eader must imagine the same process in a context where hundreds, if not thousands, of simultaneous and independent ses- sions are sustained. Implementing the TCP protocol traditionally meant that software engineers would 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. STORAGE NETWORK PROCESSORS (SNPS) STORAGE NETWORK PROCESSORS (SNPs) 207 e.g. File transfer Application layer Presentation layer Session layer Transport Layer Offload Engine Network layer Ethernet frame Data link layer CAT5 cable or optical fiber Physical layer FIGURE 11.4 TCP termination engines assume the burden of running the TCP portion of the protocol offloading a significant weight from the host CPU. create a lookup table where the session-related data for each active session is kept. However, this is good for simple software implementations on low-bandwidth devices such as a PC where a user will not have thousands of long-lived TCP sessions going on at the same time. Compared to this realm, the SNP requirements are radically different. If the same traditional imple- mentation approach is to be followed here, gigantic lookup tables will be required because multiple lookup operations occur per second for each session. Therefore, the multiplicative effect of traffic means that for thousands of sessions, hundreds, if not millions, of lookup operations per second must be performed. As a result, the following items of a TOE solution will be significant: The physical size Speed Power consumption Reliability (as multiple components will fail more frequently than a single highly integrated one for different reasons, including heat emitted by other components) If the TCP implementation does not radically change, an inefficient board-level product will have to be used. Of course, this does not mean that all boards are inefficient. The distinction is made more along the direction of 