SNA Server lets you connect an IBM AS/400 or mainframe to a Windows NT LAN, as you see in Figure A. The SNA Server gateway needs to support only the SNA protocol that's required to communicate with the AS/400 or mainframe host, and the PC nodes on the LAN need to support only the network transport required to connect to the network.

To make this communication between client and host happen, an SNA Server client module on each PC encapsulates the client's SNA requests in the network transport protocol and sends the network packets directly to the SNA Server system. For example, if the LAN uses the IPX/SPX protocol, the IPX packets contain the SNA requests, and if the LAN uses the TCP/IP protocol, the TCP/
IP packets contain the SNA requests. The SNA Server system pulls the packets off the network, strips the SNA requests from the packets, and routes the SNA requests to the host. The host sends SNA responses back to the SNA Server gateway, which packages them in the appropriate network transport protocol and directs the network packets to the appropriate client systems.