Networking 102: Cables and Standards

[Haru]

Networking 101 is here: http://linustechtips.com/main/forum/...first-3-layers

In this guide I'll cover the cables and standards that you need to know and quite a bit of history.

Before reading this please watch Linus’ guide to Ethernet standards, I will be assuming you watched it during this write up.

Older standards/history:

In the year 1969 the first message was sent over ARPANET. All it said was "lo", pretty cryptic until you realize it was supposed to say "login" but UCLA's system crashed. At the time they had made custom interfaces to network these computer systems together since there weren't any standards for it (foreshadowing). In this period there were many custom connectors which didn’t really change until standards like X.25 came out. X.25 is more of a wide area network standard, so I’m not going to go into too much detail about it here. Wide area networks are for communicating outside of your own network, and considering the only people who had computers at this time were universities, using this standard sufficed.

Fast forward to 1983 and the first standard for ethernet is written, this used what we call a category 3 cable. Category 1 and 2 aren’t really all that important to know about, which usually isn’t an excuse I give for not including a piece of information, but the fact of the matter is that I just don’t know any of the details about those two standards. In Linus’ video he only mentioned as far back as category 5, and category 5’s current standards, it was for good reason, you never really see them. The reason I’m including them, however, it because I have encountered them during work, so it’s important to note that some old stuff is still out there. The first well known Ethernet cable for computer networks was the cat3 cable, it was rated for 10Mbs. Ethernet uses the OSI layer model (yes, I’m implying there are other layer models out there), which means it identifies you by address (mac or ip) and it also has error checking and redundancy. Moving on to 1984 (I’ll get more into the layer model later) Token Ring was introduced, it was rated for 4MBs. “Why would anyone use it?†I hear some of you asking. In my networking 101 article I talked about collision rates. Briefly it’s when two packets of data hit each other and you don’t get your stuff. The way token ring works makes it so there isn’t any collisions, at all. Only someone who had the token could send a packet at any given time, when the packet gets delivered the token moves on to the the next person that needs data moved (the closest in proximity, not the device that’s been waiting the longest). That describes the token part of it, but the ring refers to the topology. Logically this kind of network looks like a ring where the token travels to every device on the network until finding the one it needs. Physically this might not actually look like a ring, you can have the token ring equivalent of a switch (called a media access unit) with a bunch of computers plugged into it and still have it be a ring network. I’ll cover Network topology in detail in 104 most likely.

Copper standards:

There are other protocols and cables that were used but these are the ones that were really historically relevant. Now to get down into the current and relevant. In Linus’ video he mentioned the speeds of cat5 and cat5e cables at being gigabit, this wasn’t always the case. Cat5 was originally rated for 100Mbs, the same with Cat5e (Cat5e improved the physical standard for the cable) but there was a drastic change in how data was sent over the cable. This was explained to me by saying that data is purposefully sent in both directions on the cable, and by subtracting the data that you sent from the collision ridden data that you get, you get what you originally wanted. Like sending cars down a highway in both directions and then magically coming out the other end okay. Cat6 is the only cable TRULY rated for gigabit as there is a key difference between 6 and 5/5e, 6 has a high gauge of wire of 23 where 5/5e is 24 (smaller number is bigger wire). So while cat5 and cat5e will do gigabit, they aren't guaranteed that speed at all times like 6 is even if your cable is in relatively good condition. It’s also the same with 6, which can do 10Gb but only up to 37 meters. Cat6a, the current standard being pushed is the only cable/standard TRULY rated for 10Gbs.

(I'm currently writing up a guide for wireless and fiber, so keep watch of this thread.)

[treodeo]

Could do with a quick Table at the end, like the one I made. Please correct me on if Cat6A can do higher than 10GbE at less than 100 Meters.

[bradscoolio]

These collage named "courses" of yours are really informative, please keep em coming :)

I'm quite the networking n00b