Nowadays, reconfigurable optical add/drop multiplexers (ROADMs) are mainly based on broadcast and select (B&S) and route and select (R&S) architectures. Moreover, the most used components to implement the colorless, directionless and contentionless (CDC) ROADM add/drop structures are the multicast switches (MCSs) and the wavelength selective switches (WSSs). In-band crosstalk, amplified spontaneous emission (ASE) noise accumulation and optical filtering are physical layer impairments (PLIs) that become more enhanced in a CDC ROADM cascade. In this work, we investigate the impact of these PLIs in a cascade of CDC ROADMs based on both B&S and R&S architectures, with MCSs and WSSs-based add/drop structures and for nonreturn-to-zero (NRZ) and Nyquist pulse shaped signals. We show that the optical filtering impairment is more limiting for a
R&S architecture. We also show that the ASE noise accumulation after 32 cascaded ROADMs leads to a 10
dB optical signal-to-noise ratio (OSNR) penalty. Finally, we conclude that the in-band crosstalk introduced in CDC ROADMs based on B&S is more harmful than with a R&S architecture. An OSNR penalty of 1 dB due to in-band crosstalk, is reached after 13 and 24 cascaded 16-degree CDC OADMs for, respectively, NRZ and Nyquist pulse shaped signals.