Samsung Ubigate iBG2016, Configuration Manual

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CHAPTER 6. Digital Voice Port
534
© SAMSUNG Electronics Co., Ltd.
T1-CAS FXO Features
Foreign eXchange(FX) signaling was originally developed to connect remote
Private Branch Exchanges(PBX’s) to the(Bell System) Central Office.
These PBXs(and other Central Offices) were considered ‘Foreign’ not because
they were outside the country, but because they didn’t belong to the ‘Phone
Company.’ A FXS(FX-Subscriber) interface will be connected to a matching
FXO(FX-Office) interface at the far end.
Note that audio paths(such as the ‘CO sends Dial Tone’ path) are not usually
considered part of the FX signaling. They are included to make the examples
easier to understand.
Figure 6.9 T1 CAS FXS/FXO signaling operation
Loop Start
As shown in the POTS diagram above, Loop Start signaling uses only two
basic states: Ringing(sent to the FXO interface) and Off-Hook(sent to the FXS
interface). Loop Start signaling is the most common type of signaling
deployed in the PSTN.
Although it is very common, problems can occur whenever automatic
answering equipment is used as the phone. Since there is no way for the CO to
tell the phone to hang up(go On-Hook), if the answering equipment never times
out then the circuit can be permanently seized. This is usually not a problem for
‘real’ phones, since the end user will realize that there is no one on the call and
hang up. This problem can be solved by using Ground Start signaling.
T1
Circuit
FXS FXO FXS ‘FXO’
CENTRAL
OFFICE
SWITCH
Loop Start
Phone
Originating Call
Loop Start
Phone
Terminating Call
CO Rings FXO
FXO goes OFF Hook
FXO goes OFF Hook
CO sends Dial Tone
FXS Rings Phone
Phone goes OFF Hook
Phone goes OFF Hook
Dial Tone heard