ll competitive carriers that do not have and do not want to build a heavy company structure with test labs and research departments, fre- quently leave the network optimization to a specific vendor that becomes a sort of reference partner. In this case, integration of transmission and routing machines can be exploited at best. Transponders are also very important for the incumbent carri- ers providing high-speed transport wholesale services. As a matter of fact, in this case, the limit between the carrier network and the customer network is exactly the transponder, SO that if an SLA has to be respected on both parts, the carrier needs sufficient monitoring capability to assess independently the incoming signal quality. Multiplexers and demultiplexers: These devices are generally hosted in dedicated cards, even if their functionality is not as complex as the transponder one. The reason is that, while a transponder processes one or few channels, a multiplexer and a demultiplexer have to process all the channels that have to arrive from Telecommunication Networks connectors located on the card front end. Depending on the engineering choices regarding the mechanical system design, it could be even impossible to host all the needed connectors on the front of a single card. In this case, either the card is design SO to occupy more than one slot into its subrack or the mux/demux is designed as a multistage component, locating different stages in different cards. Amplifier cards: These are the cards hosting optical amplifiers with all their struc- tures, comprising pumps, filters, and SO on. Different cards generally host differ- ent amplifiers (e.g., preamplifiers or in-line amplifiers). OADM cards: These are the cards hosting OADMs with all their structure, com- prising in case, all the support needed for dynamic switching. Protection cards: If optical protection is adopted, generally optical protection switches are hosted in specific cards. 6.5.1.2 Support Cards Support cards perform functionalities that are needed to