Verilink PRISM 4051 (34-00253.2) Product Manual - Manual (Page 33)

Software Configuration 27
Loop Mode
Gives the user a choice of how the data is to be looped back: BIDIRECTIONAL or
UNIDIRECTIONAL.
The following loops can be activated on the 4051.
Line Loop. This loop takes place at the
DDS network interface. The loop is
activated by the reversal of the
simplex, 20-mA sealing current. This
loop may be either unidirectional 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 only when
the unit is in DDS I
mode. The data loop is
activated when the 4051
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 command 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.
Latching Loop. The latching loop takes place at the data port (DTE) interface and
only when the unit is in DDS II mode. The latching loop is the same as the data
loop except that it activates upon receiving DSU latching loop code. The latching
loop deactivates upon receiving DSU unlatch loop code.
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 are either 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
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