CUCM Allocate MTP Resources limitation on outgoing calls - fast busy

[Lazarus_telecomTech]

Hello all! 

I've just installed a new ISR4321 as a CUBE and connected it with a SIP trunk on a CUCM 11.5, using an MTP.  The CUBE connects to the ISP's SBC.  The client is able to receive and make incoming and outgoing calls, however, during high call volume, some users are complaining of an intermittent fast busy when trying to call out.  I have found this in the CUCM traces:

43533691.013 |11:18:15.622 |AppInfo |MediaTerminationPointControl(1)::getResourcesAllocated -- allocateErrBitset=0x0
43533691.014 |11:18:15.622 |AppInfo |MediaTerminationPointControl(1)::waiting_AllocateMtpResourceReq - MTP usage (23) >= configured throttle percent (95) of Total Resources (24). Attempt to allocate a diffferent MTP.
43533691.015 |11:18:15.622 |AppInfo |MediaTerminationPointControl(1)::incRequestsThrottledCounter Count=1
43533691.016 |11:18:15.622 |AppInfo |MediaTerminationPointControl(1)::SendMTPResourceErrToSender - ERROR AllocateMtpResourceReq failed -- Ci=31645717, errBitset=0x2

and

43533695.019 |11:18:15.623 |AppInfo |MediaTerminationPointControl(1)::logResourceStatusinTrace -- Device Name=MTP_2 ResourceAvailable=0 ResourceUsed=24

In the Enterprise Parameters of the CUCM, there is a configuration for that "configured throttle percent" of 95.  It states there that it's 95% of the Call Count, which is a service parameter in the Cisco IP Voice Media Streaming Application.  I checked, and that value is set to 48 by default.  (I set it to 100, but it made no difference).  The error above says that the total resources are 24, and it attempts to allocate a different MTP.  But there is no other MTP, so the call fails.

Where is it getting this value of 24?  Could that be coming from the CUBE itself??  I took a look at the MRGL and MRG and MTP parameters, but nowhere is there any indication of the number of resources.  I want to increase this to 50, because we have purchased 50 call paths to the ISP, and we have licenses for 50 call paths in the CUBE. 

(Concerning call path licenses in the CUBE, my understanding is that they are honors-based, so there's no need to install them?  I couldn't find any indication of activation of these licenses anywhere, please can someone confirm?)

Any suggestions as to where such a configuration change should be made?

Note that this is part of a migration from the use of a PRI trunk with 24 channels, to the SIP trunk.  So it makes sense that this value of 24 as the total resources was configured somewhere.  But now that we have more call paths, this should be increased.  Any suggestions?

Thanks in advance!!

Laz

PS  I took a look at some other threads, some had relevant info, but none indicated where that value of total resources is configured.

[Nithin Eluvathingal]

How many CUCM nodes you have ?

What MTP you use, software or hardware. I

If software, How many software MTP  available on the MRG ?

Media Termination Point Types

MTP Type	Description
Cisco IOS Enhanced Media Termination Point	This type supports Cisco 2600XM, Cisco 2691, Cisco 3725, Cisco 3745, and Cisco 3660 Access Routers and the following MTP cases: For software-only implementation that does not use DSP but has the same packetization time for devices that support G.711 to G.711 or G.729 to G.729 codecs, this implementation can support up to 500 sessions per gateway. For a hardware-only implementation with DSP for devices that use G.711, G.729a, and G.729b codecs, 200 sessions can occur per NM-HDV2, and 48 sessions can occur per NM-HD. Note    For more information on using G.729 codecs over SIP trunks, see Session Initiation Protocol This type can support Network Address Translation in a service provider environment to hide the private address. In Cisco Unified Communications Manager Administration, ensure that you enter the same MTP name that exists in the gateway Command Line Interface (CLI).
Cisco Media Termination Point Software	A single MTP provides a default of 48 MTP (user configurable) resources, depending on the speed of the network and the network interface card (NIC). For example, a 100-MB Network/NIC card can support 48 MTP resources, while a 10-MB NIC card cannot. For a 10-MB Network/NIC card, approximately 24 MTP resources can be provided; however, the exact number of MTP resources that are available depends on the resources that other applications on that PC are consuming, the speed of the processor, network loading, and various other factors.

https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/10_0_1/ccmsys/CUCM_BK_SE5FCFB6_00_cucm-system-guide-100/CUCM_BK_SE5FCFB6_00_cucm-system-guide-100_chapter_011011.html

[Lazarus_telecomTech]

Thanks, Nithin for your quick reply!

