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100 mb only transfering only 10%efficent

By JOE.HUTCHINSON1 ·
i am wonderin if the is an overhead issue as to why i can only get about 10-12% effienecy out of a connection when both cards are 100mb and it is a x over cable between them i seem to get the same from my 1MB BB connecitons were my max download speed is 115k. just wondering as i would have thought that as this is a full duplex transfer between my 2 pc's this should be faster

any info would be gratefuly accepted

joe

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by Oldefar In reply to 100 mb only transfering o ...

I am not sure how you are determining your efficiency but let me try to clear up some misconceptions.

First off is the advantage of full versus half duplex. If you are running two machines and one session then their communication will be like a conversation. One talks, the other responds. The responses are typically based on what the other said, so you get minimum gain from full duplex. Each end has to make sure the other has buffer space for the packet being sent to prevent overruns and retransmissions.

Next you have the processing from application down the protocol stack to the NIC and then out the wire, and back up from the other side. The last bench mark I saw for essentially a data transfer (FTP) maxed out at 40% (40 Mbps) in a setup like yours. That was a couple of years ago, but I haven't noticed any major changes that would improve on this dramatically. In short, at 10 Mbps the transfer was waiting on the wire, but at 100 Mbps the wire is doing the waiting.

Other issues include packet size. A simple response in TCP is 50% overhead. A full size ethernet packet is about .1% overhead. Large packets are the preferred way to go. However, some applications were designed for older and less reliable circuits. These put an MTU cap at about 500 bytes to reduce the size of retransmissions. Other protocols have their own overheads to account for, and encapsulation adds to the overheads. MTU adjustments may be necessary at serveral points to get optimize the data transfer.

Even on 10 Mbps half duplex LANs, most application tasks only spend 10% of the total time in data transfer. The rest is in processing at either end. This analysis was done with scripted keystrokes to eliminate user performance variables.

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by Chris910 In reply to 100 mb only transfering o ...

Are you sure that your crossover cable is good?

Just as a reference I use ghost to restore workstations and move Images that are about 3.5GB (after compression)from my laptop to the desktop in about 16 Min. useing a crossover cable.

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