|  | 5.6 | Dial-on-Demand Routing
| 5.6.1 | DDR considerations
When building networking applications, you must determine how ISDN connections will be initiated, established, and maintained. DDR creates connectivity between ISDN sites by establishing and releasing circuit-switched connections as needed by networking traffic. DDR can provide network routing and directory services in numerous ways to provide the illusion of full-time connectivity over circuit-switched connections. To provide total control over initial DDR connections, you must carefully consider the following issues: Which sites can initiate connections based on traffic? Is dial-out required to SOHO sites? Is dial-out required for network or workstation management? Which sites can terminate connections based on idle links? How are directory services and routing tables supported across an idle connection? What applications need to be supported over DDR connections? For how many users do they need to be supported? What unexpected protocols might cause DDR connections? Can they be filtered?
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