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Community Member

CUBE deploy with transoding and PSTN

Hello to everyone,

I would like to deploy a CUBE connect together a CUCM 7.1 and 2  UC500(Callmanager express 8.6). We would like to use SIP trunk between  them, a H233-to-SIP. I have several doubts about this deploy and I will  be very grateful if you can help me.

1, We would like to use the same router we are using to connect to PSTN,  there is any drowback in using that router as a CUBE? As fas as I  understood from documentation there is no problem, anyway I not very  sure if I can use the same router for PSTN(There is there an E1  connected to it) and CUBE with transcoding. If I configure the DSP in a  farm for transcoding, I can get some problem with E1 connection,  actually I don't know if DSP resources are normally used when you place a  call from/to PSTN.

2. For a H323 to SIP CUBE I have to implement a special configuration to manage call transfert? Should I have to config a MTP on that router ?

3. Should I have to deploy a UBE configuration on the UC500 too?

Thank you a lot in advance for your help.



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Hall of Fame Super Silver

CUBE deploy with transoding and PSTN


1.  Yes you can share the PSTN GW as CUBE Gateway.  DSP resources are used for TDM calls such as E1, but not needed for SIP calls unless you are using transcoding. 

2. Depends on SIP trunk capabilities, normally MTPs are not required unless things such as DTMF conflicts are encountered, so as a good practice it is good to have these, you can build IOS software MTPs which use router CPU and not DSPs.

3. By creating IP-IP configuration which you will need to essentially are building CUBE.



Community Member

CUBE deploy with transoding and PSTN

Hi Chris,

thank you so much for replaying.

About point 1.

Actually I need to configure transcoding,  I would like to use a SIP  trunk with G.729 but I am pretty sure I will have only few calls pass  through that trunk. Now the big question is: if I allocate my DSP for  transcoding my router will stop to place calls to PSTN, or the DSP  resource (I have just one PVDM installed)will be shared with PSTN card,  so in the worst scenario it can be happen the DSP card will be  oversubscribed and I could not place a call over PSTN or over SIP  trunk?.

Thank you a lot Chris.


Cisco Employee

Re: CUBE deploy with transoding and PSTN


DSP Pool for dspfarm and for TDM_IP legs is different, so there will not be any issue in one pool accessing the others. i.e TDM-IP call will not use dsp allocated for dspfarm configured for transcoding. However, if you use flex mode, there is room for oversubscription for TDM-IP legs, even then it will not use the pool allocated for dspfarm.

Can you give the exact PVDM part# (from show inventory) and how many E1 you have ? And what codec you will be using in the IP leg.  You can use DSP calculator from to scale the needs. 

If not, first bring up E1 PRI/CAS, and try to configure dspfarm. When you configure max sessions in dspfarm profile it will show you how many max sessions it can use, if you dont have any to honor transcoding request it will show  0 sessions. Make sure to configure dspfarm under voice card, if you dont configure there, it will still show 0 sessions too.

Let us know if you have problem using dspcalculator, I will calculate that for you.



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