A TCP acceleration algorithm for a wireless link using rate adaptation based on round-trip-time and virtual receiver window information

Fast transmission control protocol (TCP) was previously proposed for high capacity network environments with long delay, and "FAST TCP with Snoop" performs better than conventional TCP enhancements in mobile wireless network environments. However, FAST TCP has limitations when used over a dynamic mobile wireless link with a high frame error ratio (FER) and frequent delay changes due to the variable rate. We propose an enhanced TCP acceleration algorithm at the TCP sender side which efficiently adapts to the maximum transmission rate of a mobile wireless link using the round trip time (RTT) and virtual receiver window (RWND) information. The proposed algorithm provides superior performance over mobile wireless network environments.     

Suitability of DAMA and Contention-Based Satellite Access Schemes for TCP Traffic in Mobile DVB-RCS

The problem of optimizing access and bandwidth sharing among transmission control protocol (TCP) connections in the mobile digital video broadcasting return channel via satellite (DVB-RCS) is tackled in this paper. After sketching the general system architecture, we explicitly deal with the dynamic assignment of bandwidth to TCP connections on the return link, which is accomplished by a network control center (NCC) placed onboard the satellite. Mobile users access the satellite in multifrequency time-division multiple access (MF-TDMA), whereas they receive data from the NCC in time-division multiplexing (TDM). Two different techniques, based on deterministic and random access, are compared in terms of bandwidth usage and average completion time per connection, when the mobile user acts as both server and client. In the server case, to increase the TCP throughput, both packet-level forward error correction (FEC) on data sent by mobile users and a duplicated and delayed acknowledgment technique for TCP acknowledgment traffic from the NCC to the mobile users are applied. An analysis of the packet losses and a simulation campaign of file transfers by employing a realistic channel model has been carried out. The results of the analysis show the convenience of adopting a technique, in addition to the optimal data redundancy in different cases, such as the server or client role of users, their willingness to pay, the file size, and the environment type.     

TCP/IP performance with random loss and bidirectional congestion

With the growth in Internet access services over networks with asymmetric links such as asymmetric digital subscriber line (ADSL) and cable-based access networks, it becomes crucial to evaluate the performance of TCP/IP over systems in which the bottleneck link speed on the reverse path is considerably slower than that on the forward path. In this paper, we provide guidelines for designing network control mechanisms for supporting TCP/IP. We determine the throughput as a function of buffering, round-trip times, and normalized asymmetry (defined as the ratio of the transmission time of acknowledgment (ACK) in the reverse path to that of data packets in the forward path). We identify three modes of operation which are dependent on the forward buffer size and the normalized asymmetry, and determine the conditions under which the forward link is fully utilized. We also show that drop-from-front discarding of ACKs on the reverse link provides performance advantages over other drop mechanisms in use. Asymmetry increases the TCP already high sensitivity to random packet losses that occur on a time scale faster than the connection round-trip time. We generalize the by-now well-known relation relating the square root of the random loss probability to obtained TCP throughput, originally derived considering only data path congestion. Specifically, random loss leads to significant throughput deterioration when the product of the loss probability, the normalized asymmetry and the square of the bandwidth delay product is large. Congestion in the reverse path adds considerably to TCP unfairness when multiple connections share the reverse bottleneck link. We show how such problems can be alleviated by per-connection buffer and bandwidth allocation on the reverse path     

TCP Window Control for Variable Bandwidth in Wireless Cellular Networks

Most of TCP schemes in wireless networks assume that the bandwidth of the bottleneck link remains constant over time. However, in wireless cellular networks, to effectively manage the limited resources, the bandwidth is controlled based on radio condition over time. Such varying bandwidth can cause the networks congestion or underutilization. In this letter, we propose a new window control algorithm to improve TCP performance in wireless cellular networks with variable bandwidth. Simulation results illustrate that our proposal improves the performance of TCP in terms of fairness and link utilization     

Efficient resource allocation for China's 3G/4G wireless networks

The all-IP DiffServ model is expected to be the most promising architecture for QoS provisioning in China's next-generation wireless networks, due to its scalability, convenience for mobility support, and capability of interworking heterogeneous radio access networks. This article focuses on efficient resource allocation in a wireless DiffServ architecture. Resource utilization efficiency is particularly important for China's wireless networks as the mobile user density in China is and will continue to be much higher than that in other countries. More specifically, we propose a novel buffer sharing scheme to provide assured service for real-time layer-coded multimedia traffic, which can guarantee the specific packet loss requirement of each layer with UDP as the transport layer protocol. An adaptive optimal buffer configuration can be applied to achieve maximum resource utilization over the time-varying channel. Assured service is also provided to TCP data traffic for guaranteed throughput, where the cross-layer coupling between the TCP layer and link layer is exploited to efficiently utilize the wireless resources.     

