Modeling a mixed TCP Vegas and TCP Reno scenario

In this paper we describe and validate the analytic model of a mixed TCP Reno and TCP Vegas network scenario. There is experimental evidence that TCP Vegas overcomes the widespread TCP version, called TCP Reno, in a number of network environments. The incompatibility between TCP Vegas and TCP Reno in heterogeneous network scenarios has been also verified by means of several simulations. The model presented in this work allows to quantitatively evaluate this incompatibility, by computing the average throughput of a TCP Vegas source in presence of a concurrent TCP Reno source. This model can help us to better understand the reasons of the vulnerability of TCP Vegas in competing with TCP Reno sources

Investigating TCP Single Source Behavior in Time-Varying Capacity Network Scenarios

Some recent simulation works have pointed out that TCP appears to suffer the variability of the available bandwidth when it shares the network resources with higher priority traffic. This paper describes an analytic model able to reproduce TCP behavior under a time-varying available capacity. The aim is to investigate the interaction between TCP and high-priority real-time traffic (e.g., voice and video). The accuracy of the model against simulations is shown to be satisfactory and superior with respect to other popular TCP models in a definite range of network scenarios. Besides, by means of the proposed model and the several simulations carried out in this work we gain air interesting insight on TCP behavior in the considered network environment

Simple Models and their Limits for TCP/IP Network Analysis and Dimensioning

The analysis and design of TCP/IP networks is a key component in the development of the Internet. We consider how simple analytical modelling of the key network elements can yield sufficiently accurate performance results by means of simulations with actual TCP sources. The defined modelling approach, named the fixed point model, is exploited to state a dimensioning problem of an IP network dominated by TCP traffic. The procedure for the TCP/IP network capacity dimensioning is based on the definition of a user satisfaction index, suitable for a best-effort scenario

Experimental Analysis of TCP and UDP Traffic Performance over Infra-structured 802.11b WLANs

In 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 NewVegas: Providing Good TCP Performance in both Homogeneous and Heterogeneous Environments

Its more refined congestion control mechanisms, based on the estimation of the round trip delays, allow TCP Vegas to outperform the more widespread TCP Reno congestion control, based only on the packet loss detection, in a number of network environments. However, these mechanisms make TCP Vegas less aggressive with respect to TCP Reno; thereby TCP Vegas sources show high weakness in taking the available bandwidth when competing with TCP Reno sources. This is a major reason that hinders the spread of TCP Vegas among Internet users. This paper proposes a new adaptive mechanism for TCP Vegas, called TCP NewVegas, in order to improve its behavior even in heterogeneous network scenarios. The simulations show that TCP NewVegas guarantees good performance even in mixed network environments, without canceling the desirable features (e.g. fairness) that TCP Vegas exhibits in homogeneous environments

Investigating interactions between ARQ mechanisms and TCP over wireless links

In 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

Optimal design of hybrid FEC/ARQ schemes for TCP over wireless links with Rayleigh fading

In 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

Analysis and Enhancement of TCP Vegas Congestion Control in a Mixed TCP Vegas and TCP Reno Network Scenario

Its more refined congestion control mechanisms, also based on the estimation of round trip delays, allow TCP Vegas to outperform the more widespread TCP Reno congestion control, based only on the packet loss detection, in a number of network environments. However, these mechanisms make TCP Vegas less aggressive with respect to TCP Reno; thereby TCP Vegas sources show high weakness in taking the available bandwidth when competing with other TCP Reno sources. This is a major reason that hinders the spread of TCP Vegas among Internet users. In this work, after a preliminary analytic study about the limits of TCP Vegas in mixed network environments, we describe a new adaptive mechanism for TCP Vegas, called TCP NewVegas, designed in order to improve its performance even in heterogeneous network scenarios. The large number of simulations, presented in this paper, show that TCP NewVegas guarantees good performance even in mixed network environments, without canceling the desirable features (e.g. fairness) that TCP Vegas exhibits in homogeneous environments. © 2003 Elsevier Science B.V. All rights reserved