The distributed model combines the high-capacity, server-to-host communication benefits of the centralized model with the branch model’s ability to confine heavy client-server traffic to a localized WAN segment, such as a branch office LAN. The result is a deployment model that possesses the advantages of each of the two models, while minimizing the disadvantages of each.
The distributed plan provides even greater flexibility than the branch or centralized plans when load-balancing is implemented. For example, multiple SNA Server computers at a branch location can be configured to provide fault tolerance and load balancing for each another. These servers, in turn, can be connected to the SNA host using link services shared by the centralized SNA Server computers. If any of the servers fail, the other servers at the same location can take over for the failed units.
The use of distributed link services can also simplify your routing and network protocol choices. For your branch offices, Microsoft Networking, IPX/SPX, or other LAN protocols can be used. Between the branch and central SNA Server computers, you can implement a more efficient, routable protocol like TCP/IP. SNA traffic is isolated to the connection between the high-speed SNA Server computers and the host system. SNA protocols do not need to be routed or bridged across the WAN, thereby simplifying network management.
In general, the distributed deployment model provides the most flexible and robust SNA Server solution. This strategy is recommended for medium to large-sized environments that require the best performance and reliability. The distributed model is also easily scalable to meet your future needs.