This document discusses TCP performance with delayed acknowledgements in wireless networks. It finds that TCP throughput does not always benefit from unrestricted delayed acks, and that there exists an optimal delay window size producing the best throughput for a given topology and flow pattern. Too small a window causes too many acks, while too large a window induces interference and losses from bursty transmissions. The document proposes adaptive delayed ack schemes for ad hoc and hybrid networks to dynamically select appropriate delay window sizes based on path length. It also addresses the issue of unfriendliness between standard and delayed ack TCP.
- The TCP/IP model was created by the Department of Defense to provide reliable networking and data integrity during disasters. It is now the predominant networking model used today.
- The TCP/IP model layers correspond to layers in the OSI model. Key protocols at each TCP/IP layer include IP, TCP, UDP, ARP, and Ethernet at the network/data link layers.
- TCP provides reliable, connection-oriented communications using sequence numbers, acknowledgments, and retransmissions. UDP provides simpler, connectionless delivery without guarantees.
- TCP is a connection-oriented protocol that establishes a full-duplex connection between two endpoints to deliver a byte stream in order with no message boundaries.
- It uses sequence numbers and acknowledgments to ensure reliable and in-order delivery of all bytes. The sender will not overwhelm the receiver due to flow control.
- TCP headers include source/destination ports, sequence numbers, acknowledgments, window size and checksum to establish connections, send data, and implement flow control and reliability.
This document summarizes several internet protocols including IP, TCP, UDP, and ICMP. It describes key aspects of each protocol such as their purpose, packet structure, error handling mechanisms, and how they interact to enable communication over the internet. IP is a connectionless protocol that forwards packets based on destination addresses. TCP and UDP are transport layer protocols, with TCP providing reliable connections and UDP being connectionless. ICMP provides error reporting and control for IP. Port numbers and sockets are used to direct communication to specific applications.
- TCP and IP are core protocols of the Internet Protocol Suite, with TCP operating at the transport layer and providing reliable data transmission, and IP operating at the internet layer and routing packets between hosts.
- TCP establishes a virtual connection between hosts and provides services like flow control, error checking, and reliable ordered delivery. It uses port numbers to identify applications.
- Common applications that use TCP include Telnet, FTP, and TFTP, with Telnet using port 23, FTP using ports 20 and 21, and TFTP using port 69.
The document provides an introduction to TCP/IP and compares it to the OSI model. It discusses the following key points:
- TCP/IP has 4 layers (Application, Transport, Internet, Link) while OSI has 7 layers. TCP/IP is based on standard protocols while OSI is protocol independent.
- Packet encapsulation involves applying headers at each layer, with the TCP/IP headers being Application data, TCP/UDP header, IP header, and network frame header.
- The TCP header is explained, listing the purpose of fields like source/destination port, sequence/acknowledgment numbers, flags, window size, checksum, and options.
In this presentation, we will discuss in details about the TCP/ IP framework, the backbone of every ebusiness.
To know more about Welingkar School’s Distance Learning Program and courses offered, visit:
http://www.welingkaronline.org/distance-learning/online-mba.html
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Students are producing ppt´s related with their learning content to share with each other.
This presentation is related with TCP/IP Internet layer
The document provides an overview of TCP/IP (Transmission Control Protocol/Internet Protocol). It discusses the history and development of TCP/IP, how it relates to the OSI model, IP addressing, TCP and UDP protocols, and how connections are established and torn down using TCP. Key points covered include TCP/IP covering the network and transport layers, IP providing unreliable datagram delivery, TCP providing reliable byte-stream delivery, and the three-way handshake used to open TCP connections.
- The TCP/IP model was created by the Department of Defense to provide reliable networking and data integrity during disasters. It is now the predominant networking model used today.
- The TCP/IP model layers correspond to layers in the OSI model. Key protocols at each TCP/IP layer include IP, TCP, UDP, ARP, and Ethernet at the network/data link layers.
- TCP provides reliable, connection-oriented communications using sequence numbers, acknowledgments, and retransmissions. UDP provides simpler, connectionless delivery without guarantees.
- TCP is a connection-oriented protocol that establishes a full-duplex connection between two endpoints to deliver a byte stream in order with no message boundaries.
- It uses sequence numbers and acknowledgments to ensure reliable and in-order delivery of all bytes. The sender will not overwhelm the receiver due to flow control.
- TCP headers include source/destination ports, sequence numbers, acknowledgments, window size and checksum to establish connections, send data, and implement flow control and reliability.
This document summarizes several internet protocols including IP, TCP, UDP, and ICMP. It describes key aspects of each protocol such as their purpose, packet structure, error handling mechanisms, and how they interact to enable communication over the internet. IP is a connectionless protocol that forwards packets based on destination addresses. TCP and UDP are transport layer protocols, with TCP providing reliable connections and UDP being connectionless. ICMP provides error reporting and control for IP. Port numbers and sockets are used to direct communication to specific applications.
- TCP and IP are core protocols of the Internet Protocol Suite, with TCP operating at the transport layer and providing reliable data transmission, and IP operating at the internet layer and routing packets between hosts.
- TCP establishes a virtual connection between hosts and provides services like flow control, error checking, and reliable ordered delivery. It uses port numbers to identify applications.
- Common applications that use TCP include Telnet, FTP, and TFTP, with Telnet using port 23, FTP using ports 20 and 21, and TFTP using port 69.
The document provides an introduction to TCP/IP and compares it to the OSI model. It discusses the following key points:
- TCP/IP has 4 layers (Application, Transport, Internet, Link) while OSI has 7 layers. TCP/IP is based on standard protocols while OSI is protocol independent.
- Packet encapsulation involves applying headers at each layer, with the TCP/IP headers being Application data, TCP/UDP header, IP header, and network frame header.
- The TCP header is explained, listing the purpose of fields like source/destination port, sequence/acknowledgment numbers, flags, window size, checksum, and options.
In this presentation, we will discuss in details about the TCP/ IP framework, the backbone of every ebusiness.
To know more about Welingkar School’s Distance Learning Program and courses offered, visit:
http://www.welingkaronline.org/distance-learning/online-mba.html
http://ictintocurriculum.forumotion.net/
Students are producing ppt´s related with their learning content to share with each other.
This presentation is related with TCP/IP Internet layer
The document provides an overview of TCP/IP (Transmission Control Protocol/Internet Protocol). It discusses the history and development of TCP/IP, how it relates to the OSI model, IP addressing, TCP and UDP protocols, and how connections are established and torn down using TCP. Key points covered include TCP/IP covering the network and transport layers, IP providing unreliable datagram delivery, TCP providing reliable byte-stream delivery, and the three-way handshake used to open TCP connections.
The document describes the TCP/IP protocol stack and its layers, including the application, transport, internet, and link layers. It explains the roles and functions of each layer, such as how the application layer provides access to network resources, the transport layer prepares data for transport, and the internet layer handles logical addressing and routing. Key protocols like IP, TCP, UDP, and Ethernet are also discussed in relation to how they operate within the TCP/IP model and enable communication across networks and the internet.
The document discusses the Transmission Control Protocol (TCP) which provides reliable, ordered, and error-checked delivery of data between applications running on hosts communicating via an IP network. TCP is connection-oriented and provides a byte stream service on top of the unreliable IP datagram service. It uses acknowledgments and timeouts with retransmission to provide reliability and implements flow control using a sliding window approach. TCP connections are identified by the endpoints - the IP addresses and port numbers of both the hosts. Connection establishment involves a three-way handshake and connection termination involves an orderly four-segment closing sequence.
The document describes the TCP/IP model and its layers:
1. The application layer contains common protocols like FTP, SMTP, HTTP, and DNS.
2. The transport layer contains TCP and UDP which manage end-to-end message transmission and error handling.
3. The network layer is IP which handles routing and congestion of data packets.
4. The lower layers include the data link layer which manages reliable data delivery to physical networks, and the physical layer which defines the physical media.
The document discusses TCP/IP basics and networking concepts. It provides an overview of the OSI model and describes the layers from physical to application. It then focuses on the lower layers including Ethernet, IP addressing, ARP, and introduces TCP and UDP at the transport layer.
TCP/IP is an internet protocol suite developed by DARPA that defines the rules and standards for communication between electronic devices connected to the internet. It operates on four layers - application, transport, internet, and network interface. Key protocols include TCP and IP which work together to break data into packets and route them to the correct destination. ARP and RARP protocols map IP addresses to MAC addresses to enable communication between devices on a local network.
This document discusses the four layers of the TCP/IP model and how they coordinate with each other. It explains the processes of encapsulation and decapsulation as data moves between layers. Encapsulation involves each layer adding a header to data packets as they move down the stack, while decapsulation is the reverse process of removing headers as packets move up the stack at their destination. Figures and references are provided to illustrate these TCP/IP concepts.
TCP/IP is a set of communication protocols used to connect devices on the internet. It includes lower level protocols like IP that handle basic transport of data and higher level protocols like TCP that ensure reliable delivery of data between applications. TCP establishes connections between clients and servers that allow for reliable transmission of data streams. UDP provides a simpler transmission model without ensuring delivery but is useful for applications like broadcasting.
User Datagram Protocol (UDP) is a connectionless protocol that provides datagram socket services. It is simpler than TCP with less overhead but does not guarantee delivery or order of packets. The Java API provides the DatagramSocket and DatagramPacket classes to send and receive data packets. A MulticastSocket subclass of DatagramSocket allows sending data to multiple recipients by joining them to a multicast group.
The document describes the TCP 3-way handshake process used to establish a connection between a client and server in a TCP/IP network. It involves 3 steps: 1) the client sends a SYN packet to the server, 2) the server responds with a SYN-ACK packet to acknowledge the client's SYN and identify its own sequence number, and 3) the client sends an ACK packet to the server to acknowledge receiving the SYN-ACK and complete the handshake process, allowing data transfer to begin.
TCP/IP is a set of communication protocols that enable data transmission across networks and between devices. It involves two main protocols: TCP and IP. TCP establishes reliable connections and ensures reliable delivery of data packets. IP handles addressing, routing packets between networks, and fragmentation/reassembly of packets. Key features of TCP/IP include logical addressing, routability, name resolution, multiplexing, and interoperability. TCP/IP operates on four layers - network interface, internet, transport, and application - with each layer building on the services of the layer below.
TCP and UDP are transport layer protocols that package and deliver data between applications. TCP provides reliable, ordered delivery through connection establishment and packet sequencing. UDP provides faster, unreliable datagram delivery without connections. Common applications using TCP include HTTP, FTP, and SMTP. Common UDP applications include DNS, DHCP, and streaming media.
This document discusses the TCP/IP protocol suite and its layers. It begins by explaining that the OSI model was developed in 1970 as a networking standard, while TCP/IP was developed prior as a stack of protocols. It then notes that TCP/IP layers correspond to the OSI model layers. The document proceeds to describe some of the key protocols in each TCP/IP layer: application layer protocols include HTTP, FTP, SMTP, and Telnet; transport layer protocols are TCP and UDP; and internet layer protocols comprise IP, ARP, RARP, ICMP, and IGMP. Finally, it states that the host to network layers do not specify any special protocols.
The document compares the TCP/IP and OSI network models. It notes that while the OSI model has 7 layers, TCP/IP has 4 layers: Network Access, Internet, Transport, and Application. The Network Access layer combines the functions of the OSI Data Link and Physical layers. It provides details on the protocols and functions of each TCP/IP layer, including common protocols like IP, TCP, UDP, HTTP, and FTP.
