On the determination of early cell differentiation in amphibian embryos

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On the TCP minimum retransmission timeout in a high-speed cellular network

HS-DSCH is a high-speed shared radio channel extension for WCDMA which is used for cellular mobile telephony. The algorithm for distributing the channel resources together with the characteristics of the radio medium result in delay variations. The TCP minimum retransmission timeout interval has effectively alleviated delay variations in its range from deteriorating TCP performance. But recently, this bound has been shortened in modern widely spread TCP implementations. The aim of our study is to find out how a shorter minimum retransmission timeout affects TCP performance over HS-DSCH. We have implemented a model of HS-DSCH in the network simulator ns-2. Our simulations cover a wide range of different minimum retransmission timeout settings and loads, two types of schedulers (Round-Robin and Signalto-Interference-Ratio (SIR) scheduling) and two versions of TCP (SACK and NewReno). Our results show that the number of spurious timeouts increase with the load. The SIR scheduler causes fewer spurious timeouts than the RR scheduler for shorter minimum retransmission timeout settings, however, for longer settings the RR scheduler causes fewer spurious timeouts compared to the SIR scheduler. The minimum retransmission timeout has consequences for goodput fairness, but it does not affect the total system throughput. Both TCP versions produced similar results.Godkänd; 2005; 20061227 (ysko

Kännedom, attityd och levnadsmönster bland högskolestuderande angående kost, motion och trötthet

Upprättat; 2003; 20160601 (andbra

Congestion control in a high-speed radio environment

This paper explores interactions between congestion control mechanisms at the transport layer and scheduling algorithms at the physical layer in the High-Speed Down-link Packet Access extension to WCDMA. Two different approaches to congestion control - TCP SACK and TFRC - are studied. We find that TCP SACK and TFRC in most respects perform the same way. SIR scheduling give a higher system throughput for both protocols than RR scheduling, but introduces delay variations that lead to spurious timeouts. The no feedback timeout of TFRC was shown to exhibit a similar sensitivity to delay spikes as the retransmit timeout in TCP SACKGodkänd; 2004; 20071026 (saral

Buffer management for TCP over HS-DSCH

In this paper we investigate the influence of buffer management for TCP on performance of the High Speed Downlink Channel (HS-DSCH) introduced in WCDMA release 5. HS-DSCH is a shared channel, but user data is buffered individually prior to the wireless link. Three queue management principles, e.g., passive queuing, the Packet Discard Prevention Counter (PDPC) method and the Random Early Detection (RED) algorithm were evaluated for a number of buffer sizes and scenarios. Also, a buffer large enough to prevent packets from being lost was included for reference. For round robin (RR) scheduling of radio-blocks, PDPC and the passive approach, that both manage to keep the buffer short, gave the best system goodput as well as the shortest average transfer times together with the excessively large buffer. With signal-to-interference ratio (SIR) scheduling, the strategy to avoid all packet losses, resulted in a lower system goodput than for the short buffers. As illustrated in this article, peak transfer rates may not be achieved with very small buffers, but buffers of 10-15 IP packets seem to represent a good trade-off between transfer rates, delay and system goodput. We would like to investigate how to make use of system parameters such as the current amount of data offered for HS-DSCH in total to regulate individual buffer sizes.Godkänd; 2005; 20071026 (saral

Congestion control in a high-speed radio environment

This paper explores interactions between congestion control mechanisms at the transport layer and scheduling algorithms at the physical layer in the High-Speed Down-link Packet Access extension to WCDMA. Two different approaches to congestion control - TCP SACK and TFRC - are studied. We find that TCP SACK and TFRC in most respects perform the same way. SIR scheduling give a higher system throughput for both protocols than RR scheduling, but introduces delay variations that lead to spurious timeouts. The no feedback timeout of TFRC was shown to exhibit a similar sensitivity to delay spikes as the retransmit timeout in TCP SACKGodkänd; 2004; 20071026 (saral

Scheduling support for mixed VoIP and web traffic over HSDPA

HSDPA (high-speed downlink packet access), introduced in WCDMA release 5, provides a high-bandwidth shared channel with short transmission time interval (TTI). The short TTI together with appropriate scheduling enable HSDPA to support efficient multiplexing of traffic. We explain the performance of four scheduling algorithms when transmitting a traffic mix consisting of both conversational (VoIP) traffic and background (Web) traffic over the high-speed downlink shared channel (HS-DSCH) of HSDPA. We consider both cell throughput and user satisfaction. The proportional fair (PF), the maximum rate (MR) scheduler and two extended versions of MR, are tested for different VoIP scheduling delay budgets and varying load. To understand the behaviour of the schedulers, we use the ns-2 simulator extended with a model of HS-DSCH to simulate a mixed traffic scenario. Our results show that a scheduler that gradually increases the VoIP priority and considers the user's current possible rate, performs well. A more drastic increase in VoIP priority is however needed when the delay budget is short. Furthermore, attempting to uphold quality for both VoIP and Web traffic makes the system sensitive to overload situations.Validerad; 2007; 20071026 (saral