If an Ethernet device receives a damaged frame, it silently discards it. That is true. But a half-duplex Ethernet sender knows when a collision occurs with a frame that is sending and retransmits. That's the CD part of CSMA/CD.
If a frame got damaged for some other reason, say noise or crosstalk or whatever, the Ethernet sender wouldn't know, however. Very few protocols have any sort of method for explicitly telling a sender that a packet got damaged. The sender simply figures out that a frame got lost because it never gets ACKed. This usually happens at an upper layer, such as TCP. There are some exceptions to this implicit behavior. LLC2 and LAPB have an explicit REJ and FRMR, for example. LLC2 is usually end-to-end, but it can be router-to-router in DLSW+, for example. And, then there's BISYNC. It has a NAK and a WAK! Priscilla At 12:11 AM 5/7/02, Michael L. Williams wrote: >I agree with you.... transparent bridges are just that, transparent. Any >retransmittal of corrupt or lost frames would need to be done by the end >station.... AFAIK, (with ethernet) even if a device receives a corrupt >frame, at layer 2, it simply discards it.... it doesn't "request >retransmittal" as that is left to higher protocols to correct. > >Mike W. > >"Kaminski, Shawn G" wrote in message >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > I've always known routers to "route" and bridges to "learn, filter, >forward, > > and flood". A co-worker said that if a router is configured with >transparent > > bridging, it can re-transmit a frame. He said that he heard this >somewhere. > > I'm pretty sure he's wrong because this just isn't something that a > > router/bridge is meant to do. I also searched CCO but came up >empty-handed. > > > > For example, say you have two segments connected to a router; one segment > > off of e0 and one segment off of e1. If a host on the e0 segment sends a > > frame to a host on the e1 segment and a collision occurs on the e1 segment > > before reaching the destination host, then I believe that the host on e0 >is > > responsible for re-transmitting the frame, not the router/bridge. > > > > Has anyone heard of a router configured with transparent bridging > > re-transmitting frames? I just can't see how this could happen. However, > > I've seen stranger things happen, so I just wanted to get the opinions of > > others on this group. > > > > Shawn K. ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=43468&t=43459 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
