Ascend Archive
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: (ASCEND) max6k 100Mb FD?


> > > > Does anyone know offhand if any special configuration is required to
> > > > get a MAX 6000 into 100Mb full duplex mode?  Yes, the MAX is going
> > > > into a 100Mb switch that can do full duplex.  
> > > 
> > > Is that a good idea anyway? My understanding is that FDX Ethernet 
> > > can actually DECREASE performance on very busy wires from excessive 
> > > collisions, retries, and lost packets.
> 
> > Huh??  That's the point of full-duplex, eliminate collisions.
> 
> I thought I remembered reading something about that in the Novell 
> list...Here's the message:
> 
> /** begin quoted message **/
> Subject:      Re: ....full duplex servers....
> From:         Joe Doupnik <JRD@CC.USU.EDU>
> 
>   We've discussed this at length previously, but here again is        
> the obvious. How does a transmitter know when to shutup because a 
> wire is busy? FDX lacks the feedback to tell it. Frames will be lost, 
> "the network is slow" phone calls happen.
>   Switches/routers in series between transmitter and receiver        
> can buffer some frames, but only some and you don't know how many 
> (because some are in use from other traffic).
>   FDX does not double throughput, in can markedly reduce        
> throughput (because of lost frames). Unless you can demonstrate no 
> problems and a strong need then turn it off.
>         Joe D.
> /** end quoted message **/

This makes no sense at all. TP Ethernet has separate transmit and receive 
wires. Lets say you have a fully switched network and Computer A is 
sending a file to the server while Computer B is receiving one. Where is 
the contention? Where are the lost frames? If A & B were on the same 
segment and that segment was half duplex, yeah, I can see where collisions 
would be a problem. I think it depends on the topology and traffic 
patterns (content) of your network on whether full duplex can help.

With switches priced as low as they are, I just use them instead of hubs 
(except for some incredibly slow devices such as printers, terminal 
servers, etc.) That way I can have a wide mix of 10 / 100 Half and full 
duplex devices and no problems. I monitor my traffic and even under fairly 
heavy loads I don't see many collisions or lost frames.

++ Ascend Users Mailing List ++
To unsubscribe:	send unsubscribe to ascend-users-request@bungi.com
To get FAQ'd:	<http://www.nealis.net/ascend/faq>
Follow-Ups: References: