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QoS Concepts
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Traffic Characteristics
Network Traffic Trends
Data traffic is not real-time and has unpredictable bandwidth need. Data traffic can temporarily burst, as when a large file is being downloaded. This bursting can consume the entire bandwidth of a link
Voice
Voice traffic is predictable and smooth, as shown in the figure. However, voice is very sensitive to delays and dropped packets. It makes no sense to re-transmit voice if packets are lost; therefore, voice packets must receive a higher priority than other types of traffic
Video
Video traffic tends to be unpredictable, inconsistent, and bursty compared to voice traffic. Compared to voice, video is less resilient to loss and has a higher volume of data per packet
Data
Data applications that have no tolerance for data loss, such as email and web pages, use TCP to ensure that, if packets are lost in transit, they will be resent. Data traffic can be smooth or bursty
Queuing Algorithms
Queuing Overview
Queuing is a congestion management tool that can buffer, prioritize, and, if required, reorder packets before being transmitted to the destination
First In First Out
In its simplest form, First In First Out (FIFO) queuing, also known as first-come, first-served queuing, buffers and forwards packets in the order of their arrival. When FIFO is used, important or time-sensitive traffic can be dropped when there is congestion on the router or switch interface
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QoS Models
Best Effort
The best-effort model is similar in concept to sending a letter using standard postal mail. Your letter is treated exactly the same as every other letter. With the best-effort model, the letter may never arrive, and, unless you have a separate notification arrangement with the letter recipient, you may never know that the letter did not arrive
Integrated Services
. IntServ explicitly manages network resources to provide QoS to individual flows or streams, sometimes called microflows. It uses resource reservation and admission-control mechanisms as building blocks to establish and maintain QoS
Differentiated Services
The differentiated services (DiffServ) QoS model specifies a simple and scalable mechanism for classifying and managing network traffic.
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