臺灣博碩士論文加值系統

DOCSIS 是為了在混合光纖同軸電纜(hybrid fiber coaxial)上傳輸資料所發展的標準，在 DOCSIS 1.1 中定義了讓系統供應商能提供保證頻寬給纜線數據機(cable modem;CM)使用戶。它定義了五種上傳頻道排程服務(upstream service flow scheduling services)類型以增進輪循(poll)或需求(grant)服務的效率。為了設定排程服務與其相關的品質服務(quality of service;QoS)參數，頭端(headend)必須預估上傳頻道的延遲及總量以在適當的時間提供纜線數據機輪詢或需求的機會。然而，品質服務參數可能因同時有多個資料流要求相同的區間而無法符合。
在本文中我們提出一個迷你時槽(mini-slot)先進先服務(first come first serve;FCFS)指定演算法以減少品質參數違反的機會並提高系統的整體輸出。我們以各種不同的VoIP協定來驗證演算法的效能，並針對VoIP在混合光纖同軸電纜網路下排程方式提出說明。在10%的品質參數違反率的限制下，G.723與 G.729可以允許系統有最多的VoIP數據資料流。但是同時我們也發現到越小的數據資料量將因系統有太多的數據資料流存在而使系統的利用率大為降低。因此在使用較先進的VoIP編碼方式的同時也必須對系統上限做限制以提高系統的利用率。

DOCSIS (data over cable service interface specification) is developed for data transmission over the HFC (hybrid fiber coaxial) network. The latest version of the new specification, known as DOCSIS 1.1, defines the new functionality that allows cable operators to provide the guaranteed bandwidth, i.e., quality of service (QoS), to cable modem customers. It defines five upstream service flow scheduling services. Scheduling services are designed to improve the efficiency of the poll/grant process. By specifying a scheduling service and its associated QoS parameters, the cable modem termination system (CMTS) can anticipate the throughput and latency needs of the upstream traffic and provides polls and/or grants at the appropriate times. However, the QoS parameters may be violated if the same interval is assigned to several flows.
In this paper, we introduce a new mini-slots assignment algorithm, which is called mini-slot-based FCFS (first come first serve) assignment algorithm, to reduce the QoS violation. We will simulate it by several different VoIP algorithms and analyze the performance. By 10% of the limitation of QoS violation boundary, G.723 and G.729 can accommodate the maximum VoIP data flows in the system. Meanwhile, we also find the fewer data rate of VoIP data flows will reduce the utilization of the system because there are too many data flows in the system simultaneously. Therefore, we should limit the upper boundary of the system when using advanced VoIP coders to increase the system utilization.

1.Introduction 1
2. DOCSIS1.1 Overview 4
2.1 DOCSIS MAC protocol 4
2.1.1 Service Flows 4
2.1.2 Mini-slots 4
2.1.3 MAC Protocol Operation 5
2.2 Upstream Service Flow Scheduling Services 8
2.2.1 Unsolicited Grant Service 9
2.2.2 Real-Time Polling Service 10
2.2.3 Unsolicited Grant Service with Activity Detection 12
2.2.4 Non-Real-Time Polling Service 13
2.2.5 Best Effort Service 14
2.3 Payload Header Suppression 15
3. Mini-slot-based FCFS assignment algorithm 18
3.1 Motivation 18
3.2 Satisfying Region 18
3.3 Algorithm Exposition 21
3.4 Example 25
4. Simulation Results 26
4.1 Model 26
4.2 Results 29
4.2.1 Number of Calls 29
4.2.2 System Load 33
4.2.3 Number of Supported Calls 35
5. Conclusions 38
References 40

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