萬代 雅希

Out-of-order packet problem incurs severe degradation of throughput performance of Multipath TCP (MPTCP) with heterogeneous communication links. In this paper, we propose an extended version of MPTCP to solve the out-of-order packet problem. The proposed method defines two types of ACK: Regular ACK and Extended ACK. When a receiver receives a data packet, the receiver sends a Regular ACK to the original path through which the data is transmitted, and Extended ACKs to all the other paths. If the Extended ACK arrives earlier than the Regular ACK, the proposed method solves the out-of-order packet problem. We evaluate the performance of the proposed method via NS-3 computer simulations, and show that the proposed method can improve the throughput performance when RTT of paths is heterogeneous.

In this paper, we propose a dynamic Quality of Experience (QoE)-aware live streaming algorithm by utilizing client clustering and similarity metrics. Encoding scheme of the proposed system finds a sufficient bitrate of the video and creates quality levels adapted to the distribution of clients' bandwidth to improve overall average of user's QoE. We show that the proposed system can improve structural similarity method (SSIM) performance when the client's bandwidth is distributed in low or middle bandwidth, and decreases the number of clients who stop play back.

In this paper, we propose and implement a cross layer protocol for ad hoc networks using directional antennas. In the proposed protocol called RSSI-based MAC and routing protocol using directional antennas (RMRP), RSSI is used for computing the direction of the receiver and also used for controlling backoff time. Moreover, the backoff time is weighted according to number of hops from a source node. In addition, simple routing functions are introduced in the proposed RMRP. We implement the proposed RMRP on a testbed with the electronically steerable passive array radiator (ESPAR) antenna and IEEE 802.15.4. From some experimental results, we confirm some throughput improvement and show the effectiveness of the proposed RMRP. Especially, the proposed RMRP can achieve about 2.1 times higher throughput than a conventional random backoff protocol in a multi-hop communication scenario.

一般にキャンパスネットワークにおける幹線から支線への拡張手段として，スイッチングハブの多段接続が用いられることが多い．このような接続形態では，ハブ間の接続ポート部に通信データが集中し，輻輳が発生しやすいという問題点がある．しかし，輻輳の発生時にはTCPウインドウ制御など通信の抑制による方法がほとんどであり，ネットワークのスループットが低下することは避けられない．一方で通信効率を向上させるために複数のパケットを排他的論理和で多重化するネットワークコーディングが注目されている．本研究では，スイッチングハブの多段接続による潜在的なボトルネック問題をコンシューマ向けの市販実機によって明らかにするとともに，ネットワークの輻輳制御におけるフレーム処理方法にネットワークコーディングを活用し，スループットの向上と輻輳の緩和を同時に可能とする輻輳制御方式を提案する．実験環境として提案方式をアプリケーション層に実装し，提案方式の優位性を立証する．さらにキャンパスネットワークにおける実際の通信環境を分析し，提案方式が有効に機能する環境であることを明らかにした．In general, LANs are enhanced by cascade connection of switching hubs. In a LAN with the cascade connection, the communication at the port of connected points, congestion is subject to occur at the point. For the problem TCP's window control has been already proposed for a congestion control in full duplex Ethernet. However, throughput degrades due to controlling the transmission rate in these methods. On the other hand, the network coding is attracted attention as a technology that improves the bandwidth efficiency. In this paper, we clarify a potential problem by the cascade connection of switching hubs, and we propose a congestion control method that enables the throughput improvement and the congestion reduction at the same time. We implement the proposal method on application layer to prove the effectiveness of the proposal method. Furthermore, we analysis real communication data in a campus network and revealed that a proposal method functioned in this environment.