Steady-State analysis of a split-connection scheme for Internet access through a wireless terminal

TCP does not perform well in a connection that includes a lossy wireless link. Techniques intended to improve the performance of TCP for such connections can be grouped into three categories: end-to-end, link layer and split-connection approaches. Some simulations and experimental results indicate that split-connection protocols yield better performance than the other two approaches. Although analytical modeling of the end-to-end and link-layer approaches has been presented, no comparable performance analysis for split-connection protocols has been reported previously. In this paper, a stochastic model is developed and used to analyze the performance of a class of split-connection protocols which deploy TCP on the wire-line network and a light-weight transport protocol on the wireless final hop. The final hop is provided by a digital TDMA cellular system. The condition of heavy source traffic to the wireless terminal is considered. The model relates the throughput and some useful auxiliary performance measures to key system parameters such as propagation delays, the base-station buffer size, the ARQ protocol and channel-error process of the wireless link. The usefulness of the analysis is illustrated by its application to the problem of sizing the TCP receiving buffer in a base station.     

Optimal design of hybrid FEC/ARQ schemes for TCP over wireless links with Rayleigh fading

In this paper, we investigate interactions between TCP and wireless hybrid FEC/ARQ schemes. The aim is to understand what is the best configuration of the wireless link protocol in order to guarantee TCP performance and channel efficiency. Interactions between TCP and different link layer mechanisms are evaluated by means of an analytic model that reproduces: 1) a Rayleigh fading channel with FEC coding, 2) a generic selective repeat ARQ Protocol, and 3) the TCP behavior in a wired-cum-wireless network scenario. The analytic model is validated-by means of ns-based simulations. The analysis represents a contribution to the optimal design of link layer parameters of wireless networks crossed by TCP/IP traffic. The main findings can be summarized as follows: 1) fully reliable ARQ protocols are the best choice for both TCP performance and wireless link efficiency and 2) optimal values of FEC redundancy degree from the point of view of energy efficiency maximizes TCP performance as well.     

Removing redundant TCP functionalities in wired‐cum‐wireless networks with IEEE 802.11e HCCA support

The TCP was originally designed for wired networks, assuming transmission errors were negligible. Actually, any acknowledgment time‐out unconditionally triggers the congestion control mechanism, even in wireless networks in which this assumption is not valid. Consequently, in wireless networks, TCP performance significantly degrades. To avoid this degradation, this paper proposes the so‐called split TCP and UDP. In this approach, the access point splits the TCP connection and uses a customized and lighter transport protocol for the wireless segment. It takes advantage of the IEEE 802.11e Hybrid Coordination Function Controlled Channel Access (HCCA) mechanisms to remove redundant TCP functionalities. Specifically, the HCCA scheduler allows disabling of the congestion control in the wireless link. Similarly, the IEEE 802.11e error control service makes possible to eliminate TCP acknowledgments, therefore reducing the TCP protocol overhead. Finally, the usage of an HCCA scheduler permits providing fairness among the different data flows. The proposed split scheme is evaluated via extensive simulations. Results show that split TCP and User Datagram Protocol outperforms the analyzed TCP flavors—specifically designed for wireless environments—and the split TCP solution, achieving up to 95% of end‐user throughput gain. Furthermore, the proposed solution is TCP friendly because TCP flows are not degraded by the presence of flows by using this approach. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance evaluation of TCP/RLP protocol stack over CDMA wireless link

Due to the high frame error rate in wireless communication channels, an additional link layer protocol, Radio Link Protocol (RLP), has been introduced in the newly approvedData Services Option Standard for Wideband Spread Spectrum Digital Cellular System. In this paper, we investigate performance issues of a typical Cod Division Multiple Access (CDMA) wireless link using the protocol stack given in the standard. In particular, we focus on the dynamics of the TCP and RLP layers of the protocol stack since the fluctuation of system performance is largely caused by Automatic Repeat Request (ARQ) mechanisms implemented at these two layers. We compare the network performance of default parameter setting to those of other possible parameter settings. Analytical and simulation results presented in this paper can provide guidance to those attempting to further improve performance of interest.     

WLAN中TCP性能改进的跨层方案仿真

随着无线网络的迅速发展,如何改进TCP在无线网络中的传输性能这一课题,已经成为国内外研究的热点.文章分析了现有的几种典型的TCP改进方案,并在此基础上介绍一种新的跨层方案.通过在传输层和链路层之间引入ARQ Snoop代理,在链路层检测并重传ARQ分组的同时,协调WLAN MAC子层的ARQ机制与TCP的ARQ策略.     

On the impact of link layer retransmission schemes on TCP over 4G satellite links

We study the impact of reliability mechanisms introduced at the link layer on the performance of transport protocols in the context of 4G satellite links. Specifically, we design a software module that performs realistic analysis of the network performance, by utilizing real physical layer traces of a 4G satellite service. Based on these traces, our software module produces equivalent link layer traces, as a function of the chosen link layer reliability mechanism. We further utilize the link layer traces within the ns‐2 network simulator to evaluate the impact of link layer schemes on the performance of selected Transmission Control Protocol (TCP) variants. We consider erasure coding, selective‐repeat automatic request (ARQ) and hybrid‐ARQ link layer mechanisms, and TCP Cubic, Compound, Hybla, New Reno and Westwood. We show that, for all target TCP variants, when the throughput of the transport protocol is close to the channel capacity, using the ARQ mechanism is most beneficial for TCP performance improvement. In conditions where the physical channel error rate is high, hybrid‐ARQ results in the best performance for all TCP variants considered, with up to 22% improvements compared to other schemes. Copyright © 2014 John Wiley & Sons, Ltd.     

Transmission control protocol performance enhancement for mobile broadband interactive satellite communication system: a cross‐layer approach

Mobile broadband interactive satellite communication system is of great interest in both academic and industrial communities. However, the conventional strict‐layered protocol stack architecture and the standard TCP version perform poorly over satellite link. In this paper, we propose a comprehensive cross‐layer Transmission Control Protocol (TCP) optimization architecture while considering the main factors that affect the TCP performance. In our proposed architecture, we adopt two TCP split connection performance enhancing proxies to isolate the satellite link from the terrestrial part of the broadband satellite communication system. Then, based on the proposed cross‐layer architecture, we present an analytical model for the TCP throughput by taking the modulation and coding (ModCod) mode and the allocated bandwidth into account. In addition, we put forward a TCP‐driven bandwidth sharing and ModCod mode optimization algorithm to maximize the TCP throughput in satellite link. Extensive simulation results illustrate that our proposed comprehensive cross‐layer TCP optimization approach is able to improve the TCP throughput significantly. Copyright © 2014 John Wiley & Sons, Ltd.     

Internet connection with UMTS

Mobile telecommunication new services are based on data networks specially Internet. These services include http, telnet, ftp, Simple Mail Transfer Protocol, etc. Besides, we recognize a mobile network as a multiuser network. Transmission Control Protocol (TCP)/Internet Protocol which is sensitive to link congestion in wireline data links is also used in wireless networks. In order to improve the system performance, the TCP layer uses flow control and congestion control. Besides, radio link control (RLC) and medium access control sublayers have been introduced to compensate the deficiency of TCP layer in wireless environment. RLC has an important role in quality of service enhancement of the Universal Mobile Telecommunications System (UMTS). In this paper, we review the protocol stack of UMTS Terrestrial Radio Access Network which is based on Third-Generation Partnership Project. Then, we evaluate its layer 2 error control mechanisms and verify TCP over automatic repeat request error control mechanism and finally quality of service improvement results from it in fading channels.     

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.     

