以SIP為基礎並輔以Push機制的VoIP行動無線通訊網路之設計與實作

Abstract

由於可攜式裝置越來越普及，所以如何讓這些行動裝置隨時隨地皆可連上網路變成重要的課題。文中，我們開發一個以SIP為基礎並整合MANET(Mobile Ad-Hoc Network)及行動網路的架構，實作行動網路與VoIP(Voice over IP)服務。我們提出車上行動用戶可自成一MANET網路並透過一個配備兩網路介面的SIP行動網路閘道(SIP Mobile Network Gateway, SIP-MNG)來上網與打網路電話。然而當系統一旦啟始，因為SIP-MNG對外利用行動介面撥接、連結網際網路，而且必須一直保持對外的通訊，所以對系統而言無論在電力和價格上都是個負擔，開得越久，網路存取費用收得越多，電力也消耗越快。考慮到語音服務的需求並非一直存在，我們提出一個push 機制，使得語音服務不存在的時候，SIP-MNG可以關掉對外的介面，只有當語音服務的需求發生時，才透過push機制“wake up”SIP-MNG上的對外介面，保證系統不會遺失任何語音通話，同時達到省電與節費的要求。文中並且包含我們系統的實作成果。這個系統具有架設簡單、結構彈性的優點，並提供使用者具移動性、彈性、以及服務無間隙功能的語音服務。

As portable devices are gaining more popularity, maintaining Internet connectivity anytime and anywhere becomes critical, especially for mobile and vehicular networks. Network mobility(NEMO) and IP mobility are gaining more and more importance. In this work, we develop a SIP-based mobile network architecture to support network mobility for vehicular applications. We propose to form a mobile ad-hoc network (MANET) by the mobile hosts (MHs) inside a vehicle or a cluster of vehicles. The MANET is connected to the outside world via a SIP-based Mobile Network Gateway (SIP-MNG), which is equipped with one or multiple external wireless interfaces and some internal IEEE 802.11 interfaces. The external interfaces of the SIP-MNG are to support Internet connectivity by aggregating users' tra±cs to and from the Internet. In addition, exploiting session information carried by SIP signaling, the SIP-MNG supports resource management (RM) and call admission control (CAC) for the MHs. Wireless access, however, incurs charges, power consumption, and overheads of mobility management. So, it is desirable to allow the SIP-MNG to disconnect its external interfaces when necessary. To guarantee that users inside the mobile network will not lose any incoming request, we propose a push mechanism through short message services (SMS) to wake up these wireless interfaces in an on-demand manner. We show the detail signaling to support such mechanism. The proposed system is fully compatible with existing SIP standards. Our real prototyping experience and some experimental results are also reported.