同儕介接技術之奧窔－網路電話輯論

Abstract

本論文以統計探討兩種學術界極少著墨的同儕介接技術之缺陷：一、雙介接，即一通網路電話的兩個方向使用相異的介接點，可能導致介接路徑於語音品質上的不對稱。本研究所收集的樣本中約三分之一為雙介接，其中百分之四十七因介接點之一不穩定且表現低落而有一定期間的失衡。於用戶端採樣雙介接通話的前數秒，輔以網路電話軟體中即時抽換介接點的功能，能有效防止介接路徑不對稱的情形。二、工作中的介接點帶來的處理延遲會顯著地降低網路電話的品質。受話方緩衝雖然能吸收處理延遲的負面影響，在靜態的緩衝設計下仍有百分之三十一的模擬通話衰退，並且這已是比適應性緩衝來得好的數字。本文定義節點的「忙碌度」配合其當地上班時間判斷其是否勝任介接的角色。為取得必要資料，本研究亦發展出毋須大規模部署的處理延遲量測和計算方法。

Two of the rarely discussed hazards of peer-to-peer relaying are statistically analyzed in this thesis under a voice-over-IP context: 1) Relay path asymmetry in voice quality is a potential consequence of bi-relaying, or using two distinct relays for the opposite directions of the same call. About one third of all relayed calls collected are bi-relayed, and 47% of them are unbalanced for a significant portion of time, mostly due to the instability and poor performance of one of the two relays. Client sampling through the first seconds of a bi-relayed call combined with the voice-over-IP application’s feature to hot-swap relays form a proved method to avoid relay path asymmetry. 2) Processing delay on a loaded relay can serious degrade an Internet telephone call. Playout buffers absorb some of the negative impact of processing delays, but still 31% of the calls simulated suffered with the static scheme, which generally outperforms adaptive buffers. Busy level is the proposed indicator of whether a peer node is too occupied to relay, along with its local work hour. A novel methodology is devised to collect the necessary traces for computing processing delays without large-scale deployment.