The impact of multihop wireless channel on TCP performance

This paper studies TCP performance in a stationary multihop wireless network using IEEE 802.11 for channel access control. We first show that, given a specific network topology and flow patterns, there exists an optimal window size W* at which TCP achieves the highest throughput via maximum spatial reuse of the shared wireless channel. However, TCP grows its window size much larger than W* leading to throughput reduction. We then explain the TCP throughput decrease using our observations and analysis of the packet loss in an overloaded multihop wireless network. We find out that the network overload is typically first signified by packet drops due to wireless link-layer contention, rather than buffer overflow-induced losses observed in the wired Internet. As the offered load increases, the probability of packet drops due to link contention also increases, and eventually saturates. Unfortunately the link-layer drop probability is insufficient to keep the TCP window size around W'*. We model and analyze the link contention behavior, based on which we propose link RED that fine-tunes the link-layer packet dropping probability to stabilize the TCP window size around W*. We further devise adaptive pacing to better coordinate channel access along the packet forwarding path. Our simulations demonstrate 5 to 30 percent improvement of TCP throughput using the proposed two techniques.     

Performance Modelling of TCP Enhancements in Terrestrial–Satellite Hybrid Networks

In this paper, we focus on the performance of TCP enhancements for a hybrid terrestrial–satellite network. While a large body of literature exists regarding modeling TCP performance for the wired Internet, and recently over a single-hop wireless link, the literature is very sparse on TCP analysis over a hybrid wired–wireless (multi-hop) path. We seek to make a contribution to this problem (where the wireless segment is a satellite uplink) by deriving analytical estimates of TCP throughput for two widely deployed approaches: TCP splitting and E2E (End-to-End) TCP with link layer support as a function of key parameters such as terrestrial/satellite propagation delay, segment loss rate and buffer size. Our analysis is supported by simulations; throughput comparisons indicate superiority of TCP splitting over E2E scheme in most cases. However, in situations where end-to-end delay is dominated by terrestrial portion and buffering is very limited at intermediate node, E2E achieves higher throughput than TCP splitting.     

Evaluation of a Split-Connection Mobile Transport Protocol

A performance evaluation is presented for a split-connection protocol for wireless Internet access which is denoted Split-Connection Mobile Tranport Protocol (SCMTP). It uses the general approach of the previously introduced Mobile End Transport Protocol (METP) but with differences that include a wireless-link channel-access protocol better matched with current cellular networks and more general ARQ methods for error control in the wireless link. In common with METP, SCMTP uses a standard TCP protocol on the wire-line connection and isolates the data flow in the wire-line network from the effect of wireless packet errors.Performance is considered for the important case of a single SCMTP split connection between a fixed host and a mobile host with heavy downlink traffic from the fixed host to the mobile host. It is shown for these conditions that if the wire-line packet-error rate is small, a steady state is reached in which the connection's data flow in the wire-line network remains under the control of the receiver-advertised window of the TCP entity at the base station. Performance is evaluated for the steady-state operation of the SCMTP protocol, and relationships are established between the key properties of the split connection and the end-to-end performance of the connection.It is shown that for heavy downlink traffic, the delay in the wire-line part of the connection does not affect steady-state throughput if the receiver buffer is sized appropriately. It is also shown that use of the go-back-N ARQ protocol on the wireless link yields better performance than the stop-and-wait ARQ protocol, although the performance with go-back-N ARQ is more sensitive to the characteristics of the wireless channel. It is shown that under a broad range of conditions, SCMTP with go-back-N ARQ provides nearly optimal utilization of the capacity of the wireless link.     

