Canon FAX L1000 Service Manual page 483

b) Next, the 4 digits "1088" of the service error code "##1088" are registered in service
data #4C ISDN BASIC G4/G3 Fallback, and another outgoing call is made to the G4.
In this situation, with the first outgoing call, a) D-channel cannot be connected in the
same way, but after receiving the RELCOMP message from the network, the Bearer
Capability information element included in the SETUP message is changed from
"unrestricted digital" to "3.1kHz audio" and the SETUP message is sent again.Example)
FAX-L1000
SETUP (BC: Unrestricted digital)
Figure 5-57 G4 / / / / / G3 Fallback Procedure (2)
CALL PROC
DISC (Cause number: "88")
REL
REL COMP
G4/G3 Fallback
procedure
SETUP (BC: 3.1kHz audio)
CALL PROC
CONN
CONN ACK
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FAX-L1000 Chapter 5: Appendix
ISDN
G3 machine
BC: Bearer Capability