problem with DSP complexity

Unanswered Question
Nov 7th, 2007

Hi TechPro Community.

I had:

Cisco IOS Software, 2800 Software (C2800NM-IPVOICEK9-M), Version 12.4(11)T3, RELEASE SOFTWARE (fc4)

msk-vg1#sh inventory

NAME: "2811 chassis", DESCR: "2811 chassis"

PID: CISCO2811 , VID: V03 , SN: FCZ104372DD

NAME: "VWIC2-2MFT-T1/E1 - 2-Port RJ-48 Multiflex Trunk - T1/E1 on Slot 0 SubSlot 0", DESCR: "VWIC2-2MFT-T1/E1 - 2-Port RJ-48 Multiflex Trunk - T1/E1"

PID: VWIC2-2MFT-T1/E1 , VID: V01 , SN: FOC11070JE2

NAME: "VWIC2-2MFT-T1/E1 - 2-Port RJ-48 Multiflex Trunk - T1/E1 on Slot 0 SubSlot 1", DESCR: "VWIC2-2MFT-T1/E1 - 2-Port RJ-48 Multiflex Trunk - T1/E1"

PID: VWIC2-2MFT-T1/E1 , VID: V01 , SN: FOC11305A7S

NAME: "PVDMII DSP SIMM with four DSPs on Slot 0 SubSlot 4", DESCR: "PVDMII DSP SIMM with four DSPs"

PID: PVDM2-64 , VID: V01 , SN: FOC11310CXD

I already configured 2 ISDN PRI Groups that controlled by CM:

controller E1 0/0/0

framing NO-CRC4

clock source line primary

pri-group timeslots 1-31 service mgcp


controller E1 0/1/1

framing NO-CRC4

clock source internal

pri-group timeslots 1-31 service mgcp

Codec complexity is set to Flex.

But when I try to add one more pri-group I had an error:

msk-vg1(config-controller)#pri-group timeslots 1-31 service mgcp

% Not enough DSP resources available to configure pri-group on controller E1 0/0/1

% The remaining dsp resources are enough for 4 time slots.

% For current codec complexity, 2 extra dsp(s) are required to create this voice port.


*Nov 7 17:56:57.019: %XCCTSP_VOICE-3-NOSDB: No signaling data block is available to build the

voice interface(0/1:15) or DSP may not be present

Tell me please, what can I do?

I have this problem too.
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Overall Rating: 3.5 (3 ratings)
Paolo Bevilacqua Wed, 11/07/2007 - 09:42

You need to procure a minimum of one additional PVDM2-32.

You have PVDM2-64, supporting the 60 voice channels already configured, the router is correctly telling you that you have resources enough for only 4 channels more, and need more DSP hardware.

Hope this helps, please rate post if it does!

allan.thomas Wed, 11/07/2007 - 10:35

The codec complexity determines the number of actual DSPs that are required, especially if you will be using them as transcoding or conference bridge resources in the future.

In this case the codec complexity has been configured as FLEX, which ensures higher call density.

The problem this creates, is if you decide to change the complexity to medium/high in order to utilise hardware resources in the future.

The actual limitation is the hardware and how many dsps it supports and the number required, which in turn has detrimental impact on CPU.

In order to support 120 G711 calls you will require 8 DSPS or two PVDM2-64 modules.

Whilst looking into the DSP requirements for a 2811, I was alerted to the fact that if you configure all four E1s, the configuration may exceed the CPU capacity of the Cisco 2811 router platform, and Cisco recommend a higher capacity platform.




anton_ntbs Wed, 11/07/2007 - 14:22

Hi Allan.

I know that the loading of my pri groups will be very low, and I will have 45-50 concurent calls at all in all of four E1. And I don't want to buy more DSP, cause it will not needed for processing calls. I hope you understand what I need.

For 45 G711 calls I need one PVDM2-64 and nothing more.

But how can I tell it to my router?

