Improving goodputs of IP packets under ATM UBR traffic with port-based queueing schemes

Abstract

ATM networks are widely adopted as backbone networks. TCP/IP are the most popular protocols today and it is quite possible that packets are forwarded by ATM networks. In ATM networks, UBR (unspecified bit rate) service and ABR (available bit rate) service are common in transmitting IP packets. Because TCP has its own flow control mechanism, the flow control of ABR service could become redundant. Moreover, it could interfere with the TCP flow control. In this paper, we will focus on buffer management schemes of ATM switches with UBR service. Researchers have proposed several buffer management schemes for UBR service. However, all schemes do not consider the influence of output rates. In addition, most researchers assume that each port has its own buffers. A basic scheme called dedicated buffers per port is compared with four proposed schemes. The paper considers the situation that switch buffers are shared among all output ports and proposes a scheme called shared buffers among all ports. Then, two schemes, dedicated buffers with early packet discarding (EPD) and shared buffers with EPD, are proposed. The EPD scheme is modified. Instead of using a threshold for each flow, only one threshold is applied to buffers of each output port. The fifth proposed scheme is called shared buffers with EPD + differential buffer allocation (DBA), which also considers the effects of various output rates. Results show that goodputs are increased apparently by applying the DBA scheme. Results also show that for goodputs, when packets pass two or more switches, packet discarding schemes are far more important than whether we adopt schemes of shared buffers or schemes of dedicated buffers. Hence, we can simply adopt schemes of dedicated buffers, which are easy to implement, and incorporate a packet-discarding scheme in most cases.