網路語音電話(VoIP)是現今相當普及的一項服務。在一般網路語音電話協定(如:SIP)的信號交換階段中(signaling phase)，是透過集中式伺服器來交換使用者的訊息。發話者需先連到伺服器，取得受話者的資訊(如: IP位址)，再去和受話者做連線。但集中式管理有許多缺點，如負載不均，單點癱瘓等等。因此當前研究提出使用同儕式網路(peer-to-peer)方式運作在信號交換階段，但在使用同儕式網路上搜尋資訊會需要更多的時間，過長的等待時間會使得使用者不欲使用此項服務。當前世界上便有許多研究便想改進其效能。於是，我們研究分析在真實世界網路語音環境中，何種同儕式網路協定效能較佳，並評估人們對此實驗數據的實際感受程度。我們的收集真實世界的Skype使用者IP位址及上線時間，並取得所有IP位址的經緯度，描繪出使用者的地理位置拓樸。並找出拓樸分佈及上線時間的模型，以供未來模擬使用。之後，我們模擬各種同儕式網路在我們收集的網路拓樸之上，比較個別的查尋時間。我們做了集中式管理的模擬，再做了Chord的模擬。因為Chord是屬於平坦式分散式雜湊表(FDHT)，因此我們做了階層式雜湊表(HDHT)，但不考量鄰近因素。接著再做考量鄰近因素的分散式雜湊表(PDHT)。我們得到了各別的數據，但都是在秒以下的差距。我們欲了解使用者的感受程度如何，於是我們利用成對比較(Paired-comparison)來做使用者經驗的實驗，以得到感受程度差異。

Voice over IP (VoIP) is a popular application nowadays. In signaling phase of general VoIP protocol (e.g. SIP), users exchange information of each other by central server. The caller needs to connect to central server to get the callee’s information (e.g. IP address), then connects to callee. But centralized manner has some drawbacks, for example, load imbalance, single point failure, etc. There are some researches utilize peer-to-peer (P2P) protocols in signaling phase. However P2P technique takes more time in querying information. The too long waiting time stops user willing to use this service. There are many researches want to improve its performance. Therefore, we study which P2P protocol works better in realistic VoIP network and evaluate the user subjective feeling degree for the experiment results.
We have collected Skype user IP address and session time in the real world, obtained lat/longitude of all IP addresses, and depicted the user geographic topology. We also model the topology and session time distribution for simulation purpose. We simulate various P2P protocols on our collected topology to compare each lookup latency. We simulate centralized manner and Chord. Because Chord is a kind of flat DHT, we then simulate hierarchical DHT without concerning proximity. Then we simulate proximity DHT. After above simulation we get each result but the difference is under one second. We want to realize the user perception degree. Therefore we utilize paired comparison to do the experiment for quality of experience and to get the difference perception degree.

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