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ISDN Call Processing Overview
November 2009 323
ISDN Overlapped Dialing
The Euro-ISDN protocol only allows 20 digits to be sent as a group
(en-block) when placing a call. For longer phone numbers, the
application must use overlapped dialing— the process of sending
extra digits after the initial call setup. This process allows:
The application to dial very large phone numbers
The remote end to start answering a call before it receives all the
digits
The Bfv API automatically performs overlapped dialing on Euro-
ISDN outgoing calls using E1 or BRI lines when the phone number
is longer than 20 digits. Users will be able to place a call with up to
255 digits in the dial string on Euro-ISDN without requiring changes
in the application.
Applications automatically send overlapped digits when the user
calls BfvCallSetup, BfvLineDialString or
BfvLineOriginateCall and provides a dial string of more than 20
digits when Euro-ISDN is being used.
The feature divides the dial string into banks of 20 digits and uses
the overlapped dialing feature in Euro-ISDN to send one block of
digits at a time.
ISDN Call Clearing - Initiated by Module
A typical module-initiated call clearing (tear down) sequence is
illustrated in Figure 50. The following message exchange is relative
to the module:
1. The host initiates the call clearing procedure by sending an
L4L3mCLEAR_REQUEST message to the module.
2. Upon receipt of the L4L3mCLEAR_REQUEST message, the
module sends a DISCONNECT message to the network.