Talk:Fast Ethernet

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This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.

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[edit] The Merge

I merged in 100BASE-TX, 100BASE-T, 100BASE-SX, and 100BASE-FX into this collective article. It still needs a lot of work. KelleyCook 18:44, 14 June 2006 (UTC)

I've pulled in some items from the Ethernet physical layer page. That page says that 100BASE-TX uses NRZI, not MLT-3; the talk page for that page says
Not in a single place in a standard MLT-3 is mentioned. I allowed myself to edit that article to reflect this. In fact, 100BASE-T4 uses very different scheme from that mentioned in MLT-3 patent (not to speak of 100BASE-TX).
MLT-3 is used by FDDI, but that's mostly it.
I'll check my copy of the 802.3 standard and update this page as appropriate. Guy Harris 22:34, 14 June 2006 (UTC)
I fixed the MLT-3 stuff.oakad 07:49, 16 June 2006 (UTC)

[edit] Cat5 wiring

utp cat5 consists of 4 twisted pairs instead of 2 —The preceding unsigned comment was added by 81.241.228.203 (talk • contribs) 05:19, 29 June 2006 (UTC).

It is true that standard cat5 cables have 4 pairs and the standard connectors have 8 positions but the dominant fast ethernet standard (100baseTX) still only uses two pairs (1000baseT uses all 4 though). Plugwash 16:51, 11 October 2006 (UTC)

[edit] no half duplex FX?!

in http://en.wikipedia.org/w/index.php?title=Fast_Ethernet&diff=next&oldid=111062033 soccerman58 claims that there is no such thing as half duplex 100BASE-FX as there is no "need for it". This seems to be contradicted by the relavent section in 802.3 (confusingly they have a general X section which applies to both TX and FX) which explicitly talks about half duplex and is nonsensical (TX and FX both have seperate transmit and receive pairs but both need to be able to run in half duplex mode to support hubs). Plugwash 01:23, 22 March 2007 (UTC)

Just as confirmation, there is most certainly 100base-FX half duplex. You can end up with a duplex mismatch between two ethernet switches, for instance, where one is set to full and the other to half. The Full side would intermittently step on the half side, causing serious performance problems on the link. It's a common task for admins to check the duplex setting on the ethernet switches involved to ensure they are both set to full. Kmwiki (talk) 20:58, 15 January 2008 (UTC)

[edit] LX

As part of the same edit mentioned about a mention of single mode fiber was added to the FX standard, later a bracketed 100BASE-LX was added after this. Is this an unoffical standard? an unofficial name for using a fiber type that is out of spec but works? something else? Plugwash 01:47, 22 March 2007 (UTC)

Plugwash, if its any consolation, I've never heard of 100base-LX, now 1000base-LX is a different story.

The common ethernet standards are currently (beginning 2008):

(10mbps finally being phased out at the chip level due to ROHS european elimination of lead-based stuff)

10base-5, aka 10mbps Thicknet

10base-2, aka 10mbps Thinnet

10base-T, aka 10mbps Twisted-pair


100base-TX, aka 100mbps twisted-pair

100base-FX, aka 100mbps over fiber

100base-SX, UNPOPULAR 100mbps over mm fiber only standard, 300m maximum, cheaper 850nm optics.


1000base-SX aka gigabit over mm

1000base-LX/LH aka gigabit over SM (usually, unless you use a mode-conditioning patch cable on both sides and run it over mm)

1000base-ZX aka gigabit over sm super long haul.


Don't ask me about 10gig yet. :)

Kmwiki (talk) 21:34, 15 January 2008 (UTC)

"10mbps finally being phased out at the chip level due to ROHS european elimination of lead-based stuff"
I don't see why the elimination of lead would pose a problem for 10mbps ethernet controllers, the only thing that could be an issue is chips that are no longer manufactured but still in large stock becoming unusuable for products that must be rohs compliant. Indeed microchip introduced a new ethernet controller not so long ago which afaict has only ever been produced in rohs compliant packaging. Plugwash (talk) 23:18, 17 January 2008 (UTC)

[edit] Connectors for FX

I've put in the connectors list from 802.3 but it appears there may be other connectors in use, does anyone have any sources for what if any unofficial connectors are common? Plugwash 01:47, 22 March 2007 (UTC)

Plugwash --- I'm not sure about sources, I could probably scrounge some up if necessary.