Congestion control with dynamic threshold adaptation and cross‐layer response for TCP Vegas over IEEE 802.11 wireless networks

Wireless technologies provide mobile access and enable rapid andcost‐effective network deployment. But a wireless link is generally accompanied by high interference, transmission errors and a varying latency. The erratic packet losses usually lead to a curbing of the flow of segments on the TCP connection, and thus limit TCP performance. This paper presents a threshold control mechanism with cross‐layer response approach for improving TCP Vegas performance in IEEE 802.11 wireless networks. By making slight modifications to the legacy IEEE 802.11 MAC and TCP, the numerical results reveal that the proposed scheme provides a significant improvement in TCP performance under IEEE 802.11 wireless environments. Copyright © 2013 John Wiley & Sons, Ltd.     

TCP performance issues over wireless links

This article discusses the problems arising when the TCP/IP protocol suite is used to provide Internet connectivity over existing and emerging wireless links. Due to the strong drive toward wireless Internet access through mobile terminals, these problems must be carefully studied in order to build improved systems. We review wireless link characteristics using wireless LANs and cellular communications systems as examples. We then outline the performance problems of the TCP/IP protocol suite when employed over those links, such as degraded TCP performance due to mistaking wireless errors for congestion. We present various proposals for solving these problems and examine their benefits and limitations. Finally, we consider the future evolution of wireless systems and the challenges that emerging systems will impose on the Internet protocol suite     

On TCP performance enhancing proxies in a wireless environment

TCP performance enhancement in wireless access networks is an important ongoing area of research. It is known that the hostile nature of the wireless channel and the mobile nature of wireless users interact adversely with standard TCP congestion control mechanisms [1], causing a drastic reduction in throughput. This article surveys a selection of different approaches to managing TCP performance over wireless links, and presents the results of simulation and field trial results of a novel TCP performance enhancing proxy over diverse cellular radio access technologies based on the GSM, cdma2000, and UMTS standards. The proposed TRL TCP performance enhancing proxy has the advantages of being completely transparent to both TCP endpoints and tunable to different access technologies, and frequently achieves the maximum throughput available from any of the studied radio access technologies.     

A study on a receiver‐based management scheme of access link resources for QoS‐controllable TCP connections

Although the bandwidth of access networks is rapidly increasing with the latest techniques such as DSL and FTTH, the access link bandwidth remains a bottleneck, especially when users activate multiple network applications simultaneously. Furthermore, since the throughput of a standard TCP connection is dependent on various network parameters, including round‐trip time and packet loss ratio, the access link bandwidth is not shared among the network applications according to the user's demands. In this thesis, we present a new management scheme of access link resources for effective utilization of the access link bandwidth and control of the TCP connection's throughput. Our proposed scheme adjusts the total amount of the receive socket buffer assigned to TCP connections to avoid congestion at the access network, and assigns it to each TCP connection according to characteristics in consideration of QoS. The control objectives of our scheme are (1) to protect short‐lived TCP connections from the bandwidth occupation by long‐lived TCP connections, and (2) to differentiate the throughput of the long‐lived TCP connections according to the upper‐layer application's demands. One of the results obtained from the simulation experiments is that our proposed scheme can reduce the delay of short‐lived document transfer perceived by the receiver host by up to about 90%, while a high utilization of access link bandwidth is maintained. Copyright © 2006 John Wiley & Sons, Ltd.     

Performance study of link layer and MAC layer protocols to support TCP in 3G CDMA systems

Providing support for TCP with good quality link connection is a key issue for future wireless networks in which Internet access is going to be one of the most important data services. A number of schemes have been proposed in literature to improve the TCP performance over wireless links. In this paper, we study the performance of a particular combination of link layer protocol (e.g., radio link protocol or RLP) and MAC retransmissions to support the TCP connections over third generation (3G) wireless CDMA networks. We specifically investigate two metrics - the packet error rate and the delay provided by RLP and MAC retransmissions - both of which are important for TCP performance. For independent and identically distributed (i.i.d) error channels, we propose an analytical model for RLP performance with MAC retransmission. The segmentation of TCP/IP packets into smaller RLP frames, as well as the RLP buffering process, is modeled using a Markov chain. For correlated fading channels, we introduce an analytical metric called RLP retransmission efficiency. We show that: 1) the RLP frame size has significant impact on the overall 3G system performance, 2) MAC layer retransmissions significantly improve the TCP performance, and 3) the RLP retransmission scheme performs better in highly correlated channels, while other scheme performs better in low correlated channels. Simulation results also confirm these conclusions.     

