以IEEE 802.11為輔的快速無線網路基地台交換

Abstract

當可攜式無線設備進行基地台轉換的時候,會有一段時間無法接收封包。在連接上新的基地台之前,無論封包的傳送者或是可攜式無線設備的原網域之代理伺服器皆無法得知新基地台的相關資訊。送給這個可攜式無線設備的封包還是會被先送往舊的機地台,但舊基地台已無法和可攜式無線設備取得聯繫,因此,這些封包會遺失在舊基地台。 為了解決這個問題,很多改進的方式已經被提出來,其中一種是舊基地台會幫可攜式無線設備將封包暫存起來,使得當可攜式無線設備移開後,封包不至於會遺先,並在它連上新的基地台之後,將這些封包轉送給它。 但是,將封包暫存封包的時機是很值得研究的,因為漫無目的地暫存會行成記憶體的浪費。本篇論文中,使用基地台和可攜式無線設備間快速地RTS/CTS訊息交換,來偵測可攜式無線設備是否離開基地台的傳送範圍。如果離開了,便為給它的封包暫存起來。等到新基台確定後,再予以轉送。

During handover period, packets for the mobile node maybe lost in its old foreign agent (FA), because it will attach to another new FA and has detached from the old one. We want to keep these packets and forward them to the mobile node. However, when to buffer and to forward packets is a big subject. If packets are buffered too often, the buffer size will be wasted too much. In our scheme, we use RTS/CTS messages exchange between FA and the mobile node to detect if the mobile node still attaches to the FA or not. When a FA have send RTS for several times but not being responded by the mobile node, it buffer packets for the mobile node. After the mobile node attaches to a new FA, the old FA forwards these packets to the mobile node. We reduce packet loss rate and handover time successfully.