Yes, that is an off-hook tone, not a disconnect tone and is dependent on which device or provider has detected the condition, usually by detecting the circuit is still off-hook. It is a function that follows the disconnect. It is not the extension card that provides that in a PBX, but the sensing of the condition when one end has ended and the other side is still on and the processor of the system generates the tone and sends to the afflicted extension via the card.
In this case, it is a GXW connected to an IP-PBX. It seems clear that when a call is terminated by the IP system, it sends a BYE to the GXW. The GXW in turn, must send something to the SLC16. This part appears to work, given the statement of -
“when analog (TDE 200 Panasonic phones which connected to gateway) hang up the phone , IP phones not hangup and still ringing .it appear when a analog phone try to connect to IP phone”.
So, my thought is that given it is an extension card that expects to have an analog phone that will not react to CPC, off-hook or other tones - other than to let you listen to them it does not send a standard CPC type of tone disconnect.
However, you have hit upon the idea that if one knows what that off-hook tone generation is, then perhaps it could be set in the GXW. The only issue is the amount of time needed for the off-hook tone to come about. But as I suspect that this is generated by the PBX and may not represent a standard for a given country, it may be problematic to find. The off-hook tone by a provider in the UK is different than that in the US and so I suppose also true for the PBX makes. I can find no reference to an off-hook tone in the TDE200 manual or in the 2 versions of the SLC16. I can find others, but nothing of interest.
Thoughts? Go SIP?