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Wired Ethernet

LAN 101: Networking Basics
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With tens of millions of computers connected by Ethernet cards and cables, Ethernet is the most widely used data-link layer protocol in the world. You can buy Ethernet adapters from dozens of competing manufacturers, and most systems sold in the past decade incorporate one or more built-in Ethernet ports. Older adapters supported one, two, or all three of the cable types defined in the standard: Thinnet, Thicknet, and unshielded twisted pair (UTP). Current adapters support only UTP. Traditional Ethernet operates at a speed of 10 Mb/s, but the more recent standards push this speed to 100 Mb/s (Fast Ethernet) or 1000 Mb/s (gigabit Ethernet). Most desktop and even laptop systems now incorporate gigabit Ethernet. In the future we will likely see 10 gigabit Ethernet (also known as 10G Ethernet) appearing in desktop PCs. 10G Ethernet runs at 10 000 Mbps and is used primarily in enterprise data centers and servers.

Note: Throughout the remainder of this chapter, be aware that discussion of older Ethernet solutions (such as those using Thicknet or Thinnet) as well as alternative networks (such as Token-Ring) are only included for reference. You will usually encounter those technologies only when working on older, existing networks. New network installations today normally use Gigabit, Fast, or Wireless Ethernet.

Fast Ethernet

Fast Ethernet requires adapters, hubs, switches, and UTP or fiber-optic cables designed to support its rated speed. Some early Fast Ethernet products supported only 100 Mb/s, but almost all current Fast Ethernet products are combination devices that run at both 10 Mb/s and 100 Mb/s, enabling backward compatibility with older 10 Mb/s Ethernet network hardware.

Note: Some specifications say that Fast Ethernet supports 200 Mb/s. This is because it normally runs in full-duplex mode (sends/receives data simultaneously), which gives it an effective speed of 200 Mb/s with both directions combined. Still, the throughput in any one direction remains the same 100 Mb/s. Full-duplex operation requires that all hardware in the connection, including adapters and switches, be capable of running in full-duplex and be configured to run in full-duplex (or automatically detect full-duplex signals).

Both the most popular form of Fast Ethernet (100BASE-TX) and 10BASE-T standard Ethernet use two of the four wire pairs found in UTP Category 5 cable. (These wire pairs are also found in Cat 5e, Cat 6, and Cat 6a cable.) An alternative Fast Ethernet standard called 100BASE-T4 uses all four wire pairs in UTP Category 5 cable, but this Fast Ethernet standard was never popular and is seldom seen today.

Gigabit Ethernet

Gigabit Ethernet also requires special adapters, hubs, switches, and cables. When gigabit Ethernet was introduced, most installations used fiber-optic cables, but today it is far more common to run gigabit Ethernet over the same Category 5 UTP cabling (although better Cat 5e/6/6a is recommended) that Fast Ethernet uses. Gigabit Ethernet for UTP is also referred to as 1000BASE-T.

Unlike Fast Ethernet and standard Ethernet over UTP, Gigabit Ethernet uses all four wire pairs. Thus, gigabit Ethernet requires dedicated Ethernet cabling; you can’t “borrow” two wire pairs for telephone or other data signaling with gigabit Ethernet as you can with the slower versions. Most gigabit Ethernet adapters can also handle 10BASE-T and 100BASE-TX Fast Ethernet traffic, enabling you to interconnect all three UTP-based forms of Ethernet on a single network.

Gigabit Ethernet hardware was initially very expensive, thus limiting the use of gigabit Ethernet to high-end network interconnections. More recently, the prices of cables, adapters and especially switches has fallen dramatically, making gigabit the recommended choice for all new cable, adapter, and switch installations.

Neither Fast Ethernet nor gigabit Ethernet support the use of thin or thick coaxial cable originally used with traditional Ethernet, although you can interconnect coaxial cable–based and UTP-based Ethernet networks by using media converters or specially designed hubs and switches.

10 Gigabit Ethernet

10 gigabit Ethernet is a high-speed networking standard that incorporates many different types of physical interconnections including several that are fiber optic and copper based. Of all of the possible connection types, the only one relevant to PCs is called 10GBASE-T, which uses standard twisted-pair cables and 8P8C (RJ45) connectors just like Fast and gigabit Ethernet.

10 gigabit Ethernet (10GBASE-T) requires Category 6a (or better) cabling for support of connection distances up to 100 meters (328 feet). Lower grade Cat 6 cable can be used if the distance is limited to 55 meters (180 feet). Just as with gigabit Ethernet, all four pairs in the cable are used.

10 gigabit Ethernet hardware is currently very expensive, and limited to high-end network interconnections, typically between servers or as a backbone connection between multiple gigabit Ethernet networks. Once the prices of adapters and switches falls to be close to those for gigabit Ethernet, we will see 10 gigabit Ethernet start to become popular for PC-based networks. To prepare for a future upgrade to 10 gigabit Ethernet, consider installing only Category 6a or better cabling in any new installations.

