Difference between Half-duplex and Full-duplex throughput

Posted on 2004-04-12
Last Modified: 2008-02-01

This may be a simple networking question but no one I've asked seems to have a concrete answer. My question is what is the difference in throughput between a half and a full duplex connection, i.e. if I have a 10Mb connection am I really getting 5Mb in a half-duplex, is one slower than the other or is this comparing apples and oranges? Thanks.
Question by:cuba_joe
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Expert Comment

by:Pete Long
ID: 10804942
Thin of data like a voice conversation............

half duplex is like CB Radio data can only go in one direction at any time

full duplex is like telephone, data can go in both directions at once
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Expert Comment

by:Gareth Gudger
ID: 10804943
No you can get 10MB in half duplex.

10MB is the speed or bandwidth of the connection.

Duplex mere means whether of not you can send and listen. Or send and receive at the same time.

Full Duplex - send and receive at the same time (like using a phone)
Half Duplex - only one can send at a time (like a CB radio)
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Expert Comment

by:Gareth Gudger
ID: 10804946
Wow...Pete we posted at the same time and gave the same gosh darn analogy.....seems like us old folk are partial to out CB radios :)
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Expert Comment

by:Pete Long
ID: 10804976
ROFL - its the best analogy there is, and the one I always use when the question comes up :)
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Expert Comment

by:Gareth Gudger
ID: 10805003
Aye, that be right.

Now for some reason I am thinking of that evil trucker movie and the traumatic CB chatter....."Candy cane...where's my caaaandy-caane."
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Expert Comment

by:Pete Long
ID: 10805139
:) Yeah I've seen that one :)
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Expert Comment

by:Gareth Gudger
ID: 10805184
Dont mind us cuba_joe, we are just overtaking your thread talking about CB radios, truckers and horror movies.


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Accepted Solution

lrmoore earned 50 total points
ID: 10805538
I like to show the math.
On a half-duplex connection, because of the inevitable collisions and the collision detect/avoidance mechanisms built into Ethernet, the maximum practical bandwidth consumption is ~ 60% of the total bandwidth. This is, of course, dependent on the total number of users sharing that 10Mb.
For example, if you have 10 hosts all connected to a 10Mb HUB (all half-duplex), then all 10 users only get a portion of the 10Mb, reduced down to effective 6Mb, or .6Mb per host.
If that 10Mb HUB was replaced by a 10Mb SWITCH where each port is full-duplex, then you would have full, dedicated, 10Mb to each and every host. And, since it is full-duplex, you can send 10Mb and receive 10Mb at the same time, therfore your throughput is now 20Mb.
So the difference between half-duplex @ .6Mb and full-duplex @ 20Mb throughput is significant.


Author Comment

ID: 10805900
Thanks lrmoore. Although the answers above were good, I know the difference in concepts between half and full duplex, but you provided the practical aspect of how the network traffic is adversely affected, which is exactly what I was looking for. Thanks again.

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