Packet-Optical Add/Drop Multiplexer Technology: a pragmatic way to introduce optical packet switching in the next generation of metro networks

The Fibre-to-the-Home Technology (FTTH) by offering new opportunities at the subscriber side in terms of high bit rate applications, creates new capacity needs in metropolitan and backbone networks. Equipments manufacturers are then looking at new technical approaches to propose networks able to handle higher capacities than today, in a flexible way and at low cost. One existing solution to have high efficient metro ring network is to implement a full electronic Ethernet solution. At each Ethernet node, all the wavelengths are demodulated and all the traffic is processed to switch the Ethernet frames on the correct output port with no collision. One drawback of this solution is that the capacity of an Ethernet switch follows the ring capacity independently from the real required capacity coming from the client layer. The Packet-Optical Add/Drop Multiplexer (POADM) [1] has then been introduced to separate the client capacity from the ring capacity. By proposing a pass through without electronic processing for the packets in transit, only the packets that need to be dropped or added will be processed. The POADM is very close to the Reconfigurable-OADM technology. The fundamental difference is the switching granularity : packets for the POADM and wavelengths for the reconfigurable-OADM. POADM architecture description The principle of the architecture of the POADM is depicted in figure 1a. Each wavelength is carrying optical containers with a fixed time duration called optical packets, including a variety of client protocols (Ethernet frames, IP packets, ...).