The data traffic flowing in a network can be generated by end users or control traffic. Users generate traffic by using applications. Control traffic can be generated by intermediary devices or by activities related to the operation, administration, and management of the network. Today, users utilize many applications. The traffic created by these applications differs in its characteristics. Usage of applications can affect network performance and, in the same way, network performance can affect applications. Usage translates to the user’s perception of the quality of the provided service—in other words, a user experience that is good or bad. Recall that QoS is implemented to prioritize network traffic and optimize the user experience.
網路中流動的資料流量可能由終端使用者產生，也可能是控制流量。使用者透過使用應用程式產生流量。控制流量則可能由中介裝置產生，或由網路的操作、管理與維運相關活動所產生。現今使用者會使用許多應用程式，這些應用程式所產生的流量特性各不相同。應用程式的使用會影響網路效能；同樣地，網路效能也會影響應用程式。這種使用感受會轉化為使用者對所提供服務品質的認知，換句話說，就是好或壞的使用者體驗。回想一下，實作 QoS 的目的就是為網路流量排定優先順序並最佳化使用者體驗。
User applications can be classified to better describe their traffic characteristics and performance requirements. It is important to know what traffic is flowing in your network and describe the traffic in technical terms. An example of traffic types found in today’s network is given in the figure. This knowledge is used to optimize network design.
使用者應用程式可以加以分類，以便更清楚地描述其流量特性與效能需求。了解網路中有哪些流量，並以技術術語描述這些流量，是很重要的。下圖列出現今網路中常見流量類型的範例。這些知識可用來最佳化網路設計。
To classify applications, their traffic, and performance the requirements are described in terms of these characteristics:
為了對應用程式、其流量與效能需求進行分類，會以下列特性來描述：
- Interactivity: Applications can be interactive or noninteractive. Interactivity presumes that a response is expected for the normal functioning of the application for a given request. For interactive applications, it is important to evaluate how sensitive they are to delays—some might tolerate larger delays up to practical limits, but some might not.互動性（Interactivity）：應用程式可分為互動式與非互動式。互動性的前提是，應用程式要正常運作，對於某個請求必須得到回應。對互動式應用程式而言，評估其對延遲的敏感程度很重要：有些在實際可行的限度內可容忍較長的延遲，有些則不行。
- Real-time responsiveness: Real-time applications expect a timely data serving, and they are not necessarily interactive. An example of a real-time application is like a football game video streaming (live streaming) or video conferencing. Real-time applications are sensitive to delay. Delay is sometimes used interchangeably with the term latency. Latency refers to the total amount of time from the source sending data to the destination receiving it. Latency accounts for the propagation delay of signals through media, the time required for data processing on devices it crosses along the path, etc. Because of the changing network conditions, latency might vary during data exchange: some data might arrive with less latency than other data. The variation in latency is called jitter.即時回應性（Real-time responsiveness）：即時應用程式期望資料能及時送達，但它們不一定是互動式的。即時應用程式的例子包括足球賽的影音串流（直播）或視訊會議。即時應用程式對延遲很敏感。延遲（delay）有時與 latency 一詞互換使用。Latency 指的是從來源端送出資料到目的端收到資料的總時間，包含訊號在媒介中的傳播延遲、資料在路徑上所經裝置進行處理所需的時間等。由於網路狀況不斷變化，資料交換期間的延遲可能會變動：有些資料到達時的延遲比其他資料短。這種延遲的變動稱為抖動（jitter）。
- Amount of data generated: Some applications produce a low quantity of data, such as voice applications. These applications do not require much bandwidth, and they are usually referred to as benign bandwidth applications. Video streaming applications produce a significant amount of traffic and are termed bandwidth greedy.產生的資料量（Amount of data generated）：有些應用程式只產生少量資料，例如語音應用程式。這些應用程式不需要太多頻寬，通常稱為頻寬友善（benign bandwidth）應用程式。影音串流應用程式則會產生大量流量，被稱為頻寬貪婪（bandwidth greedy）應用程式。
- Burstiness: Applications that always generate a consistent amount of data are referred to as smooth or nonbursty applications. On the other hand, bursty applications at times create a small amount of data, but they can change behavior for shorter periods. An example, is web browsing. If you open a page in a browser that contains a lot of texts, a small amount of data is transferred. But, if you start downloading a huge file, the amount of data will increase during the download.突發性（Burstiness）：總是產生固定資料量的應用程式稱為平穩（smooth）或非突發（nonbursty）應用程式。相反地，突發（bursty）應用程式有時只產生少量資料，但可能在較短的時間內改變行為。網頁瀏覽就是一個例子。如果你在瀏覽器中開啟一個包含大量文字的頁面，只會傳輸少量資料。但如果你開始下載一個巨大的檔案，下載期間的資料量就會增加。
- Drop sensitivity: Packet loss is losing packets along the data path, which can severely degrade the application performance. Some real-time applications (such as video on demand) are sensitive to the perceived packet loss when using the network resources. You can say that such applications are drop-sensitive.丟棄敏感性（Drop sensitivity）：封包遺失是指封包在資料路徑上遺失，這可能嚴重降低應用程式的效能。有些即時應用程式（例如隨選視訊）在使用網路資源時，對可感受到的封包遺失很敏感。可以說這類應用程式是丟棄敏感（drop-sensitive）的。
