1 nJ/bit sus routing capacity. (After Tuker, R., Modeling energy consumption of IP networks, European Conference on Optical Communications (ECOC 2008) Symposium, September 21-25, 1 Mbit/s 1 Gbit/s 1 Tbit/s 1 Pbit/s 2008, Brussels, Belgium.) Core router throughtput 100 nJ/bit FIGURE 7.29 10 nJ/bit Historical trend of the energy needed to 1 nJ/bit route a bit in a core routers versus the router capacity. (After Tuker, R., Modeling energy consumption of IP networks, European Conference on Optical Communications (ECOC 2008) Symposium, September 21-25, 1 Mbit/s 1 Gbit/s 1 Tbit/s 1 Pbit/s 2008, Brussels, Belgium.) Core router throughput Switching Systems: Architecture and Performances transparent OXCs and routers seem farer and farer the promise of a drastic reduction of the power consumption while the capacity has a further increase is sufficient to justify quite an intense activity in this field. We will review the results on transparent OTN and on optical packet switching in Chapter 10. 7.6.4.1 Services As we previously mentioned the router, besides its main forwarding function, assures a set of other services, like packet filtering and firewall. These services have to be carried out at an extremely fast speed in a core router, and all has to be designed having in mind these characteristics. 7.6.5 Availability The amount of traffic a core switching machine manages causes a failure of the equipment to impact dramatically the network. For this reason, these machines have to be character- ized by a very high availability degree that is reached by hardware duplication and soft- ware modular design. Almost always the switch fabric is completely redundant and works either in hot standby, or (in case of packet switching) in load sharing. In the first case, the traffic is constantly sent to both the switch fabrics and only the receiving line card selects the data coming from one of them. In the case of failure, every line card switches very rapidly on the data coming from the second fabric with SO small a delay that the rou