Dynamic control frames in reservation-based packet scheduling for single-hop WDM networks

In reservation-based packet scheduling algorithms for single-hop WDM networks, one of the wavelengths is used as a control channel which is shared by all of the nodes for transmitting reservation information. Time on the control channel is divided into control frames of fixed length. Each of the control frames is further divided into a number of control slots. Before transmitting a data packet, a node sends a control packet in a control slot to inform all other nodes of its intention to send a data packet. The data packet can then be scheduled for transmission. Each of the nodes in the system is assigned a dedicated control slot. Free control slots in the control frames cannot be used by other nodes. The control packets generated by those nodes that have more data packets to send must be transmitted in the next or later control frames although there are a number of free control slots. The result of delaying the transmissions of control packets is increased packet delays. This effect has significant impact on packet delays under nonuniform traffics. To increase the utilization of the control slots and reduce the packet delays, we propose to adjust the lengths of the control frames dynamically according to the traffic patterns of the nodes. We propose a dynamic control frame structure with variable number of control slots. A scheme is devised to enable the nodes in the network to dynamically acquire and release control slots depending on their loads. Thus, the control frames will include only necessary control slots for those nodes that have or potentially have data packets to send. Therefore, the control slots on the control channel can be used efficiently and the packet delays can be reduced. Simulations are performed to study the performance of the proposed dynamic control frame structure. Our simulation results show that dynamically adjusting the lengths of the control frames can effectively increase the utilization of the control slots and reduce the mean packet delay under nonuniform traffic compared with using fixed-length control frames.