TCP/IP is a four-layer model used for communication between computers, consisting of the physical, data link, internet, and transport layers. The physical and data link layers combine to form the link layer, which includes protocols like Ethernet that define hardware connections. The internet layer, responsible for routing packets between sources and destinations, uses IP as its main protocol. The transport layer ensures reliable or unreliable end-to-end delivery using protocols like TCP and UDP. The top application layer supports user-facing services through various protocols.
TCP/IP is a set of protocols that defines how data is transmitted and formatted so that networked systems can communicate. It originated from ARPAnet, which was developed by the Department of Defense to create a decentralized network resilient to attacks. TCP/IP provides logical addressing, routing between networks, name resolution from names to addresses, error checking and flow control for reliable data transmission, and support for multiple applications simultaneously through the use of ports. It is overseen by various standards organizations to ensure interoperability.
TCP/IP is a set of communication protocols used to connect devices on the internet and other networks. It has two main protocols - TCP for reliable transmission of data between devices, and IP for addressing devices and routing packets across networks. TCP/IP uses ports to allow multiple applications to run simultaneously on a single device. Routers use IP addressing and routing tables to determine the best path for sending packets between devices on different networks.
TCP provides reliable data transfer over unreliable packet networks by using acknowledgments, retransmissions, and adaptive congestion control. It works with IP to transfer data through routers that may drop packets. While TCP ensures reliable delivery, it must control its transmission rate to avoid overwhelming network capacity and causing congestion collapse. This is achieved through additive-increase, multiplicative-decrease of the congestion window and techniques like active queue management.
The document provides an overview of the OSI model and TCP/IP networking model. It describes the seven layers of the OSI model from the physical layer to the application layer and their responsibilities in networking. It also discusses the four layers of the TCP/IP model and compares it to the OSI model. Key protocols like TCP, UDP, IP, Ethernet, and HTTP are explained in their respective layers along with functions like encapsulation and data flow between layers. Network analysis tools like Wireshark are also mentioned.
Although the OSI reference model is universally recognized, the historical and technical open standard of the Internet is Transmission Control Protocol / Internet Protocol (TCP/IP).
The TCP/IP reference model and the TCP/IP protocol stack make data communication possible between any two computers, anywhere in the world, at nearly the speed of light.
This document discusses the User Datagram Protocol (UDP) which provides a connectionless mode of communication between applications on hosts in an IP network. It describes the format of UDP packets, how UDP checksums are calculated, and UDP's operation including encapsulation, queuing, and demultiplexing. Examples are provided to illustrate how a UDP control block table and queues are used to handle incoming and outgoing UDP packets. The document also discusses when UDP is an appropriate protocol to use compared to TCP.
A short but packed course on TCP Dynamic Behavior. It starts by explaining TCP from scratch so the dynamic parts can be understood. Then it dives deep into how TCP behaves in real IP networks in the face of packet losses, delays and other phenomena.
CS4344 09/10 Lecture 10: Transport Protocol for Networked GamesWei Tsang Ooi
The document discusses transport protocols for networked games and compares TCP and UDP. While TCP provides reliable delivery, it has higher latency than UDP. UDP has lower overhead but is unreliable. The document examines why certain popular games use TCP or UDP and outlines strategies to make TCP perform better for games, such as reducing delays, retransmitting bundles of data, and combining thin streams. It suggests the Stream Control Transmission Protocol (SCTP) as a potentially ideal transport for games since it allows flexibility in reliability and ordering of messages.
The document describes the TCP/IP protocol stack and its layers, including the application, transport, internet, and link layers. It explains the roles and functions of each layer, such as how the application layer provides access to network resources, the transport layer prepares data for transport, and the internet layer handles logical addressing and routing. Key protocols like IP, TCP, UDP, and Ethernet are also discussed in relation to how they operate within the TCP/IP model and enable communication across networks and the internet.
The document discusses the Transmission Control Protocol (TCP) which provides reliable, ordered, and error-checked delivery of data between applications running on hosts communicating via an IP network. TCP is connection-oriented and provides a byte stream service on top of the unreliable IP datagram service. It uses acknowledgments and timeouts with retransmission to provide reliability and implements flow control using a sliding window approach. TCP connections are identified by the endpoints - the IP addresses and port numbers of both the hosts. Connection establishment involves a three-way handshake and connection termination involves an orderly four-segment closing sequence.
The document describes the TCP/IP model and its layers:
1. The application layer contains common protocols like FTP, SMTP, HTTP, and DNS.
2. The transport layer contains TCP and UDP which manage end-to-end message transmission and error handling.
3. The network layer is IP which handles routing and congestion of data packets.
4. The lower layers include the data link layer which manages reliable data delivery to physical networks, and the physical layer which defines the physical media.
The document discusses TCP/IP basics and networking concepts. It provides an overview of the OSI model and describes the layers from physical to application. It then focuses on the lower layers including Ethernet, IP addressing, ARP, and introduces TCP and UDP at the transport layer.
TCP/IP is an internet protocol suite developed by DARPA that defines the rules and standards for communication between electronic devices connected to the internet. It operates on four layers - application, transport, internet, and network interface. Key protocols include TCP and IP which work together to break data into packets and route them to the correct destination. ARP and RARP protocols map IP addresses to MAC addresses to enable communication between devices on a local network.
This document discusses the four layers of the TCP/IP model and how they coordinate with each other. It explains the processes of encapsulation and decapsulation as data moves between layers. Encapsulation involves each layer adding a header to data packets as they move down the stack, while decapsulation is the reverse process of removing headers as packets move up the stack at their destination. Figures and references are provided to illustrate these TCP/IP concepts.
TCP/IP is a set of communication protocols used to connect devices on the internet. It includes lower level protocols like IP that handle basic transport of data and higher level protocols like TCP that ensure reliable delivery of data between applications. TCP establishes connections between clients and servers that allow for reliable transmission of data streams. UDP provides a simpler transmission model without ensuring delivery but is useful for applications like broadcasting.
User Datagram Protocol (UDP) is a connectionless protocol that provides datagram socket services. It is simpler than TCP with less overhead but does not guarantee delivery or order of packets. The Java API provides the DatagramSocket and DatagramPacket classes to send and receive data packets. A MulticastSocket subclass of DatagramSocket allows sending data to multiple recipients by joining them to a multicast group.
The document describes the TCP 3-way handshake process used to establish a connection between a client and server in a TCP/IP network. It involves 3 steps: 1) the client sends a SYN packet to the server, 2) the server responds with a SYN-ACK packet to acknowledge the client's SYN and identify its own sequence number, and 3) the client sends an ACK packet to the server to acknowledge receiving the SYN-ACK and complete the handshake process, allowing data transfer to begin.
TCP/IP is a set of communication protocols that enable data transmission across networks and between devices. It involves two main protocols: TCP and IP. TCP establishes reliable connections and ensures reliable delivery of data packets. IP handles addressing, routing packets between networks, and fragmentation/reassembly of packets. Key features of TCP/IP include logical addressing, routability, name resolution, multiplexing, and interoperability. TCP/IP operates on four layers - network interface, internet, transport, and application - with each layer building on the services of the layer below.
TCP and UDP are transport layer protocols that package and deliver data between applications. TCP provides reliable, ordered delivery through connection establishment and packet sequencing. UDP provides faster, unreliable datagram delivery without connections. Common applications using TCP include HTTP, FTP, and SMTP. Common UDP applications include DNS, DHCP, and streaming media.
This document discusses the TCP/IP protocol suite and its layers. It begins by explaining that the OSI model was developed in 1970 as a networking standard, while TCP/IP was developed prior as a stack of protocols. It then notes that TCP/IP layers correspond to the OSI model layers. The document proceeds to describe some of the key protocols in each TCP/IP layer: application layer protocols include HTTP, FTP, SMTP, and Telnet; transport layer protocols are TCP and UDP; and internet layer protocols comprise IP, ARP, RARP, ICMP, and IGMP. Finally, it states that the host to network layers do not specify any special protocols.
The document compares the TCP/IP and OSI network models. It notes that while the OSI model has 7 layers, TCP/IP has 4 layers: Network Access, Internet, Transport, and Application. The Network Access layer combines the functions of the OSI Data Link and Physical layers. It provides details on the protocols and functions of each TCP/IP layer, including common protocols like IP, TCP, UDP, HTTP, and FTP.
TCP/IP is a four-layer model used for communication between computers, consisting of the physical, data link, internet, and transport layers. The physical and data link layers combine to form the link layer, which includes protocols like Ethernet that define hardware connections. The internet layer, responsible for routing packets between sources and destinations, uses IP as its main protocol. The transport layer ensures reliable or unreliable end-to-end delivery using protocols like TCP and UDP. The top application layer supports user-facing services through various protocols.
TCP/IP is a set of protocols that defines how data is transmitted and formatted so that networked systems can communicate. It originated from ARPAnet, which was developed by the Department of Defense to create a decentralized network resilient to attacks. TCP/IP provides logical addressing, routing between networks, name resolution from names to addresses, error checking and flow control for reliable data transmission, and support for multiple applications simultaneously through the use of ports. It is overseen by various standards organizations to ensure interoperability.
TCP/IP is a set of communication protocols used to connect devices on the internet and other networks. It has two main protocols - TCP for reliable transmission of data between devices, and IP for addressing devices and routing packets across networks. TCP/IP uses ports to allow multiple applications to run simultaneously on a single device. Routers use IP addressing and routing tables to determine the best path for sending packets between devices on different networks.
TCP provides reliable data transfer over unreliable packet networks by using acknowledgments, retransmissions, and adaptive congestion control. It works with IP to transfer data through routers that may drop packets. While TCP ensures reliable delivery, it must control its transmission rate to avoid overwhelming network capacity and causing congestion collapse. This is achieved through additive-increase, multiplicative-decrease of the congestion window and techniques like active queue management.
The document provides an overview of the OSI model and TCP/IP networking model. It describes the seven layers of the OSI model from the physical layer to the application layer and their responsibilities in networking. It also discusses the four layers of the TCP/IP model and compares it to the OSI model. Key protocols like TCP, UDP, IP, Ethernet, and HTTP are explained in their respective layers along with functions like encapsulation and data flow between layers. Network analysis tools like Wireshark are also mentioned.
Although the OSI reference model is universally recognized, the historical and technical open standard of the Internet is Transmission Control Protocol / Internet Protocol (TCP/IP).
The TCP/IP reference model and the TCP/IP protocol stack make data communication possible between any two computers, anywhere in the world, at nearly the speed of light.
This document discusses the User Datagram Protocol (UDP) which provides a connectionless mode of communication between applications on hosts in an IP network. It describes the format of UDP packets, how UDP checksums are calculated, and UDP's operation including encapsulation, queuing, and demultiplexing. Examples are provided to illustrate how a UDP control block table and queues are used to handle incoming and outgoing UDP packets. The document also discusses when UDP is an appropriate protocol to use compared to TCP.
A short but packed course on TCP Dynamic Behavior. It starts by explaining TCP from scratch so the dynamic parts can be understood. Then it dives deep into how TCP behaves in real IP networks in the face of packet losses, delays and other phenomena.
CS4344 09/10 Lecture 10: Transport Protocol for Networked GamesWei Tsang Ooi
The document discusses transport protocols for networked games and compares TCP and UDP. While TCP provides reliable delivery, it has higher latency than UDP. UDP has lower overhead but is unreliable. The document examines why certain popular games use TCP or UDP and outlines strategies to make TCP perform better for games, such as reducing delays, retransmitting bundles of data, and combining thin streams. It suggests the Stream Control Transmission Protocol (SCTP) as a potentially ideal transport for games since it allows flexibility in reliability and ordering of messages.
