Abstract
無線非同步傳輸模式網路系統為未來網路發展的趨勢，越來越多的移動式產品應用在無線網路的環境，它們提供各種多媒體的應用：有聲音、視訊和資料傳輸；但無線網路的有限頻寬限制，使其難以支援具有不同品質保證需求的多媒體服務，因此如何做好無線非同步傳輸模式上的流量管理成為目前的熱門研究課題。希望達到下列的目的：1.處理不同資料形態的多媒體資料並提供品質保證。2.有效的管理使用頻寬資源。3.與未來的寬頻網路系統具高度配合性。 為了提供較短的細胞延遲、低細胞遺失率和提高無線頻寬的有效使用率，無線非同步傳輸模式上的流量管理必須能使各式各樣的多媒體資料符合其品質保證。我們提出的無線非同步傳輸模式上的流量管理，主要是採用分時多重存取(TDMA)方式針對下傳的資料流作一些控制，整合了緩衝器管理、細胞排程、資料速率控制和資料流量管理。在資料速率控制和資料流量管理部分 : 有線端(ATM交換機與基地台之間)利用資源管理細胞傳輸一些資訊(例如 : CI及 NI)用來顯示網路狀況並依此訊息控制可傳輸速率(ACR)，採用通用細胞速率演算法(GCRA)，來控制變速率資料(VBR)和餘速率(ABR)資料的傳輸速率，以保證資料的品質。無線端部份(基地台到可移動式端點)，在基地台設一個滲漏的筒(Leaky Bucket)來調節基地台送出細胞的速率。由基地台集中管理送出去的資料速率與行程，使其不會因為溢出而導致資料遺失。而且不用浪費無線網路的頻寬在傳輸資源管理細胞，因此它可以滿足即時資料低延遲的保證和非即時性資料的品質保證。此外，我們將緩衝器視為四個不同的佇列(queue)具有不同的優先權(priority)並可互相分享，分別用來放常速率細胞(CBR)、資源管理細胞、變速率細胞、餘速率細胞。緩衝器設置有兩個限度(Threshold)，當緩衝器的佇列長度達到緩衝器容量的30% (最小限度)，就將餘速率資料的傳輸速率降為最小傳輸速率；當緩衝器的佇列長度達到緩衝器容量最大值(最大限度)，就將變速率資料的傳輸速率降為最小傳輸速率。因此，緩衝器就較不會滿溢而導致細胞流失。 我們提出的無線非同步傳輸模式上的流量管理整合了緩衝器管理、細胞排程、資料速率控制和資料流量管理。它可以滿足即時資料低延遲的保證和非即時性資料的低細胞遺失率保證，並且提高無線端資源的使用率。未來的方向如下 : 首先，考慮移動性終端的傳遞(handoff)。再則，我們將找出限度跟資料類型及負荷的相關性，並動態調整限度，以提高品質保證。Wireless communication networks have been growing rapidly inrecent years. In the wireless network, there are various mobiledevices, such as mobile handset, personal digital assistant(PDA) and portable computer, used to transmit voice, video, anddata. It implies that there are various services with differenttrans-mission rates and qualities in the wireless communicationnetwork.As a result, it is important to find out the ways toguarantee the Quality-of-Service (QoS) for each kind of trafficin the wireless network. Since the existing wirelessnetworks are bandwidth-limited, it is difficult to supportmultimedia services with different QoSrequirements. For thisreason, we propose a scheme supporting QoSguarantee fordifferent traffic in the wireless network. ProvidingQoSguarantee for each kind of traffic in the wired networkenvironment, Asynchronous Transfer Mode (ATM) technology is apromising solution for integration of multimedia services over awireless network. Since the wired ATM network is a high speednetworkwith a bandwidth larger than wireless network, the CellLoss Ratiowill be large due to congestion in the wirelessnetwork when a large amount of traffic is transmitted to themobile terminal (i.e. the traffic load is heavy in the wirednetwork). In order to solve this problem, several trafficmanagement schemes are proposed, including buffer control andAvailable BitRate (ABR) flow control. Buffer control scheme hasthe advantageof providing QoS guarantee for various traffic butneeds a largebuffer size in the BS. ABR flow control schemetransmits ResourceManagement (RM) cells to control ABR trafficin both wired and wireless interface. It can control ABRtransmitting rate to reducethe cell loss but wastes the wirelessbandwidth for RM cells. The traffic management schemeproposed herein integrates flowcontrol and buffer management forthe downlink traffic (from thesource to the mobile terminal)based on Time-Division Multiple Access (TDMA) protocol. It canprovide the services with real-timeconstraints and QoS-guaranteefor both real-time and non-real timetraffic. Additionally, itwill also reduce the buffer size in BS and does not wastewireless bandwidth for RM cells. In the cellulararchitecture, a Base Station (BS) is located inthe center of acell with mobile terminals (MTs) dispersed inside the cell. Theinterface between a MT and a BS is the radio link, and a BSconnects to a switch (SW) with the wired link. Each BS providesa centralized scheduling discipline for all radio connections.The BS ensures that all radio connections receive theQoSparameters negotiated at connection set-up time. The radiointerface protocols provide buffering and retransmission for theconnections. In our proposed scheme, it uses RM cells tocontrol the trans-mitting rate between the switches and the basestation, i.e. RM cells are just transmitted in the wirednetwork. This method can prevent buffer overflow in BS to reducethe probability of cell loss. Instead of transmitting RM cellsin the wireless network, it uses a leaky-bucket in the BS toshape the transmitting rate between the BS and MTs. So it canreduce cell loss probability and enhance utilization in thewireless network. Additionally, the scheme we proposed setstwo thresholds in the buffer with small buffer size, one isminimum threshold (30% of the buffer size) and the other ismaximum threshold (full buffersize). When the queue length isunder the minimum threshold, the source sends each kind oftraffic at best effort, i.e. the source sends each kind oftraffic at its Allowed Cell Rate (ACR). When the queue lengthgrows up to minimum threshold, the source sends Constant BitRate (CBR) and Variable Bit Rate (VBR) traffic at ACRand ABRtraffic just at the Minimum Cell Rate (MCR). When thequeuelength reaches the maximum threshold, the source sends VBRand ABR traffic at the their MCR. So the buffer will notoverflow, and the queueing delay is short. Thus, this scheme canguarantee Cell Delay(CD) and Cell Loss Ratio (CLR) for VBR andABR traffic. It implies that our scheme involves cellscheduling, buffer management, traffic shaping, and flowcontrol. It can guarantee QoS(cell delay, cell loss ratio) forboth real time (VBR) and non-realtime (ABR) traffic in thewireless ATM network, simultaneously. And it does not need alarge buffer size in BS. It will enhance the performance inwireless ATM networks for multimedia services.