SIP User's Manual 642 Document #: LTRT-12804
Mediant 800 MSBG
SIP Response Description
ISDN Release
Reason
Description
600 Busy everywhere 17 User busy
603 Decline 21 Call rejected
604 Does not exist anywhere 1 Unallocated number
606* Not acceptable 38 Network out of order
* Messages and responses were created because the ‘ISUP to SIP Mapping’ draft does
not specify their cause code mapping.
10.3 ISDN Overlap Dialing
Overlap dialing is a dialing scheme used by several ISDN variants to send and/or receive
called number digits one after the other (or several at a time). This is in contrast to en-bloc
dialing in which a complete number is sent.
The device supports the interworking of ISDN overlap dialing to SIP based on RFC 3578.
Interworking ISDN overlap dialing to SIP (Tel to IP): The device sends collected
digits each time they are received (initially from ISDN Setup and then from subsequent
Info Q.931 messages) to the IP, using subsequent SIP INVITE messages. You can
also define the minimum number of overlap digits to collect before sending the first
SIP message (INVITE) for routing the call, using the MinOverlapDigitsForRouting
parameter.
The device stops collecting digits when:
• Receives Sending Complete IE in the ISDN Setup or Info messages to signal that
no more digits are going to be sent.
• The inter-digit timeout (configured by the TimeBetweenDigits parameter) expires.
• The maximum allowed number of digits (configured by the MaxDigits parameter)
is reached.
• A match is found with the defined digit map (configured by the DigitMapping
parameter).
The device can also mute in-band DTMF detection until the device receives the full
destination number from the ISDN. This is configured using the MuteDTMFInOverlap
parameter. With ISDN overlap dialing, DTMF digits can be sent in-band in the voice
stream or out-of-band using Q.931 Info messages. If Q.931 Info messages are used,
the DTMF in-band detector must be disabled. Note that when at least one digit is
received from the ISDN (Setup message), the device stops playing a dial tone.
Interworking SIP to ISDN overlap dialing (IP to Tel): For each received INVITE
pertaining to the same dialog session, the device sends an ISDN Setup (and
subsequent ISDN Info Q.931 messages) with the collected digits to the Tel side. For
all subsequent INVITEs received, the device sends a SIP 484 "Address Incomplete"
response to the IP in order to maintain the current dialog session and to receive
additional digits from subsequent INVITEs.
The device can optionally support ISDN overlap dialing for incoming ISDN calls for the
entire device or per E1/T1 span, using the ISDNRxOverlap parameter.
To play a Dial tone to the ISDN user side when an empty called number is received, set the
ISDNINCallsBehavior parameter to 65536 (bit #16). This results in the Progress Indicator
being included in the SetupAck ISDN message.
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