| Summary: | 碩士 === 國立臺灣科技大學 === 資訊工程研究所 === 88 === ATM (Asynchronous Transfer Mode) has been adopted as the switching and transport infrastructure for the future B-ISDN (Broadband Integrated Services Digital Network). It has the advantage of offering end-to-end multimedia capabilities with guaranteed QoS (Quality of Service). W-ATM (Wireless ATM) provides the extension of broadband services to the wireless environment. Extension of ATM network services to the wireless environment faces many interesting problems. The original ATM network was designed for high-speed, noiseless, and reliable channels. None of these characteristics are applicable to the wireless channel. Generally speaking, the radio link presents problems such as noise, interference, and limited channel bandwidth. The interference depends greatly on the cell size covered by the BS (Base Station) and the mobility of the MTs (Mobile Terminals). One of the most critical aspects of W-ATM network is the MAC (Medium Access Control) protocol used by MTs to request service from the BS. It has to consider the QoS of the specific application and is tightly related to the actual physical layer adopted.
PRMA/DA (Packet Reservation Multiple Access/ Dynamic Allocation) is a MAC protocol for wireless networks. It adds a dynamic allocation scheme to the original PRMA to obtain better performance and better bandwidth utilization. But PRMA/DA still has some problems. It can not serve many MTs at the same time. If a large amount of MTs tries to access the BS at the same time, the network performance will become poor. The bandwidth allocating is another problem. PRMA/DA wastes some bandwidth in channel allocation. In this thesis, we propose some schemes to solve these problems.
We devise a MAC protocol for wireless local area networks (LANs) that is capable of supporting various types of traffic demands, such as CBR (Constant Bit-Rate), VBR (Variable Bit-Rate), and packet data. The protocol is called PRMA/DATP (Packet Reservation Multiple Access/ Dynamic Allocation with Two Periods). We design new dynamic allocation scheme to have an expeditious network access and to use bandwidth resource efficiently. In addition, the proposed protocol provides a seamless connectivity to a broadband network. The simulation results show the improvements of dynamic channel allocation with two periods over the dynamic channel allocation scheme in terms of key performance metrics such as: network access delay, delay of CBR service, delay of VBR service, delay of ABR service and first contending lost rate.
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