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What Causes Defered Transmits?

Chad Kasper
Occasional Advisor

What Causes Defered Transmits?

I have a 4104gl at G_07_93. I have a few 10/100 and 10/1000 ports that have registered more than a few "Defered TX".

For Example
Bytes Rx: 23,682,034
Bytes Tx: 251,146,516
Defered Tx: 892

I have some ports that just show defered Tx in a high thousand range. Is it a port speed mismatch meaning a gigabit port is cramming down a 100Mb ports throat? I have almost all of my ports set to auto along with the clients set to auto. Port status confirms full speeds for all connected devices. Shouldn't Flow Control take care of this?

Thanks,
Chad
4 REPLIES
Matt Hobbs
Honored Contributor

Re: What Causes Defered Transmits?

I believe that you should only see Deferred TX's on half-duplex links. They occur when the device goes to send a frame, but sees that there is already activity on the wire and therefore has to defer the transmission until the wire becomes available.

I'd start by focusing on the ports that are seeing Deferred TX's incrementing the most, double check their speed/duplex settings on both ends (auto is preferred) and cabling.

Chad Kasper
Occasional Advisor

Re: What Causes Defered Transmits?

Thank you for the reply, Matt. Does this suggest a congested switch necessarily, or just a congested port?
Matt Hobbs
Honored Contributor

Re: What Causes Defered Transmits?

It would be more just the port itself is busy with traffic. If it is running at half duplex you will probably be seeing a fair amount of collisions on that same port too.
Ralph Bean_2
Trusted Contributor

Re: What Causes Defered Transmits?

Chad -

The numbers you presented do not necessarily indicate a problem.

A certain number of deferrals or collisions are normal on a half-duplex link. These are not "unexpected" Ethernet errors.

On the other hand, "unexpected" Ethernet errors include excessive deferrals, late collisions, excessive collisions, and a few others (which are specific to specific Ethernet techologies/speeds), and are worth worrying about.

Do you have reason to believe that there is a performance problem with the ports in question?

Ralph