ON PROVIDING RATE GUARANTEES FOR INTERNET TRAFFIC OVER THE ATM GFR SERVICE

Abstract

Guaranteed Frame Rate (GFR) is an improvement of the Unspecified Bit Rate (UBR) ATM service category. It intends to provide legacy applications, especially TCP/IP data applications, with minimum rate guarantees at the frame level. Research focuses on the design of switches that may provide the specified guarantees. The basic methods for supporting rate guarantees — policing, buffer management, and scheduling — are integrated into the GFR implementations. These are divided into three parts; the service conformance, frame eligibility and frame forwarding mechanisms. We first present some most. significant GFR mechanisms proposed in the literature and highlight important conclusions derived. We.then investigate the performance of TCP traffic over ATM networks using the GFR service category. We first consider the Simple FIFO based scheme with frame tagging mechanism. It discards arriving cells based on the buffer occupancy and the frame priority, i.e. whether the frame is tagged or untagged. We then implement per-VC threshold & scheduling and per-VC scheduling & RED mechanisms. Both of them rely on .per-VC queuing while the frame discard decision is based on the per-VC accounting, total buffer occupancy and the frame priority. Simulation shows that the second mechanism is more efficient in comparison to other mechanism proposed for the same task. Sirpulations show that the simple FIFO-based implementation performs poor, in terms of efficiency and fairness, as compared to the per-VC queuing counterpart. We propose a method that uses a shaping mechanism with simple switch to provide rate guarantees. Simulations show that our scheme, when used with simple FIFO, per-VC threshold & scheduling and per-VC scheduling & RED mechanisms gives better results.