate
state makes TCP slow down if the packet loss is believed to be due to contention rather than congestion.
Cautionary state suspends the TCP variables and after route reestablishment resumes with conservative
values. Congestion state calls congestion control when network is actually congested and normal state
works as standard TCP. Simulation results show that network state based CTCP is more appropriate for
MANET than packet loss based traditional TCP.
This document discusses challenges with TCP in mobile networks and various approaches to address them. It introduces indirect TCP, which splits the TCP connection to isolate the wireless link. Snooping TCP has the foreign agent snoop packets and acknowledgements to enable local retransmissions. Mobile TCP uses a supervisory host and window size adjustments to handle disconnections. Other optimizations discussed include forced fast retransmit after handovers, freezing TCP timers during disconnects, and selective retransmissions. The document compares the advantages and disadvantages of these different "mobile TCP" approaches.
AN EXPLICIT LOSS AND HANDOFF NOTIFICATION SCHEME IN TCP FOR CELLULAR MOBILE S...IJCNCJournal
With the proliferation of mobile and wireless computing devices, the demand for continuous network connectivity exits for various wired-and-wireless integrated networks. Since Transmission Control Protocol (TCP) is the standard network protocol for communication on the Interne, any wireless network with Internet service need to be compatible with TCP. TCP is tuned to perform well in traditional wired
networks, where packet losses occur mostly because of congestion. However cellular wireless network
suffers from significant losses due to high bit errors and mobile handoff. TCP responds to all losses by
invoking congestion control and avoidance algorithms, resulting in degraded end-to-end performance. This
paper presents an improved Explicit Loss Notification algorithm to distinguish between packet loss due to congestion and packet loss due to wireless errors and handoffs. Simulation results show that the proposed protocol significantly improves the performance of TCP over cellular wireless network in terms of throughput and congestion window dynamics.
6th International Conference on Machine Learning & Applications (CMLA 2024)ClaraZara1
6th International Conference on Machine Learning & Applications (CMLA 2024) will provide an excellent international forum for sharing knowledge and results in theory, methodology and applications of on Machine Learning & Applications.
A review on techniques and modelling methodologies used for checking electrom...nooriasukmaningtyas
The proper function of the integrated circuit (IC) in an inhibiting electromagnetic environment has always been a serious concern throughout the decades of revolution in the world of electronics, from disjunct devices to today’s integrated circuit technology, where billions of transistors are combined on a single chip. The automotive industry and smart vehicles in particular, are confronting design issues such as being prone to electromagnetic interference (EMI). Electronic control devices calculate incorrect outputs because of EMI and sensors give misleading values which can prove fatal in case of automotives. In this paper, the authors have non exhaustively tried to review research work concerned with the investigation of EMI in ICs and prediction of this EMI using various modelling methodologies and measurement setups.
ACEP Magazine edition 4th launched on 05.06.2024Rahul
This document provides information about the third edition of the magazine "Sthapatya" published by the Association of Civil Engineers (Practicing) Aurangabad. It includes messages from current and past presidents of ACEP, memories and photos from past ACEP events, information on life time achievement awards given by ACEP, and a technical article on concrete maintenance, repairs and strengthening. The document highlights activities of ACEP and provides a technical educational article for members.
Using recycled concrete aggregates (RCA) for pavements is crucial to achieving sustainability. Implementing RCA for new pavement can minimize carbon footprint, conserve natural resources, reduce harmful emissions, and lower life cycle costs. Compared to natural aggregate (NA), RCA pavement has fewer comprehensive studies and sustainability assessments.
Harnessing WebAssembly for Real-time Stateless Streaming PipelinesChristina Lin
Traditionally, dealing with real-time data pipelines has involved significant overhead, even for straightforward tasks like data transformation or masking. However, in this talk, we’ll venture into the dynamic realm of WebAssembly (WASM) and discover how it can revolutionize the creation of stateless streaming pipelines within a Kafka (Redpanda) broker. These pipelines are adept at managing low-latency, high-data-volume scenarios.
We have compiled the most important slides from each speaker's presentation. This year’s compilation, available for free, captures the key insights and contributions shared during the DfMAy 2024 conference.
