We currently have 2 sites seperated by about 4 miles. Currently the two sites are connected over ATM. The physical layer is single mode point-to-point fiber; I.E. the actual fiber run is direct from one site to another site. The current DB loss reported by the TDR is -27DB. Currently this is working very well.
However, when we try to convert over to GigE the link will not come up. The Link LED will not turn green nor is there any connection. We have tested these and other modules and proved to be good. All equipment is Cisco 6500 and 4000, down to the Gbics SX / LH. We are using SM fiber end-to-end. Our team tends to think it's the DB loss. Any thoughts? Any URLs? Thanks.
This url <http://www.cisco.com/warp/public/534/21.html> documents our optical power budgets so is a good start. At -27dB you have a lot of loss for that distance and don't have the buget for LH or SX interfaces so I would suggest a ZX or CWDM interface (these have roughly 30dB of budget).