交換式路由器之設計

Abstract

在乙太網路中,要將資料封包傳送至接收端,路由器是不可或缺的。一個 要傳送到遠端 (remote)網路的封包,必須由路由器轉換標頭 來指定下一級轉送路由器的MAC(media access control) 位址,並且將封包正確的由路由器輸入埠送至對應的輸出埠。而交換式的 結構(switching fabric)能減低乙太網路競爭特性所引起的高碰撞率( collision probability),並 提高系統效能。 本篇論文主要是設計一個交換式的乙太路由器架構,針對不定長度的封包 作記憶體管 理,以硬體的方式作MAC位址的轉換。交換機的 部分是屬於輸出暫存的交換機,所有輸 出入埠分享一個分 時多工的匯流排,所有的封包儲存在一塊共享的記憶體,來提高記憶 體使用效率,由於所有的封包都事先經過切割成固定長度的資料片段,所以 能提供 cut-through及EPD(early packet discarding)的功能。 In Ethernet, to transmit packets to received end host in remote LAN, a Router is unavoidable. Router can translate header to indicate the next redirect Router's MAC address, and transport packet from its input port to its desired output ports. Switching fabric can decrease collision probability due to Ethernet contention characteristic, and boots system performance. This thesis focus on designing a Ethernet Router on switching fabric, variable length packet buffer management, and MAC address exchanging with hardware. This output-queue switch has a shared memory to increase memory usage efficiency. Besides, because all packets segment into fixed length blocks, it can provide cut-through and EPD(early packet discarding).