3Com Dual 56K manual Understanding, Multilink PPP, Other Line Usage, Options

	Understanding Multilink PPP and Other Line Usage Options 27
Callback Capability with	When you configure the LAN Modem for dial-in support, you can choose to
Dial-in Calls	enable Callback in each Dial-User profile that you create. When Callback is
	enabled, the LAN Modem is designed to identify the authorized Dial-in User, drop
	the incoming call, and immediately place a return call to that user. This provides
	security for the network attached to the LAN Modem, as well as potential cost
	savings for the Dial-in User.
	In order for dial-in Callback to work, the calling device at the other end must also
	be set up with a Callback feature.
Understanding	When the Dual 56K LAN Modem’s two analog lines are used independently, each
Multilink PPP and	uses the PPP (Point-to-Point Protocol), which is commonly used for the
Other Line Usage	establishment of dial-up connections, such as to the Internet. In some
Options	configurations of the Dual 56K LAN Modem, you will encounter the following
	protocols, used in connection with PPP.
Multilink Point-to-Point	Multilink PPP is a protocol which allows two or more PPP connections to be
Protocol (MLPPP)	combined to form a single, high-bandwidth connection or channel. In the case of
	the Dual 56K LAN Modem’s two 56K lines, Multilink PPP is used to combine these
	two 56K connections into a virtual, single 112K connection.
BACP/BAP	In conjunction with Multilink PPP, the protocol pair BACP/BAP (Bandwidth
	Allocation Control Protocol and Bandwidth Allocation Protocol) are used to
	negotiate the addition and removal of the second modem connection with the
	receiving device, based on a user-defined threshold. The advantage of BACP/BAP
	is that it provides a higher probability of establishing a Multilink PPP call by
	providing a specific telephone number for the second modem to call during high
	traffic conditions.
Dynamic Bandwidth	Dynamic Bandwidth Allocation (DBA) is another protocol used in conjunction with
Allocation (DBA)	Multilink PPP to maximize efficiency of line usage. With Dynamic Bandwidth
	Allocation enabled, if a Multilink call is in progress, the LAN Modem can
	automatically and temporarily remove one of the channels from the call and use it
	to place a data call to another service provider without disturbing the original call.
	The only effect on the original call is that speed is temporarily reduced from
	Multilink PPP to one analog channel. Once the second outgoing data call ends,
	that channel is then returned to the Multilink PPP call, assuming that “Add Second
	Channel As Required” has been configured for that service provider. Although
	throughput is reduced while the second call is active, the reliability of the Multilink
	PPP call is maintained.

Multilink PPP If you enable Multilink PPP when you configure the Dual 56K LAN Modem, you Configuration Options will be able to choose from among the following Multilink PPP options:

■Use One Channel

When this option is configured, only one modem channel is used when connecting to a remote destination. In this case, Multilink PPP is disabled, and neither DBA nor BACP/BAP is used.

■Use Two Channels