Tiene pinta de que el windows domain no esta negociando el manejo de los protocolos, para optimizar la transmision de datos.
--- http://www.psc.edu/networking/projects/tcptune/ ---
Tuning TCP for Mac OS X
Mac OS X has a single sysctl parameter, kern.ipc.maxsockbuf, to set the maximum combined buffer size for both sides of a TCP (or other) socket. In general, it can be set to at least twice the BDP. E.g:
sysctl -w kern.ipc.maxsockbuf=8000000
The default send and receive buffer sizes can be set using the following sysctl variables:
sysctl -w net.inet.tcp.sendspace=4000000
sysctl -w net.inet.tcp.recvspace=4000000
If you would like these changes to be preserved across reboots you can edit /etc/sysctl.conf.
RFC1323 features are supported and on by default. SACK is present and enabled by defult in OS X version 10.4.6.
Although we have never tested it, there is a commercial product to tune TCP on Macintoshes. The URL is http://www.sustworks.com/products/prod_ottuner.html. I don't endorse the product they are selling (since I've never tried it). However, it is available for a free trial, and they appear to do an excellent job of describing perf-tune issues for Macs.
--- http://www.psc.edu/networking/projects/tcptune/ ---
La mejor prueba seria un windows virtual en la iMac. Si el windows anda como tejo en su cajita, entonces tu problema es que el windows domain, no sabe (o no le importa) negociar los buffers tcp/ip
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