Modelling of wireless TCP for short‐lived flows

The transmission control protocol (TCP) is one of the most important Internet protocols. It provides reliable transport services between two end‐hosts. Since TCP performance affects overall network performance, many studies have been done to model TCP performance in the steady state. However, recent researches have shown that most TCP flows are short‐lived. Therefore, it is more meaningful to model TCP performance in relation to the initial stage of short‐lived flows. In addition, the next‐generation Internet will be an unified all‐IP network that includes both wireless and wired networks integrated together. In short, modelling short‐lived TCP flows in wireless networks constitutes an important axis of research. In this paper, we propose simple wireless TCP models for short‐lived flows that extend the existing analytical model proposed in [IEEE Commun. Lett. 2002; 6 (2):85–88]. In terms of wireless TCP, we categorized wireless TCP schemes into three types: end‐to‐end scheme, split connection scheme, and local retransmission scheme, which is similar to the classification proposed in [IEEE/ACM Trans. Networking 1997; 756–769]. To validate the proposed models, we performed ns‐2 simulations. The average differences between the session completion time calculated using the proposed model and the simulation result for three schemes are less than 9, 16, and 7 ms, respectively. Consequently, the proposed model provides a satisfactory means of modelling the TCP performance of short‐lived wireless TCP flows. Copyright © 2005 John Wiley & Sons, Ltd.     

Syndrome: a light‐weight approach to improving TCP performance in mobile wireless networks

It is well known that the performance of TCP deteriorates in a mobile wireless environment. This is due to the fact that although the majority of packet losses are results of transmission errors over the wireless links, TCP senders still take packet loss as an indication of congestion, and adjust their congestion windows according to the additive increase and multiplicative decrease (AIMD) algorithm. As a result, the throughput attained by TCP connections in the wireless environment is much less than it should be. The key problem that leads to the performance degradation is that TCP senders are unable to distinguish whether packet loss is a result of congestion in the wireline network or transmission errors on the wireless links. In this paper, we propose a light‐weight approach, called syndrome, to improving TCP performance in mobile wireless environments. In syndrome, the BS simply counts, for each TCP connection, the number of packets that it relays to the destination host so far, and attaches this number in the TCP header. Based on the combination of the TCP sequence number and the BS‐attached number and a solid theoretical base, the destination host will be able to tell where (on the wireline or wireless networks) packet loss (if any) occurs, and notify TCP senders (via explicit loss notification, ELN) to take appropriate actions. If packet loss is a result of transmission errors on the wireless link, the sender does not have to reduce its congestion window. Syndrome is grounded on a rigorous, analytic foundation, does not require the base station to buffer packets or keep an enormous amount of states, and can be easily incorporated into the current protocol stack as a software patch. Through simulation studies in ns‐2 (UCB, LBNL, VINT network simulator, http://www‐mash.cs.berkeley.edu/ns/ ), we also show that syndrome significantly improves the TCP performance in wireless environments and the performance gain is comparable to the heavy‐weight SNOOP approach (either with local retransmission or with ELN) that requires the base station to buffer, in the worst case, a window worth of packets or states. Copyright © 2001 John Wiley & Sons, Ltd.     

Performance evaluation of TCP under dynamic allocation scheme for down‐link transmission rate in W‐CDMA systems

IMT‐2000 has attracted much attention as the Next Generation Mobile Communication System. IMT‐2000 can provide high‐bit‐rate data communication service, so that a great number of packets conveyed by TCP (transmission control protocol) can be transmitted over a wireless link. W‐CDMA, standardized in 3GPP (which standardizes IMT‐2000), allows dynamically allocating transmission rates to flow over a wireless link in response to a changing FER for each flow, which is thought to be essential for a next generation mobile communication system. Therefore, in this paper, we study the characteristics of the dynamic allocation scheme when TCP flows share a wireless link, and, in particular, we focus on the throughput performance of these TCP flows. First, we use simulations to examine the effectiveness of the dynamically allocating down‐link transmission rate for TCP flows in response to changing the frame error rate (FER). Through the simulation results, we will show how it can improve the total throughput performance of TCP flows. Furthermore, we can obtain an effective way to allocate transmission rates to flows with different FERs in order to achieve high total throughput. Finally, we will deal with a case of multiple flows from a fixed host to a mobile host. In actual networks, this often happens. In this case, we will show that the total throughput of TCP flows degrades less than in the single‐flow case, even when the FER is high. Copyright © 2004 John Wiley & Sons, Ltd.     

