payload Packets synchronizers (in the realistic case of asynchronous transmission) Moreover, even if OTDM is not necessary for an optical packet switching, it is really com- plementary, creating very-high-speed TDM streams that would be very difficult to man- age with electronic systems. In the following section, we will review part of the research activity on these compo- nents, while in the sections following thereafter, we will discuss both a few optical packet network architectures and the way in which a potential optical packet layer can be inte- grated into the whole network. 10.4.1 Transparent Optical Packet Network Enabling Technologies 10.4.1.1 Optical Memories This is a key component if a packet switch has to be realized. To better clarify the possible optical technologies to realize a memory, we can distinguish two types of memories: 1. Memories whose scope is to delay the signal for a given time, and in some cases, to maintain the order of the incoming signals while delaying them 2. Memories that store the data carried out by the signal and make the access pos- sible to any part of the data at any moment One example of memories of the first type is the First In First Out queue, which is realized SO that a signal entering the first cell has to travel through all the cells to exit from the last. The most important example of the second type is the random access memory (RAM). A simpler example of the first type of optical memory is a linear amplified ring, as shown in Figure 10.37. This is simply a large ring where the signal is inserted through a directional coupler that also has the role of point of extraction. Along the ring, a low-gain SOA compensates part of the loss of the ring (comprises those due to the passage into the coupler) and a switch has the role of closing and opening the memory. The scheme is simple, but it is easy to notice that if we want the single passage loss to be small, the ring design has to be carried out with particular care SO to avoid lasing of the structure. If the design o