Modeling TCP SACK performance over wireless channels with semi-reliable ARQ/FEC

Providing reliable data communications over wireless channels is a challenging task because time-varying wireless channel characteristics often lead to bit errors. These errors result in loss of IP packets and, consequently, TCP segments encapsulated into these packets. Since TCP cannot distinguish packet losses due to bit corruption from those due to network congestion, any packet loss caused by wireless channel impairments leads to unnecessary execution of the TCP congestion control algorithms and, hence, sub-optimal performance. Automatic Repeat reQuest (ARQ) and Forward Error Correction (FEC) try to improve communication reliability and reduce packet losses by detecting and recovering corrupted bits. Most analytical models that studied the effect of ARQ and FEC on TCP performance assumed that the ARQ scheme is perfectly persistent (i.e., completely reliable), thus a frame is always successfully transmitted irrespective of the number of transmission attempts it takes. In this paper, we develop an analytical cross-layer model for a TCP connection running over a wireless channel with a semi-reliable ARQ scheme, where the amount of transmission attempts is limited by some number. The model allows to evaluate the joint effect of stochastic properties of the wireless channel characteristics and various implementation-specific parameters on TCP performance, which makes it suitable for performance optimization studies. The input parameters include the bit error rate, the value of the normalized autocorrelation function of bit error observations at lag 1, the strength of the FEC code, the persistency of ARQ, the size of protocol data units at different layers, the raw data rate of the wireless channel, and the bottleneck link buffer size.     

Performance evaluation of a TCP proxy in WCDMA networks

The article addresses the end-to-end performance of TCP in a scenario where WCDMA is used as the access link. In particular, the performance gain that can be achieved by placing a TCP split connection proxy in the WCDMA core network is examined. It is well known that performance enhancing proxies are able to improve the performance of TCP over wireless links that suffer from impairments. However, while previous work on TCP proxies for wireless systems either focused on other wireless systems, like wireless LAN or satellites, or provided a more generic framework, we address in detail the characteristics of a WCDMA access scenario supported by a TCP proxy. The characteristics of WCDMA as perceived by TCP are discussed thoroughly. We argue that the motivation for introducing a proxy is only to overcome problems stemming from a large bandwidth delay product and not to assist local transport layer error recovery at the wireless link. Based on simulations that consider both link layer protocols and TCP, the end-to-end performance for file downloads is investigated. Simulation results show that a proxy can significantly improve performance in the case of high data rates like 384 kb/s. For lower data rates, like 64 and 128 kb/s, it is sufficient to use a well configured TCP implementation.     

TCP-Jersey for wireless IP communications

Improving the performance of the transmission control protocol (TCP) in wireless Internet protocol (IP) communications has been an active research area. The performance degradation of TCP in wireless and wired-wireless hybrid networks is mainly due to its lack of the ability to differentiate the packet losses caused by network congestions from the losses caused by wireless link errors. In this paper, we propose a new TCP scheme, called TCP-Jersey, which is capable of distinguishing the wireless packet losses from the congestion packet losses, and reacting accordingly. TCP-Jersey consists of two key components, the available bandwidth estimation (ABE) algorithm and the congestion warning (CW) router configuration. ABE is a TCP sender side addition that continuously estimates the bandwidth available to the connection and guides the sender to adjust its transmission rate when the network becomes congested. CW is a configuration of network routers such that routers alert end stations by marking all packets when there is a sign of an incipient congestion. The marking of packets by the CW configured routers helps the sender of the TCP connection to effectively differentiate packet losses caused by network congestion from those caused by wireless link errors. This paper describes the design of TCP-Jersey, and presents results from experiments using the NS-2 network simulator. Results from simulations show that in a congestion free network with 1% of random wireless packet loss rate, TCP-Jersey achieves 17% and 85% improvements in goodput over TCP-Westwood and TCP-Reno, respectively; in a congested network where TCP flow competes with VoIP flows, with 1% of random wireless packet loss rate, TCP-Jersey achieves 9% and 76% improvements in goodput over TCP-Westwood and TCP-Reno, respectively. Our experiments of multiple TCP flows show that TCP-Jersey maintains the fair and friendly behavior with respect to other TCP flows.     

