![]() ![]() Of great interest is the fact that although the DoD's Arpanet was heralded as a high-speed network back in the early 1980s, today most users are unhappy with its performance. What has caused this change? In an effort to seek answers, it was reasoned that to identify the inherent, indispensable characteristics of high-speed networks, one must first search for a definition of high-speed networks, one that is mathematical yet simple but, most important, physically intuitive. Then, for key past and present networks, their high-speed characteristic must be computed to help us trace the evolution in networking from the perspective of their high-speed nature. Next, utilizing the definition as a reference and recognizing the key functions of a network, one would have to identify the fundamental attributes of networks. The exercise will provide valuable understanding of networks, especially the fundamental limitations, if any. This, in turn, will help us consider the important issues while designing new network architectures and provide us insight into their ultimate potential.Ī thorough literature search on the fundamental characteristics of high-speed networks revealed sparse results. In characterizing high-speed local area networks (HSLANs), Abeysundara and Kamal compute a quantity, ‘ a’, labeled normalized propagation delay. ![]() It is defined as the ratio of the physical propagation delay between a given pair of source and destination points to the packet transmission time, for a representative packet size for LANs. They report findings that for a packet size of 200 bits, transmission speed of 2×10 8 m/s, and a link bandwidth of 100 Mb/s, ‘ a’ equals 1.25 and 2.5 for LANs spanning 5000 and 10,000 m, respectively. They conclude that as the value of ‘ a’ approaches or even exceeds unity, the LAN may be viewed as operating at high-speeds. Furthermore, higher the value of ‘ a’, the more high-speed the LAN. While a pioneering work, the effort incurs three limitations. Second and more important, the concept of ‘ a’ fails to reflect the quality of service (QoS) considerations associated with a message communication. Third, Abeysundara and Kamal fail to link their choice of the definition of ‘ a’ to any scientific reference. In characterizing network performance, Stallings defines a symbol ‘ a’, exactly as in Ref. That helps mask it's inaccuracy at the expense of higher latency., but uses it to explain why congestion control is difficult in networks that exhibit high values of ‘ a’. It appears the way this GPS calculates speed is by an average of data from the previous 5 or so seconds. I slowed down to ~5mph at around 0:06 in that video but the speed from the GPS does not go down to that number until 0:13 into the video. It is the same issue when it is stamped on the video by the mini, so it's not a problem with the subtitles. You can the GPS appears to be over 5 seconds behind compared to the speed I was actually going. The subtitle idea worked great, btw (video below). I don't want someone saying I tried to drive through a bunch of cornfields since the GPS shows me in the middle of a farm when I'm actually on the road. ![]() You can see how poorly this GPS performs here: It is not something that would be reliable enough for insurance or court purposes, so if I ever need to use a video as evidence it will have the inaccurate data removed. Sometimes it takes 3 minutes to lock on to the point where it records any data at all, and then for the first 30 seconds or so after that it will have me in the wrong place on the map since it has not completely locked on. It's just not trustworthy in the mini's case due to the frequent loss of gps. Still, for personal use, it is something I like to have. The GPS speed also has a latency on the mini cameras (like many dash cams) and is 3+ seconds or so behind due to the way it calculates the speed. ![]() The reason I don't like the GPS data hard coded is that it is not accurate (my GPS will frequently lose signal and show up as a "gray" line on the map in Registrator Viewer). ![]()
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