一個用於共用緩衝區非同步傳輸模式交換器的新型多播架構

Abstract

以非同步傳輸模式(ATM)為基礎的寬頻整體數位服務網路(B-ISDN)被 寄予厚望在未來能提供多樣化的通訊服務。支援多播(multicast)的能力 對於提供視訊會議之類的通訊服務而言是非常重要的。在本論文中我們為 ATM交換機提出一個新型的多播架構。這個架構擁有很高的流通性能（ throughput），簡單有彈性的硬體架構以及很好的硬體效率。在此架構中 ，所有的多播胞元都先貯存在多播佇列中，然後再轉換標頭並投至適當的 輸出埠，因此每一個多播胞元只佔用一個緩衝記憶單元，因此可以達到極 低的胞元漏失機率。這些多播佇列與其他佇列共用同一記憶體，這更提高 了硬體效率且降低了硬體的複雜度。在多播轉換表的設計上採用模組化的 設計，這在轉換表的設計上給了系統設計師很大的彈性。統設計師可以依 照系統需求串接多個轉換表晶片以組成一個較大的轉換表。另外，為了縮 短轉換標投的時間，我們設計了一個鎖相回路時鐘脈波產生器以加速標頭 的轉換。此脈波產生器可以在晶片內部產生四倍於系統時鐘的脈波供內部 電路使用以加速晶片運作的速度。 B-ISDN is expected to provide versatile communication service based on ATMtechnology. The capability of multicast is important to support many servicessuch as VOD (video-on-demand), video conference, LAN emulation, etc. In thisthesis, we present a new architecture to support multicast virtual connectionin an ATM switch. This architecture is designed to achieve high throughput,efficiency and flexibility. By queuing input multicast cells in multicastqueues, each multicast cell occupies only one-cell buffer space, this archi-tecture can achieve very low cell loss probability. These multicast queues also share the same buffer memory with all other unicast queues, the utili- zation of buffer memory is very efficient. And the structure of buffer memory is the same with that for unicast, no special design is needed. The multicast table is also shared by all ports to improve table utilization. Modular designenables the flexibility of table size, multiple table chipscan be cascaded to construct a larger multicast table to meet system requirement. Because the multicast table is shared by all ports, short translation delay is critical inthe improvement of throughput. We also present a PLL clock generator with on-chip RC filter, which can generate an internal clock of quad frequency, that will be integrated to raise the processing speed.