Solution:

Fiber Optic laser connectors fall into two categories: Angle Polished Connectors (APC) and Ultra Polished Connectors (UPC). The major physical difference between the two is the end-face geometry; the APC ferrule end-face is polished at an 8° angle, while the UPC is polished at a 0° angle. The APC 8° becomes significant when considering return loss issues. UPC connectors have been historically implemented on Ethernet network equipment, such as media converters, serial devices and fiber-based switches. APC connectors are usually implemented for FTTX and PON, the “triple play” to multiple customers, and ISPs increasingly use APC. B&B Electronics uses UPC connectors. Also, please note that it is not possible to connect UPC to APC.