TCP and UDP are the main protocols used for network programming with sockets. TCP provides reliable connections using three-way handshakes and four-way handshakes for connection establishment and termination. UDP provides simpler datagram transmissions without establishing connections. Sockets provide an interface for applications to communicate over networks, with socket addresses containing IP addresses and ports. HTTP is a widely used request-response protocol that can use various request methods like GET and POST to transfer resources over TCP connections. Unix systems support multiple I/O models including blocking I/O, non-blocking I/O, I/O multiplexing, signal-driven I/O, and asynchronous I/O.
The document discusses various topics related to flow and error control in computer networks, including stop-and-wait ARQ, sliding window protocols, and selective reject ARQ. Stop-and-wait ARQ allows transmission of one frame at a time, while sliding window protocols allow multiple outstanding frames using sequence numbers and acknowledgments. Go-back-N ARQ requires retransmission of frames from the lost frame onward, while selective reject ARQ only retransmits the lost frame to minimize retransmissions.
Fourth lesson of the Computer Networking class. Covers reliable transport principles and the introduction for sharing resources (MAC and congestion control)
A dynamic performance-based_flow_controlingenioustech
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Performance Evaluation of TCP with Adaptive Pacing and LRED in Multihop Wirel...ijwmn
Transmission Control Protocol (TCP) was designed to provide reliable end-to-end delivery of
data over unreliable networks. In practice, most TCP deployments have been carefully designed in the
context of wired networks. Ignoring the properties of wireless and Ad-hoc Networks can lead to TCP
implementations with poor performance. In a wireless network, however packet losses occur more often
due to unreliable wireless links than due to congestion. When using TCP over wireless links, each packet
loss on the wireless link results in congestion control measures being invoked at the source. This causes
severe performance degradation. If there is any packet loss in wireless networks, then the reason for that
has to be found out. If there is congestion, then only congestion control mechanism has to be applied.
This work shows the performance of TCP with Adaptive Pacing (TCP-AP) and Link Random Early
Discard (LRED) as queuing model in multihop transmission when the source and destination nodes are
in mobile nature. The adaptive pacing technique seeks to improve spatial reuse. The LRED technique
seeks to react earlier to link overload. This paper consists of simulated environment results under
different network scenarios. This work proves that the combination of TCP-AP and LRED give much
better result than as the individual technique. Simulations are done with the use of NS-2.
Analysis of Rate Based Congestion Control Algorithms in Wireless TechnologiesIOSR Journals
The document analyzes various rate-based congestion control algorithms for wireless technologies. It finds that TCP Vegas performs better than other TCP variants in terms of delivery fraction and delay. However, TCP Vegas has a consistent window size. Congestion avoidance is more effective at resolving congestion and has higher throughput than slow start. Cross-layer congestion control requires significant power and memory. The document then analyzes the performance of AIMD, TFRC, and TCP congestion control protocols via simulation. It finds that GAIMD performs better than TFRC in terms of throughput, while TFRC is better than GAIMD in terms of smoothness.
This document analyzes and compares the congestion window behavior of three TCP variants (HS-TCP, Full-TCP, and TCP-Linux) over a Long Term Evolution (LTE) network model using network simulation. It first reviews related work that has analyzed TCP performance but with assumptions like equal window sizes or only considering uploads/downloads. The document then describes the topology and parameters used to simulate the LTE network in NS-2. Simulation results are presented that analyze the slow-start and congestion avoidance phases of each TCP variant individually, and also compare their congestion window behavior over the full simulation period.
Sky X products provide performance enhancement for data transmissions over satellite networks by replacing TCP with a custom protocol called Sky X that is optimized for satellite conditions like long latency and high bit error rates. The Sky X Gateway intercepts TCP connections and converts the data to the Sky X protocol for transmission over the satellite. This solution increases web and file transfer speeds by 3 to 100 times compared to TCP over satellite. The Sky X products transparently replace TCP and do not require any client or server modifications.
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.
The document proposes a Crosslayered and Power Conserved Routing Topology (CPCRT) for congestion control in mobile ad hoc networks. CPCRT aims to distinguish between packet loss due to link failure versus other causes like congestion. It takes a cross-layer approach using information from the physical, MAC, and application layers. The proposed method also aims to conserve power during packet transmission by adjusting transmission power levels based on received signal strength. Simulation results show that CPCRT can better utilize resources and conserve power during congestion control compared to other approaches.
CPCRT: Crosslayered and Power Conserved Routing Topology for congestion Cont...IOSR Journals
The document describes a proposed Crosslayered and Power Conserved Routing Topology (CPCRT) for congestion control in mobile ad hoc networks. The CPCRT aims to improve transmission performance by distinguishing between packet loss due to link failure versus other causes, while also conserving power used for packet transmission. It builds upon an earlier Crosslayered Routing Topology (CRT) approach by incorporating power conservation. The CPCRT is intended to identify the root cause of packet loss, avoid unnecessary congestion handling from link failures, allow congestion handling at specific high-traffic nodes rather than all nodes, and optimize resource and power usage for packet routing in mobile ad hoc networks.
Efficient and Fair Bandwidth Allocation AQM Scheme for Wireless NetworksCSCJournals
Heterogeneous Wireless Networks are considered nowadays as one of the potential areas in research and development. The traffic management’s schemes that have been used at the fusion points between the different wireless networks are classical and conventional. This paper is focused on developing a novel scheme to overcome the problem of traffic congestion in the fusion point router interconnected the heterogeneous wireless networks. The paper proposed an EF-AQM algorithm which provides an efficient and fair allocation of bandwidth among different established flows. Finally, the proposed scheme developed, tested and validated through a set of experiments to demonstrate the relative merits and capabilities of a proposed scheme
PERFORMANCE EVALUATION OF SELECTED E2E TCP CONGESTION CONTROL MECHANISM OVER ...ijwmn
TCP is one of the main protocols that govern the Internet traffic nowadays. However, it suffers significant
performance degradation over wireless links. Since wireless networks are leading the communication
technologies recently, it is imperative to introduce effective solutions for the TCP congestion control
mechanisms over such networks. In this research four End-to-End TCP implementations are discussed,
they are TCP Westwood, Hybla, Highspeed, and NewReno. The performance of these variants is compared
using LTE emulated environment in terms of throughput, delay, and fairness. Ns-3 simulator is used to
simulate the LTE networks environment. The simulation results showed that TCP Highspeed achieves the
best throughput results. Although TCP Westwood recorded the lowest latency values comparing to others,
it behaved unfairly among different traffic flows. Moreover, TCP Hybla demonstrated the best fairness
behaviour among other TCP variants
Packet losses at IP network are common behavior at
the time of congestion. The TCP traffic is explained as in
terms of load and capacity. The load should be measured as
number of sender actively competes for a bottleneck link and
the capacity as the total network buffering available to those
senders. Though there are many congestion mechanism
already in practice like congestion window, slow start,
congestion avoidance, fast transmit but still we see erratic
behavior when there is a large traffic. The TCP protocol that
controls sources send rates degrades rapidly if the network
cannot store at least a few packets per active connection. Thus
the amount of router buffer space required for good
performance scales with the number of active connections
and the bandwidth utilization by each active connections. As
in the current practice, the buffer space does not scale in this
way and router drops the packet without looking at bandwidth
utilization of each connections. The result is global
synchronization and phase effect as well as packet from the
unlucky sender will be frequently dropped. The simultaneous
requirements of low queuing delay and of large buffer
memories for large numbers of connections pose a problem.
Routers should enforce a dropping policy by proportional to
the bandwidth utilization by each active connection. Router
will provision the buffering mechanism when processing slows
down. This study explains the existing problem with drop-tail
and RED routers and proposes the new mechanism to predict
the effective bandwidth utilization of the clients depending
on their history of utilization and drop the packet in different
pattern after analyzing the network bandwidth utilization at
each specific interval of time
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.
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
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.
ANALYSIS OF LINK STATE RESOURCE RESERVATION PROTOCOL FOR CONGESTION MANAGEMEN...ijgca
With the wide spread of WiFi hotspots, concentrated traffic workload on Smart Web (SW) can slow down the network performance. This paper presents a congestion management strategy considering real time activities in today’s smart web. With the SW context, cooperative packet recovery using resource reservation procedure for TCP flows was adapted for mitigating packet losses. This is to maintain data consistency between various access points of smart web hotspot. Using a real world scenario, it was confirmed that generic TCP cannot handle traffic congestion in a SW hotspot network. With TCP in scalable workload environments, continuous packet drops at the event of congestion remains obvious. This is unacceptable for mission critical domains. An enhanced Link State Resource Reservation Protocol (LSRSVP) which serves as dynamic feedback mechanism in smart web hotspots is presented. The contextual behaviour was contrasted with the generic TCP model. For the LS-RSVP, a simulation experiment for TCP connection between servers at the remote core layer and the access layer was carried out while using selected benchmark metrics. From the results, under realistic workloads, a steady-state throughput response was achieved by TCP LS-RSVP to about 3650Bits/secs compared with generic TCP plots in a previous study. Considering network service availability, this was found to be dependent on fault-tolerance of the hotspot network. From study, a high peak threshold of 0.009 (i.e. 90%) was observed. This shows fairly acceptable service availability behaviour compared with the existing TCP schemes. For packet drop effects, an analysis on the network behaviour with respect to the LS-RSVP yielded a drop response of about 0.000106 bits/sec which is much lower compared with the case with generic TCP with over 0.38 bits/sec. The latency profile of average FTP download response was found to be 0.030secs, but with that of FTP upload response, this yielded about 0.028 sec. The results from the study demonstrate efficiency and optimality for realistic loads in Smart web contexts.
Analysis of Link State Resource Reservation Protocol for Congestion Managemen...ijgca
With the wide spread of WiFi hotspots, concentrated traffic workload on Smart Web (SW) can slow down
the network performance. This paper presents a congestion management strategy considering real time
activities in today’s smart web. With the SW context, cooperative packet recovery using resource
reservation procedure for TCP flows was adapted for mitigating packet losses. This is to maintain data
consistency between various access points of smart web hotspot. Using a real world scenario, it was
confirmed that generic TCP cannot handle traffic congestion in a SW hotspot network. With TCP in
scalable workload environments, continuous packet drops at the event of congestion remains obvious. This
is unacceptable for mission critical domains. An enhanced Link State Resource Reservation Protocol (LSRSVP)
which serves as dynamic feedback mechanism in smart web hotspots is presented. The contextual
behaviour was contrasted with the generic TCP model. For the LS-RSVP, a simulation experiment for TCP
connection between servers at the remote core layer and the access layer was carried out while using
selected benchmark metrics. From the results, under realistic workloads, a steady-state throughput
response was achieved by TCP LS-RSVP to about 3650Bits/secs compared with generic TCP plots in a
previous study. Considering network service availability, this was found to be dependent on fault-tolerance
of the hotspot network. From study, a high peak threshold of 0.009 (i.e. 90%) was observed. This shows
fairly acceptable service availability behaviour compared with the existing TCP schemes. For packet drop
effects, an analysis on the network behaviour with respect to the LS-RSVP yielded a drop response of about
0.000106 bits/sec which is much lower compared with the case with generic TCP with over 0.38 bits/sec.
The latency profile of average FTP download response was found to be 0.030secs, but with that of FTP
upload response, this yielded about 0.028 sec. The results from the study demonstrate efficiency and
optimality for realistic loads in Smart web contexts.
