光信号交换基础剖析.ppt

光信号交换基础 谭雪松 电信号交换 VS 光信号交换 电信号交换 S接线器：电子开关矩阵 T接线器：存储器RAM 光信号交换 如何构造光信号的S接线器和T接线器？ * * 根据电信号S接线器的构造原理 * * 将电子开关换为光信号的反射镜片 * * 朗讯公司设计的光信号S接线器 缺点：镜片切换速度过慢（通常为ms级） * * 4条单位长度的光纤延迟线 5?5 光信号S接线器 读出 写入 光信号随机接入存储器 (RAM)的一种构造方式 * * 示例：该存储器已存储了分组A、B和C，而分组 D正被写入 CAB D 5?5 光信号S接线器 * * 交换场景I?读出分组C 0 0 1 1 2 2 3 3 4 4 CAB D * * 0 0 1 1 2 2 3 3 4 4 CA BD 交换场景I?读出分组C * * 0 0 1 1 2 2 3 3 4 4 CA BD C ABD 交换场景I?读出分组C * * 交换场景II?无分组被读出 0 0 1 1 2 2 3 3 4 4 CAB D * * 0 0 1 1 2 2 3 3 4 4 CA BD 交换场景II?无分组被读出 * * 0 0 1 1 2 2 3 3 4 4 CABD CABD 交换场景II?无分组被读出 * * 0 0 1 1 2 2 3 3 4 4 CABD CABD 交换场景II?无分组被读出 缺点：大规模S接线器难构造，光信号存储时间受限。 * * * The basic building block of fiber memory is a switch with most of the I/O connected to unit-length delay lines. It serves as a random access memory, which, in every timeslot, receives a packet from the bottom input and transmits one from the top output. * Here is a scenario for the operation. In this scenario, three unit-length delay lines store three packets A, B, and C, and another delay line is empty. Meanwhile, a packet D is arriving at the bottom input. * Depending on whether there is an output packet, an input is selected for connection to the top output. When a stored packet or the arriving packet is to exit, the input for this packet is selected. * For example, when the stored packet C is to exit, the input 1 will be selected because the packet C is looped back to the input 1. Then, the switch performs this connection by choosing an appropriate one-to-one connection pattern between inputs and outputs. * Through this way, the packet C exits, the packet D enters the storage, and the remaining