A communication system can include a telephony application server and at least one speech engine, where the system uses a standardized messaging protocol that specifies a standard for media resources. The telephony application server can have at least one voice server component. The speech engines can be allocated to handle requests for the voice server component on a per turn basis. The standardized messaging protocol can define a message format for request messages sent from the voice server component to a selected speech engine, a message format for response messages sent from the speech engine to the voice server component, and a message format for event messages sent from the speech engine to the voice server component. Each message format can include a field for a call identifier.