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MUM Europe 2020
 
imadloo
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Joined: Wed Dec 12, 2018 9:47 pm

Port speed

Thu Jan 16, 2020 4:04 pm

My problem concerns the download speed depending on the port speed setting.
If auto-negotiation is set. The port is set up at 100Mbps Full duplex. Downloading and sending is within 95 Mbps.
However, when I turn off auto-negotiation and set rigidly 100 Mbps and Full duplex, downloading is within 50 Mbps and sending within 5 Mbps.
Tested on several models. Could there be a problem?
 
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skylark
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Re: Port speed

Thu Jan 16, 2020 4:20 pm

If you force speed at the one end, the same should be done on the other one as wel.
 
imadloo
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Re: Port speed

Fri Jan 17, 2020 7:58 pm

You're right.
Problem solved.
 
bpwl
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Re: Port speed

Sat Jan 18, 2020 11:54 pm

If you set fixed mode (no negotiation) the other end which is set to auto ,will hear no answer, and so will assume its an old half-duplex interface, and will go to half-duplex.

Setting hardcoded full duplex is only good if the other side is also set to hardcoded full duplex.
Setting hardcoded half-duplex will work with either hard coded half duplex or auto-negotiation (which will choose half-duplex)
Setting auto--negotiation will work with auto-negotiation (in full duplex) or hard coded half-duplex.(in half duplex)
Auto-Auto can miss the negotiation, and can select the wrong mode !

Having half-duplex connected to full-duplex is very bad for the performance, as the full-duplex will send a packet regardless of the incoming packet, and the half side will back off because it detects a collision.
Collision counters on the half-duplex side (Tx stats on MKT) rapidly go to extreme high values when connected to a full-duplex interface.
Some devices do not give you a clue on what mode they support.

The negotiation problem only exits in the 100 Mbps. 1Gbps is always full duplex.
 
mkx
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Re: Port speed

Sun Jan 19, 2020 11:54 am

Auto-Auto can miss the negotiation, and can select the wrong mode !

With modern devices, where autonegotiation works fine in vast majority of cases, the miss-negotiated mode likely indicate marginal cable connecting devices. Could be unprofessionally done wall outlets or patch pannels which work 99% of time, but are out of specs never the less.

The negotiation problem only exits in the 100 Mbps. 1Gbps is always full duplex.
Successful autonegotiation is, per standard, prerequisite for 1Gbps (and higher). Forced 1Gbps should not even exist.
BR,
Metod

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