autonegotiation and media converters

ok, trying to post with a browser is a big pain. hopefully you can make out that the diagram shows switch1 connected via twisted pair to MC1, which is connected via fiber to MC2 which is connected via twisted pair to switch2.

Mark, My limited experince says Murphy will stick his head in there. We had varying results (Allied Telesyn) where sometimes the auto negotiation would work, sometimes not. And we're talking about the same pair of machines, one restart they negotiated properly, the next it didn't. Allied makes a converter for the 100 meg that is basically a 2 port switch - that type of converter does fairly well. If it's a fiber switch feeding a convert to a copper host/switch, the negotiation generally works. The configuration you ask for is ususally begging for the settings to be forced at the swtiches.

Jay Drew

This is exactly my question. Jay's yielding to Murphy aside, if the immediately adjacent converter is not autonegotiating, isn't it true that the autonegotiation would then happen with the remote switch? Autonegotiation consists of sending a 16-bit link code word adverstising capabilities. I'm assuming, and have some empirical evidence confirming, that if the adjacent converter isn't autonegotiating, it is going to just pass the link code word on, making its way to the remote switch.

One possible problem, which may have to do with Jay's observations, is that if the remote converter is set to autonegotiate, the remote switch will be receiving link code words from the near switch *and* the remote converter. Worse, the link code words sent by the remote switch will be consumed by the remote converter, leaving the near switch to assume the neighbor isn't autonegotiating (which ends up being true).

thanks for the responses, mb

As there is no autonegotiation defined on a 100BaseFX any possible negotiation is local to the switch and its adjacent converter. If the switches are mangeable and are set to a fixed configuration everething is fine. To be usefull with autonegotiating-only switches as well todays mdiaconverters negotitiate full-duplex unconditionally. This way the configurations kids tend to have at home will work automagically. On the other hand, awkward onfigurations like a n-way switch to a fast ethernet hub will not work at all using such gear.

No. The code word cannot make it to the other side as there is no FLP defined on fiber.

The autonegotiation is independent of the fiber side and soley a matter of the hardware configuration of the MC. There may be difficulties with link establishment (oszillations) due to "missing link" features and/or auto-mdix specially if the capaciators in the MC start to degrade.