tocol- independent format. It is characterized by a 6-byte header, a payload between 1 and 56 bytes (usually 64 bytes long), and a 2-byte trailer. The CFrame is supported by most commercially available switch fabrics. It is an interesting concept as it supports in-band flow control both per I/O port and per class per destination. On the other hand, the NPF Streaming Interface (NPF-SI) is not based on the CFrame and its flow control is structured as an out-of-band scheme instead. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. SWITCH FABRICS SWITCH FABRICS multiprocessor units that can handle thousands of packet transfers simultaneously and over parallel paths using different techniques for the actual transfer between inputs and outputs. Traffic from input buffers is scheduled according to specific criteria and then transferred over the fabric core. Output buffers temporarily store data after the switching operation occurs and until any potential congestion at an egress port has been successfully resolved. At the egress ports, some sort of scheduler is often needed again to supervise buffering and arbitrate access to the line-card resources. Except for some fundamental definitions, we do not intend to expand on details over circuit switching, as network-pro- cessing technology is predominantly tuned to the packet-switching realm. All these concepts are cov- ered in fundamental textbooks on the subject (see, for example, footnote 12). A time-slot interchanger (TSI) is the basis of time-division switching. It reads a sequence of sam- ples, which usually arrive in parallel from multiple ports, serializes them, and then reorders them into a new serialized sequence. If the input sequence is labeled 1, 2, 3, 4 or A-B-C-D as consecutive slots in a TDM system, then a TSI could rearrange them into new sequences as B-D-A-C or 2, 4, 1, 3 among multiple 