This document summarizes a survey and analysis of various host-to-host congestion control proposals for TCP data transmission. It discusses the basic principles that underlie current host-to-host algorithms, including probing available network resources, estimating congestion through packet loss or delay, and quickly detecting packet losses. The document then analyzes specific algorithms like slow start, congestion avoidance, and fast recovery. It also examines calculating retransmission timeout and round-trip time, congestion avoidance and packet recovery techniques, and data transmission in TCP. The overall goal of these proposals is to control congestion in a distributed manner without relying on explicit network notifications.
An adaptive power controlled mac protocol forambitlick
The document summarizes an adaptive power controlled MAC protocol called ATPMAC that is proposed to improve network throughput in wireless ad hoc networks using a single channel and transceiver. ATPMAC allows concurrent transmissions without interference by controlling transmission power. It improves on prior work by requiring only one RTS/CTS exchange for multiple concurrent transmissions, avoiding additional signaling overhead, and providing synchronization solutions so concurrent data transmissions can occur despite propagation delays. Simulations showed ATPMAC improved network throughput by up to 136% compared to IEEE 802.11.
The document discusses challenges with using TCP in mobile ad hoc networks (MANETs) and evaluates potential solutions. Specifically, it finds that:
1) TCP performs poorly in MANETs due to high packet loss from route failures and wireless errors, which TCP misinterprets as congestion.
2) TCP variants like Westwood and Jersey that more accurately estimate bandwidth perform better but are not sufficient.
3) A new transport protocol like ATP that is rate-based rather than window-based and leverages intermediate nodes may better address MANET issues.
Similar to TCP with delayed ack for wireless networks (20)
LAND USE LAND COVER AND NDVI OF MIRZAPUR DISTRICT, UPRAHUL
This Dissertation explores the particular circumstances of Mirzapur, a region located in the
core of India. Mirzapur, with its varied terrains and abundant biodiversity, offers an optimal
environment for investigating the changes in vegetation cover dynamics. Our study utilizes
advanced technologies such as GIS (Geographic Information Systems) and Remote sensing to
analyze the transformations that have taken place over the course of a decade.
The complex relationship between human activities and the environment has been the focus
of extensive research and worry. As the global community grapples with swift urbanization,
population expansion, and economic progress, the effects on natural ecosystems are becoming
more evident. A crucial element of this impact is the alteration of vegetation cover, which plays a
significant role in maintaining the ecological equilibrium of our planet.Land serves as the foundation for all human activities and provides the necessary materials for
these activities. As the most crucial natural resource, its utilization by humans results in different
'Land uses,' which are determined by both human activities and the physical characteristics of the
land.
The utilization of land is impacted by human needs and environmental factors. In countries
like India, rapid population growth and the emphasis on extensive resource exploitation can lead
to significant land degradation, adversely affecting the region's land cover.
Therefore, human intervention has significantly influenced land use patterns over many
centuries, evolving its structure over time and space. In the present era, these changes have
accelerated due to factors such as agriculture and urbanization. Information regarding land use and
cover is essential for various planning and management tasks related to the Earth's surface,
providing crucial environmental data for scientific, resource management, policy purposes, and
diverse human activities.
Accurate understanding of land use and cover is imperative for the development planning
of any area. Consequently, a wide range of professionals, including earth system scientists, land
and water managers, and urban planners, are interested in obtaining data on land use and cover
changes, conversion trends, and other related patterns. The spatial dimensions of land use and
cover support policymakers and scientists in making well-informed decisions, as alterations in
these patterns indicate shifts in economic and social conditions. Monitoring such changes with the
help of Advanced technologies like Remote Sensing and Geographic Information Systems is
crucial for coordinated efforts across different administrative levels. Advanced technologies like
Remote Sensing and Geographic Information Systems
9
Changes in vegetation cover refer to variations in the distribution, composition, and overall
structure of plant communities across different temporal and spatial scales. These changes can
occur natural.
Walmart Business+ and Spark Good for Nonprofits.pdfTechSoup
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Temple of Asclepius in Thrace. Excavation resultsKrassimira Luka
The temple and the sanctuary around were dedicated to Asklepios Zmidrenus. This name has been known since 1875 when an inscription dedicated to him was discovered in Rome. The inscription is dated in 227 AD and was left by soldiers originating from the city of Philippopolis (modern Plovdiv).
Beyond Degrees - Empowering the Workforce in the Context of Skills-First.pptxEduSkills OECD
Iván Bornacelly, Policy Analyst at the OECD Centre for Skills, OECD, presents at the webinar 'Tackling job market gaps with a skills-first approach' on 12 June 2024
Philippine Edukasyong Pantahanan at Pangkabuhayan (EPP) CurriculumMJDuyan
(𝐓𝐋𝐄 𝟏𝟎𝟎) (𝐋𝐞𝐬𝐬𝐨𝐧 𝟏)-𝐏𝐫𝐞𝐥𝐢𝐦𝐬
𝐃𝐢𝐬𝐜𝐮𝐬𝐬 𝐭𝐡𝐞 𝐄𝐏𝐏 𝐂𝐮𝐫𝐫𝐢𝐜𝐮𝐥𝐮𝐦 𝐢𝐧 𝐭𝐡𝐞 𝐏𝐡𝐢𝐥𝐢𝐩𝐩𝐢𝐧𝐞𝐬:
- Understand the goals and objectives of the Edukasyong Pantahanan at Pangkabuhayan (EPP) curriculum, recognizing its importance in fostering practical life skills and values among students. Students will also be able to identify the key components and subjects covered, such as agriculture, home economics, industrial arts, and information and communication technology.
𝐄𝐱𝐩𝐥𝐚𝐢𝐧 𝐭𝐡𝐞 𝐍𝐚𝐭𝐮𝐫𝐞 𝐚𝐧𝐝 𝐒𝐜𝐨𝐩𝐞 𝐨𝐟 𝐚𝐧 𝐄𝐧𝐭𝐫𝐞𝐩𝐫𝐞𝐧𝐞𝐮𝐫:
-Define entrepreneurship, distinguishing it from general business activities by emphasizing its focus on innovation, risk-taking, and value creation. Students will describe the characteristics and traits of successful entrepreneurs, including their roles and responsibilities, and discuss the broader economic and social impacts of entrepreneurial activities on both local and global scales.
B. Ed Syllabus for babasaheb ambedkar education university.pdf
TCP with delayed ack for wireless networks
1. Available online at www.sciencedirect.com
Ad Hoc Networks 6 (2008) 1098–1116
www.elsevier.com/locate/adhoc
TCP with delayed ack for wireless networks
Jiwei Chen *, Mario Gerla, Yeng Zhong Lee, M.Y. Sanadidi
University of California, Los Angeles, CA 90095, United States
Received 5 May 2006; received in revised form 25 October 2007; accepted 30 October 2007
Available online 6 November 2007
Abstract
This paper studies the TCP performance with delayed ack in wireless networks (including ad hoc and WLANs) which
use IEEE 802.11 MAC protocol as the underlying medium access control. Our analysis and simulations show that TCP
throughput does not always benefit from an unrestricted delay policy. In fact, for a given topology and flow pattern, there
exists an optimal delay window size at the receiver that produces best TCP throughput. If the window is set too small, the
receiver generates too many acks and causes channel contention; on the other hand, if the window is set too high, the bur-
sty transmission at the sender triggered by large cumulative acks will induce interference and packet losses, thus degrading
the throughout. In wireless networks, packet losses are also related to the length of TCP path; when traveling through a
longer path, a packet is more likely to suffer interference. Therefore, path length is an important factor to consider when
choosing appropriate delay window sizes. In this paper, we first propose an adaptive delayed ack mechanism which is suit-
able for ad hoc networks, then we propose a more general adaptive delayed ack scheme for ad hoc and hybrid networks.
The simulation results show that our schemes can effectively improve TCP throughput by up to 25% in static networks, and
provide more significant gain in mobile networks. The proposed schemes are simple and easy to deploy. The real testbed
experiments are also presented to verify our approaches. Furthermore, a simple and effective receiver-side probe and detec-
tion is proposed to improve friendliness between the standard TCP and our proposed TCP with adaptive delayed ack.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: TCP; Congestion control; Adaptive delayed ack; Wireless medium access/contention; Friendliness
1. Introduction networks, several other inherent factors attribute to
the TCP performance deterioration, including
The Transport Control Protocol (TCP) is the unpredictable channel errors, medium access con-
most widely used reliable transport protocol over tention complicated by hidden/exposed terminal
the Internet. TCP was originally designed for wired problems, and frequent route breakages caused by
links where buffer overflows account for most node mobility. All these factors pose great chal-
packet losses. However, in multihop ad hoc wireless lenges to the design of TCP protocols to provide
efficient and reliable end-to-end communications.
*
Many researchers have made valiant effort to pro-
Corresponding author.
E-mail addresses: cjw@ee.ucla.edu (J. Chen), gerla@cs.
pose various methods to make TCP survive in such
ucla.edu (M. Gerla), yenglee@cs.ucla.edu (Y.Z. Lee), medy@cs. challenging environments. In this paper, we focus
ucla.edu (M.Y. Sanadidi). on studying the effect of delayed acks on TCP
1570-8705/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.adhoc.2007.10.004
2. J. Chen et al. / Ad Hoc Networks 6 (2008) 1098–1116 1099
performance. Then based on our findings, we pro- in turn causes severe packet interference with each
pose adaptive schemes that address the aforemen- other. When packet loss rate becomes high, the
tioned factors effectively. benefit of delaying acks, via reducing ack packets,
In standard TCP the receiver generates one ack disappears. Consequently, TCP performance
for each data packet, or more popularly, two in- degrades after reaching the peak at the optimal
order data packets with the standard delayed ack delay window size.
option [1]. This mechanism works well in wired net- Armed with the deep understanding of delayed
works. In multihop wireless networks, however, this ack impact on TCP performance over multihop
mechanism can be further improved due to: wireless links, we propose an adaptive scheme based
on the hop count of a TCP path. The basic idea
• Since the data and ack packets usually take the behind this scheme is, for a short path where inter-
same route (or spatially close routes), they inter- ference problem is minimal, we delay the ack as
fere with each other. The interference increases much as possible to maximally improve TCP
with the number of acks generated. throughput; while for a long path, we apply an
• Generating acks wastes scarce wireless resources. appropriate delay window size restriction to avoid
Though acks are essential to provide reliability, high packet loss to achieve optimal TCP perfor-
generating more acks than necessary is not desir- mance. Furthermore, we propose an end-to-end
able in wireless networks. Ideally, the receiver delay based scheme tailored for hybrid wired/wire-
should generate minimal number of acks less networks. These two schemes can be deployed
required for reliable data recovery. separately, but are also compatible with each other
to provide better performance in heterogenous net-
Recently, the delayed ack strategy has been stud- works. It is also worth noting that our proposed
ied to improve TCP performance [2,3]. However, schemes only reside in transport layers at the end
this field is not fully exploited and many issues hosts, thus no modification on intermediate nodes
remain unsolved. Some important questions is needed.
