A study on generalization of packet discard schemes for TCP over ATM

In order to ease the impact of the packet fragmentation problem and to avoi d network congestion in TCP over UBR, packet discard schemes in ATM layer ( such as PPD and EPD) have been proposed. These schemes drop packets before they reach their intended destinations if the network is congested and the packets are to be partially discarded. On the other hand, TCP also regulate s data flow with its own flow control method. Due to restriction of data fl ow at the TCP layer, buffer space is not fully used in an ATM switch. In or der to make use of more buffer resources, this paper generalizes the PPD an d EDP schemes. From this generalization, an optimistic packet discard schem e named the "Probability-Based Delayed Packet Discard" (PDPD) scheme is pro posed. Depending on a particular probability, this scheme sets a discard fl ag to delay actual discard operation. This paper presents the results of se veral simulated models to find out the potential of improvement of goodput by PDPD. The results of these simulations indicate that PDPD obtains higher goodput than ordinary schemes when the packet size is large and the input load is not light. This author concludes that a PDPD scheme should achieve effective goodput and link utilization while using more buffer resources ef fectively.