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John Peters
John Peters

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Is there such a thing as "Full Duplex" in an Ethernet environment?

When we think about what CSMA really does; we have to ask this question. In an Ethernet environment with only 1 NIC card, is "Full Duplex" mode really able to send and receive at the same time?

My original thought was no, until I was reminded by @riturajborpujari below that NIC cards can operate in full duplex mode. He reminded me of crossover cables, which establish two point to point connections. In this mode CSMA is turned off.

Is there such a thing as Full Duplex in an Ethernet Environment? Yes

  • CrossOver cables are true duplex
  • Any network with switches (which work at Mac layer) establish 'logical' point to point connections
  • Routers can use both switches and or a technique named Mutipexing (Muxing)

Interesting Links:

Ever wondered about the maximum throughput of GigaBit Ehternet

Bandwidths for all known devices

Did you know, that telephone companies were charging around $2,000.00 per month for T1 service throughout the 90's? At 1.5Mb/s that's equivalent to your wireless router @ 2Mb/s for a one time fee of $99.00 (for a good one) which may last 10 years.

DS1 / T1 (and ISDN Primary Rate Interface)  1.544 Mbit/s    1990
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Oldest comments (5)

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riturajborpujari profile image
Rituraj Borpujari

I don't know if that's true though. I mean doesn't ethernet NICs have the capability to work in full-duplex mode.
How does the connections in a network switch handles connection then?

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jwp profile image
John Peters

The ability to have full duplex is point to point logically direct connections. This must be done via switches which operate on MAC address. How many MAC address does a single NIC card have?

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riturajborpujari profile image
Rituraj Borpujari • Edited

You are right. The ability to have full duplex is point to point logically direct connections.
Fortunately, NICs, which obviously has only one hardware MAC address, can have separate send and receive paths. They can use them at the same time without collision.
In half duplex, they use CSMA/CD to avoid collision. But this is unnecessary for full duplex mode.
So ethernet NICs are able to operate in full duplex mode.
However, not all medium can support this. For eg, coaxial cable cannot operate in full duplex mode, but fiber can.

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jwp profile image
John Peters • Edited

Oh yes as in crossover cable... forgot that part. New summary

  • Full Duplex must have a logically directs connection to the other side.
  • Full Duplex does not use CSMA
  • MAC addresses can send and receive at same time (e.g. CrossOver Cable) because there are two channels in twisted pair wires.

Question, when the converstion hits a series or routers across the internet, they too must maintain that point to point connection right? Do you know, how this is done? Must have something to do with multiplexing whereby each converstation is muxed into existing channels...

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riturajborpujari profile image
Rituraj Borpujari

Yes. Routers use multiplexing to handle multi connections.
For eg wifi standards 802.11a/g/n uses Orthogonal Frequency Division Multiplexing, while the newer 802.11ac uses multiple antenna and Spatial Division Multiplexing along with OFDM to achieve greater speeds.