include: what is the relation between delayed acks However, TCP with untraditional delayed ack
and TCP performance, how to choose the proper (with delay window larger than 2) would cause
delay window (the number of in-order data packets friendliness to the standard TCP. Since TCP sender
to be waited for before generating an ack) for TCP, increases the congestion window (cwnd) by usually
and how to deal with the loss of acks in multihop counting the number of acks received in the current
wireless networks. In this paper we carry out a sys- popular implementations, the TCP with untradi-
tematic study to understand the effect of delayed tional delayed ack is slower in increasing the cwnd
acks on TCP over wireless links. We investigate than the standard TCP. If they coexist, the TCP
TCP performance and delayed ack related packet with untraditional delayed ack would not get fair
loss characteristics, under various wireless network share with the standard TCP. The unfriendliness
scenarios and flow patterns. problem was largely avoided in previous research
Our objective is to clearly identify the relation- and stays unsolved. In the paper, we address the
ship between TCP throughput and delayed ack over problem with a simple and intelligent end-to-end
multihop wireless links. We reveal several interest- receiver-side detection mechanism. If the receiver
ing findings, which are tremendously beneficial to detects other competing traffic, it switches to the
deeply understand TCP behavior in wireless multi- standard TCP, and vice versa. With this adaptive
hop networks, and to design enhanced TCP proto- switching scheme, the friendliness of the standard
cols. First, we found that TCP does not always TCP and our proposed adaptive delayed ack scheme
benefit from arbitrary delaying of acks. In fact, for is significantly improved.
a given network topology and flow pattern, there Another challenge for TCP with adaptive
exists an optimal delay window size at the receiver, delayed ack comes from mobile ad hoc networks.
at which TCP achieves maximum throughput. Sec- Although delayed acks may potentially improve
ond, since 802.11 does not guarantee collision free TCP throughput regardless of underlying routing
packet transmission, a packet is more likely to be protocols. Different routing mechanisms, however,
interfered with when going through a long path. If have great impact on TCP performance [4], and to
a large delay window is used over a long path, it what degree delayed acks can benefit TCP perfor-
causes large bursts of packets in transit, and this mance. The problem of more packet losses due to
3. 1100 J. Chen et al. / Ad Hoc Networks 6 (2008) 1098–1116
mobility could have more impact on TCP with than the transmission range, request-to-send (RTS)
untraditional delayed ack since fewer acks are gen- and clear-to-send (CTS) in 802.11 MAC cannot
erated. In this paper, we investigate the TCP-DCA ensure collision free transfer of packets. This causes
(Delayed Cumulative Ack) which addresses the hidden/exposed terminals leading to packet loss in
ack loss issue in mobile networks. Meanwhile, the ad hoc multihop wireless paths [8]. Many research
performance of various TCP schemes are presented efforts have been made to adapt TCP to the unique
over popular ad hoc routing protocols, namely, Ad- characteristic of wireless ad hoc network, e.g.
Hoc On-Demand Distance Vector Routing Transport layer ‘‘Fixed RTO’’ in [4], delayed ack
(AODV) [5], Dynamic Source Routing [6] and in [2,3], network layer support [9–11] and even
Greedy Perimeter Stateless Routing (GPSR) [7]. lower-layer assistance, for example, MAC support
The reason we include GPSR in our study is that in [8].
Geo-routing is a recently developed routing scheme Although a TCP ack packet is small, typically
promising to be scalable, and robust to node 40 bytes, the transmission of TCP ack packets
mobility. may require the same overhead as that of data pack-
While our work shares the common concept with ets in 802.11 MAC depending on the RTS thresh-
previous research in that the TCP receiver delays old. If interference from TCP acks could be
ack up to a certain number of data packets, we reduced, data packets would suffer less collisions
undergo a more complete and optimized study to resulting in higher throughput. Several approaches
understand the delayed ack impact and propose to delay acks have been proposed [2,3,12]. TCP-
more effective solutions suitable for various scenar- ADA (Adaptive Delayed Ack) [12] proposed to
ios. To the best of our knowledge, our proposed decrease the number of acks to improve TCP per-
schemes are the first existing mechanisms suitable formance. They claimed that maximum TCP
for both static/mobile wireless and hybrid networks, throughput is achieved when one ack acknowledges
and taking the ack loss and friendliness into account the full cwnd. However, the scheme did not address
as well. several important issues, such as packet loss and
The remainder of this paper is organized as fol- out-of-order packet reception. In fact, as we will
lows. Background work is provided in Section 2. show in this paper, TCP does not always benefit
A thorough study of delayed ack impact on TCP from delaying ack as much as possible.
performance is presented in Section 3 under various Altman and Jimenez [2] presented a basic delayed
network topologies and traffic patterns. We present ack scheme which was further improved in [3] where
our adaptive delayed ack (TCP-DCA) scheme in TCP-DAA (Dynamic Adaptive Acknowledgement)
Section 4. The issue of the loss of ack packets is dis- was proposed. In TCP-DAA, the receiver adjusts
cussed. Section 5 evaluates TCP-DCA on static and the delay window according to the channel condi-
mobile ad hoc networks, and hybrid wired/wireless tion (packet loss event). A TCP-DAA receiver
networks as well. Several enhancements are pre- delays acking until it receives a certain number of
sented to improve TCP-DCA’s efficiency and data packets, ranging from 2 to 4 packets. When
friendliness. Section 6 discusses a few issues to fur- there is no packet loss, the TCP-DAA receiver waits
ther improve TCP with untraditional delayed ack. for more data packets (up to 4) before generating an
We conclude the paper in Section 7. The impact of ack, but reduces the number to 2 in case of out-of-
different routing protocols on TCP is also consid- order packet arrival. However, since a TCP sender
ered in proper sections. automatically cuts the cwnd when packet loss
occurs, i.e. automatically adapting to the channel
2. Related work state at the sender side, the receiver side adaptation
provides little extra improvement. We will show
The standard TCP assumes that a packet loss is that in our adaptive delayed ack scheme, the recei-
invariably due to buffer overflow and reduces the ver does not respond dynamically to packet loss,
cwnd by half when packet loss happens. However, yet achieves better performance.
in ad hoc network, packet loss caused by buffer In [3], the ack time is set to be one average packet
overflow is rare. Instead, it is more likely due to inter-arrival time. That is, an ack is generated when
medium contention as shown in [8]. The fundamen- no data packet arrives after one average packet
tal problem resides in the limitations of IEEE 802.11 inter-arrival time since last unacknowledged data
MAC. Since the interference range is usually longer packet. In wireless networks, the inter-arrival time
4. J. Chen et al. / Ad Hoc Networks 6 (2008) 1098–1116 1101
is highly variable due to random MAC contention for further improvement. As it is a primarily recei-
and back-off, so it is very difficult to get accurate ver-side modification, it could be combined with
enough statistics in a complex large system. Another other sender-side schemes or low layer approaches.
impact of this timer implementation is that the For example, at sender-side, [15] studied the perfor-
receiver operates insensitively to the number of acks mance of TCP on three different routing protocols
(2–4) to be delayed because any unexpected extra and proposed a TCP modification called fixed
delayed data packet will trigger an ack. RTO, which essentially freezes the TCP RTO value
An important aspect of TCP with untraditional whenever there is a route loss. Recent work [9–11]
delayed ack is the delay window size selection. In are approaches at the network layer. Chandran
TCP-DAA [3], the receiver may delay up to four et al. [9] discussed a mechanism called TCP-Feed-
ack packets and this number is limited by the sender back, which uses route failure and re-establishment
cwnd, which is fixed at four packets. The similar notifications to provide feedback to TCP, and thus
delay window size of 3–4 packets is also picked in reduce the number of packet retransmissions and
[2] heuristically. There are issues in this scheme that TCP back-offs during route calculation, to improve
desires further clarification and improvement. First, throughput. Holland and Vaidya [10] evaluated an
although a small cwnd limit helps TCP operation in explicit link failure notification technique (ELFN)
wireless networks, it is not suitable for hybrid wired in the context of improving TCP performance over
and wireless network where a high bandwidth multi-hop ad-hoc networks. They studied the effect
delay product exists. Second, if the cwnd is not lim- of link failures due to mobility on throughput and
ited by four packets, the choice of a delay window showed through simulations that ELFN improves
size of 4 may no longer be suitable. In this paper, the performance of TCP. Xu et al. [11] proposed a
we address the above issues and provide more effec- Neighborhood RED (NRED) scheme, which
tive and general solutions that apply to various extended the RED concept to the distributed
environments. neighborhood queue, to address significant TCP
The delayed ack has impact on the TCP sender. unfairness in ad hoc wireless networks. These mech-
Since the receiver does not ack as frequently as in anisms are promising schemes to be integrated with
the standard TCP, the congestion window increas- our mechanism for more robustness against packet
ing rate for delayed ack is slowed down. Such slower loss and TCP fairness.
probing rate improves TCP performance in ad hoc
networks, as reported in [13]. The conservative win- 3. TCP throughput vs. delay window
dow increase, however, hinders efficient transmis-
sion in wired network where delay bandwidth In this section, we investigate the impact of the
product may be large. In this paper, we solve this receiver ack delay window size on TCP perfor-
problem and allow TCP-DCA to cope with ad hoc mance. The conclusion we draw is that, when the
and hybrid wired/wireless networks via adaptive path length is short, TCP achieves better perfor-
schemes. mance with a delay window as large as the entire
We also study the impact of cwnd limit at the sender cwnd. When the path length increases, how-
sender. A small sender cwnd can decrease interfer- ever, a large delay window triggers bursty transmis-
ence and maximize pipeline effect. [8] revealed that sions, which results in mutual data packet
there exists an optimal TCP cwnd size that maxi- contention and higher losses. In fact, for long paths,
mizes spatial channel reuse. Further increasing the there exists an optimal delay window size that
window size does not lead to better performance. achieves maximum TCP throughput. We verify the
On the contrary, it results in increased link layer delay ack impact using various network topologies,
contention and degraded TCP throughput. In [14], including cross and grid topologies with various
the optimal congestion window limit is determined flow patterns. Real testbed measurement results
based on the hop count for maximum pipeline effect are also presented to reinforce our conclusions.
and the interference/transmission range ratio. In the Firstly, we study a basic scheme with fixed delay
paper, we will show that in our scheme TCP-DCA, window limit to illustrate the impact of the delay
the sender’s cwnd is not limited, and yet, performs window size on TCP performance, named as TCP-
better than the case of the limited cwnd used in [3]. FDCA. We use static routing to investigate delayed
TCP-DCA resides at TCP layer, and it has poten- ack performance without any routing interference.
tial to be combined with other TCP enhancements Routing impact will be shown in Section 5.
5. 1102 J. Chen et al. / Ad Hoc Networks 6 (2008) 1098–1116
3.1. TCP with fixed delay window limit choose b as 0.8 and a as 1.5. The receiver also gen-
(TCP-FDCA) erates an ack within 500 ms of the arrival of an
unacknowledged data packet in accordance with
TCP-FDCA maintains a variable delay window RFC2581 [1].
