Nearly every PBX in existence has some way to take outside audio and use it for music on hold. In the past, Cisco sold a nifty little USB device (MOD-USB-AUDIO=) that would allow you to connect any audio source to a Call Manager server. This worked great up until Call Manager 9; with Call Manager 10, all UC servers only support installation on virtual hardware. In theory you could configure USB pass-through and add a USB device to your VM, but the audio quality is pretty poor and is not supported by Cisco. Now what?

The only official solution from Cisco is to use an FXO or E&M module to connect the audio source to an ISR router, which can generate a G.711 audio stream and send it to a multicast address. There are a couple of hurdles to overcome though:

Most audio sources are stereo but the FXO/E&M modules only take mono input. You could just take one channel but you could be missing half your music, or you can twist the R&L channels together but then you risk damage to equipment or feedback. I have yet to see CD player or radio with an RJ-xx output.

The 3.5mm to RJ-11/RJ-45 issue seems simple. Some other blogs and forums have recommended this little adapter from Omnicron: MOD-SC. I contacted the vendor and asked about the pinout; it turns out that the tip connects to pin 3 and the ring connects to pin 4, which translates to pin 4 & 5 on the RJ-45 for the E&M module. Reading the CME MOH configuration guide reveals this little tidbit:

MOH requires that you specify 4-wire operation with this command for E&M ports.

Then over at the E&M Configuration and Troubleshooting guide you find this:

Note: For the four-wire audio setup, Pin 6 (Tip) and 3 (Ring) on the router transport the audio path from the PBX to the router. Pin 5 (Tip1) and 4 (Ring 1) on the router transport the audio path from the router to the PBX.

So MOD-SC will only work if you want to send audio FROM the router to another device. At this point I realize I have to build something. While I’m building something new, I may as well tackle the problem of converting stereo to mono. After some Google-fu and hitting a couple audio forums I found a simple solution that only requires a couple resistors. All of the parts cost about $4 at a local electronics shop.

RJ-11 jack

3.5mm stereo jack

(2) 600Ω resistors

PCB

Project Box

Quick circuit diagram:

Inside the box.

Putting the the parts together. I wasn’t happy with the solder joints so I went back and fixed them after I took this photo.

Mostly assembled. The store I went to didn’t have 600Ω resistors so I got 300Ω and hooked a couple in series.

I also built a test rig so that I could move the pins around if needed because I had some issues with getting the E&M card to pick up the audio properly. To do this I cut a Cat5 cable in half and soldered the pins to some breadboard headers.

Aaand the finished product!

Now that the hardware hacking is complete, we can actually get down to the configuration!

voice-port 0/2/0 auto-cut-through operation 4-wire signal immediate input gain -3 ! dial-peer voice 7777 pots destination-pattern 7777 port 0/2/0 ! telephony-service max-ephones 24 max-dn 192 ip source-address 10.1.192.6 port 2000 max-conferences 8 gain -6 moh "flash:/moh/ColdFunk-G711.wav" ! Backup audio multicast moh 239.1.192.1 port 16384 transfer-system full-consult ! ephone-dn 55 number 5555 moh out-call 7777

In CUCM, you need to setup multicast MOH and make sure the multicast address for one of the streams matches the address configured on the ISR router. You should select “Increment Multi-cast on: IP Address”. The 1st stream will be your base address, then each successive stream will increment by 4 (.5, .9, .13, etc). In this case I used the base address and set the TTL for that stream to 1; this prevents the CUCM audio stream from leaving the local VLAN.

Now you just set your device(s) to use Stream #1 for MoH and you should hear the music playing through the ISR Router!

References:

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This entry was posted on 2015/03/27 at 18:33 and is filed under Cisco, Technology. You can subscribe via RSS 2.0 feed to this post's comments.

Tags: cisco, cme, cucm, multicast

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