Electric vehicle and photovoltaic advanced roles in enhancing the financial p...IJECEIAES
Climate change's impact on the planet forced the United Nations and governments to promote green energies and electric transportation. The deployments of photovoltaic (PV) and electric vehicle (EV) systems gained stronger momentum due to their numerous advantages over fossil fuel types. The advantages go beyond sustainability to reach financial support and stability. The work in this paper introduces the hybrid system between PV and EV to support industrial and commercial plants. This paper covers the theoretical framework of the proposed hybrid system including the required equation to complete the cost analysis when PV and EV are present. In addition, the proposed design diagram which sets the priorities and requirements of the system is presented. The proposed approach allows setup to advance their power stability, especially during power outages. The presented information supports researchers and plant owners to complete the necessary analysis while promoting the deployment of clean energy. The result of a case study that represents a dairy milk farmer supports the theoretical works and highlights its advanced benefits to existing plants. The short return on investment of the proposed approach supports the paper's novelty approach for the sustainable electrical system. In addition, the proposed system allows for an isolated power setup without the need for a transmission line which enhances the safety of the electrical network
International Conference on NLP, Artificial Intelligence, Machine Learning an...gerogepatton
International Conference on NLP, Artificial Intelligence, Machine Learning and Applications (NLAIM 2024) offers a premier global platform for exchanging insights and findings in the theory, methodology, and applications of NLP, Artificial Intelligence, Machine Learning, and their applications. The conference seeks substantial contributions across all key domains of NLP, Artificial Intelligence, Machine Learning, and their practical applications, aiming to foster both theoretical advancements and real-world implementations. With a focus on facilitating collaboration between researchers and practitioners from academia and industry, the conference serves as a nexus for sharing the latest developments in the field.
DEEP LEARNING FOR SMART GRID INTRUSION DETECTION: A HYBRID CNN-LSTM-BASED MODELgerogepatton
As digital technology becomes more deeply embedded in power systems, protecting the communication
networks of Smart Grids (SG) has emerged as a critical concern. Distributed Network Protocol 3 (DNP3)
represents a multi-tiered application layer protocol extensively utilized in Supervisory Control and Data
Acquisition (SCADA)-based smart grids to facilitate real-time data gathering and control functionalities.
Robust Intrusion Detection Systems (IDS) are necessary for early threat detection and mitigation because
of the interconnection of these networks, which makes them vulnerable to a variety of cyberattacks. To
solve this issue, this paper develops a hybrid Deep Learning (DL) model specifically designed for intrusion
detection in smart grids. The proposed approach is a combination of the Convolutional Neural Network
(CNN) and the Long-Short-Term Memory algorithms (LSTM). We employed a recent intrusion detection
dataset (DNP3), which focuses on unauthorized commands and Denial of Service (DoS) cyberattacks, to
train and test our model. The results of our experiments show that our CNN-LSTM method is much better
at finding smart grid intrusions than other deep learning algorithms used for classification. In addition,
our proposed approach improves accuracy, precision, recall, and F1 score, achieving a high detection
accuracy rate of 99.50%.
1. Mobile Transport Layer Mobile Computing
Unit-4
Mukesh Chinta
Asst Prof, CSE, VNRVJIET 1
Unit-4: Mobile Transport Layer: Traditional TCP ,Indirect TCP ,Snooping TCP
,Mobile TCP, Fast retransmit/fast recovery ,Transmission /time-out freezing ,Selective
retransmission, Transaction oriented TCP
Traditional TCP
The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol
suite, often simply referred to as TCP/IP. TCP is reliable, guarantees in-order delivery of data
and incorporates congestion control and flow control mechanisms.
TCP supports many of the Internet's most
popular application protocols and resulting
applications, including the World Wide Web,
e-mail, File Transfer Protocol and Secure Shell.
In the Internet protocol suite, TCP is the
intermediate layer between the Internet layer
and application layer.
The major responsibilities of TCP in an active
session are to:
• Provide reliable in-order transport of data:
to not allow losses of data.
• Control congestions in the networks: to not
allow degradation of the network
performance,
• Control a packet flow between the
transmitter and the receiver: to not exceed
the receiver's capacity.
TCP uses a number of mechanisms to achieve high performance and avoid 'congestion
collapse', where network performance can fall by several orders of magnitude. These
mechanisms control the rate of data entering the network, keeping the data flow below a rate
that would trigger collapse. There are several mechanisms of TCP that influence the efficiency
of TCP in a mobile environment. Acknowledgments for data sent, or lack of acknowledgments,
are used by senders to implicitly interpret network conditions between the TCP sender and
receiver.
