Why a mux? I have connected four school districts that get their Internet feeds via 100-meg media converters attached to single mode fiber (out to 40km max.), which connect back to their ISP. The ISP plugs a matching media converter at their end into a Cisco 10/100 switch port, and controls/throttles bandwidth at their end. Or, monitors bandwidth utilization over 24-hour period, averages it out, and charges for usage. (Depends on the contract that was worked out.)
Are you running other services back to the ISP like voice or video? Or other data feeds? If it's just Ethernet at 10/100/1000 speed, there's a media converter out there that will probably get the job done at less cost than the mux.
We also connect to our ISP over fiber, over a 100-meg media converter. Goes into a Catalyst 3548 at our end, and an HP ProCurve L2 switch at theirs. (The HP uplinks into a Cat5500 chassis.) They monitor our utilization in case we exceed the bandwidth we're paying for (256kbps) on a regular basis, but we never do. Sure is nice to surge into the multi-mbps arena for the occasional big download, then idle along for the rest of the day.
And we have installed fiber and designed network equipment strategies for two counties, who use Ethernet switches and fiber uplinks to tie all school districts together, then share a common fat Internet pipe. One county uses a T3, I think, and Nortel switches; the other uses Cisco switches, and runs a 100-meg media converter 75km into downtown Philadelphia to tap into Internet2 with a university there.
FWIW, all the media converters discussed above are made by Transition Networks.
Hope this helps.
