runt and duplex mismatch

[sarahr202]

Hi everybody.

I was reading wikipedia link which says  if we have duplex mismatch, then full duplex end will  usually register runt frame.

I understand why full dupex end will register runts frame.  But  my book  shows an example where  half duplex end  has high number of runt frame.

It does not make any sense to me. for e.g

Let say we have  host1 and host2

host1(full)--------------(half)H2

The condition which could cause h2  to increase its runt counter when it detects a collision while receiving a frame.  Since  we have only two hosts,, therefore the only possible source which could cause collision is h2.

If h2 is to cause collision while receiving the frame from h1, it must transmit a frame while receiving the frame from h1. Since h1 is half duplex therefore it can not transmit the frame while it is receiving a frame from h1. The question is then what could cause h2 to increase its runt counter?

Any input will greatly be appreciated.

thanks and have a nice weekend

[Richard Burts · Accepted solution]

In a situation with a duplex mismatch I can certainly understand seeing runts on the full duplex machine since the half duplex machine could start transmitting and detect a collision and terminate, creating a runt. I do not understand a reason why the half duplex machine would record receiving runts since I believe that the full duplex machine would complete sending any frame that it started. If your book has an example where the half duplex machine is registering runts then I believe that it is a bad example or a mistake in editing the book.

I can think of some situations where the half duplex machine might register runts:

- if there is a problem with the network (perhaps faulty media) that causes some bits to be dropped during transmission, then it might produce runts.

- if a device in the middle of the data path is operating in cut through mode it might produce runts.

But both of these are very unusual and represent more of a problem environment and not anything that relates to half duplex/full duplex.

HTH

Rick