‘‘w’’ representing the number of data packet arrivals One drawback to this approach is that the TCP-
before acking at the receiver. This delay window w is FDCA receiver needs to be informed of sender’s
bounded by a delay window limit, and also limited cwnd size to prevent delay window larger than cwnd
by the cwnd size to prevent the delay window from leading to unnecessary delaying at the receiver. To
exceeding the cwnd which results in delaying the address this problem, we propose two possible
ack, but for possibly non-existent packets. If data methods. One is to imbed the cwnd size in an option
packets arrive in order, the receiver generates one field of the packet header. The other is to reuse some
cumulative ack for every w data packets. If an out TCP header field. For example, the sender could
of order packet is received, or a packet that fills a reuse the advertised window field in data packet
gap in the sequence space of packets in the receiver header for ‘‘advertising’’ its cwnd size to the recei-
buffer (that is, recovery from earlier packet loss), the ver. This method is not unrealistic due to the fact
receiver acks immediately to inform the sender of that current TCP connection is mostly used for
the packet loss/recovery in a timely manner. The one direction, i.e. there is only data packets from
receiver also keeps a fall-back delay ack timer which the sender to the receiver and no backward data,
estimates the expected time to receive w data pack- so the advertised window field from the sender is
ets. At the TCP sender, when it receives a cumula- usually wasted. Even if two-way TCP data is
tive ack acknowledging w data packets, it updates included, it is still possible to reuse the advertised
the cwnd and sends out a burst of at least w packets, window field, for example every other packet with
provided such packets are ready for transmission in one bit in the reserved field to indicate whether
the sender buffer. cwnd or advertised window size is used. The lowed
To get the delay timer period, the receiver moni- frequency of cwnd notification is not expected to
tors the data packet inter-arrival interval and com- affect TCP-FDCA much since TCP-FDCA receiver
putes a smoothed interval through a low-pass does not need to know the exact cwnd so often, as
filter. The average inter-arrival interval is used to we will see later in the paper.
set the ack delay timer based on the current delay
window size. In TCP-FDCA, an accurate delay 3.2. Chain topology
timer is not needed and the timer is solely for fall
back purpose. In fact, our inter-arrival time compu- In order to understand TCP-FDCA, its perfor-
tation is rather simple and loose: the receiver sam- mance is shown over a chain topology in Ns2 [16].
ples the inter-arrival time of any consecutively The chain topology is general used to study TCP
arrived data packets, not necessarily in-order pack- performance since TCP typically runs over a single
ets. Therefore, the inter-arrival sample is an inflated path. Fig. 1 shows a chain example. The TCP con-
value compared with inter-arrival between in-order nection is sourced at the first node (node 1) and
packets. A TCP-FDCA receiver smoothes such packets travel over the chain to the end node (node
inflated inter-arrival samples through a low-pass 6). The interference range is 550 m and transmission
filter range is 250 m. We place the nodes at 200 m inter-
vals, so that nodes are 4 hops away can transmit
I iþ1 ¼ bI iavg þ ð1 À bÞI s ;
avg ð1Þ
simultaneously without interference. Notice that a
where I avg is the average of inflated packet inter-ar- node that is 3 hops away is a ‘‘hidden node’’. IEEE
rival time (I s ). I avg is used to set delay ack timer (T w ) 802.11 is the underlying MAC. Data rate on the
which defines the total time for receiving a whole de- wireless channel is 2 Mbps and one simulation run
lay window of in-order data packets lasts 300 s. Each data point represents an averaged
result of 5 simulation runs with different random
T w ¼ awI avg ; ð2Þ
seeds. The packet size is 1000 bytes and the TCP-
where w is the delay window size, a is a parameter to Newreno is adopted as it is the most popular TCP
tolerate high dynamic packet delay. Obviously, the protocol nowadays. The delay window limit applied
delay ack timer is rather inflated and quite robust at the TCP receiver ranges from 1 to the current
to high inter-arrival variation. In the paper, we cwnd size.
6. J. Chen et al. / Ad Hoc Networks 6 (2008) 1098–1116 1103
1600
1hop
2hop
3hop
1400
Throughput (Kbps)
1200
1 2 3 4 5 6
1000
800
600
Fig. 1. Chain topology. The solid-line circle denotes a node’s 400
valid transmission range. The dotted-line circle denotes a node’s 1 2 3 4 5 6 7 8 9 10 ...CW
Delay Window Limit (packets)
interference range. Node 4’s transmission will interfere with node
1’s transmissions to node 2. (a) Path Length h ≤ 3
350
4hop
5hop
6hop
3.2.1. Single TCP flow 7hop
8hop
TCP performance over wireless multihop inevita- 9hop
bly depends on the path length (hop count). The
Throughput (Kbps)
300
longer the path is, the lower the throughput would
be. We present TCP-FDCA throughput as a func-
tion of delay window limits on a path with different
lengths in Fig. 2. Fig. 2a shows that when a sender 250
and a receiver are within 3 hops, TCP-FDCA gets
steady performance gain by increasing the delay
window size up to the entire cwnd size. For the
200
one hop case, the fastest throughput increase can 1 2 3 4 5 6 7 8 9 10 ...CW
be seen when the delay window is small, say less Delay Window Limit (packets)
than 5. The increasing trend becomes slower for (b) Path Length 10 > h >3
delay windows larger than 5 and the throughput
240
approaches the limit when the delay window reaches 10hop
12hop
the cwnd size (denoted by CW). The same trend is 230 14hop
16hop
also observed when the path length is 2 and 3. 220
18hop
20hop
The reason for this performance gain is that
Throughput (Kbps)
802.11 MAC provides nearly collision free packet 210
transmissions for short paths. Since the interference 200
range is larger than 2 times the transmission range,
190
when the sender and receiver are within 2 hops,
every node along the path can sense all other nodes 180
transmissions. In this case, no hidden nodes exist,
170
thus packet loss is minimal. When the hop length
is 3, the TCP receiver is the only node hidden from 160
1 2 3 4 5 6 7 8 9 10 ...CW
the TCP sender. If the receiver acks only after Delay Window Limit (packets)
receiving all packets in a cwnd, no data packet (c) Path Length 20 ≥ h ≥ 10
can be interfered. The maximal performance gain
is achieved when the receiver acks after receiving Fig. 2. TCP-FDCA throughput vs. delay window on chain
all packets in a cwnd, and attains up to 25% topology. (a) Path length h 6 3. (b) Path length 10 > h > 3.
(c) Path length 20 P h P 10.
throughput gain relative to the TCP with delay win-
dow at 1.
Since the interference range is larger than the solve the hidden/exposed terminal problem. As the
transmission range, RTS/CTS cannot completely path becomes longer than 3 hops, packet collision
7. 1104 J. Chen et al. / Ad Hoc Networks 6 (2008) 1098–1116
is unavoidable. For example, node 1 and node 4 are ver are used for 802.11b devices and the devices are
interfering nodes in Fig. 1, so simultaneous packet set to ad-hoc mode. The topology of the testbed is a
transmissions on them will be interfered. The hidden chain and the route is statically configured. There is
terminal results in packet loss and this problem one source laptop and one selected destination lap-
becomes more severe for longer paths because a top among other 5 laptops depending on the num-
packet has more chances to be interfered with. ber of hops in our experiments. We use ‘‘Iperf’’ to
Another problem is that when the sender receives generate FTP traffic with packet size of 1000 bytes.
a cumulative ack, it immediately sends a burst of From the experiment results shown in Fig. 3, we
packets. The larger the delay window, the larger confirm that the TCP-FDCA throughput vs. recei-
the burst and the more packet loss due to increased ver delay window follows the same trends as in
interfering. (Note that the packet burst size is the simulation results shown in Fig. 1.
directly related with the receiver delay window since Fig. 4 compares TCP-FDCA throughput for 1
it is at least equal to the size of the delay window.) hop and 5 hops paths from simulation and actual
When the packet loss becomes high, the TCP- testbed, when delay window limit is equal to 1 and
FDCA throughput gain from delaying ack is lost cwnd respectively. We note that the average differ-
due to the increased packet losses. Fig. 2(b) shows ence between the testbed TCP throughput and the
this tradeoff of TCP-FDCA performance gain with simulation results is below 10%. Such difference is
delay window size for paths larger than 3 hops.
When the hop count is 4 or 5, we do observe unsuc-
cessful packet transmissions caused by interference,
1600
however, since a TCP sender is able to recover 1hop
2hop
packet loss rather rapidly due to the small round 3hop
1400
trip time (RTT), TCP-FDCA maintains perfor-
mance gain by delaying ack for more data packets.
1200
Throughput (Kbps)
After peak performance at certain delay window,
the TCP-FDCA performance gets worse due to
1000
more packet losses. Similar trend also exists for
paths longer than 5 hops, where TCP-FDCA 800
achieves throughput gain only when the delay win-
dow size is small; for large delay window size, delay- 600
ing ack cannot maintain throughput gain because of
excessive data packet losses. Further, now that RTT 400
is larger, TCP-FDCA spends more time detecting 1 2 3 4 5 ...CW
Delay Window Size (packets)
packet loss and recovering lost packets by entering
fast retransmit/recovery in which only one packet (a) 1 to 3 hop
is recovered per RTT. Therefore, for long paths, 370
large delay window is not preferred. 4hop
5hop
360
We also show TCP-FDCA performance over a
350
very long path h P 10 in Fig. 2(c) which has similar
results with Fig. 2(b). TCP-FDCA only gets perfor- 340
Throughput (Kbps)
mance gain for small delay window size. For large 330
delay window size, TCP-FDCA gets poor 320
throughput.
310
300
3.2.2. Real testbed verification
We investigate the effectiveness of our TCP- 290
FDCA in an actual ad-hoc network testbed. Our 280
testbed consists of six laptops equipped with Ori- 270
noco 802.11b PCMICA cards with channel rate of 1 2 3 4 5 ...CW
Delay Window Size (packets)
2Mbps. The laptops run Mandrake Linux distribu-
(b) 4 and 5 hop
tion 7 with kernel version 2.4.3. Linux PCMCIA
package version 3.2.0 and Orinoco wavelan2-cs dri- Fig. 3. Real testbed measurement. (a) 1 to 3 hop. (b) 4 and 5 hop.
8. J. Chen et al. / Ad Hoc Networks 6 (2008) 1098–1116 1105
1500
d
3.3. More complex topologies and flow patterns
1
dCW
We expand our study to scenarios of more com-
plex topologies and flow patterns, including cross
Total Throughput (Kbps)
1000 and grid topologies. For all cases, we observe the
similar results to what is described above, i.e., when
the path is short, TCP-FDCA achieves optimal
throughput by delaying acks as much as possible,
500 up to the entire sender’s cwnd. On the other hand,
when the path becomes longer, a large delay win-
dow hinders performance gain and deteriorates
TCP throughput gradually. We show that there
0 exists a certain delay window size, at which TCP-
Simulation Experiment
FDCA achieves optimal throughput performance.
(a) 1 hop
The following provides a summary of results on
300
multiple flows and various topologies. The perfor-
d
1 mance over random topologies will be shown in Sec-
d
250
CW
tion 5.2.
Total Throughput (Kbps)
200
3.3.1. Multiple TCP flows
Fig. 5 exhibits result for 5 concurrent TCP-
FDCA flows on a chain topology with hop count
150
varying from 3 to 7, and has similar results to Fig. 2.
100
3.3.2. Cross and grid topology
Fig. 6 shows examples of cross and grid topolo-
50
gies with a 4 hop path for each TCP-FDCA flow,
and the results with different delay window size are
0
Simulation Experiment shown in Fig. 7. Additionally the results from vary-
(b) 5 hop ing path lengths are shown. Similar trend is observed
again. We also run extensive simulations on cross
Fig. 4. Simulation vs. experiment. (a) 1 hop. (b) 5 hop.
and grid topologies with multiple overlapped flows
instead of one flow. The results, not included here,
mainly caused by parameter setting in the testbed also confirm the same trends discussed above.
measurements. In our testbed experiments, RTS/
CTS control packets are adopted for unicast data
500
packets to overcome the hidden terminal problem 3hop
5hop
only if the packet size is above the minimum thresh- 7hop
450
old 256 bytes. Since the size of TCP ack packet
Aggregate Throughput (Kbps)
(40 bytes) is below the minimum RTS/CTS threshold
400
in Linux settings so that no RTS/CTS handshake is
performed when transmitting acks in testbed experi-
350
ments. Compared with simulation results where
RTS/CTS is always performed regardless of packet
300
size, such ‘‘zero’’ MAC overhead in testbed measure-
ments has impact on the performance: the through-
250
put gain derived from TCP-FDCA in the testbed
measurements is lower than the corresponding results
200
in the simulations because of the lack of RTS/CTS 1 2 3 4 5 6 7 8 9 10 ...CW
reduction for acks in simulations. Other than this Delay Window Limit (packets)
slight difference, the results are similar in simulation Fig. 5. TCP-FDCA throughput vs. delay window on chain
and in testbed measurements. topology (5 flows).
