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AMA-CUCM Troubleshooting: Best Practices for Reading Trace Files


MLPP between CUCMS and SBC's


Does anyone ever do MLPP inter 2 CUCMS?

So my configuration is like that: I have my CUCM and SBC in my network in the back of a firewall.

I am going out using a n.i.p. (network interconnection point).

My n.i.p. has several BGP partners.

One of my partners have also the n.i.p. and then the SBC and CUCM in the back of his firewall


My question is: Can I call from my voice network in his network with mlpp?

I have tried and enabled MLPP on my CUCM on the sip trunk to my SBC.

I also have configured something on my SBC for mlpp on the incoming dial-peer from my CUCM and on the outgoing and incoming dial-peer of my partner.

However any time I try to place a priority or normal call my SBC returns the 417 Resource priority failed message.

My partner has also enabled the mlpp on his sip trunk and on the incoming dial-peer from me.

The problem is, I think my call does not even reach my partner SBC...


If that is helpful here is my SBC mlpp configuration:


voice class mlpp 1

service domain dsn


voice mlpp

preemption trunk group

preemption user

preemption tone timer 3

preemption reserve timer 5

service-domain midcall-miss method 2

service digit

route code

preemption VoIP-trunk sip

service-domain dsn identifier 000001


Everyone's tags (6)
Rising star

Re: MLPP between CUCMS and SBC's


The Cisco Unified CM currently provides MLPP capability over the SIP Trunk for DSN/DRSN namespaces as defined by RFC4412; however it is geared to DoD requirements. Three namespaces are defined by the draft to cater to different service domains:

  • dsn--Adopted by U.S. Defense Switched Network and DISA. It defines five precedence values: routine, priority, immediate, flash, flash-override.
  • q735--Used by Signaling System 7 (SS7) networks based on ITU Q.735.3. It also defines five precedence values: 4, 3, 2, 1, 0.
  • drsn--Used in U.S. DRSN. It defines six precedence values: routine, priority, immediate, flash, flash-override, flash-override-override.

With this being described in Cisco documents, I am not sure whether it can work between to private SBC's. To confirm the functionality, you can open a Cisco TAC case.





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Thanks, Vaijanath S.
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