4
Answering a Call
When configured to answer a call, AnswExtBU (in the DBM option set) is enabled. The DSU raises DSR and
monitors its DTR lead. When the modem raises DSR, raising DTR and indicating that a call is being established,
the DSU switches data to the backup line – the alternate port. When the external modem’s DSR signal goes low,
indicating that a call is not established, the DSU lowers DSR to disconnect the call and switches the data back to
the DDS line.
NMS Support Considerations
This firmware release is supported by the 6800 Series NMS, but slight variations in configuring the DSU are
required. NMS configuration options are mapped to the following DSU (with external backup capability)
configuration options:
DSU option set:
AggrSwitch – mapped to ExtBU configuration option
DBM option set:
Rate(Kbps) – mapped to different Rate(Kbps) configuration option
AutoAnswer – mapped to AnswExtBU configuration option
DCE Clock Source – mapped to DDS on the NMS
To the NMS, when the DSU is configured for external backup, it appears that a V.32 DBM is installed. The
“V.32 DBM” rate from the NMS will be doubled automatically by a DSU that has this firmware release. The only
valid NMS-entered rates are:
9.6 kbps – converted to 19.2 kbps by the DSU
12.0 kbps – converted to 24.0 kbps by the DSU
14.4 kbps – converted to 28.8 kbps by the DSU
For example, for the DSU to operate at 19.2 kbps for external backup, the NMS operator configures the
“V.32 DBM” to operate at 9.6 kbps. At the DSU, the unit is configured for 19.2 kbps backup.
Configuring the Unit
To configure the DSU from the DCP so that the external modem can originate or answer a backup call:
Procedure
1. Load the factory-set configuration for either a control (FacC) or tributary (FacT).
2. Go to the DBM option set and verify that ExtBU (External Backup) is enabled, then select Next (F1).
ExtBU determines whether an external modem is being used.
The AnswExtBU (Answer External Backup) configuration option appears.
3. Change the AnswExtBU configuration option setting, if needed, and then select Next (F1). AnswExtBU
determines whether the DSU originates or answers backup.
• To originate a call, set to Disab.
• To answer a call, set to Enab.
The factory setting is Disab for a control DSU and Enab for a tributary. If you change the setting for the
control, you must also change the setting for the tributary; if one originates the call, the other must answer
the call. (Note: If changing the originate-answer configuration, always change external modem
configurations before changing the DSU configurations to prevent the modem from initiating dial backup
prematurely.)
4. Select the DBM Configuration option rate, Rate(Kbps), and then select Next (F1).
5. Press the
key until you return to the Edit/Save screen, and Save to Activ.