reduced. This is why ASICs have such a big success in the line cards of large switching machines. These are quite complex subsystems, including a large processing capacity besides the physical interface with the transmission systems and besides memories, and all that is needed to complement a fast dedicated processor. In Chapter 7 we will see that complex operations in a switching machine are carried out directly in the line card, such as QoS management. Telecommunication Networks Concentrating a large number of functionalities in a single ASIC is in these cases a key tool to ease the design and maintain, despite the complexity, high performances. The development and manufacture of an ASIC design including the ASIC layout is a very expensive process. In order to reduce the costs, there are different levels of customiza- tion that can be used. These can enable costs to be reduced for designs where large levels of customization of the ASIC are not required. Essentially there are three levels of ASIC that can be used [54]: 1. Gate array: This type of ASIC is the least customizable. Here the silicon layers are standard but the metallization layers allowing the interconnections between dif- ferent areas on the chip are customizable. This type of ASIC is ideal where a large number of standard functions are required which can be connected in a particular manner to meet the given requirement. 2. Standard cell: For this type of ASIC, the mask is a custom design, but the silicon is made up from library components. This gives a high degree of flexibility, pro- vided that standard functions are able to meet the requirements. 3. Full custom design: This type of ASIC is the most flexible because it involves the design of the ASIC down to transistor level. The ASIC layout can be tailored to the exact requirements of the circuit. While it gives the highest degree of flexibility, the costs are much higher and it takes much longer to develop. The risks are also higher as the whole design is untested and not built up from library e