Always On / Dynamic Isdn (Ao/Di); Dhcp Address Lease Time - Cisco 761M Installation Manual

Product Features
Cisco 700 Fast Step runs on Microsoft Windows 95, Windows 98, and Windows NT
systems. It is provided with your router on the Cisco Fast Step CD-ROM. The application
is also available on Cisco Connection Online (CCO).

Always On / Dynamic ISDN (AO/DI)

The Always On/Dynamic ISDN (AO/DI) networking service provides an always-available
connection to packet-based services through the WAN. For the user, AO/DI reduces costs
by using the D channel to make low-speed data transfers. For service providers, AO/DI
removes a significant amount of data traffic from the voice network.
The D channel is an always-available, packet-oriented link between the remote office and
the central office. The customer premises equipment (CPE) can use the D channel to pass
Multilink Point-to-Point Protocol (PPP) and Transaction Control Protocol and Internet
Protocol (TCP/IP) encapsulated in X.25. The D-channel X.25 packets are handled at the
central office by the X.25 packet handler, so these packets can be routed without crossing
the circuit-switched switch fabric.
When D-channel bandwidth exceeds a defined threshold, the router places one or more
ISDN B-channel calls to increase bandwidth. When bandwidth requirements fall below a
defined threshold, the B channels are released.
A maximum of four switched virtual circuits (SVCs) can be used for AO/DI. If a D-channel
connection is not available, the router uses the first available B channel for a call. After the
D channel PPP link is established, it is not torn down. If Bandwidth Allocation Control
Protocol (BACP) is configured, Bandwidth on Demand (BOD) is negotiated by using
BACP.
Performance of the multilink protocol declines when the bandwidth of the underlying links
varies widely; therefore, the router idles the D channel when the B channels are in use.
(RFC 1990 describes how packets can be redirected using the multilink procedure.) After
the number of links drops to one and that link is idle, the router returns to normal operation.

DHCP Address Lease Time

With Cisco 700 series router software Release 4.2(2), you can specify the lease time for all
the addresses. (The previous Cisco 700 series router DHCP server implementation assigned
an IP address to the DHCP client with an infinite lease time.)
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Cisco 700 Series Router Installation Guide