BNR Switch Wave-Mux Switch

OPTOELECTRONIC PACKET SWITCHES 289

11.2.4 BNR Switch

Munter et al. introduced a high-capacity packet switch based on advanced w x electronic and optical technologies 20 . The main components of the switch are input buffer modules, output buffer modules, a high-speed switching core, and a central control unit, as shown in Figure 11.7. The core switch contains a 16 = 16 cross-connect network using optical links running at 10 Gbitrs. The central control unit receives requests from input buffer modules and returns grant messages. Each request message indicates the number of queued packets in the input buffer module, which is later used to determine the size of burst allowed to transmit to the switch fabric. A connection can only be made when both input and output ports are free. A control bus is used by the free input ports to broadcast their requests, and by the free output ports to return grant messages. An arbitration frame consists of 16 packet time slots for a 16 = 16 core switch. In each slot, the corresponding output port polls all 16 inputs. For Ž . example, in time slot 1, output port 1 if it is idle will choose the input that has the longest queue destined for output port 1. If the input is busy, another input port that has the second longest queue will be examined. This opera- Ž tion repeats until a free input port is found. If a match is found free input, . free output, and outstanding request , a connection is made for the duration corresponding to the number of packets queued for this connection. So the switch is a burst switch, not a packet switch. In time slot 2, output port 2 Fig. 11.7 Diagram of BNR switch. OPTICAL PACKET SWITCHES 290 repeats the above operation. The switch capacity is limited by the speed of the central control unit. Packet streams can have a long waiting time in the input buffer modules under a high traffic load.

11.2.5 Wave-Mux Switch

Nakahira et al. introduced a photonic ATM switch based on input᎐output w x buffering 21 . Basically, this switch consists of three kinds of modules: the Ž . Ž . input group module IGM , switching module SWM , and output group Ž . module OGM , as shown in Figure 11.8. They are connected by means of fiber optical lines. The inputs are divided into p groups of size n , and each 1 group is connected to an IGM. The cells arriving through optical lines are first converted to electronic signals by optical-to-electronic converters, and their header information is electrically processed at the header converter in IGMs. Both the header and the payload of the arriving cell are processed Ž . and stored in an electronic random access memory RAM . An optical sorter in each IGM is used to sort the cells with respect to their OGM requests and delivers them to the SWM in one cell slot time. There are p optical switches in the SWM. Each optical switch transmits optical wavelength multiplexed cells from IGM to OGM. In each cell time slot, these p optical switches deliver at most p trunks of wavelength-multi- plexed cells from IGMs, which are destined to the different OGMs. In each Ž . Fig. 11.8 Architecture of the wave-mux switch. 䊚1995 IEEE. THE 3M SWITCH