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66 Chapter 3 Preparing the TAPI environment
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Remote procedure calls and trust relationships
When a remote TAPI client communicates with a TAPI server, two remote
procedure calls (RPCs) are required. This requirement often causes problems
because network administrators do not usually configure their networks to allow
reverse RPC requests which are not necessary for most network services.
Telephony services are an exception because they rely on domain-based
validation, which requires reverse RPCs.
In a typical TAPI call, the following communication occurs:
• The client sends an RPC request to the TAPI server over a TCP/IP
connection.
• The TAPI server verifies the client by communicating with the primary
domain controller of the server machine domain.
• If the server machine domain trusts the user domain, the client is validated
and the TAPI server looks up what lines the clients has permission to use.
• The TAPI Server sends a second (reverse) RPC request to the primary domain
controller for the client machine domain to verify the client.
• If the client machine domain trusts the server user domain, the validation
succeeds.
In this example, the following trust relationships are necessary:
• The server machine domain must trust the server user domain.
• The client machine domain must trust the client user domain to enable client
users to log in.
Trust relationships are simplified if the server machine domain is the same as the
server user domain, or if the user machine domain is the same as the user domain.
These groups can be configured as members of just one domain, or they can be
configured as four separate domains, depending on network requirements.
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Note:
The behaviour described in this section does not occur in a
network where Windows 2000 client machines are validated by a
Windows 2000 or Windows 2003 server. A second RPC is not required in
such a network configuration.