Algorithms for supporting disconnected write operations for wireless Web access in mobile client-server environments

In a wireless mobile client-server environment, a mobile user may voluntarily disconnect itself from the Web server to save its battery life and avoid high communication prices. To allow Web pages to be updated while the mobile user is disconnected from the Web server, updates can be staged in the mobile host and propagated back to the Web server upon reconnection. In this paper, we analyze algorithms for supporting disconnected write operations for wireless Web access and develop a performance model to identify the optimal length of the disconnection period under which the cost of update propagation is minimized. The analysis result is particularly applicable to Web applications which allow wireless mobile users to modify Web contents while on the move. We show how the result can be applied to real-time Web applications such that the mobile user can determine the longest disconnection period such that it can still propagate updates to the server before the deadline so that a minimum communication cost is incurred.     

TCP-BIAD for Enhancing TCP Performance in Broadband Wireless Access Networks

In this paper a new TCP variant, named TCP-Binary Increase, Adaptive Decrease is presented. The suggested congestion control algorithm is a joint approach of Westwood and an enhanced version of BIC, for improving TCP performance in broadband wireless access networks. BIAD has been evaluated with respect to other TCP variants such as Reno, Westwood, BIC, CUBIC, HSTCP and STCP with the use of network simulator 2. The results indicate that the proposed solution achieves high network utilization levels in a wide range of network settings, including wireless channel errors, link asymmetry and congestion. We also evaluated TCP-BIAD when multiple flows share a bottlenecked access link and we show that it demonstrates the fairness features required for network deployment.     

DHTTP: an efficient and cache-friendly transfer protocol for the web

Today's HTTP carries Web interactions over client-initiated TCP connections. An important implication of using this transport method is that interception caches in the network violate the end-to-end principle of the Internet, which severely limits deployment options of these caches. Furthermore, while an increasing number of Web interactions are short, and in fact frequently carry only control information and no data, TCP is often inefficient for short interactions We propose a new transfer protocol for the Web, called Dual-Transport HTTP (DHTTP), which splits the traffic between UDP and TCP channels. When choosing the TCP channel, it is the server who opens the connection back to the client. Through server-initiated connections, DHTTP upholds the Internet end-to-end principle in the presence of interception caches, thereby allowing unrestricted caching within backbones. Moreover, the comparative performance study of DHTTP and HTTP using trace-driven simulation as well as testing real HTTP and DHTTP servers showed a significant performance advantage of DHTTP when the bottleneck is at the server and comparable performance when the bottleneck is in the network.     

Optimizing Web delivery over wireless links: design, implementation, and experiences

World over wide-area wireless Global System for Mobile Communication (GSM) networks have been upgraded to support the general packet radio service (GPRS). GPRS brings "always-on" wireless data connectivity at bandwidths comparable to that of conventional fixed-line telephone modems. Unfortunately many users have found the reality to be rather different, experiencing very disappointing performance when, for example, browsing the Web over GPRS. In This work, we show what causes the web and its underlying transport protocol TCP to underperform in a GPRS wide-area wireless environment. We examine why certain GPRS network characteristics interact badly with TCP to yield problems such as: link underutilization for short-lived flows, excess queueing for long-lived flows, ACK compression, poor loss recovery, and gross unfairness between competing flows. We also show that many Web browsers tend to be overly aggressive, and by opening too many simultaneous TCP connections can aggravate matters. We present the design and implementation of a web optimizing proxy system called GPRSWeb that mitigates many of the GPRS link-related performance problems with a simple software update to a mobile device. The update is a link-aware middleware (a local "client proxy") that sits in the mobile device, and communicates with a "server proxy" located at the other end of the wireless link, close to the wired-wireless border. The dual-proxy architecture collectively implements a number of key enhancements-an aggressive caching scheme that employs content-based hash keying to improve hit rates for dynamic content, a preemptive push of Web page support resources to mobile clients, resource adaptation to suit client capabilities, delta encoded data transfer of modified pages, DNS lookup migration, and a UDP-based reliable transport protocol that is specifically optimized for use over GPRS. We show that these enhancements results in significant improvement in web performance over GPRS links.