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Old 18-01-2007, 03:05 PM   #1
Icewolf
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Situation is this:
In a GigaBit-LAN there are some PC that only have 10/100-network-cards.
These cards can handle full-duplex-mode.

Question:
When a network-card runs full duplex, doesn't that mean it trasfers twice the non-duplex capacity?!
So a 10/100 card transmits 200MBit/sec?

I'm very thankful for every answer you can give me!
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Old 18-01-2007, 03:07 PM   #2
The Fifth Horseman
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I don't think it would. Besides, PCI bus would be a major bottleneck for that anyway.
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Old 19-01-2007, 04:55 AM   #3
carpetsmoker
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no, if you have a 100mbit card then this is 100mbit full-duplex.
If you run half-duplex then you have 50mbit.

Note that this are theoretical speeds, You will never achieve 100mbit, this is because of extra meta-data (mainly headers) added by various protocols in the network layers.

Also note that half-duplex will always be less than half the speed of full duplex, this is because your NIC's will have to wait until the line is clear (turnaround time).

Quote:
I don't think it would. Besides, PCI bus would be a major bottleneck for that anyway.[/b]
PCI 33MHz has a theoretical speed if 133MB/s per second, which is way faster than 100Mbit, and even 1Gigabit.
If I remember correctly most computers nowadays have either PCI2 (66MHz) or PCI2.3 (100MHz), which are even faster.

Quote:
doesn't that mean it transfers twice the non-duplex capacity[/b]
Infinitely faster, since non-duplex is 0mbit/sec

You can either have:
simplex - one way traffic, for example your TV
half-duplex - two-way traffic, one machine sends, other receives, can't send and receive at the same time.
full duplex - both machines can send and receive at the same time.
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Old 19-01-2007, 07:46 AM   #4
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<div class='quotetop'>QUOTE(carpetsmoker @ Jan 19 2007, 06:55 AM) [snapback]275603[/snapback]</div>
Quote:
PCI 33MHz has a theoretical speed if 133MB/s per second, which is way faster than 100Mbit, and even 1Gigabit.
If I remember correctly most computers nowadays have either PCI2 (66MHz) or PCI2.3 (100MHz), which are even faster.[/b]
Yep, that's what I read, too.
Quote:
<div class='quotetop'>QUOTE
Quote:
doesn't that mean it transfers twice the non-duplex capacity[/b]
Infinitely faster, since non-duplex is 0mbit/sec [/b][/quote]I meant not using the duplex mode, so that would've been... err... simplex? :blink:
Quote:
Originally posted by carpetsmoker
full duplex - both machines can send and receive at the same time.
So it's just the way they're communicating, not the transferring speed...

Ah, I got it! :w00t:
Thanks! k:
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Old 19-01-2007, 10:38 AM   #5
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Quote:
So it's just the way they're communicating, not the transferring speed...[/b]
yes, it is the way they are communicating.
This DOES affect your transfer speed (among other things of course).

Simplex is one way traffic, you can either only receive data, or only send data.
An example is Cable TV, you can receive data and watch TV, but you can't send data back to the network.
On the other side the network (let's say ZDF) can only send data to you, ZDF can't receive data from your TV.
Note: I am aware that there is digital television, but I think you get my point.
Using a 100Mbit NIC, your network speed would be ~95mbit (but only one way!)

You can more or less forget this method of communication where computers are concerned, it's practically never used.

(funny story: a friend of me broke his CAT5 cable, the idiot just knotted all four wires into one big knot, amazingly he still had internet! it was very slow tough ....3Com NIC's are the best! its transparently switched to simplex!)

Half-Duplex provides communication in both directions, you can send and receive data, but not simultaneously!
So, if I'm sending data to you, you have to wait until I've finished sending data before you can send a reply, and vice versa.
An example is radio (walkie-talkie's), if more than two people talk at the same time you'll get only static.

Again, this isn't used allot in computers nowadays, some peripherals use it (bluetooth, certain Parallel cable devices)

Using a 100Mbit NIC, your network speed would be ~45Mbit avarage.
You are able to send of data at ~100Mbit speeds, and recieve it at ~100Mbit to, but because of all the waiting the average speed will be about ~45Mbit.

Full duplex means that both computers can send and receive data at the same time, they don't have to wait for each other to finish.
This is what you're probably using, and how most of today's networks use.
Using a 100Mbit NIC, your network speed would be ~100Mbit

Half-Duplex is always slower, since only one computer can send at the same time, you might want to compare it to talking:
I say something for 5 seconds, and after I'm finished you say something for 3 seconds, total talking time: 8 seconds. (This would be "half-duplex")

Now we both start talking at the same time, we'll be finished sooner because we don't have to wait for each other (total time is now 5 seconds), this would be full-duplex.

And if I would do all the talking and you wouldn't say anything we would be communicating in simplex

Also, the receiving computer will have to wait until they're sure that the sending computer stopped sending data, which will slow these even further down (This is called turnaround time)
You can compare this to your reaction time in the talking example above.

On Unix-like systems (linux, BSDs, solaris) you can view your connection type with ifconfig
Example (bold line, ignore the SIMPLEX in flags):
Quote:
# ifconfig -a
xl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
options=9<RXCSUM,VLAN_MTU>
inet 192.168.100.13 netmask 0xffffff00 broadcast 192.168.100.255
ether 00:04:75:f3:b0:64
media: Ethernet autoselect (100baseTX <full-duplex>)
status: active[/b]
I have no idea how to look this up in Windows (ipconfig /a perhaps....?)

If you're really interested in data communication, then you might want to consider buying the TCP/IP bible, a very good book which covers all the important subjects!
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Old 19-01-2007, 11:58 AM   #6
Icewolf
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Wow! :w00t:
Thanks a lot for that thorough information!!!!!1111 k:
for your knowledge! (or your knowledge-bases... )
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Old 19-01-2007, 07:41 PM   #7
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Wow all this information is stuff I never knew existed I never thought networking was this complex.
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Old 19-01-2007, 08:13 PM   #8
carpetsmoker
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hm?
The TCP/IP bible, which deals with most, but not all, networking issues is ~500 pages...

Anyway, your welcome Icewolf, if you have any questions, then by all means ask them!
You probably know the proverb:
The only stupid question is the question that is never asked.
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Old 22-01-2007, 09:45 AM   #9
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Yeah, thanks I will. k:

I know it like: There are no stupid questions. There's only stupid answers.
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Old 25-01-2007, 12:41 AM   #10
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<div class='quotetop'>QUOTE(Icewolf @ Jan 22 2007, 11:45 AM) [snapback]275931[/snapback]</div>
Quote:
I know it like: There are no stupid questions. There's only stupid answers.
[/b]
Correction: There are no stupid questions. There's only stupid persons. :wallbash:
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