Panasonic KX-TD500 System Reference Manual page 334

Routing Procedure 2: (2) When a tie call comes in on your PBX from other PBXs.
Is there your PBX's No
extension number in
the received digits?
Yes
No
Does that extension
actually exist?
Yes
No
Sends busy
Is it idle?
Yes
Calling to the
specified extension.
Analyzing digits sent
from the other PBX.
Does the leading 3-
digit of the received
No
digits match your
PBX Code?
Is your PBX's CO
access code or
extension number
included in the
received digits?
Is there a CO
No
access code of
your PBX in the
received digits?
Is "TIE - CO
Restriction" of the
selected trunk group
set to "Yes"?
Sends reorder tone.
Is it an extension
number of other
PBX's?
Trunk group for
making an outgoing
tie call is decided by
a Routing Table.
tone.
Is "TIE Trunk Relay
Restriction" of the
selected trunk group
set to "Yes"?
Sends reorder tone.
3-F-74
Yes
No
Yes
Yes
No
Calling to CO.
Yes
No
Sends reorder tone.
Yes
No
received from one
PBX to another.
Yes
Sends digits