3Com ISDN Modem User Manual page 86

5-2 C 5: A C
HAPTER DVANCED ONFIGURATION
QuickSelect
The QuickSelect feature (S71=0, by default) automatically
detects and implements the protocol required for each
digital call, either V.120 or Async-Sync PPP. Typically, V.120 is
used for communication between two computers, whereas
PPP is used for communication between a computer and an
Internet service provider.
Dynamic Bandwidth Allocation
DBA (S70=3, by default) is a method of automatically
reallocating bandwidth to allow you to place or receive a
voice call while a Multilink PPP call is active (i.e., both B
channels are in use).
In this situation, when you lift the handset to place an
outgoing call or to answer an incoming call, one of the B
channels is temporarily removed from the Multilink PPP call
and is used for the voice call.
Once the voice call ends, that B channel is automatically
returned to the Multilink PPP call. Although throughput is
reduced to one channel while the voice call is active, the
integrity of the Multilink PPP call is maintained.
If you are on the receiving end of a Multilink PPP call (i.e.,
someone has dialed into your 3C882 ISDN modem) and you
place a voice call, one of the B channels will still be allocated
for the new voice call. However, once the voice call ends, that
B channel cannot be returned to the incoming Multilink PPP
call. The B channel can only be returned to the Multilink PPP
call for outgoing Multilink PPP calls.
Outgoing DBA takes precedence over incoming DBA. For
example, during a Multilink PPP call, you receive an incoming
voice call over Phone port 1. You may, however, prefer to
place an outgoing call over Phone port 2 and ignore the
incoming call. When you place your call over Phone port 2,