Backing Up Primary Wan Connections; Analog Backup Connections - HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual

Backing Up Primary WAN Connections

To ensure that users can always exchange data between two offices, you may
want to lease a dial-up WAN connection—such as an Integrated Services
Digital Network (ISDN) or telephone line—which can be used as a redundant
line in case a primary WAN connection fails. Dial-up WAN connections work
well as backup connections because you pay only for the time when the
connection is in use.
Like other WAN connections, dial-up connections are provided through the
public carrier network. In North America, dial-up connections are provided
through the public switched telephone network (PSTN). Outside of North
America, each country's public telephone and telegraph (PTT) authority
provides dial-up connections.
All WAN connections, including dial-up connections, consist of three basic
elements:
the physical transmission media
electrical signaling specifications for generating, transmitting, and receiv-
ing the signals that transmit data through the telephone cables
Data Link Layer protocols, which provide logical flow control for moving
data between the router and the public carrier's central office (CO)
Just as you configure both a Physical Layer and a Data Link Layer for primary
WAN connections, you must configure these layers for backup connections.
Configuring the Physical and Data Link Layers for backup connections is a
slightly different process, however, because you must specify when and how
the backup connection is initiated.

Analog Backup Connections

If you want to create a backup connection over the existing telephone cabling,
you can use an analog modem, which establishes a dial-up connection to its
peer—another analog modem at the remote office. To initiate a physical
connection, the analog modem places a telephone call to its peer and then
negotiates a logical link with the peer using a Data Link Layer protocol. After
the connection is established, the analog modem translates digital data into
analog signals. When the two peers are finished exchanging data, the analog
modem terminates the connection just as a person would hang up a call.
Configuring Backup WAN Connections
Backing Up Primary WAN Connections
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