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2. Mobile Transport Layer Mobile Computing
Unit-4
Mukesh Chinta
Asst Prof, CSE, VNRVJIET 2
Congestion Control
A transport layer protocol such as TCP has been designed for fixed networks with fixed
end- systems. Congestion may appear from time to time even in carefully designed networks.
The packet buffers of a router are filled and the router cannot forward the packets fast enough
because the sum of the input rates of packets destined for one output link is higher than the
capacity of the output link. The only thing a router can do in this situation is to drop packets. A
dropped packet is lost for the transmission, and the receiver notices a gap in the packet stream.
Now the receiver does not directly tell the sender which packet is missing, but continues to
acknowledge all in-sequence packets up to the missing one.
The sender notices the missing acknowledgement for the lost packet and assumes a
packet loss due to congestion. Retransmitting the missing packet and continuing at full sending
rate would now be unwise, as this might only increase the congestion. To mitigate congestion,
TCP slows down the transmission rate dramatically. All other TCP connections experiencing the
same congestion do exactly the same so the congestion is soon resolved.
Slow start
TCP’s reaction to a missing acknowledgement is quite drastic, but it is necessary to get rid of
congestion quickly. The behavior TCP shows after the detection of congestion is called slow
start. The sender always calculates a congestion window for a receiver. The start size of the
congestion window is one segment (TCP packet). The sender sends one packet and waits for
acknowledgement. If this acknowledgement arrives, the sender increases the congestion
window by one, now sending two packets (congestion window = 2). This scheme doubles the
congestion window every time the acknowledgements come back, which takes one round trip
time (RTT). This is called the exponential growth of the congestion window in the slow start
mechanism.
But doubling the congestion window
is too dangerous. The exponential
growth stops at the congestion
threshold. As soon as the congestion
window reaches the congestion
threshold, further increase of the
transmission rate is only linear by
adding 1 to the congestion window
each time the acknowledgements
come back.
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3. Mobile Transport Layer Mobile Computing
Unit-4
Mukesh Chinta
Asst Prof, CSE, VNRVJIET 3
Linear increase continues
until a time-out at the
sender occurs due to a
missing acknowledgement,
or until the sender detects a
gap in transmitted data
because of continuous
acknowledgements for the
same packet. In either case
the sender sets the
congestion threshold to half
of the current congestion
window. The congestion window itself is set to one segment and the sender starts sending a
single segment. The exponential growth starts once more up to the new congestion threshold,
then the window grows in linear fashion.
Fast retransmit/fast recovery
The congestion threshold can be reduced because of two reasons. First one is if the sender
receives continuous acknowledgements for the same packet. It informs the sender that the
receiver has got all the packets upto the acknowledged packet in the sequence and also the
receiver is receiving something continuously from the sender. The gap in the packet stream is
not due to congestion, but a simple packet loss due to a transmission error. The sender can
now retransmit the missing packet(s) before the timer expires. This behavior is called fast
retransmit. It is an early enhancement for preventing slow-start to trigger on losses not caused
by congestion. The receipt of acknowledgements shows that there is no congestion to justify a
slow start. The sender can continue with the current congestion window. The sender performs
a fast recovery from the packet loss. This mechanism can improve the efficiency of TCP
dramatically. The other reason for activating slow start is a time-out due to a missing
acknowledgement. TCP using fast retransmit/fast recovery interprets this congestion in the
network and activates the slow start mechanism.
The advantage of this method is its simplicity. Minor changes in the MH’s software
results in performance increase. No changes are required in FA or CH.
The disadvantage of this scheme is insufficient isolation of packet losses. It mainly
focuses on problems regarding Handover. Also it effects the efficiency when a CH
transmits already delivered packets.
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4. Mobile Transport Layer Mobile Computing
Unit-4
Mukesh Chinta
Asst Prof, CSE, VNRVJIET 4
Problems with Traditional TCP in wireless environments
Slow Start mechanism in fixed networks decreases the efficiency of TCP if used with
mobile receivers or senders.
Error rates on wireless links are orders of magnitude higher compared to fixed fiber or
copper links. This makes compensation for packet loss by TCP quite difficult.
Mobility itself can cause packet loss. There are many situations where a soft handover
from one access point to another is not possible for a mobile end-system.
Standard TCP reacts with slow start if acknowledgements are missing, which does not
help in the case of transmission errors over wireless links and which does not really help
during handover. This behavior results in a severe performance degradation of an
unchanged TCP if used together with wireless links or mobile nodes
Classical TCP Improvements
Indirect TCP (I-TCP)
Indirect TCP segments a TCP connection into a fixed part and a wireless part. The following
figure shows an example with a mobile host connected via a wireless link and an access point to
the ‘wired’ internet where the correspondent host resides.
