近年來，車載網路(VANETs)提供了許多種應用，如增加行車安全、降低道路擁塞和增加行車周邊服務等，這些都為車載網路衍伸出很多議題。當車輛有服務需求時，藉由廣播將其需求廣播給路側單元(Road Side Unit)並註冊，然而在有多個路側單元可選擇的情況下，有效的挑選出一個在當下網路拓撲的環境中能有最穩定連線的路側單元成為重要的議題之一；傳統的廣播Flooding方法提供了很好的封包觸及率(Reachability) ，但也因為設計簡單而容易造成廣播風暴(Broadcast Strom Problem)，造成有限網路資源的浪費。
由於是否能將封包廣播出去，將會影響到本研究中RSU挑選的準確度，因此我們提出一個新的廣播方法Restricted flooding，透過我們的方法可以在任何不同的道路上有效的轉傳並與Flooding有差不多的封包觸及率並且能有效的減少封包的傳送造成不必要的資源浪費。透過NS2網路模擬器的實驗證明，我們提出的演算法可以提升確實效能，而藉由封包傳輸率(Packet Delivery Ratio)也能反映出我們挑選RSU的準確度。

Vehicular Ad-hoc Networks(VANETs) have many kinds of applications such as increasing driving safety, decreasing traffic congestion and offering better driving services.When the vehicle has a service request,it broadcast its request to roadside unit by broadcasting and register. However,when there are multiple road side units selectable, how to effectively pick out a road side unit in the network topology can have a stable connection environment has become an important issue.However,when there are multiple roadside units which can be selected,how to effectively pick out a road side unit which has a stable connection environment under the network topology has become one of an important issue.The traditional method, Flooding, provides a good reachability but it may causes “Broadcast Strom Problem”, resulting in bandwidth abusing.
Depend on if it can broadcasts the packets successfully that will affect the accuracy of road side unit which was selected in this study.Therefore, we propose the restricted flooding whcich ensures bidirectional broadcasting on any roads, such that it can be suitable for any scenarios. The simulations are conducted with network simulator NS2. The simulation results show that the proposed scheme can achieve high Packet Delivery Ratio.

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