Differences between Ethernet Types

[bluewhaleCA]

I was reading an article this morning which indicated that 100BT and Gigabyte Ethernet don't use CSMA/CD. Is this true? Could anybody point me to an article or two about the differences between 10BT and the modern versions?

Thanks.


Paul

 

[Degg]

By definition, if its 'ethernet' then it is CSMA/CD, at least thats the way I understand it. Degg
Network Administrator

 

[svermill]

There is still shared 100 Mbps out there, which means that CSMA/CD is still used. As for gig-E and above, there is no more CSMA/CD. It is full duplex only, and thus CSMA/CD isn't necessary. This was decided because the minimum frame size would have need to be extened by a factor of about 10 or the maximum cable length would have had to have been reduced to a few feet. Besides, who that is using gig-E would still be using hubs?

 

[bluewhaleCA]

cool. Thanks. I thought it was fairly simple if we could find someone who's read the @##! manual.

<g>

 

[ttming]

CSMA/CD applies to shared media, how to access the shared media by multiple users? Hub is a sharing device thus CSMA/CD applies.

Switch is an one to one device which you do not have to share the media with another client, so CSMA/CD does not applied and there is no multiple access by many users, it will operate at full duplex. 10BaseT can be full duplex if you use switch, no CSMA/CD, half duplex if you use hub and CSMA/CD will applied.

Alternatively think that if you have a phone and need to share (hub) with many users, only one can use it a time, CSMA/CD will detemine only one of the many users can use the line a time.

If it is a private line (switch) and there is no need to share with others, CSMA/CD does not applied.

1Gbps switch is the predominate device in the market, 1Gbps hub?

100 Mbps hubs are less common today as the price of switches have fallen sharply.

Market demands will detemine the implementation of CSMA/CD, hub or switch?

 

[svermill]

bluewhaleCA,

I owe you a clarification. Gig-e maintained a capability to operate in half-duplex (although, as was pointed out above, market conditions probably don't support Gig-e half-duplex). This was achieved through carrier extention. The minumum frame size is still the same, except that if a frame of less than 4096 bits needs to be sent, the transmitters chipset adds padding onto the end. This is only done on the first frame if several small frames are to be sent.

10 Gig-e has terminated support for half-duplex altogether. It was initially designed for fiber only, which is pretty much a full duplex environment (I know, I know, fiber signals *can* be split by a hub but that wasn't what the Gig-e folks had in mind). It's a dedicated full-duplex technology.

Sorry for the original sloppy response. Had some cobwebs to clear apparently.