FXS, DID or FXS/DID, FXO, PRI-T1

Can anyone, pls. explain to me what is actually the relationship based on the functionality of FXS, DID or FXS/DID, FXO, PRI-T1 ?
Are the DID Trunks similar to the trunks of PRI-T1, say 24 channles ? Are these 23 b-channels and 1 d-channel for a PRI-T1 are the same as trunks of the DID service?
Dou you still need a DID service offered by telephone companies that enables callers to dial directly an extension on a PBX or packet voice system if you have already a PRI-T1 service?
Do they have the same function between DID Trunks and Voice Channels of PRI T1?

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Comments

kyrunner

FXS= Foreign Exchange Station. Mainly used for FAX Machines, Analog phones. A FXS card is used to convert analog to digital.
FXO= [FONT=arial, sans-serif]Foreign Exchange Office. Mainly used for connecting back to the Exchange Office. FXO cards are used for copper lines Example 911
I also use FXO cards to connect into a over head paging system.
PRI=24 channels 1 channel is the D channel and its reserved for the signaling [/FONT]

jeremus

Are the DID Trunks similar to the trunks of PRI-T1, say 24 channles ? Are these 23 b-channels and 1 d-channel for a PRI-T1 are the same as trunks of the DID service?
Dou you still need a DID service offered by telephone companies that enables callers to dial directly an extension on a PBX or packet voice system if you have already a PRI-T1 service?
Do they have the same function between DID Trunks and Voice Channels of PRI T1?

ebohlman

The DID trunks that FXS/DID cards are intended to connect to are analog and have to be specially ordered from the phone company. They are becoming less and less common because, if you already have a PRI from the phone comjpany, they can deliver the service (sending the digits of the called number) over it (in which case you *don't* need an FXS/DID card).

An analog DID trunk can only handle one connection at a time, whereas DID over PRI can handle 23, and can use the same trunk for incoming and outgoing calls.