適用於行動隨意網路之混和覆蓋式群播路由協定

Abstract

本論文提出一個基於行動隨意網路之群播路由協定，稱為混和覆蓋式群播路由協定(HOMRP)。行動隨意網路下現有的覆蓋式群播路由協定有高傳遞延遲之主要缺點。為了改善這個缺點，我們整合群播封包封裝與單傳隧道機制，以提供有效的資料傳遞。HOMRP針對每個群播群組建立了多個區域群播樹。在區域群播樹中，所有的父節點與子節點距離皆位於彼此的訊號範圍內，並利用群播封包封裝方式來傳遞群播封包。此種方式可以提高資料轉送的效率。另外，區域群播樹間是利用單傳隧道方式傳遞封包。此外我們為每一個區域群播樹指定一個識別碼，以避免區域群播樹間產生迴圈路由。針對行動隨意網路之高變動性，HOMRP 採用一個整併樹機制以提高封包傳遞之效率。HOMRP採用兩階段氾濫發送之機制，此機制利用指定TTL之大小，以限制控制訊息發送之範圍，以降低控制訊息的過渡氾濫。 HOMRP並沒有指定使用任何特定的單傳協定，因此它可以運作於任何單傳路由協定上。另外，HOMRP之路由維護是由群播之每一個成員所發動的。所有的群組成員只需要瞭解其鄰近群組成員，而不是所有的群組成員。在HOMRP中多個群播發送者可以共用同一種路由架構，因此可以大大地增加路由的維護效率。在模擬中，我們嘗試與ODMRP與AMRoute做比較，以封包傳遞效率來說，HOMRP與ODMRP同有較高的傳遞效率，而相較於AMRoute，HOMRP提升了50%的傳遞效率。另外，HOMRP在控制耗費上比ODMRP減少了18%，於點對點之傳輸延遲上，HOMRP比AMRoute減少了9%。總之，相較於其他群播方式本論文所提出之群播路由協定可以提供較低的控制耗費並提供較高的傳遞效率，並適合於多發送者之群播應用。

We propose a novel multicast routing protocol, called hybrid overlay multicast routing protocol (HOMRP) for MANETs (Mobile Ad hoc NETworks). Existing overlay multicast routing protocols in MANETs have the main drawback of high packet delivery delay. In order to improve this shortcoming, we integrate multicasting and unicast tunnels for efficient packet delivery. In HOMRP, it creates multiple local multicast trees. Each pair of parent node and child node in a local multicast tree is at a distance of one-hop. It uses multicasting to deliver multicast packets in local multicast trees. This will provide efficient data forwarding. Unicast tunnels are used for transmitting packets between local multicast trees. To avoid looping routes between local multicast trees, each local multicast tree is assigned a tree ID. To deal with dynamic changing of network topology in MANETs, HOMRP uses a tree consolidation scheme for highly efficient data forwarding. In addition, in order to reduce the overhead of control messages flooding, we adopt two-level flooding for member discovery by limiting the value of TTL in a packet. HOMRP does not restrict to use any specific unicast routing protocol; hence it can operate with any unicast routing protocols. Route maintenance in HOMRP is initiated by each multicast group member. Each member only needs to maintain the nearby members. The same route structure of a multicast group can be shared by multiple senders (sources); this brings high efficiency of route maintenance. Simulation results have shown that the packet delivery ratio of HOMRP is close to that of ODMRP and is 50% better than that of AMRoute. HOMRP reduces 18% control overhead compared to ODMRP and reduces 9% end-to-end packet delay compared to AMRoute. In sum, HOMRP provides lower control overhead, high packet delivery ratio and is especially suitable for multicast applications with larger number of senders, compared to other approaches.