By optical fiber transmission mode in which can be divided into single-mode and multimode. Core diameter multimode fiber 50 or 62.5+m, cladding diameter of 125+m, expressed as 50/125+m or 62.5/125+m. Single-mode fiber core diameter of 8.3+m, cladding diameter of 125+m, expressed as 8.3/125+m. A short wavelength fiber 850nm, 1310nm long wave and 1550nm. Fiber loss generally decreases with increasing wavelength, 850nm loss generally 2.5dB/km, 1.31+m loss generally 0.35dB/km, 1.55+m loss generally 0.20dB/km, which is the minimum loss of optical fiber, wavelength of 1.65+m tend to increase over the loss. Since the absorption of OH (, 900 \ 1300nm and 1340nm \ 1520nm range are loss peaks, these two areas not fully utilized.
Federal Government of the United States has built many systems based on PKI, authentication system to address the various issues between the cross-certification in 1998 proposed the concept of the bridge CA. Simply put, the Federal Bridge CA by federal policy management organizations to control, which is aimed at the credibility of the Federal PKI domains different to provide a credible path. Approved by the FPMA trusted domain can specify a primary CA, the CA is responsible for cross-certification with the Bridge CA. The establishment of the bridge CA trust to solve a different problem of information transfer between the domains, to avoid the formation of trust island.