ASCOM USER GUIDE
High Speed Base Band Modems
37
6.6.3
Remote Loop On/Off
This causes the modem to apply a loop at the far end modem such that data is looped back
to the local end. If a remote loop is on then local loop and loopback are unavailable (If the
local loop or loopback is on, then the remote loop is unavailable).
This loop can also be applied from the customer interface:
For X21:
The DTE should send the ART pattern (11001100) and have its control line “C” set OFF.
For V.35, V.36 and RS530:
Circuit 140 ON
-
Remote loop ON
Circuit 140 OFF
-
Remote loop OFF
Circuit 142 indicates that a test loop has been applied.
Circuit 108 (where available) should also be on for this test.
6.6.4
V.54 Loop On/Off
This loop is effectively a remote loop, but used in a configuration where the master to slave
pair of modems form part of a larger network.
The loop request command is sent from the slave modem via the data channel (as a V.54
pattern). This request is then ignored by master modems and passed through the network
until it reaches the ultimate slave unit. This responds to the command and applies the loop.
Note:
any rack modems in the data path will also pass through the loop request.
Slave
modem
Master
modem
Master
modem
Slave
modem
Loop request here
Loop applied here
Network
Interface
Interface
loop requested from this modem
loop applied at this modem
(same as loopback applied here)
Transmission
Sys
tem
Transmission
Sys
tem
6
36
ASCOM USER GUIDE
High Speed Base Band Modems
6.6.1
Local Loop On/Off
Turning on the local loop causes the modem to loop data back to the customer interface
(loop 3c – ITU X.150). If local loop is on then remote loop and data test are unavailable.
This loop can also be applied from the customer interface:
For X.21:
The DTE should send the ALT pattern (1111000) and have its control line “C” set OFF.
For V.35, V.36 and RS530:
Circuit 141 ON - Local loop ON
Circuit 141 OFF - Local loop OFF
Circuit 142 indicates that a test loop has been applied.
Circuit 108 (where available) should also be on for this test.
6.6.2
Loopback On/Off
This causes the modem to loop data back to the remote end of the link (loop 2b – ITU X.150).
If loopback is on then remote loop and data test are unavailable.
Interface
Interface
loop applied here
data returned to remote modem
Transmission
Sys
tem
Transmission
Sys
tem
Interface
Transmission
Sys
tem
Interface
loop applied here
data returned to user interface
Transmission
Sys
tem
