Pasi Sarolahti

Aalto Universiy, Communication, Department Member

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Alvaro Araujo

Universidad Politécnica de Madrid

Mohamed Hefeeda

Edmundo Monteiro

University of Coimbra

Amitava Ghosh

Carlos Pomalaza-Ráez

Purdue University Fort Wayne

Middlesex University

Mediterranean University of Reggio Calabria

Andrei Gurtov

Aalto University, School of Science

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Papers by Pasi Sarolahti

Modeling energy efficiency in wireless internet communication

For wireless mobile Internet users the length of the battery life is one of the most important pe... more For wireless mobile Internet users the length of the battery life is one of the most important performance factors. The energy efficiency of the data transmission over radio is a key component affecting the battery lifetime. This paper investigates WLAN energy consumption in network communication on a Mobile handset. We introduce an energy model that allows analysis and simulation of the energy efficiency of the Internet protocols on a Wireless Network Interface, and have extended the NS-2 simulation platform to allow investigating the energy consumption of the Radio Modem and the Power Amplifier in WLAN 802.11g network interface of a mobile device. We have also validated our model against measurements on real wireless hardware, and show that the simulation results closely match the real world behavior. We claim to present more detailed and accurate model of the WLAN energy consumption than what is done by the past work that allows designing and optimizing future Internet protocols towards more energy efficient behavior.

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Congestion control on spurious TCP retransmission timeouts

Spurious TCP retransmission timeouts are a considerable problem degrading the TCP efficiency in c... more Spurious TCP retransmission timeouts are a considerable problem degrading the TCP efficiency in communication over mobile 2.5G and 3G networks. They cause several unnecessary retransmissions and diminish TCP throughput. F-RTO algorithm can be used to detect spurious TCP RTOs, thus making it possible to avoid unnecessary retransmissions in such occasions and improve TCP performance. In this paper we present a SACK-based enhancement to the F-RTO algorithm that further improves the efficiency of F-RTO in detecting spurious RTOs. Additionally, we evaluate three congestion control alternatives to be applied when spurious TCP RTO is detected under different levels of congestion. The results show that choosing the most efficient congestion control alternative depends on the available link bandwidth, amount of buffering space in the bottleneck router, and the number of parallel TCP connections. If the wireless link has a low bandwidth, sufficient conservativeness at the sender not only prevents congestion losses, but also improves TCP throughput. On a faster link more aggressive congestion control yields better throughput despite of increased number of congestion losses.

F-RTO: an enhanced recovery algorithm for TCP retransmission timeouts

Computer Communication Review, 2003

... The results show that our algorithm either improves performance or gives similar throughput a... more

Designing a Resource Pooling Transport Protocol

This paper presents a design for an end-toend transport protocol for multi-homed end systems that... more This paper presents a design for an end-toend transport protocol for multi-homed end systems that pools the communication resources of multiple network paths to support a single communication session. This approach offers improved performance and resilience compared to communicating over a single path. Compared to previous efforts, deployability in the current commercial Internet, i.e., in the presence of middleboxes, filtering and restricted connectivity, was a key driver for the design of the Resource Pooling Protocol (RPP).

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F-RTO: An Algorithm for Detecting Spurious Retransmission Timeouts with TCP and SCTP

Multipath Congestion Control for Shared Bottleneck

Multipath transport protocols, which transmit data over multiple distinct paths in an end-to-end ... more Multipath transport protocols, which transmit data over multiple distinct paths in an end-to-end connection are introduced. However, they have a problem in terms of fairness. When the transmissions along several paths share the same bottleneck link, the multipath connection receives higher throughput than a competing regular TCP flow, because it executes congestion control per path with the same algorithm as TCP. We investigate a congestion control scheme that addresses this problem with the weighted congestion control approach. In our scheme, an end-to-end connection that uses flows along multiple paths can fairly compete with TCP flows at the shared bottleneck. Our scheme also maximizes the utilization of different path characteristics, such as bandwidth capacity and RTT. Our simulation results show that a bundle of multiple flows based on our scheme fairly competes with TCP flows at the shared bottleneck.

