WebSphere Application Server for z/OS routes work requests throughout the cell by using the domain name server (DNS).
The DNS accepts a generic host name from the client and maps the name to a specific system. In order to select the best available system, the DNS asks workload management (WLM) for a recommendation. Workload management analyzes the current state of the cell and considers a number of factors, such as CPU, memory, and I/O utilization, to determine the best placement of new work. The DNS then routes the client request to the optimal system for execution. This use of workload management and the DNS is optional but highly recommended because it eliminates a single point of failure.
Each system in the cell has the WebSphere Application Server for z/OS run-time (the location service daemon, node agent and Deployment Manager), plus business application servers. The client uses the CORBA General Inter-ORB Protocol (GIOP) to make requests of WebSphere for z/OS. The location service daemon acts as a location service agent. It accepts locate requests with object keys in the requests. The location service daemon uses the object key to locate a server that supports the object represented by the object key, then hands the server name to workload management. Workload management chooses the optimal server in the cell to handle the request. The location service daemon merges specific IOR information related to the chosen server with object key information stored in the original IOR. The result of this merging is a direct IOR that gets returned to the client. The client ORB uses this returned reference to establish the IOR connection to the server holding the object of interest.
The transport mechanism that WebSphere Application Server for z/OS uses depends on whether the client is local or remote. If the client is remote (that is, not running on the same z/OS system), the transport is TCP/IP. If the client is local, the transport is through a program call. Local transport is fast because it avoids the physical trip over the network, eliminates data transforms, simplifies the marshalling of requests, and uses optimized RACF facilities for security rather than having to invoke Kerberos or SSL.