Thanks for you answer, but it's not so helpful for me. Hope you or somebody can answer to me.

Paolo Bevilacqua Wed, 11/07/2007 - 14:58

Hello Anton,

I'm not sure why the low rating to my post and the contentious answer given to Allan's perfectly correct suggestion, because what we are telling you is true:

One single PVDM2-64 is INSUFFICIENT to support more than 2 full E1 PRI.

I could give you tons of evidence, beginning with the DSP calculator, however given your attitude, I doubt I can convince you.

Please do your research, and once you have got the immutable answer, please come back here and share it.

Good luck.

anton_ntbs Thu, 11/08/2007 - 01:45

Hi, Paolo. You gave very good answer but not for my question. I'm sorry that I touch you to the raw. Maybe I was to fast in my decisions.

allan.thomas Thu, 11/08/2007 - 00:09

Unfortunately regardless of how many concurrent calls that will be used across all four E1, a DSP is automatically provisioned for each timeslot when CallManager configures the pri-group timeslots.

The question is whether you actually require this many timeslots in the first instance, this is usually gauged upon the busy hour.

There are certain circumstances where you dont require all timeslots, for example you order a fracional E1 for 10 timeslots. This issue is that if you use MGCP, CallManager will still attempt to configure 'pri-group timeslot 1-31 service mgcp'.

If you only have a single pvdm2-16 installed, CallManager will configure 'pri-group timeslots 1-16 service mgcp'.

In these scenarios it is possible to free DSPs because you don't physically have the timeslots, and they you can provision these DSP for other resources.

You may have calculated for 10 G711 calls, 2 mixed conference, and 2 transcoding resources which will require a pvdm2-32 or two pvdm2-16.

Like I said before the problem is that MGCP will configure all timeslots, and consequently will will have insufficient DSP resources to configure your transcoding and conference bridges.

Therefore if have four e1 you will need two pvdm2-32 modules for all the timeslots.



Paolo Bevilacqua Thu, 11/08/2007 - 01:01

Hi Allan,

All right, but I think you meant,

if have four e1 you will need two pvdm2-64 modules for all the timeslots.

anton_ntbs Thu, 11/08/2007 - 01:39

Allan, correct me if I understand you no so clearly: if I use Pri-groups controlled by mgcp, I need to install DSP resources for ever timeslot that I programmed, but not for ever g711call.

And in other case: if I use standalone pri-groups is it the similar situation? I have to try, but can't do it in workdays, cause it is working system.

allan.thomas Thu, 11/08/2007 - 02:19

The problem you will be faced with if you change your time-slots is your route-group/route-list configuration.

When the timeslots are exhausted on one gateway in your route-group it will go to then next gateway in your route-group/list and so on until it finds an available channel.

However, if you reconfigure the pri-group to have less time-slots, firstly you need to ensure that CallManager does not update the configuration and change the time-slots back.

Secondly you need busy the channels not used within CallManager in order to ensure that calls are able to route to next gateway in the route-group/list when busy.

In your scenario, I would strongly recommend at least an additional PVDM2-32 for the third E1.

The fact that you have 30-Channels for each E1, and you want reduce this adds complexity especially when troubleshooting. Also if you are reducing the time-slots, there is strong justification for having only two E1 bearers, thus you would not require addional dsps, and no line-rental charges.

Unless you require hardward resources for transcoding/conferencing of course.



rafael.cardoso Wed, 11/28/2007 - 05:36


leaves its configured equipment in this way:


controller E1 0/0/0

framing NO-CRC4

clock source line primary

pri-group timeslots 1-15 service mgcp


controller E1 0/1/0

framing NO-CRC4

clock source internal

pri-group timeslots 1-15 service mgcp


controller E1 0/2/0

framing NO-CRC4

clock source line primary

pri-group timeslots 1-15 service mgcp


controller E1 0/3/0

framing NO-CRC4

clock source internal

pri-group timeslots 1-15 service mgcp


Good luck!



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