se is subject to the Terms of Use as given at the website. SWITCH FABRICS SWITCH FABRICS Some designers partition parts of the overall fabric function, the scheduling, the arbitration, and especially the necessary queuing buffers at ingress and/or at egress ports in a distributed fashion such as on line cards. Alternatively, these functions can be kept centrally on the switch card. However, trade-offs are involved, such as switching performance versus power dissipation versus cost (the com- plexity of the switch fabric card and the backplane) versus the overall scalability. These trade-offs affect the overall performance. Some systems offer link redundancy through multiple fabrics (and we will discuss this later in this chapter). The use of multiple switch fabrics (in a load-sharing mode) that operate in redundancy con- necting inputs to outputs is another effective way of reducing collisions inside the switch fabric itself. However, it is obvious that in this case an appropriate review of the output buffering requirements becomes imperative, as several incoming packets now may have traversed the switch fabric and will compete potentially for the same output interface. Network equipment vendor (NEV) companies, when confronted with the maze of all these per- formance issues, were forced to design their own in-house switch fabrics in ASIC form. In addition to the effort, cost, and pressure on engineering teams, the economic reality of business life imposed unusually harsh life expectancies for switch fabrics. Enterprises typically expect their equipment to last anywhere between three and eight years. Carriers are a different market with exotic needs that include an expected life span of 5 to 20 years in addition to their already tough reliability, availabil- ity, and in-service upgradability requirements. The complexity of the task, the cost (if and when the skilled design team and infrastructure was in place, otherwise the whole issue could not even be envi- sioned as a project), and the risk of failing to deliver