y to gauge an estimate of the number of realistic sessions expected at each end of the hardware offering spectrum. In the case of offloading TCP or even the entire iSCSI work, such as Alacritech's Session Layer Interface Card (SLICTM) products (www.alacritech.com), performance constraints must be consid- ered. Alacritech took an interesting approach: The whole protocol stack is collapsed and then state- fully processed in an optimized fashion in order to decrease network latency and increase data throughput. The word statefully means that the silicon-based engine on the adapter (or as a coproces- sor) simultaneously inspects and processes data structures that are traditionally handled sequentially and at different layers. Other TOE approaches offload TCP/IP, but process each layer of the protocol stack sequentially. In addition to this processing acceleration (hence the name accelerator for the company's prod- ucts), the SLIC approach does not keep multiple copies of data. It also distinguishes itself by two important architectural factors: it uses hardware direct memory access (DMA) to access memory buffers on the host system while transferring data to or from adapter memory, and it minimizes the interrupt load on the host. Traditional NIC cards using interrupt aggregation techniques have to inter- rupt the host CPU on which TCP/IP has traditionally been running with every packet or series of pack- ets that require it. The SLIC approach is iSCSI sensitive SO it interrupts the host CPU only boundaries of iSCSI commands, just like an HBA would do. Alacritech server and storage accelera- tors based on the SLIC technology support the IEEE 802.3ad Link Aggregation protocol and Cisco Systems' Fast EtherChannel and Gigabit EtherChannel protocol for failover and link aggregation. Contrary to the approach several network-processor vendors have been taking, efficient implemen- tation of the solution to this problem is not just a question of taking the TCP protocol, breaking it arbi- trarily or to one's best guess into com