Fair Packet Discarding for Controlling ABRTra c in ATM

| ATM Forum has chosen rate{ based control as the ow control scheme for available bit rate (ABR) service. However, rate{based schemes can achieve congestion control only if all users act in a cooperative manner. Even a limited number of uncooperative users can cause congestion collapse. In this paper, we propose a mechanism called fair packet discarding to provide incentives to users to participate in network congestion control , so that the network can operate in a more eecient manner. One of the current challenges in Asynchronous Transfer Mode (ATM) networks is the transparent support of the conventional connectionless LAN traac in ATM's connection oriented environment. Such traac are best served by the best{eeort method. That is, they should be allowed to send their traac whenever they need to, without reserving the band-width beforehand, but the network does not provide any strict quality of service (QoS) guarantees. Also, they should be allowed to use as much bandwidth as available, maybe including the idle bandwidth reserved for other services. However, they will be ow controlled during network congestion. Such a service class has been deened by the ATM Forum 1] as the available bit rate (ABR) service. Various ow control schemes have been proposed for ABR traac 2] and they can be classiied into two main classes, namely, end{to{end rate{based and link{by{link credit{based schemes. In late 1994, the ATM Forum selected the rate{based control as the ow control scheme for ABR service due to its simplicity. However, as discussed in 3], rate{based schemes can achieve congestion control only if all users act in a cooperative manner. Even a limited number of uncooperative users can cause congestion collapse. Therefore, an additional mechanism is necessary to ensure that all users will participate in congestion control. Fairness discarding 4] is such a mechanism. In each switch, this mechanism ensures that each user gets no more than a fair share of network resources during overload by discarding all excessive cells. The essence of this mechanism is to give incentives to users to cooperate so that the network can operate in a more eecient manner. That is, it discards cells from misbehaving users such that they are the only ones experiencing congestion. It is then up to each user to perform ow control in order to recover from cell loss and restore to its normal network usage. Therefore, this mechanism complements the role of rate{based ow …