The second concept I will describe is delay. Delay (also called latency) is how long a packet takes to get to it's destination. If you think of a packet as a car driving down the highway, it's latency is how long it takes to get from home to the destination.
Latency is typically measured in milliseconds. Ethernet connections are considered low latency (a few milliseconds), while a satellite link is considered high latency (hundreds of milliseconds). There are many factors which can affect latency.
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The next concept covered is loss. Loss is the dropping of packets in transit. As you can see below, there is no middle ground for packet loss, it's either very bad or not so bad. The reason why mission critical data transfers have a low sensitivity to packet loss, is that the upper layers are supposed recognize the loss and request a retransmission. That being said, a high number of retransmissions will result in data transfers taking a significantly longer amount of time. In video or audio applications, the audio or video stream will drop off intermittently as packets are loss.
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