2019/1/2 Experimental Analysis on Performance Anomaly for Download Data Transfer at IEEE 802.11n Wireless LAN 在IEEE 802.11n無線LAN上下載數據傳輸的性能異常的實驗分析 Author: Yoshiki Hashimoto, Masataka Nomoto, Celimuge Wu, Satoshi Ohzahata, and Toshihiko Kato – ICN 2016 Presenter: Enzo Lu Date: 2016/11/23 Department of Computer Science and Information Engineering National Cheng Kung University, Taiwan R.O.C. CSIE CIAL Lab 1

Outline Introduction Experimental Settings 2019/1/2 Outline Introduction Experimental Settings Result for UDP data transmission Result for TCP data transmission Conclusion National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

2019/1/2 Introduction When some stations are located far from their access point and others are near it, the performance of the near stations is degraded to that of far located stations. Degraded 衰退 National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Introduction The feature of our experiment is as follows. 2019/1/2 Introduction The feature of our experiment is as follows. Both TCP and UDP data transmissions are examined. The aggregation scheme in the access point is used as it is. aggregation scheme 聚合 TCP 提供的是一個連線導向(Connection Oriented)的可靠傳輸 UDP User Datagram Protocol則是一個非連線型(Connectionless)的非可靠傳輸協定 National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Experimental Settings 2019/1/2 Experimental Settings National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Experimental Settings 2019/1/2 Experimental Settings One STA (STA1) is located at a near position to the access point, and the other STA (STA2) is located in various positions in the experiment. National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Experimental Settings 2019/1/2 Experimental Settings Firmware Provided by the OpenWRT The OpenWRT firmware supports the following schemes. FIFO CoDel Stochastic Fare Queueing (SFQ) FQ_CoDel: In OpenWRT, FQ_CoDel is the default queue management scheme. OpenWrt 是一種針對嵌入式設備（通常是無線分享器）且具備高度可擴展性的 GNU/Linux 發行版本。和其他針對這些分享器的發行版本不同的是，OpenWrt 是從基礎建構成為一個功能齊全、易於修改的作業系統以提供您的分享器使用。在實踐使用上，這意味著您可以擁有只包含您需要的功能、比其他的發行版本更強勁而不臃腫的 Linux 內核。 Codel:活動隊列管理方案 旨在解決Bufferbloat問題[7]。 它 在隊列中使用分組逗留時間作為控制 參數，並在情況下丟棄數據包 數據包留在隊列中的時間太長。 It uses packet-sojourn time in a queue as a control parameter, and drops a packet in the situation that packets stay in the queue too long. SFQ:A scheme to provide a separate queue for packets of an individual flow. When sending packets, each queue is examined in the round robin scheduling, which avoids a large delay of packets against an aggressive flow.計劃 為個人的分組提供單獨的隊列 流。 發送數據包時，會檢查每個隊列 在循環調度中，避免了大 分組對侵略流的延遲。 FQ_CoDel: A scheme which combines SFQ and CoDel. A queue is prepared for an individual flow and the delay within one queue is controlled by CoDel scheme. In OpenWRT, FQ_CoDel is the default queue management scheme. 方案 CoDel。 為單個流準備隊列 並且一個隊列內的延遲由CoDel控制 方案。 在OpenWRT中，FQ_CoDel是默認值 隊列管理方案。 National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

