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ASK THE EXPERTS - Configuring and Troubleshooting SIP Trunks

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Jan 31st, 2011
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with David Whiteford

Welcome to the Cisco Networking Professionals Ask the Expert conversation. This is an opportunity to get an update on configuration and troubleshooting Session Initiation Protocol (SIP) trunks with Cisco expert David Whiteford. David has been a customer support engineer in the Cisco Systems Multiservice  Voice team since March 2009. He has over 20 years of experience in Voice. David has previously performed both software development and  interoperability testing with SIP trunking. He has a bachelor’s degree in computer engineering from Tulane University and currently holds a  CCNA Voice certification.

Remember to use the rating system to let David know if you have received an adequate response.

David  might not be able to  answer each question due to the volume expected  during this event.  Remember that you can continue the conversation on  the Collaboration, Voice and Video discussion forums shortly after the event. This event lasts through February 11, 2011. Visit this forum often to view responses to your questions and the questions of other community members.

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Overall Rating: 5 (2 ratings)
JustForVoice_2 Mon, 01/31/2011 - 12:15
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Hi David ,

Is there any recommendation from Cisco to Integrate CUCM solutions with SIP provider?

shall we use SIP trunk to SIP Provider?

Shall we use CUBE?

One more thing is there any references to understand SIP in General and how to write programs using SIP protocol and what is the preferred programming language?


dwhitefo Wed, 02/02/2011 - 06:18
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It is recommended to place a CUBE between CUCM and a SIP provider.  The advantage to this is the CUBE has the ability to modify SIP message to meet the requirements of different providers and it also provides address hiding so the customer presents a single interface to the provider and all of the customer network details are hidden.

There are plenty of good resources on the web to find out more about SIP, but start by looking at some of the IETF RFC's like RFC 3271 which is baseline RFC for SIP.  There is a good book by Darryl Sladden called "SIP Trunking" which can be found at

For programming languages, I have not seen a preferred language, but there are SIP protocol stacks available in C, C++ and other languages which would give a head start on developing a SIP application.

David Whiteford

Habib Ahmad Wed, 02/02/2011 - 21:47
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In response to your first question,

Is there any recommendation from Cisco to Integrate CUCM solutions with SIP provider?

Just wanted to share this, its been a good doc as a guide line

juan.salaiza Wed, 02/02/2011 - 09:57
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Hi david, i have a question, can you tell me what it the best practice to integrate a CUCM, a SIP PBX and a Gatekeeper.

Tthe main idea is. CUCM is already integrate with a GK, but we need to add a 2 SIP PBX´s to a GK, is it possible?. i´ll aprecciate your help.

dwhitefo Wed, 02/02/2011 - 11:36
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You have a few choices for interworking between the SIP PBX and CUCM.  You could use a CUBE to connect to the SIP PBX's and then connect to the CUCM from the CUBE using a SIP trunk or H.323.  You could also use a SIP trunk directly from the CUCM to the PBX, but the CUBE would provide much more flexibility and could provide the ability to route between the PBX's without having to go through CUCM.

mcecilia Thu, 02/03/2011 - 00:42
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Hello David,

We are deploying an scenario where PBXs from different vendors are connected to CUCM using SIP trunks. The problem comes, because we have needed MTPs for all.

In CUCM 6.1 it is not allowed to use G729 with MTPs but it is with 7.1. Is there any way to use G729 for trunks with 6.1 when MTP is needed?

Also, how does CUCM Session Manager Edition, Cisco Unified Sip Proxy and CUBE play in the SIP trunking solution?

What does any one differs from the others?


dwhitefo Thu, 02/03/2011 - 06:22
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As far as I know, you should be able to use G.729 with MTPs in CUCM 6.1.  However, the MTP's have to be on an IOS device.  It is not clear from your discription whether you have SIP trunks directly from CUCM or whether you are using a CUBE between CUCM and the SIP PBX's.  If you use a CUBE, then the CUBE will perform some of the functions provided by an MTP.  CUBE is a session border element, so it actually terminates one leg of VoIP calls and then makes a new VoIP call on the other side.  Therefore, CUBE can provide interworking between H.323 and SIP if required and can perform any needed protocol transformation using profiles on the CUBE.  The Cisco Unified SIP Proxy (CUSP) is true SIP proxy server.  It simply routes SIP messages to the correct destination and can be used as a way to do load sharing across multiple SIP devices.

mapleasant Thu, 02/03/2011 - 16:31
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First time using this and simply asking for confirmation.

dwhitefo Thu, 02/03/2011 - 19:58
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m.trautes Sat, 02/05/2011 - 13:20
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Hello David,

do you know any konfiguration between a UC540 and a MS Lync 2010 - because a new company - who we sell - has a Lync and we use a UC540.

So i´m looking for a sample configuration for a SIP Trunk between this Systems.

Thanks for Help


Nathan Compton Sun, 02/06/2011 - 21:55
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Hello David,

I'm coming up on my first CCIE Voice Lab attempt in March.  On a practice test, I was given a requirement to integrate a SIP trunk with CUCM, but CUBE was not possible due to no H323 gateways in the scenario.

Routers running CUBE have the possibility to debug sip messaging to see what is failing during a SIP call.  Is there any equivalent feature in the CUCM that would allow you to see the SIP message exchange between the CUCM and the other SIP endpoint?

joe-vieira Tue, 02/08/2011 - 10:33
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We're considering adding a SIP trunk to our hosted call center provider. Currently the signaling/data portion uses the Internet link and the voice traffic flows in the PRIs. Questions;

- Do we need just a router on our end to support this?

- Is it recommended to have separate links for the Voice and Data traffic

- Does it make a difference if it's a Lan Extension or MPLS link?

- Can you provide links to documents that detail what's involved with this installation and configuration?


dwhitefo Wed, 02/09/2011 - 07:15
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I assume you have an existing call manager in place.  So I would recommend setting up a router to act as a CUBE.  This could be an existing router depending on the hardware and whether it has the capacity.  You can have data and voice going through the same links.  For this case, you typically have a firewall or router split the data traffic from the voice traffic and ensure that you have QoS set up for your voice traffic.  It does not make a difference if you use LAN extension vs. MPLS.  With MPLS, just make sure you have enough bandwidth allocated for you voice and data needs and ask to make sure the MPLS provider will provide QoS for the voice traffic.  The set up for SIP trunking varies depending on the provider.  Here is a link to a document for AT&T as an example:

joe-vieira Thu, 02/10/2011 - 09:51
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Thanks for your reply. Unfortunately I am not able to open the link. Can you send another link that is not partner?


sebastien_michelet Fri, 02/18/2011 - 16:06
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What are the known limitations of doing media flow-around with CUCM 7.x and CUBE with G729 codec (centralized cube design)?

I have read different posts regarding this design related to hold, resume or moh not working correctly.

Is there a list of caveats posted somewhere?

Also, will CUCM 8.5 (with support of Early Offer) be able to fix any of these limitations.




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