A new ATM adaptation layer for TCP/IP over wireless ATM networks

This paper describes the design and performance of a new ATM adaptation layer protocol (AAL‐T) for improving TCP performance over wireless ATM networks. The wireless links are characterized by higher error rates and burstier error patterns in comparison with the fiber links for which ATM was introduced in the beginning. Since the low performance of TCP over wireless ATM networks is mainly due to the fact that TCP always responds to all packet losses by congestion control, the key idea in the design is to push the error control portion of TCP to the AAL layer so that TCP is only responsible for congestion control. The AAL‐T is based on a novel and reliable ARQ mechanism to support quality‐critical TCP traffic over wireless ATM networks. The proposed AAL protocol has been validated using the OPNET tool with the simulated wireless ATM network. The simulation results show that the AAL‐T provides higher throughput for TCP over wireless ATM networks compared to the existing approach of TCP with AAL 5. This revised version was published online in July 2006 with corrections to the Cover Date.     

WTCP: A Reliable Transport Protocol for Wireless Wide-Area Networks

Wireless wide-area networks (WWANs) are characterized by very low and variable bandwidths, very high and variable delays, significant non-congestion related losses, asymmetric uplink and downlink channels, and occasional blackouts. Additionally, the majority of the latency in a WWAN connection is incurred over the wireless link. Under such operating conditions, most contemporary wireless TCP algorithms do not perform very well. In this paper, we present WTCP, a reliable transport protocol that addresses rate control and reliability over commercial WWAN networks such as CDPD. WTCP is rate-based, uses only end-to-end mechanisms, performs rate control at the receiver, and uses inter-packet delays as the primary metric for rate control. We have implemented and evaluated WTCP over the CDPD network, and also simulated it in the ns-2 simulator. Our results indicate that WTCP can improve on the performance of comparable algorithms such as TCP-NewReno, TCP-Vegas, and Snoop-TCP by between 20% to 200% for typical operating conditions.     

Improving reliable transport and handoff performance in cellular wireless networks

TCP is a reliable transport protocol tuned to perform well in traditional networks where congestion is the primary cause of packet loss. However, networks with wireless links and mobile hosts incur significant losses due to bit-errors and handoffs. This environment violates many of the assumptions made by TCP, causing degraded end-to-end performance. In this paper, we describe the additions and modifications to the standard Internet protocol stack (TCP/IP) to improve end-to-end reliable transport performance in mobile environments. The protocol changes are made to network-layer software at the base station and mobile host, and preserve the end-to-end semantics of TCP. One part of the modifications, called the snoop module, caches packets at the base station and performs local retransmissions across the wireless link to alleviate the problems caused by high bit-error rates. The second part is a routing protocol that enables low-latency handoff to occur with negligible data loss. We have implemented this new protocol stack on a wireless testbed. Our experiments show that this system is significantly more robust at dealing with unreliable wireless links than normal TCP; we have achieved throughput speedups of up to 20 times over regular TCP and handoff latencies over 10 times shorter than other mobile routing protocols.This work was supported by ARPA Contract J-FBI-93-153. This paper was in part presented at the ACM Mobile Computing and Networking Conference (Mobicom '95), Berkeley, California, 14–15 November 1995.     

