Cabletron Systems, Inc.

Kabushiki Kaisha Toshiba

Tong-Bi Pei

Robert E Thomas

Kohei Abe

Cuneyt M Ozveren

An ATM scheduler in accord with the invention supports multiple transmission traffic types (e.g. CBR, VBR and ABR) for each of a plurality of virtual path connections (VPCs) on an ATM link. The scheduler maintains one or more scheduling tables defining the hierarchy of traffic types and the scheduling for each type of traffic within each virtual path. In each cell transmit time, one VPC is identified as assigned to the opportunity to transmit in the respective cell transmit time. Each virtual path connection supports at least one type of high priority traffic, such as constant bit rate (CBR) traffic, over a plurality of virtual circuit connections. The scheduler determines if there is a high priority service virtual circuit connection (VCC), from among those associated with the identified VPC, and that has been assigned the current cell time slot. If the scheduling device identifies such a VCC, then the scheduler provides the transmit opportunity for that VCC. For example, if the VCC has CBR service, a cell for that VCC is transmitted over the link in the respective cell transmit time. If the VCC has variable bit rate service, a cell is transmitted if there is in fact a cell ready to send over that VCC. Also, during processing for each cell transmit time, the ATM scheduler accesses a link list. The link list identifies at least one available bit rate (ABR) service type VCC. The link list identified is one associated with the indexed virtual path connection. The ATM scheduler preferably transfers the accessed link list to an ABR work list associated with the indexed VPC. During each respective cell transmit time, if the processing relating to the high priority service(s) did not result in cell transmission in the time slot, the scheduler examines the ABR work list to identify an ABR service type VCC for which there is a cell that is ready to transmit, and the cell for that circuit is transmitted over the link in the respective cell transmit time.

Hierarchical schedules for different ATM traffic

A scheduler in accord with the invention schedules available bit rate (ABR) traffic over an asynchronous transfer mode (ATM) link in such a manner as to provide circuits having the ABR traffic service a minimum cell rate (MCR) that may be greater than zero. The scheduler uses static scheduling information to schedule traffic for high priority services, such as constant bit rate service. The static information also specifies transmit opportunities for an ABR circuit, in a manner analogous to that for CBR traffic. The statically scheduled transmit opportunities provide a negotiated minimum cell rate that is greater than zero, for the ABR circuit. The scheduler maintains dynamic scheduling information, which it uses to schedule traffic in otherwise available transmit times. For example, the scheduler may use the dynamic information to create a work list of virtual circuit connections for ABR service. During any cell transmit time that is not used by a higher priority service (e.g. CBR or MCR), the scheduler goes to the work list to find a circuit with a cell ready for transmission and initiates transmission of the cell for that circuit. The ABR circuit having a non-zero MCR receives service from the statically scheduled opportunities and from the dynamically scheduled opportunities.

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Milpitas, CA, United States of America

Tong-Bi Pei