The all-optical network should take advantage of photonic devices of various kind that above all should provide the means for all-optical signal processing. Photonic band-gap structures (PBG, photonic crystals) are expected to be very helpful for achievement of several functions that an all-optical network asks for. To this purpose many proposals have been elaborated and an intense research is still underway. In the lecture the state-of-art and potential future applications of PBG structures in optical telecommunication systems are reviewed. Special attention is paid to fiber Bragg Gratings that are special kind of photonic band-gap structures. In wavelength-division-multiplexed systems the wavelength sensitivity of PBGs and their filtering properties resulting from it are of particular interest. Possible locations of PBG-based devices within the advanced all-optical network architecture are indicated and their functional parameters are discussed. ©2001 American Institute of Physics.