Modem Dial Backup Interactions With Other Features - Avaya G250 Administration

Modem dial backup interactions with other features

Optimal modem dial backup configuration is a complex undertaking, dependent on a large
number of factors. For an extensive discussion of network design, capacity planning, routing
configuration, device configuration, and security considerations, see Application Note - VoIP
Network Resiliency. Device and network configuration features that need to be taken into
account include:
The backup interface command allows you to designate the Dialer interface as the
●
backup to an existing WAN interface on the G250/G350. When the G250/G350 reports the
primary WAN interface down for a specified period of time, the Dialer interface is
automatically activated and the modem dials. For more information on the backup
interface command, see
The G250/G350's console port is an RJ-45 asynchronous port that can be used to support
●
the modem for dial backup. Thus the dialer can utilize the same serial modem that is used
for remote access to the device. Asynchronous dialing and modem recognition options
must be set on the console port to support creation of the Dialer interface. For more
information on configuring the console port, see
use on page 127.
The Dialer interface supports PAP and CHAP authentication for PPP connections. In
●
addition, the Dialer interface can be configured to be a member of a VPN, allowing
encryption of the modem traffic. Van Jacobsen compression is available for encrypted
traffic over the Dialer interface, allowing optimal use of bandwidth. For more information on
configuring PPP authentication and encryption, see
more information on heading compression, see
page 118.
It is recommended to filter traffic through the Dialer interface to permit only those packets
●
necessary for continued interaction with the Avaya Communication Manager server.
Filtering can be accomplished using access control lists, which specify traffic permissible
through a selected interface. For more information on configuring access control lists, see
Chapter 19: Configuring policy
Dynamic CAC can be used in conjunction with IGAR to provide a stable backup path for
●
continued IP phone function in the event of a dial backup scenario. Dynamic CAC notifies
the Avaya Communication Manager server that no bandwidth is available for bearer traffic,
keeping the dial circuit from becoming fully congested. IGAR provides a path for
gateway-to-gateway traffic destined for a remote Avaya Communication Manager server
by forcing voice calls to and from the branch office to use the PSTN for bearer traffic. For
more information on configuring Dynamic CAC, see
information on configuring IGAR, see Administrator's Guide for Avaya Communication
Manager, 555-233-506.
Static IP addressing for the Dialer interface may not be feasible. Dynamic IP addressing is
●
available to enable you to connect to the remote network through an ISP. ISPs commonly
provide IP addressing for connected ports on an as-needed basis. IP unnumbered links
Backup interfaces on page 146.
Configuring the console port for modem
Configuring header compression
on page 441.
Modem dial backup
Configuring PPP on page 139. For
Dynamic CAC on page 169. For more
Issue 1.1 June 2005
on
155