Layer 1 & Layer 2 Protocols• 7-2 •
The H.110 Basic Rate ISDN Board
INFO0 No signal (either side)
INFO1 Positive ZERO, negative ZERO, six ONEs repeated
(TE side)
INFO2 Frame with all bits of the B, D and D-echo channels
set to ZERO, bit A set to ZERO (NT side)
INFO3 Synchronized frames with operational data on the B
and D channels (TE side)
INFO4 Frames with operation data on the B, D, and D-echo
channels, bit A set to ONE (NT side)
Layer 1 operation is described by a state machine model. This model has
a different sequence of states depending on whether the device is a TE
(terminal equipment) or NT (network termination). The states for the TE
device are referred to as F states while the NT states are G states. The
states are:
TE States
F1 Inactive
F2 Sensing
F3 Deactivated
F4 Awaiting a signal, transmitting an INFO1
F5 Identifying input, awaiting an INFO2 or INFO4
F6 Synchronized, INFO2 detected, transmitting INFO3, awaiting
an INFO4
F7 Activated, INFO 4 detected, transmitting INFO3
F8 Lost framing, awaiting resynchronization by INFO2 or
INFO4 or deactivation by INFO0
NT States
G1 Deactivated
G2 Pending activation transmitting INFO2, awaiting INFO3
G3 Activated transmitting INFO4, INFO3 detected
G4 Pending deactivation
On the H.110 Basic Rate ISDN Board, the Layer 1 states sequencing
proceeds automatically at the chip level without requiring the intervention
of the application. However, indications of a change of state are reported
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