Version 7.0 535 Mediant 3000
User's Manual 27. Configuring Supplementary Services
MLPP Precedence Level PRI Precedence Level SIP Resource-Priority Header Field
Flash Override 0 8
If the network-domain field in the Resource-Priority header is any value other than
"uc", then the device sets the Precedence Level field to "0 1 0 0" (i.e., "routine").
This can be modified using the EnableIp2TelInterworkingtable field of the ini file parameter,
ResourcePriorityNetworkDomains.
Notes:
• If required, you can exclude the "resource-priority” tag from the SIP Require
header in INVITE messages for Tel-to-IP calls when MLPP priority call handling is
used. This is configured using the RPRequired parameter.
• For a complete list of the MLPP parameters, see ''MLPP and Emergency Call
Parameters'' on page 955.
27.6.1 MLPP Preemption Events in SIP Reason Header
The device sends the SIP Reason header (as defined in RFC 4411) to indicate the reason
and type of a preemption event. The device sends a SIP BYE or CANCEL request, or SIP
480, 486, 488 response (as appropriate) with a Reason header whose Reason-params can
includes one of the following preemption cause classes:
Reason: preemption ;cause=1 ;text=”UA Preemption”
Reason: preemption ;cause=2 ;text=”Reserved Resources Preempted”
Reason: preemption ;cause=3 ;text=”Generic Preemption”
Reason: preemption ;cause=4 ;text=”Non-IP Preemption”
This Reason cause code indicates that the session preemption has occurred in a non-
IP portion of the infrastructure. The device sends this code in the following scenarios:
• The device performs a network preemption of a busy call (when a high priority
call is received), the device sends a SIP BYE or CANCEL request with this
Reason cause code.
• The device performs a preemption of a B-channel for a Tel-to-IP outbound call
request from the softswitch for which it has not received an answer response
(e.g., Connect), and the following sequence of events occurs:
a. The device sends a Q.931 DISCONNECT over the ISDN MLPP PRI to the
partner switch to preempt the remote end instrument.
b. The device sends a 488 (Not Acceptable Here) response with this Reason
cause code.
Reason: preemption; cause=5; text=”Network Preemption”
This Reason cause code indicates preempted events in the network. Within the
Defense Switched Network (DSN) network, the following SIP request messages and
response codes for specific call scenarios have been identified for signaling this
preemption cause:
• SIP:BYE - If an active call is being preempted by another call
• CANCEL - If an outgoing call is being preempted by another call
• 480 (Temporarily Unavailable), 486 (User Busy), 488 (Not Acceptable Here) -
Due to incoming calls being preempted by another call.
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