Modeling, Simulation and Evaluation of TCP/IP Networks


This dissertation comprises of three parts: modeling TCP/IP networks and the protocol stack’s structure in the BSD operating system (Chapter 2); based on these models, design and implementing a new discrete event and IP-based network simulator (Chapter 3 and 4); applying the new simulator to study some specific issues in TCP/IP networks, which cannot be well-covered by other existing tools (Chapter 6).The TCP/IP network models describe the architecture of TCP/IP networks and the compositional/behavioral structures of the protocol stack in 4.4BSD implementation, employing the tools of the Fundamental Modeling Concepts (FMC).  Based on these models and review on a number of existing simulators, the Visualized IP-based Network Simulator (VINS) is designed and implemented.  Generally, VINS contributes to TCP/IP network simulation in three ways:


  • IP networking.  The network is constructed following the Classful scheme as stated RFC 791, which enables simulation of large-scale IP networks with complex topology;
  • Socket interface.  Socket bridges the discrete protocol data units in networks and the byte-streams of user data.  It allows measurement on both byte-stream and packet levels;
  • Service time models on the node (router and host).  Some resent studies reveals that the common bottleneck in today’s Internet are on the routers, instead of links.

VINS is applied in three case studies:

Firstly in the IP layer, we investigate the issues of head-of-line blocking on the node and possible packet loop caused by IP misconfiguration.  An optimized TTL control is proposed to enhance the border node and battle the negative impact of loop.

The second case study is about TCP performance evaluation.  Instead of using a commonly employed scheme by imposing fixed packet drop ratio and delay on the link, in VINS we vary the network background traffic and topology to test the competence of different TCP variants (Tahoe, Reno, NewReno and SACK).  Based on the new insights gained, some comments are made regarding to TCP’s congestion control algorithms.

Third, VINS is applied in the wireless network study where subnet changes are frequent due to link disruption and endpoint roaming.  A new mobile TCP/IP stack is proposed, implemented and tested with VINS.  We compare the new stack with an existing one (mobile IP) and conclude it may achieve better throughput and shorter packet latency.