Verilink PRISM 41TDM (34-00275.4) Product Manual - Manual (Page 42)

34 C HAPTER 4: T ERMINAL I NTERFACE
Loop Mode When set to Unidirectional, the NET
receive data is looped back to the NET
as NET transmit data and continues to
pass through the data port to the DTE
as shown in Figure 4-4. Transmit data from the DTE is terminated.
When set to Bidirectional, the NET
receive data is looped back to the NET
as NET transmit data as shown in
Figure 4-5. Transmit data from the DTE
is looped back through the data port as receive data to the DTE.
During dial backup, the loop mode field is ignored and all loops are unidirectional.
this allows testing of the DDS interface during dial backup without disrupting the
DTE/DBU data path.
Line Loop
This loop occurs at the DDS network interface and activates by the reversal of the
simplex, 20 mA sealing current. This loop can be unidirectional or bidirectional.
Circuits DSR and CD are forced Off unless set to Force On.
Data Loop
This loop occurs at the DDS network interface. In DDS-I mode, the data loop
activates when the unit receives alternating loop codes in the network receive data
stream. It activates by receiving 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 at least four pattern bytes that are not the loop command.
When the Loop Mode is set to unidirectional, this loop retransmits the PRISM
41TDM received data on the unit transmit data including the remapped loop code.
Receive data is unaffected (but includes the modified loop codes) and circuits DSR
and CD are Off. When the Loop Mode is set to bidirectional, the DTE is looped
back and does not receive the remapped loop codes.
In DDS-II mode, the data loop activates when the latching loopback sequence is
received. The sequence consists of 35 or more TIP bytes, 35 or more LSC bytes,
100 or more LBE bytes, 32 or more FEV bytes. Latching loop is deactivated when
31 or more TIP bytes are received.
V.54 Loop
This loop occurs at the DDS network interface and activates after receiving inband
V.54 loop codes for at least two seconds followed by all ones in the network
receive data stream. When the Loop Mode is set to unidirectional, this loop
retransmits the PRISM 41TDM received data on the unit transmit data including
the remapped loop code. Receive data is unaffected (but includes the modified loop
codes) and circuits DSR and CD are Off. When the Loop Mode is set to
bidirectional, the DTE is looped back and does not receive the remapped loop
codes.
DTE NET
Line Loop
Figure 4-4 Unidirectional Loop
DTE NET Local Loop
Figure 4-5 Bidirectional Loop
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