多層交換第五講ppt課件-在線瀏覽
2025-04-10 12:16本頁(yè)面
【正文】 cket Loss – Taildrops occur when the output queue is full. These are the most mon drops which happen when a link is congested. – There are also many other types of drops (input queue drop, ignore, overrun, no buffer, etc), which are not as mon and which may require a hardware upgrade. These drops are usually a result of router congestion. IP Forwarding IP IP IP IP Taildrop Page ? 20 CASE： How to Increase Available Bandwidth? – Upgrade the link—the best solution but also the most expensive. FIFO queuing IP TCP Data Fancy Queuing ? Take some bandwidth from less important applications. Compress the Headers cTCP Data ? Compress the header of IP packets. Compress the Payload Compressed Packet ? Compress the payload of Layer 2 frames. Priority Queuing (PQ) Custom Queuing (CQ) Modified Deficit Round Robin (MDRR) ClassBased Weighted Fair Queing (CBWFQ) Stacker Predictor TCP Header Compression RTP Header Compression Page ? 21 CASE： How to Reduce Delay? – Upgrade the link—the best solution but also the most expensive. FIFO queuing IP UDP Data Fancy Queuing ? Forward the important packets first. Compress the Headers cRTP Data ? Compress the header of IP packets. RTP Compress the Payload Compressed Packet ? Compress the payload of Layer2 frames (it takes time). Priority Queuing (PQ) Custom Queuing (CQ) Strict Priority MDRR IP RTP Prioritization ClassBased LowLatency Queuing (CBLLQ) Stacker Predictor TCP Header Compression RTP Header Compression Page ? 22 CASE： How to Prevent Packet Loss? – Upgrade the link—the best solution but also the most expensive. FIFO queuing IP Data Fancy Queuing ? Guarantee enough bandwidth to sensitive packets. Dropper ? Prevent congestion by randomly dropping less important packets before congestion occurs. Custom Queuing (CQ) Modified Deficit Round Robin (MDRR) ClassBased Weighted Fair Queuing (CBWFQ) Weighted Random Early Detection (WRED) Page ? 23 QoS服務(wù)模型 ?盡力而為的服務(wù)：沒(méi)有任何保證的標(biāo)準(zhǔn)連接方式。 ?集成服務(wù)（ IntServ）：又稱為硬（ hard） QoS，是一種嚴(yán)格的預(yù)定服務(wù)。 ?區(qū)分服務(wù)：（ DiffServ）：又稱為（ Soft） QoS，它以類別為基礎(chǔ)，一些類別的通信流優(yōu)先于其他類別的通信流得到處理。換而言之，區(qū)分服務(wù)將通信流分類，然后將它們加入到效率不同的隊(duì)列中。 預(yù)留 帶寬 網(wǎng)絡(luò) 優(yōu)先級(jí) 策略 服務(wù)器 Sub或 VLAN 應(yīng)用 服務(wù)器 Page ? 25 數(shù)據(jù)包分類 ?網(wǎng)絡(luò)設(shè)備或者使用幀中的第 2層 CoS（ Class of Service，服務(wù)類型）位來(lái) 進(jìn)行分類。 第 2層報(bào)頭 IP報(bào)頭 數(shù)據(jù) 前導(dǎo)碼 起始幀分隔符 DA SA 標(biāo)記 其它第 2層報(bào)頭 數(shù)據(jù) FCS ISL報(bào)頭 （ 26字節(jié) ） 被封裝的幀 FCS 版本 /長(zhǎng)度 DS 長(zhǎng)度 ID 偏移 /標(biāo)記 TTL 協(xié)議 校驗(yàn)和 IPSA IPDA 數(shù)據(jù) 3位用于 CoS IP優(yōu)先級(jí)或 DCSP Page ? 26 0 0 0 IP 數(shù)據(jù)報(bào)的區(qū)分業(yè)務(wù)字段 優(yōu) 先 級(jí) 保 留 保 留 1 6 碼 點(diǎn)（ Co d e p o in t ） X X 0 保 留 X X X X 1 1 保 留 X X X X 0 1 保 留 X X X 與原服務(wù)類型兼容 IET F 指定 本地機(jī)構(gòu)指定 用于臨時(shí)使用或?qū)嶒?yàn)?zāi)康? 區(qū)分服務(wù)（ Differentiated Services）： 8位。分為三種類別，分別由下
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