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  • 9 Hide
    iam2thecrowe , September 15, 2011 6:25 AM
    I know a lot of so called "I.T." companies that could learn a thing or two, like how to plug a cable in and how to diagnose a fualty cable/patch point, instead of calling the printer guy out to troubleshoot their network problems for them. IT guys are so lazy sometimes.
  • -5 Hide
    LORD_ORION , September 15, 2011 2:03 PM
    OK seriously, you cannot even do a book prize internationally?

    Lame.

    You suck etc...
  • 0 Hide
    nevertell , September 15, 2011 2:15 PM
    A true fileserver is running linux :>
  • 6 Hide
    Pyree , September 15, 2011 3:23 PM
    I think this should become a sticky on the network forum.
  • 0 Hide
    amk-aka-Phantom , September 15, 2011 3:59 PM
    Nice article. Bookmarked for future reference... some of my friends could use these basics and the article is well-written and simple to understand :) 
  • 8 Hide
    cangelini , September 15, 2011 4:34 PM
    LORD_ORIONOK seriously, you cannot even do a book prize internationally?Lame.You suck etc...


    Nope, we can't unfortunately. The same tax laws and rules that apply to $100 motherboards and $1000 CPUs also apply to $60 books.

    A letter to your congressman about our ridiculous tax laws would be more productive ;) 
  • 1 Hide
    amk-aka-Phantom , September 15, 2011 4:51 PM
    Quote:
    Nope, we can't unfortunately. The same tax laws and rules that apply to $100 motherboards and $1000 CPUs also apply to $60 books.

    A letter to your congressman about our ridiculous tax laws would be more productive ;) 


    Lol, I accept that explanation readily, as much as I hate all these kick-ass US-only draws. Taxes are a party crasher...
  • 1 Hide
    jryan388 , September 15, 2011 9:15 PM
    I was under the impression that cat6 cable was required for gigabit ethernet...
  • 0 Hide
    Proximon , September 15, 2011 9:59 PM
    It really is an impressively clear and complete book. It's quite a skill to cover topics like this in a way that doesn't require too much background knowledge first.
  • 0 Hide
    soccerdocks , September 16, 2011 12:33 AM
    jryan388I was under the impression that cat6 cable was required for gigabit ethernet...


    I was too. But it sounds like as long as your CAT5e cable is short enough it will work. Although probably not optimally.
  • 2 Hide
    michaelahess , September 16, 2011 2:17 AM
    Cat5e is fine for gigabit. I've had runs over 300ft work fine at 1Gb speeds.

    I didn't read very carefully but I didn't see anything in the wifi section about true transmission speeds. 54g will only net you 18-24Mb at the best, consistently. Fastest I've gotten outa any N gear is just shy of 250Mb/sec. And that was with high end Cisco gear at very short distance. Wireless is just too fickle for real high bandwidth stuff.

    I've been in the network provider (ISP) field for over 15 years. Anyone has any questions, just ask me. ;)  Ok don't really, I don't have the time!
  • 0 Hide
    Onus , September 16, 2011 4:43 PM
    ARCNet, Token Ring...that brings back a lot of memories. Then there was Corvus' Omninet...
  • 0 Hide
    chickenhoagie , September 18, 2011 9:14 PM
    guess my cisco class taught me a lot in highschool. still learned a few pointers in this article though
  • 0 Hide
    sysa , September 21, 2011 1:31 PM
    I did a little checking and found out that the 6200 series processors are Interlagos.
  • 1 Hide
    zodiacfml , September 22, 2011 3:06 AM
    wow, didn't know our ordinary ethernet only need two pairs of wires.
    i wonder why it had those extra pairs before gigabit ethernet.
  • 1 Hide
    thegame8019 , September 22, 2011 7:26 PM
    I am currently enrolled in Cisco's academy and this article has made a few things a little more clear to me.
  • 0 Hide
    PhoneyVirus , September 23, 2011 7:59 PM
    I have this book 10 feet from me but I'm not aloud with it until Christmas because the girlfriend would kill me, the only way I could look at it is I would have to where a pair of rubber gloves so there wouldn't be any finger prints on the hard cover and not to break the book in so I'll wait until Christmas and it can't come fast enough.

    Also amk-aka-phantom this book should be on your book shelf and NOT Bookmarked in the browser, Read this book remember all you can build your self a system, Read Microsoft Windows Inside Out, Remember your Keyboard Short Cuts aka Run Commands, Conquer the Command prompt, program simple VBScripts, Batch files and you will have no problem running a little PC Repair shop.

    PhoneyVirus
  • 0 Hide
    amk-aka-Phantom , September 23, 2011 8:25 PM
    Quote:
    Also amk-aka-phantom this book should be on your book shelf and NOT Bookmarked in the browser, Read this book remember all you can build your self a system, Read Microsoft Windows Inside Out, Remember your Keyboard Short Cuts aka Run Commands, Conquer the Command prompt, program simple VBScripts, Batch files and you will have no problem running a little PC Repair shop.


    Umm... thank you, but I know enough about PCs and networking without any books.