What is the meaning of "Presentation Allowed, Not Screened" prompt from Asterisk AMI event?

When I listen to events from Asterisk AMI (port 5038), I receiv开发者_开发技巧e the following event:

Events: NewCallerid
Privilege: call,all
Channel: DAHDI/9-1
CallerIDNum: 12345678
CallerIDName:
Uniqueid: 1303743360.356
CID-CallingPres: 0 (Presentation Allowed, Not Screened)

What is the meaning of

CID-CallingPres: 0 (Presentation Allowed, Not Screened)

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following is description from Asterisk

Gets or sets Caller*ID presentation on the channel. The following values are
valid:
    allowed_not_screened - Presentation Allowed, Not Screened.
    allowed_passed_screen - Presentation Allowed, Passed Screen.
    allowed_failed_screen - Presentation Allowed, Failed Screen.
    allowed - Presentation Allowed, Network Number.
    prohib_not_screened - Presentation Prohibited, Not Screened.
    prohib_passed_screen - Presentation Prohibited, Passed Screen.
    prohib_failed_screen - Presentation Prohibited, Failed Screen.
    prohib - Presentation Prohibited, Network Number.
    unavailable - Number Unavailable.

This is useful when you are using network calls through T1/E1 and while you dialing calls for setting caller*id on network call you need to send specific description to telco for setting callerid on PRI/BRI just discussed with telco what setting they allowed.