Скачать с ютуб 電腦篇14- 淺釋上網頻寛和實際傳輸率差異成因 (Computer 14- Brief Illustration of Bandwidth and Actual Data Rate) в хорошем качестве

電腦篇14- 淺釋上網頻寛和實際傳輸率差異成因 (Computer 14- Brief Illustration of Bandwidth and Actual Data Rate)

請先行閱讀免責聲明 Pls. read our disclaimer first. 購買無線路由器，不是只看路由器速度 The speed of Wifi router is not the only consideration for purchase 還要考慮選用的互聯網上網服務計劃 It should couple with the internet service plan to be subscribed 選擇前先要了解供應商所聲稱的頻寛 Before selecting the right plan, we should understand that bandwidth claimed by ISP 會高於實測傳輸速率 is higher than actual data rate 因為傳輸載荷訊息時 As the transmission of payload of data 要有管理的相關訊息和操作 incures significant metadata for operation 加上損耗和干擾，它們耗用了部份的頻寛 In addition to the interference and attenuation, they consume a portion of the bandwidth 構成消耗，以太空運輸做譬喩 as the overhead. Analogous to space travel 載具和消耗燃料重量甚至遠多於負荷 the weight of carrier rocket and fuel is even heavier than the payload itself 互聯網傳送的消耗究竟佔用多少頻寛 The bandwidth that overhead spends on internet traffic 一直是資科人員關注的問題 is always a major concern of technical personnel 一般人的觀念，速度是越快越好，但現實要花錢 In common sense, faster means better, yet it cost more in reality 這是cnet 和電訊管理局提供的網速和用途匹配參考 Here are the recommendations from CNET and OFCA CNET推荐頻寛比理論上的網速預留了空間 The recommended bandwidth by CNET reserves redundancy on top of the theoretical speed 在此我們嘗試從網絡傳輸原理作一個解釋： To elaborate, let's look into the working process of network traffic 1. 路由器速度單位是每秒位元數 The speed of router is expressed in terms of bit per second 訊息内容的單位是字節，含8位元 The basic unit of data is byte which is composed of 8 bits 字節間須要加上開始和停止位元來分隔 In between 2 adjacent bytes, a start and a stop bit must be inserted as a segregation mark 所以字節數不是簡單的將字元數除以8 Hence Byte no. is not just simply 1/8 of bit no. 2. 字節不能無限量連接傳送 Series of Bytes can't be qued up indefinitely 一定數量的字節後要封包和標韱 They're packed into packets and marked with labels containing unique id and other meta data accordinly 標韱攜帶重組訊息時的訊息如序號和位址 for the reproduction of the transmitted data on the reception side 還有用來執行傳輸和管理的指令/程式碼 Moreover, there are also processing codes and commands for the operations 3. 每台路由器或集線器，能連接包括自己在内共256件器材 Every router can connect up to 256 devices including itself 要應付局域網内所有在啟動狀態中的器材 It's destined to handle all active devices in the network 但單一通道在同一時間只能通過一個訊息包 Concurrently, every channel is allowed to transmit only 1 data packet from 1 device 同時間出現兩個或以上便有衝突，要全廢棄然後排序重發 Collision of packets from 2 or more devices will cause them to be discarded and prompt for orderly retransmission of all the data again 高階的路由器或内置頻寛控制功能 Some sophisticated routers may set priority or quality of service(QoS) 按需求來管理局域網内器材的可用頻寛 in accordance with the different needs among devices. 但過於複雜，同樣消耗頻寛 Yet the algorithm is too complicated and consumes bandwidth 一般路由器只能用先到先得原則分配 Ordinary routers only adopt "first come, first serve" principle 4. 由於干擾或硬體失誤，訊息傳輸都有容錯的算法 To contain transmission error due to interference or hardware defect 須要額外加入除錯訊息確保訊息完整 Error correction data and code must be added purposefully to ensure the integrity of data. 5. 網絡傳輸的每一個層階都要採用對應的通訊協定 Data are not transmitted in their original format but encoded and encrypted in line with specific protocol on each layer 握手訊息用作開啟和終止連接 The handshaking signal not only initializes and ends the transmission session 也定義了將載荷壓縮，提高容錯度和加密的方法 but also defines the "codecs" for the compression and encryption of payload 作為發送和接收方的訊息編碼和解碼之用 Thus decoding and decompression are enabled on the reception side. 這些額外的訊息包括： These extra data of overhead include: i. 訊息的封包和路由訊息 Data Packet Packaging and Routing Data ii. 訊息包衝突的處理訊息 Packet Collision Handling Command iii. 頻寛Bandwidth在網絡器材中的分配控制指令 Control Command For Bandwidth Distribution Among Devices iv. 容錯處理訊息 Error Handling Information v. 通訊協定的控制指令和參數 Commands and Parameters of Protocol 所以，實際的傳輸率會少於網絡服務商(ISP)所聲稱的頻寛 Hence, the actual data rate is much lower than the claimed bandwidth 網上很多博客解説稱網速用字節而不是位元為單位 Many bloggers try to explain difference with the deliberate use of Byte/s which is just 1/8 of bit/s in data rate 實際上一般測速軟件也是用bps做單位的 In fact, they are both expressed in terms of bps 測出的數值也不是頻寛的1/8而是較多 and test result isn't 1/8 or less of the claimed bandwidth 例如在300M的接入點用ac300也有28M/64M的速度 For example, the internet download/upload speed of our previous ac300 router connected to 300M access point was about 28/64M, 如是字節數便不應多於40M，11ax 的便更快 If the unit was Bps, it could hardly be greater than 40M. With 11ax, it's even faster 802.11n是2009年的技術，上限600Mbps 802.11n was firstly launched in 2009. Its upper limit is 600Mbps 不能盡用300Mbps 網速，由這級别升級，我們傾向直接上802.11ax 300Mbps Bandwidth is not fully utilized. To upgrade from 11n, we prefer 11ax 11ac是2013年的技術 11ac was firstly launched in 2013 最高階的理論速度可達6.93Gbps having an upper limit of 6.93Gbps 速度和低階的11ax重叠，可看性價比來決定選擇 overlapping with the lower end of 11ax 如果正在用11ac中高階的，是否再升級便看需要和預算了 Users of high end product of 11ac may decide on their upgrade plan based on their need and budget. 我們另一上網點升級為為Gigabit Another access point is upgraded to Gigabit 原來的11ac1300路由器不足以匹配，才升級為11ax級 The current Samsung 11ac1300 router become obsolete and upgrade to 11ax is desired 升級前後的結果，我們在下一次視頻播出 We shall release the test result in the next vid