Verilink PRISM 4001 (34-00244) Product Manual - Manual (Page 25)

Terminal Operation 4-5 PRISM 4001
Line Loop: This loop takes place at the DDS network
interface. The loop is activated by the reversal of the sim-
plex, 20 mA sealing current. This loop may be either unidi-
rectional as shown in Figure 4 -5 or bidirectional as shown
in Figure 4 -6. The unidirectional line loop ignores the DTE
transmit data and retransmits the received DDS data. In the
bidirectional line loop, network receive data is looped back
to the network as network transmit data. DTE transmit data
is looped back through the data port as receive data to the
DTE.
Data Loop: The data loop takes place at the data port
(DTE) interface and is activated when the 4001 receives
alternating loop codes in the network receive data stream.
Technically, it is activated by the receipt of at least four
consecutive loop commands and remains looped as long as
each third pattern byte is the loop command. It returns to
normal operation after receiving at least four non-loop com-
mand pattern bytes. Data loops may be either unidirectional
as shown in Figure 4-7 or bidirectional as shown in Figure
4-8. Unidirectional data loops retransmit the DSU received
data on the DSU transmit data including the loop code.
Receive data is unaffected (but includes the modified loop
codes) and circuits DSR and DCD are optionally forced
OFF. In the bidirectional line loop, network receive data is
looped back to the network as network transmit data. DTE
transmit data is looped back through the data port as receive
data to the DTE.
V.54 Loop: V.54 loops take place at the DTE data port
interface and are activated upon receipt of in-band V.54
loop codes in the network receive data stream. V.54 loops
unidirectional (Figure 4-7) and bidirectional (Figure 4-8)
Unidirectional loops return the DSU receive data to the
DSU transmit data, and then to the DDS transmit data.
Receive data is unaffected and DSR and DCD are optionally
forced OFF. In the bidirectional line loop, network receive
data is looped back to the network as network transmit data.
DTE transmit data is looped back through the data port as
receive data to the DTE.
Local Loop: The Local loop is bidirectional only and takes
place at the DDS network interface. It returns the DDS
receive data to the DDS transmit line and the DSU transmit
data to the DSU receive data output (see Figure 4-9).
For the Line Loop, Data Loop, and V.54 Loop, the user has a
choice of what the receive data sent to the DTE is. This is
determined by the setting of the Loop Mode option. When set
to UNIDIRECTIONAL, the remotely activated loops behave
as follows: The network receive data loops back to the net-
work as network transmit data and continues to pass through
the data port to the DTE. Transmit data from the DTE is ter-
minated.
When set to BIDIRECTIONAL, remotely activated loops
behave as follows: The network receive data is looped back to
the network as network transmit data. Transmit data from the
DTE is looped back through the data port as receive data to the
DTE.
In addition to activating a local loop, the user may also instruct
the 4001 to transmit in-band V.54 loop code to the remote-end
unit causing it to enter a V.54 loop as described above.
The 4001 does not transmit alternating DSU
loop code or cause sealing current reversal to
activate a loop on the remote-end unit.
Enable Far End Datalink
The Far End Datalink operation provides a means to estab-
lish end-to-end communications as a diagnostic tool. When
in the standard mode of operation, end-to-end communica-
tions can be established by changing the Data Mode on the
near end (Figure 4-4 on page 4-4) and then pressing
ENTER on the Enable Far End Datalink field. This function
changes the Data Mode on the far-end unit to TxPORT
mode also. The user can then perform functions at that end
of the circuit. Normal operation can be resumed by chang-
ing the Data Mode back to standard on the far-end unit first
and then the near end.
This operation disrupts the data path!
DTE Network
Figure 4-5 Unidirectional Line Loop
DTE Network
Figure 4-6 Bidirectional Line Loop
DTE Network
Figure 4-7 Unidirectional Data Loop and V.54 Loop
DTE Network
Figure 4-8 Bidirectional Data Loop and V.54 Loop
DTE Network
Figure 4-9 Local Loop