Hybrid routing

Hybrid routing: Routing in which numbering plans and routing tables are used to permit the collocation, in the same area code, of switches using a deterministic routing scheme with switches using a non-deterministic routing scheme, such as flood search routing.

Note: Routing tables are constructed with no duplicate numbers, so that direct dial service can be provided to all network subscribers. This may require the use of 10-digit numbers.

Source: from Federal Standard 1037C