Performance In Wireless Environments Research Articles

Dynamic adjustment of queue levels in TCP Vegas‐based networks

Transmission control protocols (TCPs) are used to control the congestion in the Internet. Various types of TCP protocols have been proposed including TCP Reno, TCP Tahoe and TCP Vegas. Although TCP Reno is widely used for wired communications, TCP Vegas is proved to have better performance in wireless environments. In TCP Reno, to achieve a certain queue level at the intermediate routers, active queue management (AQM) schemes are used. An AQM scheme marks the packets at the intermediate routers and TCP Reno source uses that mark to adjust its speed. However, in TCP Vegas, such scheme is not useable. Consequently, the queue level adjustment is not achievable. A scheme which is employed at the source and adjusts the TCP Vegas parameters dynamically to achieve a certain queue level at the intermediate router is proposed. To the best of the knowledge, this is the first attempt to dynamically adjust the queue levels when TCP Vegas is employed. Our proposed scheme plays the role of AQM in TCP Reno for TCP Vegas. The control scheme presented is designed based on integral backstepping technique and will be applied to the linearised model of TCP Vegas.

Simulation based Behavioral Study of AODV, DSR, OLSR and TORA Routing Protocols in Manet

The mobile Adhoc network is a concept of communication without planning in that mobile node communicate using different topology. The main agenda of this paper is how to receive the highest performance in wireless environments for this we evaluated some protocols like AODV, DSR , OLSR and TORA on OPNET 14.5 and analysis the performances of respective protocols on certain parameters like delay , load , media access delay, data dropped buffer-overflow, data dropped retry threshold exceeded and throughput under consider Banasthali network . Generally, Banasthali has wired network in many departments and hostels now we want to convert a total network of Banasthali into the wireless

A study of TCP performance in wireless environment using fixed-point approximation

Loss of IP packets occurring as a result of imperfect local error correction is one of the major reasons for TCP performance degradation in wireless networks. These losses are misinterpreted by TCP senders as congestion indications and subsequently lead to the sharp decrease of the sending rate. In addition to wireless losses, packets can be lost as a result of buffer overflows at the IP layer. To study performance experienced by TCP sessions sharing a wireless channel, we adopt the fixed-point approximation. We distinguish between two modes of operation: (i) packet losses are mainly caused by imperfect error correction, (ii) the packet loss process is dominated by the buffer overflow. Applying different TCP models for these two regimes we approximate TCP throughput as a function of underlying layers’ parameters. Using this approach we study the effect of various protocol parameters on TCP throughput. We also investigate the effect of the queuing system involved in our analysis and demonstrate that usage of complex models with correlated arrival processes and generally distributed service time does not qualitatively affect the estimated TCP throughput. This observation allows to use simple queuing models having closed form solutions for performance metrics of interest, e.g. M/M/1/K or Geo/Geo/1/K. Finally, we address the question of choosing appropriate queuing model for quantitative TCP analysis.

SCTP-multihoming for intra and inter-RAT data handover management

SCTP (Stream Control Transmission Protocol) provides interesting features, as multihoming and multistreaming, to enhance information transport performances over air interfaces. Additional extensions have been proposed to adapt SCTP to wireless context (mSCTP: mobile SCTP). However, published approaches do not take into account channel state information during handover processes. The present work proposes a new extension for SCTP which aims at improving transport protocol performance in wireless environments: QoS_Measurement_chunk. It relies a) on a cross-layer mechanism taking place between SCTP and the link layer and b) on a new SCTP control chunk. It allows the emission of radio information from the mobile to its SCTP peer. These information can be used by SCTP layer to adapt transmission rate to the current radio transmission conditions. So, SCTP congestion control parameters are modified to take into account new radio conditions. The combined using of QoS_Measurement_Chunk and multihoming feature provide a data handover with a performance improvement. This new mechanism is useful to perform intra or inter RAT (Radio Access Technology) data handover. The obtained simulation results are compared with the standard SCTP when downlink transmission is considered in handover situation and present better performance in terms of data throughput over the access network. Key words: Inter-RAT handover, SCTP, Qos_measurement_chunk, cwnd adaptation, flow control.

Improving TCP performance in integrated wireless communications networks

Many analytical and simulation-based studies of TCP performance in wireless environments assume an error-free and congestion-free reverse channel that has the same capacity as the forward channel. ...

Improving TCP performance in integrated wireless communications networks

Many analytical and simulation-based studies of TCP performance in wireless environments assume an error-free and congestion-free reverse channel that has the same capacity as the forward channel. Such an assumption does not hold in many real-world scenarios, particularly in the hybrid networks consisting of various wireless LAN (WLAN) and cellular technologies. In this paper, we first study, through extensive simulations, the performance characteristics of four representative TCP schemes, namely TCP New Reno, SACK, Veno, and Westwood, under the network conditions of asymmetric end-to-end link capacities, correlated wireless errors, and link congestion in both forward and reverse directions. We then propose a new TCP scheme, called TCP New Jersey, which is capable of distinguishing wireless packet losses from congestion packet losses, and reacting accordingly. TCP New Jersey consists of two key components, the timestamp-based available bandwidth estimation (TABE) algorithm and the congestion warning (CW) router configuration. TABE is a TCP-sender-side algorithm that continuously estimates the bandwidth available to the connection and guides the sender to adjust its transmission rate when the network becomes congested. TABE is immune to the ACK drops as well as ACK compression. 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. Our simulation results show that TCP New Jersey is able to accurately estimate the available bandwidth of the bottleneck link of an end-to-end path; and the TABE estimator is immune to link asymmetry, bi-directional congestion, and the relative position of the bottleneck link in the multi-hop end-to-end path. The proactive congestion avoidance control mechanism proposed in our scheme minimizes the network congestion, reduces the network volatility, and stabilizes the queue lengths while achieving more throughput than other TCP schemes.

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

AbstractIt 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 different TCP error detection and congestion control strategies over a wireless link

In this paper we present an evaluation of the two major parts of TCP that impact its performance in wireless environments, namely error detection and congestion control. We have re-implemented the most commonly used TCP error detection and congestion control strategies using a modular design technique. Using this implementation we have evaluated the performance in terms of throughput and underlying network usage of different combinations of these strategies over a lossy link with high propagation delay. Our results have shown that selective acknowledgments work well together with any congestion control mechanism and that some combinations of error detection and congestion control suffer from a high amount of unnecessary retransmissions. Consequentely we prorpose a solution to this proplem.