Standard TCP is used between the fixed computer and the access point. No computer in
the internet recognizes any changes to TCP. Instead of the mobile host, the access point now
terminates the standard TCP connection, acting as a proxy. This means that the access point is
now seen as the mobile host for the fixed host and as the fixed host for the mobile host.
Between the access point and the mobile host, a special TCP, adapted to wireless links, is used.
However, changing TCP for the wireless link is not a requirement. A suitable place for
segmenting the connection is at the foreign agent as it not only controls the mobility of the
mobile host anyway and can also hand over the connection to the next foreign agent when the
mobile host moves on.
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5. Mobile Transport Layer Mobile Computing
Unit-4
Mukesh Chinta
Asst Prof, CSE, VNRVJIET 5
The foreign agent acts as a proxy and relays all data in both directions. If CH
(correspondent host) sends a packet to the MH, the FA acknowledges it and forwards it to the
MH. MH acknowledges on successful reception, but this is only used by the FA. If a packet is lost
on the wireless link, CH doesn’t observe it and FA tries to retransmit it locally to maintain
reliable data transport. If the MH sends a packet, the FA acknowledges it and forwards it to CH.
If the packet is lost on the wireless link, the mobile hosts notice this much faster due to the
lower round trip time and can directly retransmit the packet. Packet loss in the wired network is
now handled by the foreign agent.
Socket and state migration after handover of a mobile host
During handover, the buffered packets, as well as the system state (packet sequence number,
acknowledgements, ports, etc), must migrate to the new agent. No new connection may be
established for the mobile host, and the correspondent host must not see any changes in
connection state. Packet delivery in I-TCP is shown below:
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6. Mobile Transport Layer Mobile Computing
Unit-4
Mukesh Chinta
Asst Prof, CSE, VNRVJIET 6
Advantages of I-TCP
No changes in the fixed network necessary, no changes for the hosts (TCP protocol)
necessary, all current optimizations to TCP still work
Simple to control, mobile TCP is used only for one hop between, e.g., a foreign agent and
mobile host
1. transmission errors on the wireless link do not propagate into the fixed network
2. therefore, a very fast retransmission of packets is possible, the short delay on the
mobile hop s known
It is always dangerous to introduce new mechanisms in a huge network without knowing
exactly how they behave.
New optimizations can be tested at the last hop, without jeopardizing the stability of the
Internet.
It is easy to use different protocols for wired and wireless networks.
Disadvantages of I-TCP
Loss of end-to-end semantics:- an acknowledgement to a sender no longer means that a
receiver really has received a packet, foreign agents might crash.
Higher latency possible:- due to buffering of data within the foreign agent and forwarding to
a new foreign agent
Security issue:- The foreign agent must be a trusted entity
Snooping TCP
The main drawback of I-TCP is the segmentation of the single TCP connection into two TCP
connections, which loses the original end-to-end TCP semantic. A new enhancement, which
leaves the TCP connection intact and is completely transparent, is Snooping TCP. The main
function is to buffer data close to the mobile host to perform fast local retransmission in case of
packet loss.
Snooping TCP as a transparent TCP extension
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7. Mobile Transport Layer Mobile Computing
Unit-4
Mukesh Chinta
Asst Prof, CSE, VNRVJIET 7
Here, the foreign agent buffers all packets with destination mobile host and
additionally ‘snoops’ the packet flow in both directions to recognize acknowledgements. The
foreign agent buffers every packet until it receives an acknowledgement from the mobile host.
If the FA does not receive an acknowledgement from the mobile host within a certain amount
of time, either the packet or the acknowledgement has been lost. Alternatively, the foreign
agent could receive a duplicate ACK which also shows the loss of a packet. Now, the FA
retransmits the packet directly from the buffer thus performing a faster retransmission
compared to the CH. For transparency, the FA does not acknowledge data to the CH, which
would violate end-to-end semantic in case of a FA failure. The foreign agent can filter the
duplicate acknowledgements to avoid unnecessary retransmissions of data from the
correspondent host. If the foreign agent now crashes, the time-out of the correspondent host
still works and triggers a retransmission. The foreign agent may discard duplicates of packets
already retransmitted locally and acknowledged by the mobile host. This avoids unnecessary
traffic on the wireless link.
