We typically have multimode fiber runs across our very small college campus. We are buliding a new building that is far enough away that we need to run a single mode fiber to tie the new building to the backbone. I will be deploying the Cisco 3750 switch using GLC-SX-MM SFP's. I am assuming the Cisco 3750 will handle the single mode but what SFP's are recommended? I see that my options are a GLC-LH-SM and GLC-ZX-SM. Is the difference simply the reach (10km verse 70km)?