W-CDMA方式(FOMA)パケット通信によるNOTASIP方式インターネット電話の伝達遅延時間の実験的評価と解析  [in Japanese] Experimental Evaluation and Analysis Concerning the Peer-to-Peer Transfer Latency of NOTASIP Type Internet Telephony over the Packet Communications Mode of W-CDMA System (FOMA)  [in Japanese]

peer-to-peerの双方向インターネット電話について,エンド・エンド伝達遅延時間の実験的評価を行なった.評価実験は汎用有線インターネットと商用W-CDMA方式の非対称高速パケット通信モードを組み合わせた環境で行なった.実験結果から,移動機から基地局までの無線上り方向で数秒に及ぶ遅延時間が観測された.この遅延時間の発生要因を明らかにするため,実験ネットワークの全体の構成を詳細に解析し,この上り方向での遅延発生メカニズムについて分析および推断を行なった.考えられる遅延発生要因として,ATM AAL5を適用しているパケット通信特有の区間とそれらのインターフェース区間,パケット通信運用時の無線区間(特有の誤り回復手順を適用)等の何れか,またはこれらの組み合わせが関与している可能性が高いことを示した.

The end-to-end transfer latency data of actual voice signals and ping/traceroute command responses, which were relevant to a kind of peer-to-peer two-way Internet Telephony (VolP) message transfer session, were experimentally measured. The tests were mainly focused on rather high-speed asymmetrical packet communications mode of a practical W-CDMA mobile communications access which was in combination with conventional fixed Internet environment. Through the above experimental measurement, observed were the significantly large figures (in the order of a few seconds) of end-to-end latency data, solely in the radio upward direction (i. e. from mobile station <user station> side to base station side) of packet communications mode. Then, the overall Internet environmental structure of the experimental communications sessions was analyzed, and the possible mechanisms of the above particular significant transfer latency in the upward direction side were pursued combining analysis and inference. The packet communication-peculiar portions adopting ATM AAL5 and/or their interface portions seem very much probable to be relevant to the cause of the above significant latency. Some concrete nomenclatures and their features of major system components selected and utilized in this study are as follows.・The adopted Internet telephony system: the "Simple Internet Phone" (proposed by OHTA_M, FUJIKAWA_K. et al.), which uses a signaling protocol called NOTASIP (Nothing Other Than A Simple Internet Phone) and featured by simple peer-to-peer voice signal transfer operation directly without any server-intervention such as SIP control, etc.・Major voice coding system: DVl4 (32kbps ADPCM) & G.711 (64kbps μ-law PCM)・Practical W-CDMA mobile communications access system: FOMA (Freedom Of Mobile multimedia Access) system of NTT DoCoMo, Ltd., featured by the adoption of (1) a proprietary packet datagram use in the W-CDMA radio portion between MSs (Mobile Stations) and BTSs (Base Transceiver Stations), (2) ATM-AAL2 system in it's RAN (Radio Access System) portion among BTSs & RNCs (Radio Network Control) and (3) ATM-AAL2 & AAL5 systems, corresponding to 64kbps (circuit switching) data communications mode and upward 64kbps/downward 386kbps packet communications mode, respectively, in the CN (Core Network) portion inside mobile communications system.