CoDel (Coddle) A scheduling algorithm 2019/1/2 CoDel (Coddle) A scheduling algorithm An active queue management scheme designed to resolve the Bufferbloat problem [7]. Packet-sojourn time in a queue as a control parameter, and drops a packet in the situation that packets stay in the queue too long. packet-sojourn: pocket逗留 Codel:活動隊列管理方案 旨在解決Bufferbloat (high latency in packet-switched networks caused by excess buffering of packets.) 問題[7]。 它 在隊列中使用分組逗留時間作為控制 參數，並在情況下丟棄數據包 數據包留在隊列中的時間太長。 It uses packet-sojourn time in a queue as a control parameter, and drops a packet in the situation that packets stay in the queue too long. National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Experimental Settings 2019/1/2 Experimental Settings Position 0~7 for STA2 National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Result for UDP data transmission 2019/1/2 Result for UDP data transmission National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Result for UDP data transmission 2019/1/2 Result for UDP data transmission Figure 4 (a) shows the UDP throughput of STA1 and STA2 when the UDP traffic load to STA2 is changed from 10 Mbps to 100 Mbps.(STA1 100) The queue management scheme at the access point is FIFO. 0 STA 1 (位置/路由器) UDA throughput 生慘能力 可以看出圖片 STA2越遠最造成兩者效能軍變差 National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Result for UDP data transmission 2019/1/2 Result for UDP data transmission Figure 4 (a) 0 STA 1 (位置/路由器) UDA throughput 生慘能力 可以看出圖片 STA2越遠最造成兩者效能軍變差 National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Result for UDP data transmission 2019/1/2 Result for UDP data transmission Figure 4 (b) shows the number of MPDUs per A-MPDU of STA1 and STA2 with the UDP traffic load to STA2 changed from 10 Mbps to 100 Mbps.(STA1 100Mbps) A-MSDU主要是將已經經過網路層的資料（MSDU），打上表頭之後稱為MSDU subframe，將許多MSDU subframe包在一起，就是1串A-MSDU，之後再將這串A-MSDU包上媒體層表頭和尾部的FCS偵錯。將多個MSDU subframe包在一起，就可去掉數個媒體層表頭和FCS所占去的空間。 媒體層包完的東西稱做MPDU，在進入實體層時把多個MPDU包在一起就是A-MPDU技術，除了減少實體層表頭之外，由於此層在網路階層中為最後1層，接下來傳輸時須進行無線網路通道資源的競爭，如果把5個MPDU包在一起，原先需經歷5次的資源競爭瞬間變為1次，同樣也可提升通道資源利用效率。 National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Result for UDP data transmission 2019/1/2 Result for UDP data transmission Figure 5 (a) shows the relationship between the UDP traffic load to STA2, and the UDP throughput of STA1 and STA2. when the access point uses the FQ_CoDel queue management scheme In this case, similarly to FIFO, the UDP throughput of STA1 becomes lower as the UDP traffic load to STA2 increases. We can say that the performance anomaly also occurs in this experiment. National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Result for UDP data transmission 2019/1/2 Result for UDP data transmission Figure 5 (a) National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Result for UDP data transmission 2019/1/2 Result for UDP data transmission In contrast to FIFO, where the UDP throughput of STA1 decreases slowly as STA2 is located at Position3 through Position7, FQ_CoDel introduces a sharp drop in the UDP throughput of STA1 with UDP traffic load to STA2 larger than 40 Mbps. National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Result for UDP data transmission 2019/1/2 Result for UDP data transmission Figure 5 (b) shows that the number of MPDUs per A-MPDU at STA1 becomes the same as STA2 in this range of UDP traffic load to STA2. National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Result for UDP data transmission 2019/1/2 Result for UDP data transmission In the case that the access point uses FIFO and CoDel, the data to be sent to both the far and near stations are stored in one queue. So, while the UDP traffic load to the far station is low, more data to the near station are stored in the queue. 在接入點使用FIFO和CoDel的情況下，要發送到遠端站和近端站的數據被存儲在一個隊列中。 因此，當到遠端站的UDP業務負載低時，到近端站的更多數據被存儲在隊列中。 National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Result for TCP data transmission 2019/1/2 Result for TCP data transmission Figure 6 (a) shows relationship between the STA2 position and the average TCP throughput. Fig.6 表示出 STA2的位置會完全影響到整體(STA1.STA2)效能… National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Result for TCP data transmission 2019/1/2 Result for TCP data transmission Figure 6 (b) shows the relationship between the position of STA2 and the number of MPDUs per A-MPDU. Fig.6 表示出 STA2的位置會完全影響到整體(STA1.STA2)效能… National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Result for TCP data transmission 2019/1/2 Result for TCP data transmission Figure 7 (a) shows the average cwnd versus the STA2 position. In this case, the results largely depend on the queue management scheme. Cwnd = congestion window  壅塞窗口 TCP 用來控制封包數量 National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Result for TCP data transmission 2019/1/2 Result for TCP data transmission In all queue schemes, the average cwnd is small when STA2 is located at Position6 and Position7. National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Result for TCP data transmission 2019/1/2 Result for TCP data transmission Figure 7 (b) shows the average TCP level RTT versus the STA2 position. Round trip time National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

2019/1/2 Conclusion It showed that the performance anomaly problem surely happens for the UDP data transmission. The number of MPDU aggregation of a near located station is also decreased, and this reinforce the performance degradation. In other words, for UDP, the performance anomaly problem happens only in the situation where excessive data transfer requests are added. 結論: 1.表現異常的原因就是UDA的問題 2.MPDU的聚合 也會讓效能下降 3.換句話說,對於udp,性能異常是發生在太多要求的情況下 National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab

Conclusion TCP data transmission 2019/1/2 Conclusion TCP data transmission The throughput (traffic load) is smaller than the MAC level data rate, and instead, the degradation of the congestion window size caused by packet losses decreases the throughput. More investigation is necessary for the performance analysis of TCP data transmission. 結論: TCP的異常表現 是因為throughput 小於MAC level的data rate Degradation 降解 因為cmnd(傭賽窗口)的大小害封包loss 然後就害throughput 下降 需要再調查TCP的性能分析 National Cheng Kung University CSIE Computer & Internet Architecture Lab CSIE CIAL Lab