9. 1106 J. Chen et al. / Ad Hoc Networks 6 (2008) 1098–1116
8
Flow 1
7
TCP flow 1
0 1 2 3 4
Flow 2
TCP flow 2 6
5
Flow 3
(a) Cross To pology (b) Gri d Topology
Fig. 6. More complex topologies. Left: cross topology with 4 hop path on each direction. 200 m distance between two adjacent nodes.
Right: 5 · 5 grid topology, 200 m distance between horizontal and vertical adjacent nodes. (a) Cross topology. (b) Grid topology.
340 340
4hop 5x5
6hop 5x7
8hop 5x9
320 320
Aggregate Throughput (Kbps)
Aggregate Throughput (Kbps)
300 300
280 280
260 260
240 240
220 220
200 200
1 2 3 4 5 6 7 8 9 10 ...CW 1 2 3 4 5 6 7 8 9 10 ...CW
Delay Window Limit (packets) Delay Window Limit (packets)
(a) Cross Topology (b) Grid Topology
Fig. 7. TCP-FDCA throughput vs. delay window on complex topologies. (a) Cross topology. (b) Grid topology.
4. TCP with adaptive delayed cumulative ack vation, we dynamically determine the delay window
(TCP-DCA) size based on the hop count of a TCP connection
and call it as TCP-DCA. For a short path (h 6 3),
In this section we propose TCP-DCA with adap- TCP-DCA could delay ack for a whole cwnd to
tive delayed window according to the underlying get best performance; otherwise a small delay win-
path information to optimize TCP performance. dow for long paths. Since TCP still gets slight ben-
The issue of ack loss is also discussed and a simple efit by delaying more for moderate long paths
receiver retransmission scheme is proposed. (3 < h 6 9), therefore the delay window could be
slightly larger for such paths. TCP-DCA receiver
4.1. TCP-DCA with adaptive delayed ack can get the path length information from the TTL
field in TCP packet header or from the routing
Up to now we have presented the tradeoff layer at the receiver node Table 1 lists the delay win-
between TCP-FDCA throughput and delay window dow size applied in TCP-DCA according to the path
size on different path lengths. Inspired by this obser- length.
10. J. Chen et al. / Ad Hoc Networks 6 (2008) 1098–1116 1107
Table 1 mission timer period is set to 1 s. This ack retrans-
Delay window at TCP-DCA receiver mission timer is started after sending an ack, and
Path length (h) Delay window limit canceled after receiving a data packet.
h63 Congestion window Until now all previous results were obtained
3<h69 5 without ack retransmission. This is due to two facts:
h P 10 3 first, the results with and without ack retransmission
are almost the same for static networks. Mostly
4.2. Ack loss because the ack loss is rare, and the ack retransmis-
sion timer period is large (at least 1 s). Second, with-
The standard TCP generates more acks than out the ack retransmission timer, it is easy to
TCP-DCA, due to the cumulative property of the observe the sole impact of the delay window on
ack, one ack successfully received at the TCP sender TCP performance. In the following simulations,
can makes up for all the preceding lost acks. Thus, the ack retransmission timer is enabled unless
the ack loss in standard TCP is not serious. How- explicitly mentioned.
ever, the number of acks in TCP-DCA is much less
than standard TCP, and thus an ack loss has more 5. Performance evaluation
negative impact on TCP-DCA performance. In
order to be robust to ack loss, a retransmission This section presents the TCP-DCA performance
timer at the receiver is adopted to retransmit a over wireless and hybrid networks. First, we show
cumulative ack if necessary. TCP-DCA performance on static multihop wireless
A challenge here is to estimate RTT at the recei- networks and compare it with TCP-DAA in [3]. Sec-
ver which is needed for setting the ack retransmis- ond, we demonstrate TCP-DCA performance on
sion timeouts. If TCP includes two-way data, the mobile ad hoc network, and show TCP-DCA per-
receiver can get the accurate RTT measurement formance over several ad hoc routings. Third, we
since the sender acks the data immediately. If TCP extend the hop count based approach to an end-
only has one-way data, RTT measurement at the to-end delay based scheme to further improve
receiver may not be straightforward. If the TCP TCP-DCA in hybrid wired/wireless networks. Last,
timestamp option is used, the receiver could use it we propose a simple approach to address the friend-
to estimate RTT, though such an estimate may be liness problem of TCP-DCA to TCP-Newreno with
inflated if the sender does not send data packets standard delayed option.
immediately after receiving an ack [17]. However,
in TCP-DCA, the ack retransmission timer is only 5.1. Static ad hoc network
a coarse timer for predicting when to retransmit
acks, an accurate RTT measurement is not required In this section, we show TCP-DCA performance
and thus an inflated RTT can be tolerated. In the in static ad hoc networks. Meanwhile, we compare
paper, the timestamp option is used to estimate TCP-DCA with TCP-DAA and TCP-Newreno
the RTT for a TCP flow which has one-way data. (with and without standard delayed ack option
The receiver computes the ack retransmission [1]). More specially, we use the name ‘‘original
time based on this RTT measurement. We use the TCP’’ for TCP-Newreno without standard delayed
following formula to calculate the retransmission option, and TCP-STD-DA for TCP-Newreno with
timer period: standard delayed option. AODV routing is used
unless otherwise stated.
7 1 TCP-DAA [3] is an interesting extension of [2]
SRTTr ¼ SRTTr þ RTTr ;
kþ1 k kþ1
8 8 and has shown good performance in static ad hoc
3 1 networks. It is the most recent work and the major
RTTvar ¼ RTTvar þ jRTTr À SRTTr j;
kþ1 k kþ1 kþ1
4 4 differences between TCP-DAA and TCP-DCA are
r r var
RTOkþ1 ¼ SRTTkþ1 þ 4 Â RTTkþ1 ; listed in Table 2. For fair comparison, most simula-
tions scenarios presented in this subsection were
where RTTr is the RTT estimation at the receiver, shown in [3]. Each result is the average of five sim-
SRTTr is the smoothed RTT. RTTvar and RTOr ulation runs.
are RTT variance and retransmission timer period In Fig. 8, we compare TCP-DAA to TCP-DCA
at the receiver. The minimum value of the retrans- in the chain topology with different hop count and
11. 1108 J. Chen et al. / Ad Hoc Networks 6 (2008) 1098–1116
Table 2
Design difference
TCP-DAA TCP-DCA
Sender Duplicate acks threshold to trigger retransmission is 2; CW Puts CW into advertised window field
upper limit is 4; Retransmission (RTO) timer is increased fivefold in packet header
Receiver Delay window is adaptive from 2 and 4 based on loss event Delay window is adaptive on the path
length
number of concurrent flows. Although TCP-DCA is CWL and TCP-DAA achieve best performance
designed without cwnd limit, we include TCP-DCA and their difference is small. They provide better
with cwnd limit at 4 in this experiment, named TCP- performance, about 10–25%, than the standard
DCA-CWL, to show a fair comparison with TCP- TCP (with and without delayed ack option).
DAA. Note that in TCP-DAA, the cwnd limit is With static topology and steady traffic pairs, the
set to 4 by default. Fig. 8a shows the performance variance of results is very small (less than 5%) so we
of TCP-DCA over 3 hop chain. The aggregate omit its error bar results. Also note that TCP-DCA-
throughput of TCP-DCA decreases when the num- CWL does not bring significant benefit over TCP-
ber of flows increases. When there are few flows, DCA. Since the ack flow is decreased, the optimal
since each TCP-DCA generates as few acks as pos- cwnd size could actually increase (for details, please
sible, the advantage of TCP-DCA is obvious. When refer to [14]). Although it may be interesting to
more flows coexist, the cwnd of each flow becomes investigate the optimal cwnd for TCP-DCA, we
smaller since they compete for the bandwidth, thus do not pursue it because our ultimate goal to design
the benefit of delayed ack reduces because more TCP-DCA without cwnd limit. Moreover, this
acks are generated. If the cwnd is below the cwnd property makes TCP-DCA distinct since selecting
limit in TCP-DCA-CWL, they have similar perfor- an optimal cwnd is non-trivial, which needs to know
mance. The performance of TCP-STD-DA is better a lot of underlying information to accomplish. For
than original TCP, but worse than TCP-DCA and example, it requires the knowledge of transmis-
TCP-DAA. TCP-DCA and TCP-DCA-CWL pro- sion/interference ratio [14] at the physical layer
vides better performance than other TCP variants. which is usually hard to obtain. It could also poten-
Overall, TCP-DCA achieves best performance, up tially limit the application of TCP in a variety of
to 15% improvement over TCP-DAA, and 25% over wireless networks, such as that TCP with cwnd limit
TCP-STD-DA respectively. Fig. 8b–c show the per- in wired and wireless scenario does not perform well
formance of TCP-DCA on a 5 and 7 hop path. The (will be shown in Section 5.4). Taking this into
same trend persists and TCP-DCA outperforms all account, we do not choose cwnd limit in TCP-
other algorithms in most situations. DCA and thus in the following experiments, only
Note that the cwnd limit on TCP-DCA does not TCP-DCA (no cwnd limit) is adopted.
bring considerable benefit. For a short path in
Fig. 8a, the cwnd limit could considerably restrict 5.2. Mobile ad hoc network
the TCP performance as the number of flows is
small. For a long path in Fig. 8b–c, the cwnd limit We have demonstrated that applying delayed ack
only provides slightly more performance gain for 2 scheme improves TCP performance in a static net-
flows, and this advantage disappears for more flows. work, now we show that it can improve TCP perfor-
From Fig. 8, the performance of TCP-DCA without mance in a mobile network as well. Though our
cwnd limit is better than that of TCP-DCA-CWL in delayed ack scheme is not specifically designed for
most situations. It indicates that TCP-DCA can the TCP in mobile network, we show that our
achieve the distinguished performance without set- scheme works well in mobile scenarios.
ting cwnd limit. In Fig. 10, we show the performance of the origi-
We also give results for the grid topology. This nal TCP, TCP-STD-DA, TCP-DAA and TCP-
grid topology is shown in Fig. 9a and 6 flows run- DCA running over three routing schemes: GPSR,
ning on the grid. Fig. 9b compares the performance AODV and DSR. The experiment consists of 40
of original TCP, TCP-STD-DA, TCP-DAA, TCP- nodes randomly moving within a 1000 m · 1000 m
DCA-CWL and TCP-DCA, and we observe the area. Each node moves with the same speed without
similar results as before. TCP-DCA, TCP-DCA- pause. The Random Waypoint mobility model [18]
12. J. Chen et al. / Ad Hoc Networks 6 (2008) 1098–1116 1109
550
TCP-DCA Flow 4 Flow 5 Flow 6
TCP-DCA-CWL
TCP-DAA
TCP
TCP-STD-DA Flow 1
Aggregate Throughput (Kbps)
500
Flow 2
450
400
2 4 6 8 10 12 14 16 18 20 Flow 3
Number of Flows
(a) 3 Hop Path
(a) Grid Topology
300
TCP-DCA
TCP-DCA-CWL
TCP-DAA
290 TCP TCP-
TCP-STD-DA
DCA
Aggregate Throughput (Kbps)
280
TCP-
270 DCA-
CWL
260
TCP-
250 DAA
TCP-
240 STD-
DA
230
TCP
220
2 4 6 8 10 12 14 16 18 20
Number of Flows 0 100 200 300 400 500 600 700
(b) 5 Hop Path Aggregate Throughput (Kbps)
280
(b) Aggregate Throughput for TCP variants over
TCP-DCA
TCP-DCA-CWL
Grid Topology
TCP-DAA
TCP
260 TCP-STD-DA Fig. 9. Performance comparison on grid topology. (a) Grid
topology. (b) Aggregate throughput for TCP variants over grid
Aggregate Throughput (Kbps)
240 topology.
