So I have been reading up on CVOICE material, mostly out of boredom. I was never really interested, but now that I have read up and gone through some CBTs, it really does seem interesting and cool! Anyways, the signaling end of it is really making my head spin. Do any of you guys out there know much about voice and can maybe explain some stuff to me? Mainly:

1) OK, I understand that from a voice gateway perspective you can run h.323 , SIP, or MGCP. This all makes sense to me…it is more of what is going on between the IP phones and the CallManager and the gateway that is making my brain hurt.

Originally, I thought that IP phones could either:

1) Run SCCP (Skinny) between the phone and the CallManager. Thus, the CallManager provides dial-tone, etc.

2) Run SIP between the phone and the CallManager (This is another “grey” area for me, because evidently there used to be this thing called the Cisco SIP proxy which was around before Cisco really embraced SIP…now they have SIP support IN CallManager)

So here I was thinking MGCP was just a protocol run between the gateway and the CallManager, or between gateways…then I found out that you can actually run MGCP on the phone itself??? How does that work? Can you register phones that run MGCP in CallManager like you can phones that run SIP or SCCP ? Is this just a 3rd party thing? Does anybody do this?

So mainly — I get whats going on with the gateways themselves — They basically are routers between POTS and VOIP networks, or VOIP to VOIP networks and can run either h.323 , SIP , or MGCP. From what I understand CallManager supports all of these options and with MGCP it actually controls the ports whereas with h.323 it just sees a gateway in it’s database. With SIP it seems the CallManager in todays times is actually also the SIP proxy and SIP Registrar server as well all rolled into one. So, whats with the signaling on IP phones (like a Cisco 7960). What protocols can they run, and how do they get signaling information such as dial tone? It seems that

1) If the IP phone runs SCCP it registers with CallManager and gets signaling from CallManager. From what I understand SCCP is a stripped down version of h.323. This seems to be the more popular “cisco” option

2) If the IP phone runs SIP well…things seem to have changed or are in the midst of changing. Back in the day it seems you had to purchase some other box called the Cisco SIP proxy…nowadays it seems a Cisco IP phone running a SIP image can go ahead and register with CallManager as well. CallManager itself is the SIP proxy/registrar/location server all rolled into one beast (I think). Therefore, CallManager would provide dial-tone, etc. or at least instruct the IP phone to play tones it already has in flash

3) If the IP phone runs MGCP I don’t know what the hell is going on, and I need help 🙂

Thanks voice guys!

– Joe