For data transfer from the mobile host with destination correspondent host, the FA
snoops into the packet stream to detect gaps in the sequence numbers of TCP. As soon as the
foreign agent detects a missing packet, it returns a negative acknowledgement (NACK) to the
mobile host. The mobile host can now retransmit the missing packet immediately. Reordering
of packets is done automatically at the correspondent host by TCP.
Snooping TCP: Packet delivery
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8. Mobile Transport Layer Mobile Computing
Unit-4
Mukesh Chinta
Asst Prof, CSE, VNRVJIET 8
Advantages of snooping TCP:
The end-to-end TCP semantic is preserved.
Most of the enhancements are done in the foreign agent itself which keeps correspondent
host unchanged.
Handover of state is not required as soon as the mobile host moves to another foreign
agent. Even though packets are present in the buffer, time out at the CH occurs and the
packets are transmitted to the new COA.
No problem arises if the new foreign agent uses the enhancement or not. If not, the
approach automatically falls back to the standard solution.
Disadvantages of snooping TCP
Snooping TCP does not isolate the behavior of the wireless link as well as I-TCP.
Transmission errors may propagate till CH.
Using negative acknowledgements between the foreign agent and the mobile host assumes
additional mechanisms on the mobile host. This approach is no longer transparent for
arbitrary mobile hosts.
Snooping and buffering data may be useless if certain encryption schemes are applied end-
to-end between the correspondent host and mobile host. If encryption is used above the
transport layer, (eg. SSL/TLS), snooping TCP can be used.
Mobile TCP
Both I-TCP and Snooping TCP does not help much, if a mobile host gets disconnected.
The M-TCP (mobile TCP) approach has the same goals as I-TCP and snooping TCP: to prevent
the sender window from shrinking if bit errors or disconnection but not congestion cause
current problems. M-TCP wants to improve overall throughput, to lower the delay, to maintain
end-to-end semantics of TCP, and to provide a more efficient handover. Additionally, M-TCP is
especially adapted to the problems arising from lengthy or frequent disconnections. M-TCP
splits the TCP connection into two parts as I-TCP does. An unmodified TCP is used on the
standard host-supervisory host (SH) connection, while an optimized TCP is used on the SH-MH
connection.
The SH monitors all packets sent to the MH and ACKs returned from the MH. If the SH
does not receive an ACK for some time, it assumes that the MH is disconnected. It then chokes
the sender by setting the sender’s window size to 0. Setting the window size to 0 forces the
sender to go into persistent mode, i.e., the state of the sender will not change no matter how
long the receiver is disconnected. This means that the sender will not try to retransmit data. As
soon as the SH (either the old SH or a new SH) detects connectivity again, it reopens the
window of the sender to the old value. The sender can continue sending at full speed. This
mechanism does not require changes to the sender’s TCP. The wireless side uses an adapted
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9. Mobile Transport Layer Mobile Computing
Unit-4
Mukesh Chinta
Asst Prof, CSE, VNRVJIET 9
TCP that can recover from packet loss much faster. This modified TCP does not use slow start,
thus, M-TCP needs a bandwidth manager to implement fair sharing over the wireless link.
Advantages of M-TCP:
It maintains the TCP end-to-end semantics. The SH does not send any ACK itself but
forwards the ACKs from the MH.
If the MH is disconnected, it avoids useless retransmissions, slow starts or breaking
connections by simply shrinking the sender’s window to 0.
As no buffering is done as in I-TCP, there is no need to forward buffers to a new SH. Lost
packets will be automatically retransmitted to the SH.
Disadvantages of M-TCP:
As the SH does not act as proxy as in I-TCP, packet loss on the wireless link due to bit errors
is propagated to the sender. M-TCP assumes low bit error rates, which is not always a valid
assumption.
A modified TCP on the wireless link not only requires modifications to the MH protocol
software but also new network elements like the bandwidth manager.
Transmission/time-out freezing
Often, MAC layer notices connection problems even before the connection is actually
interrupted from a TCP point of view and also knows the real reason for the interruption. The
MAC layer can inform the TCP layer of an upcoming loss of connection or that the current
interruption is not caused by congestion. TCP can now stop sending and ‘freezes’ the current
state of its congestion window and further timers. If the MAC layer notices the upcoming
interruption early enough, both the mobile and correspondent host can be informed. With a
fast interruption of the wireless link, additional mechanisms in the access point are needed to
inform the correspondent host of the reason for interruption. Otherwise, the correspondent
host goes into slow start assuming congestion and finally breaks the connection.
