Can we manage the input queue on UCS?

[ghislaintalbot]

Hi,

We raised SR 682987369 recently because when using MTP on ISR we had voice quality issues after about 80 simultaneous calls.

The TAC engineer figured out this was due to the input queue limit on the Gigabit interface of the router.

It was set by default to 75 and started to drop packets. So we increased to 1000 and it fixed the issue.

Now my question is: what about MTP on CUCM? Could there be similar issue in this scenario? If yes, is there any manageable value on the UCS?

As we previously had problems after 160 calls before we moved MTP from CUCM to ISR, I expect we have the same kind of limitation.

Any idea please?

Thanks

[Manish Gogna]

Hi,

When MTP is running in software on Cisco Unified Communications Manager, the resource supports 48 MTP sessions. It is not recommended to increase this default  number in service parameters if there are other Media resources, call processing and other functions configured oin the same server.  When MTP is running on a separate Cisco Unified Communications Manager appliance (server), the resource supports up to 128 MTP sessions. You can however have 48+48+48+48 = 192 MTP sessions if there are 4 servers in the cluster doing different functions. More details here

https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/8_5_1/ccmsys/accm-851-cm/a05dsp.html

Manish

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[ghislaintalbot]

Thanks for your answer.

Actually we have 3 subscribers dedicated for IP Voice Media Streaming.

So I would expect a minimum of 3*48=144 sessions which must be 77 simultaneous calls, right?

But the documentation states the limitation should be 48 for a CUCM running Call Control + MTP.

It says we may configure up to 512 MTP sessions when CUCM is dedicated to MTP.

So my understanding is we should be able to have 3*512= 1536 MTP sessions so 768 calls.

I was wondering if the NIC could have a limitation like the input-queue on the ISR which would have avoided us to reach the 768 calls limit.

Or perhaps the documentation is wrong and we really have a limit of 128 MTP sessions per server?

That would mean 3*128=384 MTP sessions so 192 calls.

This is close to the 160 calls we were able to setup, so could be the issue there...

[Manish Gogna]

Hi,

As per the following link

http://docwiki.cisco.com/wiki/CUCM_Media_Resources_FAQ#How_many_MTP_sessions_are_supported_by_CUCM.3F.3F

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.

48 is the default value , but can be increased , you can check the max allowed limit by clicking on the hyperlink for this setting under Service parameters on your cucm admin page.

Manish

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[ghislaintalbot]

Thanks for adding those details.

However, it's still unclear and I can understand this is quite hard to give me precise values as this depends on the type of hardware, NIC, running applications, etc.

Having a 1GB interface I guess I can use the following rule:

- For up to 30 channels, we may use MTP on CUCM (co-resident)

- For up to 60 channels, we should use MTP on a dedicated CUCM instance

- For more channels we should consider MTP on ISR

In general I would advise to use ISR when available.

Do you share my point of view?

Thanks

[Manish Gogna · Accepted solution]

Hi,

Generally speaking your points are right. Software MTP's can be configured on IOS as well without using any DSP's so it is always a good option to move/share the load from/with CUCM.

Manish

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