1 00:00:00,480 --> 00:00:07,560 ‫So either Ned has been a relatively inexpensive, reasonably fast and very popular land technology for, 2 00:00:08,010 --> 00:00:09,210 ‫gosh, several decades. 3 00:00:09,720 --> 00:00:17,670 ‫It was commercially introduced in 1980 and first standardized in 1983 as I Tripoli eight oh two to three. 4 00:00:18,600 --> 00:00:24,510 ‫It has since been refined to support higher bit rates and longer linked distances. 5 00:00:26,170 --> 00:00:31,270 ‫Ethernet has since become the most popular and probably the most widely deployed network technology 6 00:00:31,270 --> 00:00:32,140 ‫in the world. 7 00:00:32,980 --> 00:00:39,100 ‫Many of the issues involved with Ethernet are common to many network technologies, and understanding 8 00:00:39,100 --> 00:00:45,850 ‫how Ethernet addresses these issues can build a foundation that will improve your understanding of networking 9 00:00:45,850 --> 00:00:46,510 ‫in general. 10 00:00:48,500 --> 00:00:52,340 ‫So let's keep the design principles of Ethernet simple. 11 00:00:53,510 --> 00:01:01,280 ‫The basic idea of its design is it multiple computers have access to it and can send data at any time. 12 00:01:02,190 --> 00:01:06,370 ‫If two computers send data at the same time, a collision will occur. 13 00:01:06,810 --> 00:01:11,340 ‫So and when this happens, the data centers is not going to be usable. 14 00:01:12,220 --> 00:01:19,000 ‫In general, both computers will stop sending and wait a random amount of time before they'll try again. 15 00:01:19,930 --> 00:01:23,570 ‫Now, a special protocol was developed to deal with such problems. 16 00:01:23,590 --> 00:01:32,740 ‫It's called carrier sends multiple access with collision detection or might be easy to say CSM a CD. 17 00:01:34,360 --> 00:01:41,620 ‫Today, Ethernet cables look like, well, thick telephone cables, modern cables connect to hubs or 18 00:01:41,620 --> 00:01:48,970 ‫switches, and each cable runs from a computer's network interface card, the Nicey to such a box. 19 00:01:49,890 --> 00:01:52,800 ‫Now here are the most widely known Ethernet cables. 20 00:01:53,460 --> 00:01:59,670 ‫10 based two and 10 base five cables are what I would call retro coaxial cables. 21 00:02:00,120 --> 00:02:01,620 ‫You don't see them much today. 22 00:02:02,700 --> 00:02:09,090 ‫Each computer has a T plugged into it and cables plug into each side of that T. 23 00:02:10,720 --> 00:02:20,320 ‫Ten based, T100 based T-1000 based are all unshielded, twisted pair or UTP cables, which look a lot 24 00:02:20,320 --> 00:02:25,600 ‫like thick phone cables, and they go from each computer to a hub or a switch. 25 00:02:26,620 --> 00:02:33,040 ‫Initial numbers indicate the supported speed, so the 10 will stand for 10 megabits per second and a 26 00:02:33,040 --> 00:02:38,350 ‫thousands dans four 4000 megabit, also known as gigabit or one gigabit. 27 00:02:40,260 --> 00:02:48,240 ‫Ben, bass cables are the same as tin based tea, but they are fibre cables, and they'll transmit light 28 00:02:48,240 --> 00:02:52,020 ‫pulses instead of electrical signals over copper. 29 00:02:53,750 --> 00:03:00,290 ‫A data packet on an Ethernet link is called an Ethernet packet, which transports an Ethernet frame 30 00:03:00,530 --> 00:03:01,450 ‫as its payload. 31 00:03:02,530 --> 00:03:11,740 ‫An Ethernet frame is preceded by a preamble and start frame delimiter, or SFD, which are both part 32 00:03:11,740 --> 00:03:15,700 ‫of the Ethernet packet at the physical layer, right? 33 00:03:16,640 --> 00:03:18,440 ‫There are four types of Ethernet frames. 34 00:03:19,260 --> 00:03:24,840 ‫And the most common one is the Ethernet to frame, also known as DeCSS frame. 35 00:03:26,170 --> 00:03:28,660 ‫We're talking about the Ethernet to frame at the moment. 36 00:03:30,380 --> 00:03:32,300 ‫Each Ethernet frame starts with. 37 00:03:33,680 --> 00:03:40,670 ‫An Ethernet header which contains destination and source Mac addresses as its first two fields. 38 00:03:41,930 --> 00:03:47,960 ‫The middle section of the frame is payload data, including any headers for other protocols. 39 00:03:48,290 --> 00:03:51,920 ‫For example, internet protocol carried in the frame. 40 00:03:53,450 --> 00:04:02,210 ‫The frame ends with a frame check sequence, or FCX, which is a 32 bit Sekulic redundancy check used 41 00:04:02,210 --> 00:04:05,060 ‫to detect any in transit corruption of data.