As soon as the MAC layer detects connectivity again, it signals TCP that it can resume
operation at exactly the same point where it had been forced to stop. For TCP time simply does
not advance, so no timers expire.
Advantages:
It offers a way to resume TCP connections even after long interruptions of the connection.
It can be used together with encrypted data as it is independent of other TCP mechanisms
such as sequence no or acknowledgements
Disadvantages:
Lots of changes have to be made in software of MH, CH and FA.
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10. Mobile Transport Layer Mobile Computing
Unit-4
Mukesh Chinta
Asst Prof, CSE, VNRVJIET 10
Selective retransmission
A very useful extension of TCP is the use of selective retransmission. TCP acknowledgements
are cumulative, i.e., they acknowledge in-order receipt of packets up to a certain packet. A
single acknowledgement confirms reception of all packets upto a certain packet. If a single
packet is lost, the sender has to retransmit everything starting from the lost packet (go-back-n
retransmission). This obviously wastes bandwidth, not just in the case of a mobile network, but
for any network.
Using selective retransmission, TCP can indirectly request a selective retransmission of
packets. The receiver can acknowledge single packets, not only trains of in-sequence packets.
The sender can now determine precisely which packet is needed and can retransmit it. The
advantage of this approach is obvious: a sender retransmits only the lost packets. This lowers
bandwidth requirements and is extremely helpful in slow wireless links. The disadvantage is
that a more complex software on the receiver side is needed. Also more buffer space is needed
to resequence data and to wait for gaps to be filled.
Transaction-oriented TCP
Assume an application running on the mobile host that sends a short request to a server from
time to time, which responds with a short message and it requires reliable TCP transport of the
packets. For it to use normal TCP, it is inefficient because of the overhead involved. Standard
TCP is made up of three phases: setup, data transfer and
release. First, TCP uses a three-way handshake to
establish the connection. At least one additional packet
is usually needed for transmission of the request, and
requires three more packets to close the connection via a
three-way handshake. So, for sending one data packet,
TCP may need seven packets altogether. This kind of
overhead is acceptable for long sessions in fixed
networks, but is quite inefficient for short messages or
sessions in wireless networks. This led to the
development of transaction-oriented TCP (T/TCP).
T/TCP can combine packets for connection establishment and
connection release with user data packets. This can reduce the
number of packets down to two instead of seven. The obvious
advantage for certain applications is the reduction in the overhead
which standard TCP has for connection setup and connection release.
Disadvantage is that it requires changes in the software in mobile host
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11. Mobile Transport Layer Mobile Computing
Unit-4
Mukesh Chinta
Asst Prof, CSE, VNRVJIET 11
and all correspondent hosts. This solution does not hide mobility anymore. Also, T/TCP exhibits
several security problems.
Classical Enhancements to TCP for mobility: A comparison
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12. Mobile Transport Layer Mobile Computing
Unit-4
Mukesh Chinta
Asst Prof, CSE, VNRVJIET 12
Assignment Questions
1. (a) Write brief notes on congestion control in traditional TCP.
(b) Compare several enhancements to TCP for mobility giving their relative advantages
and disadvantages
2. (a) Describe transaction oriented TCP.
(b) Explain Mobile TCP. How does a supervisory host send TCP packets to the mobile
node and to a fixed TCP connection.
3. (a) How does selective transmission improve the transmission efficiency? What are the
modifications required in the TCP receiver to implement the selective retransmission
protocol.
(b)Explain snooping TCP. What are it's advantages and disadvantages?
4. Describe indirect TCP. Explain the modifications of indirect TCP as the selective repeat
protocol and mobile - end transport protocol. What are the advantages and
disadvantages of indirect TCP?
5. (a) Why mobility results in packet loss?
(b) Compare the error rate in wired networks and mobile networks.
(c) Why we cannot change TCP completely just to support mobile users? What are the
consequences of it?
6. (a) What are the applications in which packet delayed is equivalent to packet lost?
Explain.
(b) What are the applications for which packet loss can create severe problems? Explain
it
7. (a) Why Access point maintains buffers in Indirect TCP?
(b) How Indirect TCP hides the problems of wireless links from fixed host?
(c) The foreign agent can act as a gateway to translate between the different protocols
in Indirect TCP. Comment
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