Performance evaluation and fairness improvement of TCP over ATM GFR

Abstract

Asynchronous Transfer Mode(ATM) has evolved into a networking technology which is suitable for both public and private networks to support broadband network, and recently, the Guaranteed Frame Rate(GFR) service was proposed as a new service category to support non-realtime data applications such as TCP/IP and provide minimum rate guarantee. In this thesis, we have studied different buffer management and scheduling algorithms for GFR service, and compared their efficiency and fairness when TCP/IP traffic is carried over GFR. We show the results of performance evaluation and compare the performance of existing FIFO buffer management and per-VC queueing algorithms by simulation. From the simulation results, it is clear that per-VC queueing can guarantee the minimum rate of each VC which is negotiated at connection setup and shows better efficiency and fairness than FIFO based algorithms. However, the per-VC queueing greatly complicates the switching system to design and implement. Thus, this may be undesirable for such a simple service as GFR. On the other hand, FIFO based algorithms can’t guarantee the minimum throughput of TCP source with large MCR(Minimum Cell Rate) and give low fairness index. To keep simplicity of GFR as much as possible and overcome defects of FIFO based algorithms, we propose a new FIFO based algorithm, which is an extension of the Differential Fair Buffer Allocation(DFBA)[18] algorithm with the aim to improve fairness and provide minimum rate guarantee for a wider range of MCR. The key idea of proposed algorithm is controlling the number of CLP1 cells which belong to VCs that are occupying more buffer space than their fair share in order to protect TCP source with small MCR from picking up bandwidth of TCP source with large MCR, by keeping track of the number of CLP1 cells in buffer. Performance of the proposed algorithm was investigated by simulations and compared with other existing FIFO based algorithms. The simulation resul...