SGPS: Slow-Start Generalized Processor Sharing

Packet scheduling methods that approximate Generalized Processor Sharing (GPS) are currently the focus of much research in the area of Quality-of-Service (QoS) networks. The ability of GPS schedulers to provide rate guarantees as well as delay guarantees meets the demand of many network applications. This paper addresses a shortcoming of GPS which has been given little attention, however, which can have signi cant impact on the service provided by GPS. Since, with GPS, the service rate received by a session is proportional to the number of backlogged sessions in the system, the service rate of a session may change abruptly if some other session becomes active. This may result in abrupt increases of delay of consecutive packets. In this paper we propose a new scheduler, called Slow-Start GPS (SGPS), which alleviates the problem of abrupt delay increases when new sessions start transmitting. SGPS is a modi cation of GPS where sessions do not receive their guaranteed service rates immediately after they become active. Instead, the service rates of such sessions are gradually increased. This We will show that this prevents an abrupt delay increase of the other sessions. We derive delay bounds for sessions constrained by leaky buckets and we express quantitatively the advantages of the SGPS discipline.