Akhihebbal L. Ananda

TCP HACK: TCP header checksum option to improve performance over lossy links

Wireless networks have become increasingly common and an increasing number of devices are communicating with each other over lossy links. Unfortunately, TCP performs poorly over lossy links as it is unable to differentiate the loss due to packet corruption from that due to congestion. We present an extension to TCP which enables TCP to distinguish packet corruption from congestion in lossy environments resulting in improved performance. We refer to this extension as the HeAder ChecKsum option (HACK). We implemented our algorithm in the Linux kernel and performed various tests to determine its effectiveness. Our results have shown that HACK performs substantially better than both SACK and NewReno in cases where burst corruptions are frequent. We also found that HACK can co-exist very nicely with SACK and performs even better with SACK enabled.

Low cost crowd counting using audio tones

With mobile devices becoming ubiquitous, collaborative applications have become increasingly pervasive. In these applications, there is a strong need to obtain a count of the number of mobile devices present in an area, as it closely approximates the size of the crowd. Ideally, a crowd counting solution should be easy to deploy, scalable, energy efficient, be minimally intrusive to the user and reasonably accurate. Existing solutions using data communication or RFID do not meet these criteria. In this paper, we propose a crowd counting solution based on audio tones, leveraging the microphones and speaker phones that are commonly available on most phones, tackling all the above criteria. We have implemented our solution on 25 Android phones and run several experiments at a bus stop, aboard a bus, within a cafeteria and a classroom. Experimental evaluations show that we are able to achieve up to 90% accuracy and consume 81% less energy than the WiFi interface in idle mode.

TCP Vegas-A: Improving the Performance of TCP Vegas

While it has been shown that TCP Vegas provides better performance compared to TCP Reno, studies have identified various issues associated with the protocol. We propose modifications to the congestion avoidance mechanism of the TCP Vegas to overcome these limitations. Unlike the solutions proposed in the past, our solution, named TCP Vegas-A, is neither dependent on optimising any critical parameter values nor on the buffer management scheme implemented at the routers and hence can be implemented solely at the end host. Our simulation experiments over wired as well as over geosynchronous and lower earth orbit satellite links show that TCP Vegas-A is able to overcome several of the identified problems-it can obtain a fairer share of the network bandwidth in wired and satellite scenarios, tackle rerouting issues, rectify Vegass bias against higher bandwidth flows and prevail over fluctuating RTT conditions of a lower earth orbit satellite link. At the same time, Vegas-A is able to preserve the unique properties of Vegas that had made it a noteworthy protocol.

TCP HandOff: A Practical TCP Enhancement for Heterogeneous Mobile Environments

In recent years, many different kinds of wireless access networks have been deployed for the Internet and have become inseparable parts of the Internet. But TCP, the most widely used transport protocol of the Internet, was designed for stationery hosts. In particular, TCP faces severe challenges when user moves around in these networks and handoff occurs frequently. In this paper, TCP handoff (TCP-HO), a practical end-to-end mechanism, is proposed for improving TCP performance in heterogeneous mobile environments. TCP-HO assumes that a mobile host is able to detect the completion of handoff immediately and has a coarse estimation of new wireless links bandwidth. When a mobile host detects handoff completion, it will immediately notify the server through two duplicate ACKs, whose TCP option also carries the bandwidth of new wireless link. After receiving this notification, the server begins to transmit immediately and keeps updating ssthresh according to the bandwidth from mobile host and its new RTT samples. This updating will be stopped after four RTT samples or after congestion is detected. TCP-HO has been implemented in FreeBSD 5.4. Experimental results show that TCP-HO does improve TCP performance without adversely affecting cross traffic in a heterogeneous mobile environment.