- Criticality to business: This aspect of an application is "subjective" in that it depends on someone's estimate of how valuable and important the application is to a business. For instance, an enterprise that relies on video surveillance to secure its premises might consider video traffic as a top priority, while another enterprise might consider it totally irrelevant.對業務的關鍵性（Criticality to business）：應用程式的這個面向是「主觀的」，因為它取決於某人對該應用程式對企業有多大價值與重要性的評估。例如，依賴視訊監控來保護廠區安全的企業，可能將視訊流量視為最高優先；而另一家企業可能認為它完全不重要。
One way that applications can be classified is as follows:
應用程式的一種分類方式如下：
- Batch applications: Applications such as FTP and TFTP are considered batch applications. Both are used to send and receive files. Typically, a user selects a group of files that need to be retrieved and then starts the transfer. Once the download starts, no additional human interaction is required. The amount of available bandwidth determines the speed at which the download occurs. While bandwidth is important for batch applications, it is not critical. Even with low bandwidth, the download is completed eventually. Their principal characteristics are:批次應用程式（Batch applications）：FTP 與 TFTP 等應用程式被視為批次應用程式。兩者都用來傳送與接收檔案。通常使用者會選取一組需要取回的檔案，然後開始傳輸。下載一旦開始，就不需要額外的人為互動。可用頻寬的多寡決定了下載的速度。頻寬對批次應用程式雖然重要，但並非關鍵。即使頻寬很低，下載最終仍會完成。其主要特性如下：
- Typically do not require direct human interaction.通常不需要人直接參與互動。
- Bandwidth is important but not critical.頻寬重要但非關鍵。
- Examples: FTP, TFTP, inventory updates.範例：FTP、TFTP、庫存更新。
- Interactive applications: Applications in which the user waits for a response to their action are interactive. Think of online shopping applications, which are offered by many retail businesses today. Interactive applications require human interaction, and their response times are more important than for batch applications. However, strict response times or bandwidth guarantees might not be required. If the appropriate amount of bandwidth is not available, then the transaction may take longer, but it will eventually complete. The main characteristics of the interactive applications are:互動式應用程式（Interactive applications）：使用者執行動作後需等待回應的應用程式就是互動式應用程式。想想現今許多零售業者提供的線上購物應用程式。互動式應用程式需要人的參與，其回應時間比批次應用程式更重要。不過，可能不需要嚴格的回應時間或頻寬保證。如果沒有足夠的頻寬，交易可能需要較長時間，但最終仍會完成。互動式應用程式的主要特性如下：
- Typically support human-to-machine interaction.通常支援人與機器之間的互動。
- Acceptable response times have different values depending on how important the application is for the business.可接受的回應時間依應用程式對企業的重要程度而有不同。
- Examples: database inquiry, stock exchange transaction範例：資料庫查詢、證券交易
- Real-time applications:Are applications such as voice and video that may also involve human interaction. Because of the amount of information that is transmitted, bandwidth is critical. In addition, because these applications are time-critical, a delay on the network can cause a problem. Timely delivery of the data is crucial. It is also important that data is not lost during transmission because real-time applications, unlike other applications, do not retransmit lost data. Therefore, sufficient bandwidth is mandatory, and the quality of the transmission must be ensured by implementing QoS. QoS is a way of granting higher priority to certain types of data, such as VoIP. The main characteristics of the real-time applications are:即時應用程式（Real-time applications）：指語音與視訊等應用程式，也可能涉及人的互動。由於傳輸的資訊量大，頻寬至為關鍵。此外，這些應用程式對時間極為敏感，網路上的延遲可能造成問題。資料的及時送達非常重要。資料在傳輸期間不能遺失也很重要，因為即時應用程式與其他應用程式不同，不會重傳遺失的資料。因此，足夠的頻寬是必要條件，且必須透過實作 QoS 來確保傳輸品質。QoS 是一種為特定類型的資料（例如 VoIP）給予較高優先權的方法。即時應用程式的主要特性如下：
- Typically support human-to-human interaction.通常支援人與人之間的互動。
- End-to-end latency is critical.端對端延遲至為關鍵。
- Examples: Voice applications, video conferencing, and online streaming such as live sports.範例：語音應用程式、視訊會議，以及運動賽事直播等線上串流。
Applications may be required to manage different types of communications. One such application is the factory-automation application. Factory-automation applications deal with plant process-related data, such as readings from sensors and alarms, which require guaranteed delivery times and typically require feedback within a prescribed response time. On the other hand, the same factory-automation application must also handle certain device configurations and commercial data, which is not time-critical.
應用程式可能需要處理多種不同類型的通訊。工廠自動化應用程式就是一例。工廠自動化應用程式處理與廠區製程相關的資料，例如感測器讀值與警報，這些資料需要有保證的送達時間，且通常需要在規定的回應時間內得到回饋。另一方面，同一個工廠自動化應用程式也必須處理某些裝置設定與商業資料，而這些資料對時間並不敏感。
| real-time application即時應用程式 | VoIPVoIP |
| batch application批次應用程式 | FTPFTP |
| interactive application互動式應用程式 | stock exchange transaction證券交易 |