Cisco CUBE line-side SIP Proxy – Transcoding

To properly handle SRTP to RTP internetworking on your CUBE SIP proxy you will need PVDM modules. To maximize your usage you should have G711 configured as a region and “codec transparent” on your dial peers. You can do G729 however that is higher complexity and you’ll get less sessions out of your PVDM modules.

Using DSP calculator I came up with this assuming G711 between IP Phone and everything else:

0-16 Sessions = PVDM3-16; 17-24 sessions = PVDM3-32; 25-48 sessions = PVDM3-64; 49-96 sessions = PVDM3-128; 97-144 sessions = PVDM3-192; 145-192 sessions = PVDM3-256. Some model routers obviously support more than one PVDM3. Use the Cisco DSP calculator for the best answer.

If you assume high complexity G729 a PVDM3-256 can only support 60 sessions!

Configuration in the previous post mentions using SCCP and to do so requires the telephony-service along with relevant SCCP configuration. Since our transcoding will happen local to the router we can use LTI API instead of the SCCP API. If both SCCP and LTI are configured the LTI takes precedence.

IOS 15.4(2)T

Enable CUBE:

voice service voip

allow-connections sip to sip

DSP farm profile:

dspfarm profile 1 transcode universal security

trustpoint SELFSIGN (this is your selfsigned trustpoint on the CUBE, use whatever name you’ve used)

no codec g729ar8

no codec g729abr8

maximum sessions ? = this will return the maximum value allowed for the configured codecs in this profile

no tls (turn off SIPS interworking since we are transcoding local to the router for performance)

associate application CUBE (this is where we define the CUBE LTI API vs the SCCP API.

no shutdown

Verify:

CUBE1# Show dspfarm profile 1

Dspfarm Profile Configuration

Profile ID = 1, Service =Universal TRANSCODING, Resource ID = 1

Profile Description :

Profile Service Mode : secure

Trustpoint : SELFSIGN

Profile Admin State : UP

Profile Operation State : ACTIVE

Application : CUBE Status : ASSOCIATED

Resource Provider : FLEX_DSPRM Status : UP

Number of Resource Configured : 96

Number of Resources Out of Service : 0

Number of Resources Active : 0

Codec Configuration: num_of_codecs:2

Codec : g711ulaw, Maximum Packetization Period : 30

Codec : g711alaw, Maximum Packetization Period : 30

cube1#

Thanks!

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