1,720,976 research outputs found
TCP over wireless links with Rayleigh fading: some considerations about energy efficiency and TCP performance
No full textAntwerp (B
Optimal design of hybrid FEC/ARQ schemes for TCP over wireless links with Rayleigh fading
No full textIn 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
Experimental Analysis of TCP and UDP Traffic Performance over Infra-structured 802.11b WLANs
No full textIn this paper we present the results of experiments carried out in an infra-structured 802.11b WLAN comprising a single Access Point (AP) and a number of user terminals. The aim of this work is twofold: by the one hand, we validate well-known ¿TCP (UDP) over 802.11¿ analytic models by means of experimental results; by the other hand, we focus our analysis on TCP behavior over 802.11b. We present results about flow fairness, about interaction between WLAN link layer parameters (ARQ) and transport protocols and about TCP flows traffic characteristics. With respect to earlier related works, an added value of our analysis is given by a more accurate knowledge and control of key parameters that highly affect the system performance (e.g., mobile station transmission bitrate, maximum number of retransmission attempts, TCP version, etc.) that guarantees the reliability of numerical results. This is a key issue in order to confidently explain observed experimental phenomena
TCP fluid modeling with a variable capacity bottleneck link
No full textA single TCP connection with a time varying capacity bottleneck link is considered. The bottleneck capacity varies arbitrarily and independently of the TCP connection traffic; it aims at reproducing typical situations where capacity is modulated by exogenous process, such as wireless channel with link adaptation or bursty channels. The key point is to understand the interplay of the TCP congestion control evolution and the time constants of the bottleneck link capacity time variation. Fluid modeling is used to describe the time evolution of the congestion window size and of the bottleneck buffer content with a completely general capacity time function, ns-2 based simulations are used as mean to assess the fluid model accuracy. Numerical results show the existence of a "resonance" phenomena, that can significantly degrade the TCP long term performance (even more than halved). The degradation depends on the ratio between the fundamental time constant of the link capacity variation and the TCP average round trip time. © 2007 IEEE
On the effects of ARQ mechanisms on TCP performance in wireless environments
No full textIn this paper we investigate the interaction between TCP and wireless ARQ mechanisms. The aim is to understand what is the best reliability degree of the wireless link in order to guarantee TCP performance. For this purpose, we first develop a Markov model for a selective repeat ARQ protocol, widely used in the current wireless environments. Secondly, we design a cross-layer algorithm that, by exploiting the proposed model, can adapt the number of link layer transmission attempts to the end-to-end packet loss rate perceived by TCP. The interaction between TCP and link layer is evaluated in a specific case study (TCP over 3G radio access) by means of simulations carried out by using a very detailed UMTS-TDD simulator based on its. The deployment of the link layer Markov model and of the proposed algorithm allows us to derive some interesting conclusions about the design of retransmission protocols in TCP/IP network environments
End-to-end evaluation of WWW and file transfer performance for UMTS-TDD
No full textWireless data is deemed as a major booster of next generation wireless networks. In this context, the support of Inter-net applications based-on the TCP still presents several open issues. The aim of this work is to evaluate the performance of TCP data transfer over the UMTS TD-CDMA air interface, by means of a rather detailed simulation model. The evaluation includes both bulk FTP like data transfer and interactive client-server (WWW) traffic. The distinctive point of view is exploring the interaction between application and transport level protocol functions and lower layers protocols over the radio interface. The interplay of radio access and fixed core network impairments is analyzed as well. Major results deal with balancing the error recovery performance of the RLC against the radio channel correlation and the fixed network impairments
Reconfigurable Packet Scheduling for Radio Access Jointly Adaptive to Traffic and Channel
No full textAdaptive packet scheduling for wireless data access systems, including channel state information based algorithms, is a quite well established topic. We develop here an original framework to define such an algorithm in a reconfigurable context, i.e. with the ability to exploit heterogeneous communication environments. The focus is to define platform independent algorithms that can be "adapted", by a specific software, to different environments, so that the core communication functions can be defined, modified and improved once for all. The specific communication function addressed in this work is packet scheduling. For better performance the packet scheduling design exploits the cross-layering approach, i.e. information and functions from different communication layers are used. The concept is proved with reference to the UMTS and Bluetooth technologies, as representatives of a cellular system and a local access one respectively
Investigating interactions between ARQ mechanisms and TCP over wireless links
No full textIn this paper we investigate interactions
between TCP and wireless ARQ mechanisms. The aim
is to understand what is the best conguration of the
wireless link protocol in order to guarantee TCP performance,
seemingly a controversial issue. Interactions between
TCP and different link layer mechanisms are evaluated
by means of an analytic model, that reproduces a
generic selective repeat ARQ protocol (widely used in the
current wireless environments) and the TCP behavior in a
wired-cum-wireless network scenario. A numerical investigation
is carried out in a specic case study (TCP over
3G radio access) by means of simulations collected with
a very detailed UMTS-TDD simulator based on ns. Our
main nding is that fully reliable ARQ protocols are the
best choices from the TCP perspective; in fact, whereas a
residual packet loss left over by not fully reliable ARQ protocols
may not degrade appreciably TCP throughput performance
as long as it is a fraction of the overall end-to-end
TCP packet loss, no apparent performance advantages (e.g.
energy savings) come from limiting the numbe
YeAH-TCP: Yet Another Highspeed TCP
No full text— In recent years, several new TCP congestion control
algorithms have been proposed to improve TCP performance
over very fast, long-distance networks. High bandwidth delay
products require more aggressive window adaptation rules, yet
maintaining the ability of controlling router buffer congestion.
We define a relatively simple experimental scenario to compare
most current high speed TCP proposals under many metrics:
efficiency, internal fairness, friendliness to Reno, induced network
stress, robustness to random losses. Based on the gained insight,
we define Yet Another High-speed TCP, as a heuristic attempt
to strike a balance among different opposite requirements
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