Simulation-based Study of TCP’s Behaviours in Wireless Networks With OPNET Modeler

Motivation: Transmission Control Protocol (TCP) is the de facto IP network transport protocol developed by DARPA that provides connection-oriented and reliable data delivery, flow-control, full-duplexity as well as multiplexing, on top of the Internet Protocol (IP). It has been so popular (about 90 percent of the total internet traffics now days are TCP-based) that the whole protocol stack was named TCP/IP, and the great success of Internet was to a large extent due to the popularity of TCP/IP.

With the evolution of wireless communication systems towards an All-IP based Infrastructure, more and more IP data are being carried over wireless links. However TCP's congestion and flow control mechanisms, which by nature assume all losses on the way are due to congestions, are challenged by the characteristics of the wireless links. Those links are commonly known as lossy and highly dynamic, as resulted from mobility, multi-path fading, interferences and burst bit errors, and local retransmissions etc. This calls for optimizations of TCP when apply it to wireless usages. Researchers around the world have been intensively investigating improvements on traditional TCP and its different flavours for years.

OPNET Modeler is a leading industry-strength discrete event network modelling and simulation environment which enables the design and study of all major communication networks, devices, protocols, and applications with unmatched flexibility. With its object-oriented modelling approach and graphical editors, OPNET Modeler visualizes the structure of actual networks and network components, and the system designed intuitively maps to the model. Productivity and efficiency can be greatly boosted by leveraging the specialized editors, analysis tools, and off-the-shelf models. Because of its open source, new research proposals can be easily implemented, simulated, evaluated and tested, providing a good understanding of the simulation kernel. Four different flavours of TCP have been implemented in OPNET, namely the default profile, Reno TCP, Tahoe TCP and SACK TCP.

Tasks: In this project, the student will study the behaviors of TCP to exploit optimal operational parameter settings for given traffic patterns and link model. In particular, our interest would be to investigate TCP’s behaviors in the presence of link errors and jitters for the downlink channel of UMTS Uu Interface, through specifying different test scenarios and test cases that consist of various combinations of link model parameters like the Signal-to-noise Ratio (SNR), the Bit–error rate (BER), Block-error-rate (BLER), the mode of Radio Link Control Layer (RLC) and the related parameters, as well as the related TCP parameters. The TCP profile to be focused on will likely be a combination of New Reno TCP and SACK TCP. This is done through first to have a good understanding of TCP and its variants and to get familiar with the simulation workflow in OPNET Modeler. This is followed by the specifications of the network model, the node models, the process models, the link model, and the probability density functions to be used for the specific test network. The simulations will be then performed to gather necessary information. Based on that, analysis will be carried out to observe the behaviors of TCP in wireless environment and to identify the optimum parameters.

Prerequisite: Basic knowledge of computer networks and programming skills in C/C++.

Supervisors: Xiaoyuan Gu(IBR) , Matthias Dick(IBR) , Arne Specht(IFN) Christoph Heuck(IFN)

Duration: 6 months

• TCP Overview:Introduction to TCP
• The Latest Developments in TCP:Source 1 , Source 2
• OPNET Moderler: