OSF DCE Application Development Guide--Introduction and Style Guide

Binding

4.1.3 Call Routing

Once the server and client have taken all the necessary steps to set up server and client

side relationships, the call mechanism can use them to construct a complete binding and

call routing when the call is made. When the client makes a call with a binding that

lacks an endpoint (typically the case for bindings imported from the name service), the

endpoint is acquired from the endpoint mapper on the target host. The endpoint mapper

ﬁnds a suitable endpoint by searching the local endpoint map for a binding that provides

the requested interface UUID, and if requested, object UUID.

The endpoint map interface and protocol information must match in order for an

endpoint to be found, but an object UUID match may not be required. A server can

provide a default UUID match by registering the nil UUID. Calls with a nil or

unmatched object UUID will get the default endpoint.

Once an endpoint is selected, a call can be routed to one of the endpoints being used by a

compatible server instance. The server can unambiguously select the correct interface

and operation by using the interface identiﬁer and operation number contained in the

call. Recall, however, that the RPC mechanism makes it possible for a server to

implement multiple managers for an interface. Hence it may be necessary to select the

correct manager. Manager selection is based on the object UUID contained in the call.

The selection mechanism depends on two of the relationships established by the server:

the object UUID/type UUID mapping and the interface ID/type UUID/manager UUID

mapping.

For routing, the server provides a default path by registering a default manager for the nil

type UUID. Calls containing the nil object UUID, or any UUID for which the server has

not set another type UUID, will be directed to the default manager.

Once the manager is selected, the call is dispatched via the selected manager EPV using

the operation number contained in the call.

4.1.4 Routing Policy

There are many ways in which clients and servers can arrange the details of binding

among themselves, including: how bindings are exported and imported, whether object

UUIDs are used, and how object-type mappings are established. High-level resource

policy issues relating to the name service and endpoint mapper are discussed in Chapter

5. In the present chapter, some of the lower-level routing policy questions that arise from

the binding model itself will be discussed. These, in fact, have a substantial impact on

how the namespace is used by applications.

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