 also manages the autonegotiation process by which the NIC (network interface) communicates with the network to determine the network speed (10,100 or 1,000Mbps) and mode of operation (half duplex or full duplex). Physical medium attachment (PMA): This sublayer provides a medium-independent means for the PCS to support various serial bit-oriented physical media. This layer serializes code groups for transmission and deserializes bits received from the medium into code groups. Physical medium dependent (PMD): This sublayer maps the physical medium to the PCS. This layer defines the physical layer signaling used for various media. The MDI (medium-dependent interface), which is a part of PMD, is the actual physical layer interface. The XAUI comprises X 3.125 Gbit/s physical lanes with each using the 8B/10B [53] coding scheme and in order to handle the potential de-skew between the four lanes a new 8B/10B control word [A] was introduced. The [A] control word is periodically inserted, at exactly the same time, into each XAUI stream. In the receiving direction, the [As] are detected and used as alignment markers to resynchronize the four XAUI lanes. The fact that this type of interface is foreseen to be used in large volumes in any type of 10 GbE application is an important element in favor of its choice. 7.5.2 Platform Volume Value It is clear that the cost of a platform based on standard cooling and backplanes is not equal to the cost of a platform based on high-performance cooling and a very high-speed backplane. This fact has an important impact on the cost of switching network equipment, but also has an impact on architectural choices. In order to represent the aforementioned difference and to divide different factors con- tributing to it, the concept of "platform utilization cost" can be introduced. The idea is to underline the fact that when a card is plugged into an equipment to be used, not only it is necessary to pay the cost of the card, but also the cost of a certain percentage of the plat- form that is nee