TCP-aware bidirectional bandwidth allocation in IEEE 802.16 networks

In this paper, we propose a bidirectional bandwidth-allocation mechanism to improve TCP performance in the IEEE 802.16 broadband wireless access networks. By coupling the bandwidth allocation for uplink and downlink connections, the proposed mechanism increases the throughput of the downlink TCP flow and it enhances the efficiency of uplink bandwidth allocation for the TCP acknowledgment (ACK). According to the IEEE 802.16 standard, when serving a downlink TCP flow, the transmission of the uplink ACK, which is performed over a separate unidirectional connection, incurs additional bandwidth-request/allocation delay. Thus, it increases the round trip time of the downlink TCP flow and results in the decrease of throughput accordingly. First, we derive an analytical model to investigate the effect of the uplink bandwidth-request/allocation delay on the downlink TCP throughput. Second, we propose a simple, yet effective, bidirectional bandwidth-allocation scheme that combines proactive bandwidth allocation with piggyback bandwidth request. The proposed scheme reduces unnecessary bandwidth-request delay and the relevant signaling overhead due to proactive allocation; meanwhile, it maintains high efficiency of uplink bandwidth usage by using piggyback request. Moreover, our proposed scheme is quite simple and practical; it can be simply implemented in the base station without requiring any modification in the subscriber stations or resorting to any cross-layer signaling mechanisms. The simulation results ascertain that the proposed approach significantly increases the downlink TCP throughput and the uplink bandwidth efficiency.     

Optimal TCP segment size for mobile server access over wireless links of cellular networks

Internet access from mobile phones over cellular networks suffers from severe bandwidth limitations and high bit error rates over wireless access links. Tailoring TCP connections to best fit the characteristics of this bottleneck link is thus very important for overall performance improvement. In this work, we propose a simple algorithm in deciding the optimal TCP segment size to maximize the utilization of the bottleneck wireless TCP connection for mobile contents server access, taking the dynamic TCP window variation into account. The proposed algorithm can be used when the product of the access rate of the wireless link and the propagation time to mobile contents servers is not large. With some numerical examples, it is shown that the optimal TCP segment size becomes a constant value when the TCP window size (WS) exceeds a threshold. One can set the maximum segment size (MSS) of a wireless TCP connection to this optimal segment size for mobile contents server access for maximum efficiency on the expensive wireless link. Copyright © 2007 John Wiley & Sons, Ltd.     

Analysis of TCP performance under joint rate and power adaptation in cellular WCDMA networks

To improve the spectral efficiency while meeting the radio link level quality of service requirements such as the bit-error-rate (BER) requirements for the different wireless services, transmission rate and power corresponding to the different mobile users can be dynamically varied in a cellular wideband code-division multiple-access (WCDMA) network depending on the variations in channel interference and fading conditions. This paper models and analyzes the performance of transmission control protocol (TCP) under joint rate and power adaptation with constrained BER requirements for downlink data transmission in a cellular variable spreading factor (VSF) WCDMA network. The aim of this multilayer modeling of the WCDMA radio interface is to better understand the interlayer protocol interactions and identify suitable transport and radio link layer mechanisms to improve TCP performance in a wide-area cellular WCDMA network.     

Vertical optimization of data transmission for mobile wireless terminals

A major problem for TCP connections over wireless links is that errors introduced by the wireless channel interfere with the TCP protocol, leading to reduced data rates and power wastage. Based on accurate simulations for the TCP and IEEE 802.11 MAC protocols, we discuss recipes to optimize transmission. It is argued that the best approach is to restrict modifications to the mobile device. While this requires separate solutions for the uplink and downlink, the results of optimization are then available when roaming into any WLAN obeying the relevant MAC protocol. Simulation results show that the combination of specific strategies with a vertical interaction between the protocol layers can lead to the required improvements, giving a promising approach to enhance the performance of wireless mobile terminals.     

适用于卫星网络的TCP跨层改进机制

该文提出基于跨层信息交互,将链路层ARQ重传状态信息通知TCP的机制,避免了链路层重传引起的时延变化对TCP的不利影响。该机制使用完全可靠选择性重传ARQ为TCP提供可靠的链路,避免卫星链路上发生丢包,并且不必要求链路层保证包按序递交,消除了重排序的等待时延,适合带宽时延积较大的卫星网络。仿真结果表明,能显著提高TCP在卫星网中的性能,特别是在误帧率较高条件下。