 or modify equipment to accommodate new protocols. 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) 206 NETWORK PROCESSORS TCP TERMINATION ENGINES OR TCP-OFFLOAD ENGINES (TOES) TCP/IP was developed 20+ years ago, at a time when its designers thought layer 3 and 4 protocols would only run on host CPUs with large computational resources and network bandwidth was at premium. Many things have changed. The unprecedented proliferation of IP-based networks, the per- vasiveness of embedded computing, and the explosive growth in demand for bandwidth by SO many new generations of applications have completely reversed the computing landscape. TCP/IP is required now inside standalone devices such as a RAID system or a backup drive. The computing heart of such a system cannot be described as a host CPU in the traditional sense. Therefore, its com- putational capabilities are not up to par with a server. If a very high-speed throughput must be sus- tained and thousands of sessions with reliable transmission needs must be carried, the main processor must be offloaded from the protocol chores. To be more specific, Adaptec (in its ANA-7711 TCP/IP Offload Adapter Datasheet [see www.adaptec.com]) estimates that a typical 1 GHz Pentium-type processor saturates about 70 percent of its capacity with TCP processing, if it must support a 1 Gigabit Ethernet link at line speed. Depending on the number of simultaneous TCP sessions, this performance constraint can degrade even more. If a security protocol such as Secure Socket Layer (SSL) that runs at layer 5 above TCP must also be supported, TCP must be terminated before actual SSL work can be performed. Adaptec's estimates are much more liberal than the estimates in a 2002 Gartner Research Brief. The Gartner report describes the accepted rule of thumb as being that each bit per second 