User's Manual 498 Document #: LTRT-10532
Mediant 500L Gateway & E-SBC
(routing) even before all digits have been collected. For example, if the dialled (destination)
number is "3312418", the device first receives the digits "331" and then routes the call
based on these digits. It then delivers the remaining 4 digits "2418" in overlap mode. The
device supports the interworking of ISDN overlap dialing to SIP and vice versa, according
to RFC 3578.
Interworking ISDN overlap dialing to SIP (Tel to IP): The device sends the first
digits (e.g., "331") received from the ISDN Setup message to the IP side in the initial
SIP INVITE message. Each time it receives additional (collected) digits, which are
received from subsequent Q.931 Information messages, it sends them to the IP side
in SIP re-INVITE or SIP INFO messages. You can use the following parameters to
configure overlap dialing for Tel-to-IP calls:
• ISDNRxOverlap: Enables Tel-to-IP overlap dialing and defines how the device
sends the collected digits to the IP side - in SIP re-INVITE [2] or INFO messages
[3].
• MinOverlapDigitsForRouting: Defines the minimum number of overlap digits to
collect from the Tel side before the device can send the first SIP message
(INVITE) for routing the call to the IP side.
• MaxDigits: Defines the maximum number of collected digits that can be received
from the Tel side (if ISDN Sending Complete IE is not received). When the
number of collected digits reaches the maximum, the device uses these digits for
the called destination number.
• TimeBetweenDigits: Defines the maximum time (in seconds) that the device waits
between digits received from the Tel side. When the time expires, the device
uses the collected digits to dial the called destination number.
• MuteDTMFInOverlap: Enables the device to ignore in-band DTMF digits received
during overlap dialing.
Note: If the device receives SIP 4xx responses during the overlap dialing (while
collecting digits), it does not release the call.
Interworking SIP to ISDN overlap dialing (IP to Tel): The device sends the first
digits (e.g., "331") received from the initial SIP INVITE message to the Tel side in an
ISDN Setup message. Each time it receives additional (collected) digits for the same
dialog, which are received from subsequent SIP re-INVITE messages or SIP INFO
messages, it sends them to the Tel side in SIP Q.931 Information messages. For each
subsequent re-INVITE or SIP INFO message received, the device sends a SIP 484
"Address Incomplete" response to the IP side to maintain the current dialog session
and to receive additional digits from subsequent re-INVITE or INFO messages. You
can use the following parameters to configure overlap dialing for IP-to-Tel calls:
• ISDNTxOverlap: Enables IP-to-Tel overlap dialing and defines how the device
receives the collected digits from the IP side - in SIP re-INVITE [1] or INFO
messages [2].
• TimeBetweenDigits: Defines the maximum time (in seconds) that the device waits
between digits received from the IP side. When the time expires, the device uses
the collected digits to dial the called destination number.
Note: For IP-to-Tel overlap dialing, to send ISDN Setup messages without including
the Sending Complete IE, you must configure the ISDNOutCallsBehavior parameter
to USER SENDING COMPLETE [2].
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