分布式媒體分布式網(wǎng)絡(luò)-資料下載頁
2025-08-01 15:14本頁面
【正文】 GeometricNegativeExponentialnpμλT λT1p1λnp(1p)σ2p21p1λBINOMDIST(k,n,p,FALSE)NORMDIST(x,μ,σ,FALSE)POISSON(k,λ,T,FALSE)p(1p)^(m1)EXPONDIST(t,λ,FALSE)λλtep (1p)m1K!(λT)k2πσ1e2σ2(xμ)2pk1pnknk( )DMT 42 時(shí)間相關(guān) (Time Dependency) 1. 同步的， Realtime Video Applications 如， Videoconferencing 要求端－端時(shí)延小于 150ms 問題 (?)150ms如何分配？ 2. 異步的， Nonrealtime Applications 如， Multimedia Email DMT 43 雙向?qū)ΨQ性 (Bidirectional Symmetry) 1. 雙向不對(duì)稱 上行信通 (upstream channel) 下行信通 (downstream channel) 如 VOD應(yīng)用 , ADSL(Asgnchrous Digital Subscriber Loop) Upstream: Command Downstream: Data 2. 雙向?qū)ΨQ 如 Peertopeer conferencing ISDN: 2B+D/30B+D HDSL etc. DMT 44 Factors That Affect Network Performance ① 對(duì)吞吐量性能的影響 ? 業(yè)務(wù)源：時(shí)變吞吐量 ? 網(wǎng)絡(luò)吞吐量也不固定，隨時(shí)間變化？ Why? ? Node or link failures ? Congestion ? Bottleneck ? Buffer Capacity ? Flow Control DMT 45 Throughput Performance Factors (Cont.) Node/Link Failure, Bottleneck, work congestion Sender(2)Q2(1)Q1(3)Node ReceiverBottlenecklik xNetwork SelfhealingDMT 46 Buffer Capacity (Cont.) ? Buffer Limited ? Buffer 沒有及時(shí)被騰空 BufferEnd SystemInterfaceBufferEnd SystemInterfaceNetworkBuffering in EndtoEnd ConnectionsDMT 47 Flow Control(Cont.) Flow Control Protocol 對(duì)網(wǎng)絡(luò)吞吐量性能影響也很大，如 1. ARQ－ Automatic Request Repeat (自動(dòng)請(qǐng)求重發(fā) ) 2. Slide window 滑動(dòng)窗口協(xié)議 需要產(chǎn)生新的面向多媒體通信的 flow Control 協(xié)議！ 問題： TCP/IP 、 RSVP、 RTCP等是面向多媒體通信協(xié) 議嗎？ DMT 48 ② Issues in Network Error Performance ? Individual bits in packets are inverted or lost ? Packets are lost in transit ? Packets are dropped or delayed ? Packets arrive outoforder DMT 49 ③ Network Delay performance Issues ?Fixed Delay ? Random Delay *接收端使用 buffer來平滑 delay jitter,但改善有限制。 Delay傳輸距離鏈路帶寬(速率)網(wǎng)絡(luò)擁塞，Heavy Traffic ?傳輸錯(cuò)誤→重傳→D↑ 線路和交換節(jié)點(diǎn)的物理問題→ 長10adL＝36000kmD＝衛(wèi)星DMT 50 Traffic Requirements for Networks ? Throughput ? High Transmission Bandwidth ? High Storage Bandwidth ? Handling long traffic stream ? Reliability (Errors) ? 差錯(cuò)率 /差錯(cuò)控制 ? Latency(多媒體同步 ) ? Asynchronous ? Synchronous(At the same time, at the same rate) ? Isochronous (規(guī)定時(shí)延上下界 T, T+Δ T) DMT 51 (Quality of Service) ? QoS參數(shù) ： ? 51delay ? delay jitter ? throughput ? error rate etc. ? QoS控制 Reservation and Scheduling negotiations Control QoS
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