220 but with different randomly generated mobility
traces. We run the set of experiments with 40 differ-
200 ent mobility traces and plot the 95% confidence
interval as error bars on the figures.
180
We illustrate results on speed 10 m/s and 20 m/s
in Fig. 10 with one TCP flow, for other speeds and
160
2 4 6 8 10 12 14 16 18 20 multiple flows, the results are similar. From Fig. 10
Number of Flows we observe that the delayed cumulative ack contrib-
(c) 7 Hop Path utes to the performance gain compared with other
Fig. 8. Aggregate throughput for TCP variants over chain
TCP variants. TCP-DCA produces at least 10% per-
topology. (a) 3 hop path. (b) 5 hop path. (c) 7 hop path. formance gain over other TCP variants regardless of
routing protocols and mobility speed, especially
more gain for TCP over DSR. TCP-STD-DA is
is used. All results displayed are calculated as the unsurprisingly consistently better than the original
average of 40 runs with the same traffic pattern, TCP without delayed ack. However, TCP-DAA
13. 1110 J. Chen et al. / Ad Hoc Networks 6 (2008) 1098–1116
900 800
TCP-DCA TCP-DCA
TCP TCP
800 TCP-STD-DA 700 TCP-STD-DA
TCP-DAA TCP-DAA
TCP-DCA-ACK-LOSS TCP-DCA-ACK-LOSS
700
600
Throughput (Kbps)
Throughput (Kbps)
600
500
500
400
400
300
300
200
200
100 100
0 0
GPSR AODV DSR GPSR AODV DSR
(a) 10 m/s (b) 20 m/s
Fig. 10. TCP performance over mobile network. (a) 10 m/s. (b) 20 m/s.
does not show consistent improvement across differ- acks are generated and more timeouts are likely to
ent routing protocols. It performs similarly as TCP- happen. Fig. 11 illustrates the idle time of TCP dur-
STD-DA over GPSR, but does not show better ing the whole simulation time (400 s) for different
performance than TCP (with or without standard TCP variants and routing schemes. As expected,
delayed option) over DSR. TCP-DCA (considering ack loss) has least idle time
In TCP-DCA, the receiver would probe the sen- over each routing scheme, which helps TCP-DCA
der by retransmitting acks in the event of high maintain better throughput in a mobile network.
packet loss (see Section 4.2). It prevents the sender Note that TCP-DCA-ACK-LOSS has similar idle
from entering long timeout due to the severe packet time with other TCP variants, which confirms that
loss event. In Fig. 10, we also show the result of retransmission scheme is effective in improving
TCP-DCA without ack retransmission (TCP- TCP performance in mobile networks.
DCA-ACK-LOSS) to confirm the effectiveness of
ack retransmission. When packet loss is severe 5.3. Lossy network
(e.g. TCP over DSR), ack retransmission consider-
ably boosts the TCP-DCA’s performance. On the In wireless networks, the wireless link in fact
other hand, the ack retransmission does not help could become unreliable and error-prone. After
much when packet loss is not severe (e.g. TCP over studying the performance of TCP-DCA under
GPSR). Therefore, TCP-DCA only incurs more ack packet losses in mobile networks, we investigate its
retransmission overhead when needed, and works performance under lossy wireless link. BER (bit
well with packet losses in mobile networks. error rate) is used as the loss metrics at the wireless
Comparing with static ad hoc networks in Sec- link and the error is assumed to be uniformly dis-
tion 5.1, mobility poses more challenges for TCP. tributed and independent on each link. It is worth
In a mobile network, the loss of packets (or acks) pointing out that when a packet is received with
may be caused by temporary route loss as well as bit error, the IEEE 802.11 MAC layer helps in
network congestion. Higher mobility causes more recovering packet loss by retransmissions until a
route loss and thus more packet losses. Since routes maximum retransmission limit is reached [19] or
are likely to be lost frequently in high node mobility retransmission is successful. Therefore, when BER
environments, and different routing algorithms have is low, the MAC retransmission scheme can easily
different capability to repair broken routes quickly, recover the packet and would not cause much prob-
thus different TCP performance is observed over lem for TCP. While the BER is high, the heavy
different routing schemes. Moreover, The frequent packet loss would knock down TCP performance.
route breakages could put TCP into long idle state Fig. 12 illustrates a scenario where a single flow
leading to poor TCP performance, especially for goes through 5 hop chain path under varying
TCP with untraditional delayed ack where fewer BER from very low BER to high BER. Each bar
14. J. Chen et al. / Ad Hoc Networks 6 (2008) 1098–1116 1111
350 TCP-DCA
350
TCP-DCA
TCP
TCP
TCP-STD-DA
TCP-STD-DA
300 TCP-DAA 300 TCP-DAA
TCP-DCA-ACK-LOSS
TCP-DCA-ACK-LOSS
250 250
Idle Time (second)
Idle Time (second)
200 200
150 150
100 100
50 50
0 0
GPSR AODV DSR GPSR AODV DSR
(a) 10 m/s (b) 20 m/s
Fig. 11. TCP idle time. (a) 10 m/s. (b) 20 m/s.
300
TCP-DCA
account the acknowledged data covered in the acks.
TCP
TCP-STD-DA Using delayed ack could potentially cause slow
TCP-DAA
250 cwnd increase and thus hurt TCP performance.
Therefore, the pure adaptive delay window based
on the hop count appears not adequate for this sce-
Throughput(Kbps)
200
nario. For example, in WLAN where 1 hop wireless
150 client can delay the cumulative ack for the whole
cwnd, the cwnd at the sender could increase slowly,
100 particularly if a large propagation delay is encoun-
tered in the wired part. Although slow increase for
50 cwnd is helpful for improving TCP performance in
ad hoc networks as shown in our previous results,
0 it is not desirable for the hybrid network. In
2e-6 6e-6 2e-5 6e-5
Bit Error Rate
RFC3465 [20] Allman proposed to increase the
cwnd based on the number of bytes acknowledged
Fig. 12. TCP performance under random loss. by the arriving acks rather than based on the num-
ber of acknowledgments that arrive at the sender in
is an averaged result of 20 random runs. Overall, the RFC2581 [1]. However, this approach potentially
performance of TCP-DCA is no worse than other causes large bursts if the delay window is large.
variants, and quite robust to wireless loss. TCP- An appropriate delay window limit needs to be
DAA also works very well unless the loss is too investigated in this scenario.
heavy. With the increasing loss rate, all TCP vari- Another challenge of the hybrid network is that
ants gracefully reduce their performance and the the hop count information from the packet header
variance of results increase. is no longer accurate for the wireless hops since it
includes the wired path. It is possible for a wireless
5.4. Hybrid (wired and wireless) network node to get hop count from the routing table to the
base station (or gateway) to the wired network,
In this section we study TCP-DCA in the wired however, this information is not guaranteed to be
and wireless ad hoc environment. Since wired net- available all the time.
work has abundant bandwidth, it demands a much To address the problems in hybrid networks, we
larger cwnd than the pure ad hoc network for effec- tailor and propose a novel receiver-side probe mech-
tive TCP performance. In current TCP implementa- anism based on CapProbe in [21], and extend the
tion, TCP sender increases the cwnd only based on previous hop-count based approach via the recei-
the number of acks received while not taking into ver-side probe in hybrid networks.
15. 1112 J. Chen et al. / Ad Hoc Networks 6 (2008) 1098–1116
The receiver-side probe works as follows: First Table 3
the receiver passively estimate the wireless band- IEEE 802.11b MAC overhead (with long preamble), L is packet
size, R is capacity
width and minimum RTT. Second it computes the
equivalent hop count based on the minimum RTT Data frame 192 ls + 8L/R
and wireless bandwidth, then the previous hop SIFS 10 ls
count approach can be applied afterwards. DIFS 50 ls
RTS 192 ls + 160/R
Now we address the problem to estimate the end- CTS 192 ls + 112/R
to-end hybrid path bandwidth at the TCP receiver. ACK 192 ls + 112/R
CapProbe [21] is a recently proposed bottleneck
capacity and path rate estimation technique shown
to be both fast and accurate. It combines the use
Table 4
of time interval measurements and end-to-end delay
Delay window at TCP-DCA receiver (delay-based, wireless
measurements to filter out bad packet pair probing bandwidth is at 2 Mbps and TCP data packet size is 1000 bytes)
samples. It is proved to be suitable for wired and
Minimum RTT (ms) Delay window limit
last-hop wireless networks. Inspired by CapProbe,
RTTmin < 18 Congestion window
we proposed a new approach at the TCP-DCA
18 6 RTTmin 6 60 5
receiver without triggering any probing traffic. The RTTmin > 60 3
idea is that after the receiver sends a cumulative
ack, the sender would send a burst of packets. The
burst of packets can just serve as the packet pair
probing. Since the receiver knows the sequence
number of the first burst packets, it can identify
the packet pair and estimate the bandwidth when Internet BS 1 2
packet pair arrives. Our approach is based on the
CapProbe, but it is different with CapProbe. First Fig. 13. Hybrid wired/wireless topology.
our approach is imbed at the TCP receiver without
any additional probing traffic. Moreover, our
approach is a one-way (instead of round-trip in
CapProbe) estimation technique, and it is expected 1500
TCP-DCA
TCP
to work for wired, hybrid and purely wireless TCP-STD-DA
TCP-DAA
networks.
The other challenge is to estimate the minimum
Throughput (Kbps)
1000
RTT at the receiver, but this have been solved as
described in Section 4.2. After the wireless bandwidth
and minimum RTT is obtained, the receiver derives
the equivalent hop count by considering the TCP
500
data and ack packet sizes. For example, with wireless
bandwidth of 2 Mbps, data packet size of 1000 bytes
and ack size of 40 bytes, the minimum RTT for a 1
wireless hop path is about 6 ms considering various
0
overhead, such as header overhead at TCP (20 bytes), 1 hop 2 hop
IP (20 bytes) and MAC (34 bytes) and MAC layer Wireless Hop Count
fixed overhead shown in Table 3 (for details, please Fig. 14. Wired and wireless performance.
refer to [22]). In Table 4, we listed the delay window
size in a wireless network with capacity 2Mbps.
In Fig. 13, we show a TCP connection from a running with different random seeds. Similar to Sec-
wired network to a wireless network with up to 2 tion 5.1, the variance of results is very small so we
wireless hops. The one-way propagation delay on omit its error bar results. Since TCP-DAA limits
the wired link is 50 ms. The performance of TCP- the cwnd, the performance of TCP-DAA is limited.
DCA, TCP-DAA and the standard TCP (with and TCP-DCA provides best performance in both cases
without standard delayed ack option) shown in of 1 and 2 hop paths. Therefore, TCP-DCA is
Fig. 14, represents averaged result of 10 simulation extensible to hybrid networks instead of working