designer first considers a shelf with 12 slots. The designer starts doing a back-of-the-envelope calculation of what is needed. Slot 1 will be dedicated to the system host CPU card. Two half-size cards are needed for carrier- quality redundancy. Slot 2 will be the initial switch fabric card. Our designer first thinks of the 40 Gbps environment and will consider the 640 Gbps (or Tbps) realm later in a variation of the design. The initial con- cept will be based on the two PI-40SAX cards, which are half-size cards and can therefore be inserted into the same slot. Again two cards of each are needed for redundancy. Slots 3 and 4 will be occupied by two (for redundancy) full-size 10 GbE cards for the uplink con- nection to the server. Slots 5 and 6 will be dedicated to two double OC-48c cards for the ATM/POS connections. Slots 7 and 8 will each be devoted to two half-size cards. Each card will offer four 1 GbE connec- tions for a total of eight 1 GbE ports per slot and for redundancy per shelf 16X1 GbE connections. This leaves slots 9 to 12 free for the moment. If necessary, the designer should expect to expand onto a new shelf. We can consider using a frame-relay card or a TDM card as our system grows. Enough room is available to position a multiple-card switch fabric solution that expands the available bandwidth within one or even more than one shelf. The chassis will end up being quite overloaded SO power per square foot will be an issue. Our designer thinks about two system-cooling choices: an upper fan tray on top that sucks the heat away from the space between the cards or a lower fan tray that blows the air away from the boards. He or she sighs with temporary relief. Not a hurdle yet. The designer's attention turns now to the cards. First, the 4X1.25 GbE card must be able to pro- vide connections occurring over copper or fiber optics. Both this card and the TADM line card (more about it here below) will interface with the OC-48 card using either the Gigabit Media Independent Interface (GMII) or the System Packe