TCP HACK: a mechanism to improve performance over lossy links ☆

In recent years, wireless networks have become increasingly common and an increasing number of devices are communicating with each other over lossy links. Unfortunately, TCP performs poorly over lossy links as it is unable to differentiate the loss due to packet corruption from that due to congestion. In this paper, we present an extension to TCP which enables TCP to distinguish packet corruption from congestion in lossy environments resulting in improved performance. We refer to this extension as the HeAder ChecKsum option (HACK). We implemented our algorithm in the Linux kernel and performed various tests to determine its effectiveness. Our results have shown that HACK performs substantially better than both selective acknowledgement (SACK) and NewReno in cases where burst corruptions are frequent. We also found that HACK can co-exist very nicely with SACK and performs even better with SACK enabled. 2002 Elsevier Science B.V. All rights reserved.

ARIVU: Power-aware middleware for multiplayer mobile games

With the improved processing power, graphic quality and high-speed wireless connection in recent generations of mobile phone, it looks more attractive than ever to introduce networked games on these devices. While device features and application resource requirements are rapidly growing, the battery technologies are not growing at the same pace. Networked Mobile games are a class of application, which consume higher levels of energy, as they are naturally more computationally intensive and use hardware components including audio, display and network to their fullest capacities. Therefore, the main concern is the limitation of the battery power of such portable devices to support the potentially long-hour of game play. In this paper we present ARIVU, a power aware middleware that dynamically controls the energy consumption of wireless interface based on the game and system state while maintaining the user experience. ARIVU provides the relevant API for game developers to easily integrate the middleware. We measure power consumption of game play over different wireless interfaces including 3.5G (HSPA), 802.11g and ZigBee. The middleware is able to save up to 40% of the total energy consumed by the wireless interfaces (802.11g and ZigBee). In addition, we show the efficiency of ZigBee interface as potential low power interface for networked game applications.

Worst-case performance limitation of TCP SACK and a feasible solution

In the present implementation of the transmission control protocol (TCP) selective acknowledgment (SACK), every SACK block needs 8 bytes to carry information about the received packets, back to the sender. Since TCP options field has a fixed length, there is a limit on the number of SACK block that can be carried by the acknowledgment packets. Under some error conditions, this limitation can force the TCP sender to retransmit packets that have already been received successfully by the receiver. This paper puts forward a proposal to modify the present SACK implementation, in order to prevent these unwanted retransmissions. We show that the proposed implementation of SACK mechanism increases the throughput of SACK enabled TCP connections.

PGTP: Power aware game transport protocol for multi-player mobile games

Applications on the smartphones are able to capitalize on the increasingly advanced hardware to provide a user experience reasonably impressive. However, the advancement of these applications are hindered battery lifetime of the smartphones. The battery technologies have a relatively low growth rate. Applications like mobile multiplayer games are especially power hungry as they maximize the use of the network, display and CPU resources. The PGTP, presented in this paper is aware of both the transport requirement of these multiplayer mobile games and the limitation posed by battery resource. PGTP dynamically controls the transport based on the criticality of game state and the network state to save energy at the wireless network interface (WNIC) level with almost no degradation to the quality of the game play.

TCP-CM: a transport protocol for TCP-friendly transmission of continuous media

We propose a new TCP friendly transport protocol, called TCP-CM, for continuous media applications over the Internet. TCP-CM is a direct modification of TCP to support continuous media applications without compromising the congestion control feature of TCP, which is critical to the stable functioning of the Internet. We design TCP-CM API to be compatible with the BSD socket interface, which requires minimum changes for applications to adopt TCP-CM. Continuous media applications that adopt TCP-CM as the transport protocol can be relieved from burdens such as rate control and scheduling for timely delivery, and hence can focus solely on advanced coding or compression techniques for adapting the content according to the available network bandwidth. We implement the TCP-CM in Linux 2.2.15 TCP/IP protocol stack, and run extensive experiments on TCP-CM using emulated video flows. Our experiments show that TCP-CM can be used for the timely delivery of continuous media data within the constraints of the available network bandwidth and can compete with TCP connections fairly.

Dynamic lookahead mechanism for conserving power in multi-player mobile games

As the current generation of mobile smartphones become more powerful, they are being used to perform more resource intensive tasks making battery lifetime a major bottle-neck. In this paper, we present a technique called dynamic AoV lookahead for reducing wireless interface power consumption upto 50% while playing a popular, yet resource intensive, mobile multiplayer games.