What is 100Base-Tx and 1000Base-TX

I came across a question in the Cisco Learning Network which highlighted a source of confusion that many people have.

Call me pedantic, but I thought I’d set the record straight – and let you know that when people refer to 1000Base-TX, they are PROBABLY referring to the IEEE 1000BASE-T standard. NOT the TIA (the people who set cabling standards) version of the standard which they cleverly called “1000BASE-TX”, and “standardised” it as ANSI/TIA-854:

“A Full Duplex Ethernet Physical Layer Specification for 1000Mbit/s (1000BASE-TX) Operating over Category 6 Balanced Twisted-Pair Cabling,” published in March 2001, provides a data rate of 1000 Megabits/second, similar to the IEEE 802.3ab Gigabit Ethernet standard. The main difference is that it requires category 6 cabling instead of category 5e cabling.  http://www.leviton.com/OA_HTML/ibcGetAttachment.jsp?cItemId=22256&label=IBE&appName=IBE

The TIA were banking on the price of the 1000BASE-TX transceivers falling, and therefore justifying selling people more expensive Category 6 cable rather than Cat5e.  I’m afraid this is one of those things that get my goat up – Why would you run Category 6 cabling to the desktop when category 5 (the IEEE standard says 5, the TIA say 5e) is more appropriate?  Do you REALY believe you will need 10Gb/s to those desktops in the life of the building?  Category 6 is soooo much harder to terminate that you probably end up with a sub-cat5 cabling system anyway even after paying all that money.

But I digress – what I really wanted to discuss is that the Ethernet standards are set by the IEEE, and a little history will help.  All quotes are from the freely downloadable IEEE standards for 802.3 Ethernet

In the beginning was 10BASE5. The “IEEE 802.3 Physical Layer specification for a 10 Mb/s CSMA/CD local area network over coaxial cable (i.e., thicknet). (See IEEE Std 802.3, Clause 8.)”

Later came 10BASE-T. The “IEEE 802.3 Physical Layer specification for a 10 Mb/s CSMA/CD local area network over two pairs of twisted-pair telephone wire. (See IEEE Std 802.3, Clause 14.)”

Note that there is no such standard as 10BASE-TX.  Note also that the IEEE specifies the cabling specifications as nBASEyy – the BASE is in ALL CAPS.  I don’t know why – especially when you think that BASE refers to “Baseband”.  IEEE thing I guess.

So the T is for “Twisted Pair”.  Fair enough.  So why is there both a 100BASE-T and a 100BASE-TX specification?

The standards spell it out:

100BASE-T is the “IEEE 802.3 Physical Layer specification for a 100 Mb/s CSMA/CD local area network. (See IEEE Std 802.3, Clause 22 and Clause 28.)”  A closer look at Clause 21 gives more insight: “100BASE-T uses the existing IEEE 802.3 MAC layer interface, connected through a Media-Independent Interface layer to a Physical Layer entity (PHY) sublayer such as 100BASE-T4, 100BASE-TX, or 100BASE-FX.”

Curious to note that 100BASE-FX is included, so we can’t assume that the “T” in 100BASE-T has anything to do with “twisted pair”

100BASE-TX is the “Physical Layer specification for a 100 Mb/s CSMA/CD local area net- work over two pairs of Category 5 twisted-pair cabling. (See IEEE Std 802.3, Clause 24 and Clause 25.) ” but it is not the ONLY twisted pair cabling standard for 100BASE-T.

100BASE-T4 is the “Physical Layer specification for a 100 Mb/s CSMA/CD local area net- work over four pairs of Category 3, 4, and 5 twisted-pair cabling. (See IEEE Std 802.3 Clause 23.)”.  However, very few vendors produced equipment to match this standard.

Now, at the same time at the 100Mb/s standards were released, the auto-negotiation specs were published. Or more precisely, “Physical Layer link signaling for 10 Mb/s and 100 Mb/s Auto-Negotiation on twisted pair”.   Mostly this was implemented as negotiation of 10BASE-T/100BASE-TX – although the standard specifies the “Auto-Negoti- ation function also provides a Parallel Detection function to allow 10BASE-T, 100BASE-TX, and 100BASE-T4 compatible devices to be recognized, even though they may not provide Auto-Negotiation”

Not surprisingly, vendors took to abbreviating the auto-speed negotiated Ethernet as 10/100BASE-T or 10/100BASE-TX – or often as 10/100Base-TX.

When the 1000BASE-T gigabit “Physical Layer specification for a 1000 Mb/s CSMA/CD LAN using four pairs of Category 5 balanced copper cabling. (See IEEE Std 802.3, Clause 40.)” case out, it was added to the auto-negotiation clause and vendors began referring to 10/100/1000Base-TX.

But there is no IEEE 1000BASE-TX standard


About RedNectar Chris Welsh

Professional IT Instructor. All things TCP/IP, Cisco or Data Centre
This entry was posted in 1000BASE-T, 1000BASE-TX, 100BASE-T, 100BASE-TX, 802.3, Ethernet, IEEE. Bookmark the permalink.

1 Response to What is 100Base-Tx and 1000Base-TX

  1. I’ll accept anyone’s comments if not profane, but apart from being rude, I think you are missing the point – I’m the messenger – I don’t set the standards, just read them. Perhaps if you took some time to read the standards you might get some other insights – most importantly how to tell the difference between a “standard” and marketing hype. Like 1000BaseZX. Sounds like a standard right? But is it?

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