What determines whether a call is external or internal in the IPO system?

The classification of a call as either external or internal within the IPO system is primarily governed by the dialed number prefix and the defined call routes. This means that the system relies on the specific patterns and formats of the numbers dialed to determine how the call should be treated.

Internal calls are typically those that connect devices or extensions within the same system, which may have predefined prefixes that differentiate them from external numbers. Conversely, external calls are usually directed out to the public telephone network, and their routing is determined by the dial plan that specifies how different number formats should be handled. This includes identifying prefixes that are designated for external calls and ensuring that the system correctly routes these calls through the appropriate gateways or lines.

Given that the call's classification is based on defined parameters in the dialing plan rather than factors such as the caller’s device type, time of day, or geographical location, the key element is the relation of the dialed number to these configurations within the IPO system, making the correct choice effectively connected to how calls are managed based on their number structure and rules established within the system's configuration.