3Com 3C888 User Guide - Page 27

Understanding Multilink PPP and Other Line Usage Options, Configuration Options

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Understanding Multilink PPP and Other Line Usage Options 27 Callback Capability with Dial-in Calls When you configure the LAN Modem for dial-in support, you can choose to 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 Multilink PPP and Other Line Usage Options When the Dual 56K LAN Modem's two analog lines are used independently, each uses the PPP (Point-to-Point Protocol), which is commonly used for the establishment of dial-up connections, such as to the Internet. In some configurations of the Dual 56K LAN Modem, you will encounter the following protocols, used in connection with PPP. Multilink Point-to-Point Protocol (MLPPP) Multilink PPP is a protocol which allows two or more PPP connections to be 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 Allocation (DBA) Dynamic Bandwidth Allocation (DBA) is another protocol used in conjunction with 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 Configuration Options If you enable Multilink PPP when you configure the Dual 56K LAN Modem, you will be able to choose from among the following Multilink PPP options: s 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. s Use Two Channels

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Understanding Multilink PPP and Other Line Usage Options
27
Callback Capability with
Dial-in Calls
When you configure the LAN Modem for dial-in support, you can choose to
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
Multilink PPP and
Other Line Usage
Options
When the Dual 56K LAN Modem’s two analog lines are used independently, each
uses the
PPP
(Point-to-Point Protocol), which is commonly used for the
establishment of dial-up connections, such as to the Internet. In some
configurations of the Dual 56K LAN Modem, you will encounter the following
protocols, used in connection with PPP.
Multilink Point-to-Point
Protocol (MLPPP)
Multilink PPP is a protocol which allows two or more PPP connections to be
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
Allocation (DBA)
Dynamic Bandwidth Allocation (DBA) is another protocol used in conjunction with
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
Configuration Options
If you enable Multilink PPP when you configure the Dual 56K LAN Modem, you
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