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F-RTO: an enhanced recovery algorithm for TCP retransmission timeouts

Computer Communication Review, 2003

... The results show that our algorithm either improves performance or gives similar throughput a... more

Seawind: a Wireless Network Emulator

Behavior of current communication protocols as well as current and future networked applications ... more Behavior of current communication protocols as well as current and future networked applications is of fundamental importance for technical and commercial success of Mobile Internet. The forthcoming wireless Wide-Area Networks, such as GPRS and UMTS, are quite complex and network operators have a large set of parameters to tune the transfer performance of these networks. In this situation it is of great value to be able to execute practical experiments. The Seawind emulation software introduced in this paper enables measurements of protocol implementations in modeled networking environments. The Seawind software provides a rich set of ways to define transfer characteristics including delays and errors. The software has also means to conduct large sets of experiments in an automatic fashion. In addition, tools of analyzing measurement data has been integrated into the Seawind software.

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An experimental study of home gateway characteristics

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Using Quick-Start to Improve TCP Performance with Vertical Hand-offs

Vertical hand-offs between different wireless access technologies have become more relevant after... more Vertical hand-offs between different wireless access technologies have become more relevant after the introduction of multi-access mobile terminals with wireless LAN (WLAN) and wireless WAN (WWAN) technologies. While the IP mobility mechanisms are rather well known, the performance of TCP still has problems when moving between WLAN and WWAN accesses. First, with a high-latency WWAN link technology such as GPRS it takes several seconds before the TCP congestion window has reached the path capacity. Second, when the notification of the first packet loss arrives at the TCP sender, several packets have already been lost due to the slow-start overshoot and the TCP sender needs to retransmit a large number of the packets from the last transmission window. Third, after a vertical hand-off the path characteristics might have changed dramatically in which case the TCP congestion control state is not valid any more. In this paper we investigate Quick-Start, a mechanism for avoiding the initial slow-start delay, in the context of wireless multi-access terminals. We also propose an enhancement to Quick-Start to alleviate the effects of slow-start overshoot and apply Quick-Start after a vertical hand-off to quickly learn the available capacity on the new end-to-end path. An explicit cross-layer hand-off notification is employed to trigger Quick-Start when the hand-off completes. We conduct simulations with different hand-off models, and our simulations yield promising results with Quick-Start

Internet-Draft draft-amit-quick-start-03

Evaluating Quick-Start for TCP

This paper explores the Quick-Start mechanism, designed to allow transport protocols to explicitl... more This paper explores the Quick-Start mechanism, designed to allow transport protocols to explicitly request permission from the routers along a network path to send at a higher rate than normally allowed by traditional congestion control mechanisms. If the routers are underutilized, they may approve the sender's request for a higher sending rate; otherwise the sender uses the default congestion control algorithms. This paper discusses some of the design issues of Quick-Start, and evaluates the potential benefits, costs and implications of Quick-Start in different networking environments. Using simulations, we evaluate several different algorithms that routers could use to process a Quick-Start Request. This evaluation explores tradeoffs between the fraction of Quick-Start requests that are approved and the fraction of approved Quick-Start requests that result in increasing network congestion. In addition, the paper discusses the security implications of using Quick-Start and some possible mitigations for the vulnerabilities.

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Quick-Start for TCP and IP

[Docs] [txt|pdf] [draft-ietf-tsvwg-...] Diff1] [Diff2] [Errata] EXPERIMENTAL Errata Exist Network... more

Determining an appropriate sending rate over an underutilized network path

Computer Networks, 2007

Determining an appropriate sending rate when beginning data transmission into a network with unkn... more Determining an appropriate sending rate when beginning data transmission into a network with unknown characteristics is a fundamental issue in best-effort networks. Traditionally, the slow-start algorithm has been used to probe the network path for an appropriate sending rate. This paper provides an initial exploration of the efficacy of an alternate scheme called Quick-Start, which is designed to allow transport protocols to explicitly request permission from the routers along a network path to send at a higher rate than allowed by slow-start. Routers may approve, reject or reduce a sender's requested rate. Quick-Start is not a general purpose congestion control mechanism, but rather an anti-congestion control scheme; Quick-Start does not detect or respond to congestion, but instead, when successful, gets permission to send at a high sending rate on an underutilized path. Before deploying Quick-Start there are many questions that need to be answered. However, before tackling all the thorny engineering questions we need to understand whether Quick-Start provides enough benefit to even bother. Therefore, our goal in this paper is to start the process of determining the efficacy of Quick-Start, while also highlighting some of the issues that will need to be addressed to realize a working Quick-Start system.

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Modeling energy efficiency in wireless internet communication

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Congestion control on spurious TCP retransmission timeouts