In the industry, the most common connectors for 100base-FX are either ST or SC, with SC being the most popular. MT-RJ connectors are also used when you are looking for high-density. So, when you need, say (24) 100base-FX ports in a 1U switch, it's almost imperative that a smaller form factor connector be used. With the popularity of gigabit fiber, some 100base-FX devices are even being shipped with LC connectors, the common choice for SFP-based gig fiber solutions. Kmwiki (talk) 21:05, 15 January 2008 (UTC)

One other thing --- although I didn't remove this, MIC connectors on ethernet devices are pretty rare. Unless you get into some goofy industrial proprietary market, you are unlikely to find a MIC connector on a true ethernet device. Check Nortel, 3Com, Cisco, and you won't find a single vendor putting a MIC connector on an ethernet device. Kmwiki (talk) 21:23, 15 January 2008 (UTC)

[edit] 4 bits/second?

It is very easy to understand the transmit speed 100Mbps comes from 4 bits at a time, 25 Mhz per second. But, can somebody please tell me, how does a single twisted pair wire transmit four bits at a time (for one direction)? —The preceding unsigned comment was added by 221.169.12.48 (talk) 16:11, 9 April 2007 (UTC).

It doesn't, the bits are clocked at that rate over the paralell MII interface to the transceiver, in the transceiver they undergo 4B5B encoding, and are clocked out serially at 125mhz over the wire using a weired 3 level encoding to better match them to the line characteristics. Plugwash 18:01, 27 April 2007 (UTC)

Hi, I have been looking for books talking about ethernet physical layer. Now I know the parallel signals in 4 bit wide 25MHz go through a 4B5B encoding before they are serialized and transmmited to PMA sublayer. There is still one thing that confuses me. In the page of wiki talking about CAT 5 cable, it says: "Currently unrecognized by TIA/EIA. Provided performance of up to 100 MHz...". But the PMA sublayer is clocked at 125MHz, how does a CAT 5 cable designed to carry "up to" 100 MHz actually carrying 125Mhz signal in 100BASE-TX ethernet? Is there anything wrong with the page of wiki? Or the signal is actually not transmitted at 125Mhz over the wire? Or is there anything wrong with my understanding?

My understanding is that it actually is transmitted at 125 symbols/s, but the MLT-3 encoding of those symbols makes the worst-case "fundamental frequency" only 31.25 MHz. And that MLT encoding ... somehow ... avoids the bandwidth limitation of CAT 5 cable. If you ever find a good explaination, please put it in the article, OK? --75.37.227.177 21:52, 31 July 2007 (UTC)

[edit] misc

Note that today I modified the 100base-FX section to include support for both multimode and single-mode fiber. 100base-FX is called 100base-FX despite what physical media it travels over. You can have 100base-FX over mm OR 100base-FX over single-mode. The only real difference (besides the media itself) is that maximum (and sometimes minimum, research saturation etc) distance you can run. The spec specifically calls out 2km as the maximum distance of multimode for 100base-fx (also 10base-fl), but in the case of single-mode, the distance is entirely based on your optical fiber budget calculated by subtracting rx sensitivity from tx power. Normal SM optical transceivers support at least 10km, and can range up to 110km. Note that you always have to run full duplex over the 412m 100mbps limitation no matter what type of media you employ.

Support for my contention that 100base-fx supports both mm and sm can be verified by looking at Spurgeon's "Ethernet: the definitive guide" page 149. (besides the fact that I have 12+ yrs industry experience, and there are thousands of products on the market that support both mm and sm under the 100base-FX protocol) Kmwiki (talk) 21:17, 15 January 2008 (UTC)

[edit] wiring diagram

Hi. Is there any good reason why the wiring diagram shows the legacy (non-preferred according to the TIA/EIA-568-B standard) T568B wiring configuration, instead of the recommended T568A configuration? --- Joe. —Preceding unsigned comment added by 61.8.13.206 (talk) 00:26, 23 January 2008 (UTC)

[edit] What does the TX in 100base-TX stand for?

What does the TX in 100base-TX stand for? —Preceding unsigned comment added by Panarchy (talk • contribs) 03:58, 26 February 2008 (UTC)