To answer your questions:

• I have only one CUCM node
• I am using software MTP
• I only have one MTP resource in the MRG called MTP_2 (see image attached)

I have also seen the documentation you shared.  The default call count for software MTPs is 48 but you may have less if you are using a 10 Mb/s NIC connection on the server.  We have a gigabit ethernet NIC.  But even that 24 is not a hard limit that is configured, but an approximation based on resources.

What if I create a second software MTP and add it to the MRG?  Could I send all traffic exceeding 24 to the second MTP?  I tried creating a second MTP, but it remained unregistered.  I am grateful for your feedback!

Laz

[Nithin Eluvathingal]

You said, you have a single node. For second software MTP, you need another CUCM node.

You can think of hardware MTP If  you have PVDM resource available on gateway, it can be used for MTP.

When increasing the call count  value substantially you should consider using a dedicated media streaming node, means  the node should be  dedicated for MTP.

You have already increased the call count to 100 and mentioned that there is no impact . Not sure if a single node with phone registration, transcoding , IVR, annunciatior    can go beyond 48 call count.

[Lazarus_telecomTech]

Hi again Nithin

OK, so a second MTP is out of the question.  Unfortunately, there are no PVDM resources on the CUBE. 

---

@Nithin Eluvathingal wrote:

You have already increased the call count to 100 and mentioned that there is no impact . Not sure if a single node with phone registration, transcoding , IVR, annunciatior    can go beyond 48 call count.

So where does that limiting number of 24 come from?  Is it calculated automatically from all of the available resources on the server?  I don't use IVR, so if I disable that, will I get more resources on the MTP?  (The IVR resource is not included in any MRG that is in use).  In other words, what I'm asking is:

1) What is limiting the resources to 24?

2) Is there a way, with a single node, to increase this value?  (redistribute resources, increase the memory and CPU allocation on the VM, not use an MTP at all for the SIP trunk?)

3) Where can I see the actual MTP resources available?  Do I have to wait for a failure to see it in the traces only?

It seems unreasonable that a single CUCM node is unable to handle more than 24 simultaneous calls to a SIP trunk, but working with Cisco, I have found that there are such situations...  Again, any help is much appreciated!!

Laz

[Nithin Eluvathingal · Accepted solution]

This parameter specifies the maximum total number of call parties that the media termination point will support. Each media termination point that is allocated for use will have resources for 2 call parties so that the total number of available media termination point resources will be half the value of this setting. If you increase this value substantially you should consider using a dedicated media streaming node (with Cisco IP Voice Media Streaming Application activated and without Cisco CallManager activated) to prevent interference between streaming and call processing.

So if you keep Call Count 48, in reality its 24.

[Lazarus_telecomTech]

Hello Nithin

Ah yes, perfect thank you!  If that is the case, then with my increase of the value to 100, I should not see the MTP resources appearing as 24 in the trace correct?  But I have.  I suspect this has to do with the IP Voice Media Streaming Application service.  I've reset the service in the CUCM and I suspect that it should be OK now.  I will monitor throughout the day and let you know of my results.

Thanks for your help and will update you soon!

Laz

[Elliot Dierksen]

If a software MTP meets your needs, you can configure a software MTP in the CUBE router, and register that to CUCM. That would keep packet load off your CUCM node. You don't need DSP resources for a software MTP.

[Nithin Eluvathingal]

Never noticed the possibility  of using  ISR software MTP feature.

@Lazarus_telecomTech Have a look on below link if you need to make use of this Router feature.

https://www.cisco.com/c/en/us/td/docs/routers/access/4400/software/configuration/xe-16-9/isr4400swcfg-xe-16-9-book/support_for_software_media_termination_point.html

[Lazarus_telecomTech]

Hello again!

After doing a restart on the streaming service, the MTP limitation was lifted.  No more MTP limitation of 24.  @Nithin Eluvathingal thanks for your help and expertise.

Also, Thanks @Elliot Dierksen for your feedback, that's useful information.

Laz