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22 C
HAPTER
2: ISDN LAN M
ODEM
F
UNCTIONALITY
D
ESCRIPTION
and agrees to use BAP, then the Bandwidth Allocation Protocol (BAP) negotiates
the addition and removal of the second B channel with the peer equipment based
on a user-defined threshold. A key advantage of BACP/BAP is that it provides a
higher probability of establishing a Multilink PPP call during high traffic conditions
by providing a specific telephone number for the second B channel to call.
Multilink PPP Configuration Options
When configuring Multilink PPP, you can choose one of the following options
from the ISDN LAN Modem’s
Service Provider Parameters window.
■
Use One B Channel
When this option is configured, only one B channel is used to connect to this
service provider. Multilink PPP is thereby disabled and BACP/BAP is therefore
not used.
■
Use Two B Channels
When this option is configured, both B channels are always used to connect to
this service provider, regardless of the amount of traffic over each
B channel. Note that when this option is selected, the DBA feature does not
work because both B channels are being used. To use both DBA and Multilink
PPP, select the option
Add Second B Channel as Required
.
■
Add Second B Channel As Required
When this option is configured (referred to as bandwidth on demand) only one
B channel is used to connect to this service provider, and the second
B channel is automatically added only when the amount of traffic on the first
B channel reaches a threshold you define.
In order for you to use Multilink PPP, the destination you are calling must also
support Multilink PPP. For example, if you are trying to dial in to the Internet, your
ISP must also support Multilink PPP in order to successfully place a Multilink PPP
call. If you attempt to place a Multilink PPP call and the location you are calling
does not support Multilink PPP, then a single B channel PPP connection is
established.
Understanding
Dynamic Bandwidth
Allocation
Dynamic Bandwidth Allocation is used in conjunction with Multilink PPP on
demand (to use DBA, you should choose
Add Second B Channel As Required
when you configure Bandwidth Allocation). The Dynamic Bandwidth Allocation
feature allows you to automatically and temporarily remove one of the B channels
and use it either to place or receive a call (voice or data) without disturbing the
original call. The only effect on the original call is that it is reduced from a Multilink
PPP call to the speed of one B channel.
Once the interrupting call ends, that B channel is automatically returned to the
Multilink PPP call. Although throughput is reduced while the interrupting call is
active, the reliability of the Multilink PPP call is maintained.