A Windows NT domain can contain one or more SNA Server subdomains. Like 3270 LUs, LUA LUs from multiple servers in different subdomains can be assigned to the TN3270 service. This lets you distribute client sessions among the participating servers in the subdomain, thereby balancing the load.
Creating redundant connections to the mainframe and assigning them to a TN3270 service increases service availability; if one server goes down, a client can still access LUA LUs on a different server. Similarly, a single server can be configured with redundant host links to increase fault tolerance and bandwith if no other SNA Server computers are available.