A SIMPLE ERICA TYPE CORE-ALGORITHM TO SUPPORT TCP OVER ATM

A new ER-based switch algorithm core for the ERICA scheme, namely the SERICA-scheme, used for the ABR traffic flow regulation in an ATM network is derived and discussed. The network switches monitor both their load and buffer occupancy on each link, determining the corresponding factors, the available capacity, and the number of currently active virtual channels. Based on this information the algorithm developed advises the sources about the rates at which they should transmit. It is designed on a hop-by-hop architecture. Its main purpose is to derive analytically the ERICA functional parameters f(q) (depended on the queue), in order to produce the most throughput in the environment of the Congestion Avoidance strategy. Introduction Today’s challenge is to support integrated Internet based applications, known as Differentiated Services over the ABR traffic. ABR service is used to carry the traffic produced from some delay insensitive or burst data applications. It is also used when it is more desirable to use whatever bandwidth is available than to get the connection rejected. The link bandwidth is first allocated to the nonpredictable traffic of the VBR and CBR classes and the remaining, if there is something left, is first given to the ABR and then to the UBR service, resulting thus to an unpredictable ABR traffic. The above framework requires a suitable flow control mechanism to automatically adjust the service rate fluctuations of the switches. However, it is desirable such an environment to be served from a globally stable feedback mechanism, in order to auto-adjust the source emission rate and to operate safely with almost 100% utilization using a threshold of the queuing delay to prevent from buffer overflows. However, according to their traffic descriptor set, Internet based applications are classified into different Types of Services (ToS). Some ToS representatives are the typical network applications shown in Table 1 ([29]). However, to save bandwidth the so-called Differentiated Services environment is adopted. The basic characteristic of this environment is the use of the same flow control algorithm in order to serve the different ToS. The Differentiated Service environment is based on a detailed contract between the Network Service Provider (NSP) and a user which offers access on call. Depending on the network resource availability the NSP accepts or dropts the connection. In case of acceptance the requested QoS of the corresponding ToS of the application is provided and the NSP will serve the user properly, using the traffic descriptor set of parameters already negotiated in their contract. The above interface operates either with the TCP (Transmission Control Protocol) or with the UDP (User Datagram Protocol). However, we focus our interest on the TCP since it is a connection-oriented protocol using a feedback window adjusted mechanism in the client-server loop. Among all the ATM service schemes only the ABR service is able to guarantee for an adjusted to a feedback endto-end flow control algorithm. For this reason the ABR service is best suited for the TCP environment. As it is well known ([16]), an ABR connection presumes a traffic contract supporting: a Minimum Cell Rate (MCR), a Peak Cell Rate (PCR) and a Cell Delay Variation Tolerance (CDVT), which conforms the data transfer environment. However, in order to serve all kind of traffic, ATM has to guarantee that the maximum Cell Transfer Delay (maxCTD) and the deterministic part of the traffic flow, namely the Sustainable Cell Rate (SCR) are taking some predefined values. This last property gives rise for the extended ABR service and the extended ABR traffic descriptor set of parameters. Note, that all ToS may be considered as a special case of the VBR (see also Table 1). In this sense, the CBR would be seen as a rt-VBR, with MCR = Table 1. Traffic Descriptors for Typical Network Applications Typical Network Applications