Why choose H.323 vs MGCP vs SIP

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Mar 5th, 2006
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Hello all,

I am having alot of trouble userstanding why one would choose one voice control protocol over another. I understand that MGCP is master/slave and gets almosta ll of its config via callmanager, doesn't support SRST without fallback to an H.323 endpoint and such. I know that H.323 has alot more IOS config to do, dial-peers, etc., but other than that what is the difference?

Is there a feature comparison somewhere or why do you guys choose one over the other?

Thanks so much for your help!!

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Overall Rating: 3.8 (6 ratings)
Brandon Buffin Sun, 03/05/2006 - 13:39
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Here's a few differences and a link to a brief comparison of the 3.



-Uses Abstract Syntax Notation 1 (ASN.1) for call control messages

-Uses a peer-to-peer model

-Scales well in an enterprise

-Fractional PRI support

-CallerID support on analog FXO

-Many more TDM interface types and signaling

-Gateway-resident applications like TCL and VXML

-CAC network design with H.323 Gatekeepers

-No release dependencies between GWs and CCM

-Call preservation for SRST on PRIs

-NFAS support


-Not as mature as H.323

-Uses clear text for call control

-Uses a peer-to-peer model

-Allows interoperability between diverse vendor equipment


-Not as mature as H.323

-Uses clear text for call control

-Uses a client-server model

-Ideally positioned for service providers (centrally located call agents)

-Centralized management and control (Dial plan, etc.)

-Enhanced call survivability

-Better feature interaction with capabilities like CallerID

-Support of QSIG supplementary services with CCM

At-a-glance Comparison


Hope this helps. If so, please rate the post.


level3tech Sun, 03/05/2006 - 18:59
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Thanks for your reply,

I don't know why i am having such a hard time understanding all this. I looked at your link and have done quite a bit of research on the different protocols this evening.

What i am having trouble understanding is more of the conceptual ideas behind these protocols. Take h323 for instance. Its media independent, so it doesn't matter what type pstn circuit your pipe into the gateway because it terminates all of that low layer info matches dial-peers and only passes relevant info to callmanager which leads me to the big point:

What the heck does callmanager do in an h323 environment? I mean if the gateway is that smart and can do everything, and an h323 endpoint cal call another endpoint directly, how does callmanager factor in? How is your dial plan administered via CM when you have dial-peers on an h323 gateway?

Thanks very much for your help!!

chinnawo Mon, 03/06/2006 - 00:29
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I'd like to add my opinion here. H323 is more clever than MGCP. When CCM passes the call to H323, it steps out of the picture and let H323 does its job. Whereas MGCP is a dump one, CCM have to be in the picture till users hang up the call. I picked up MGCP because my customer wants CDR to keep track of the call (MGCP backhaul feature). H323 does not relay isdn signalling to CCM so CCM knows nothing about the call duration.

Actually I prefer H323 because of my familiarity with its debug output compare to the MGCP's.


Brandon Buffin Mon, 03/06/2006 - 06:59
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While an H.323 gateway does have the dial plan information it needs, Callmanager sitll plays a role. H.225 (Call setup and control) and H.245 (Capabilities exchange and logical channel negotiations) messages are exchanged between the gateway and callmanager. Once the call is established, the RTP stream goes between the 2 endpoints without passing through callmanager.

Hope this helps. If so, please rate the post.


jconi Mon, 03/06/2006 - 01:44
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I think you'll choose your protocol after some experiences which will learn you what are the advantages of these protocols for you.

For example, if you need to do Overlap Sending, you'll choose MGCP, because H323 doesn't support it. Also if you need to translate overlaping incoming number, H323 is more useful.

There are a lots of specific needs which will guide you through the best choice.

Good Luck


level3tech Mon, 03/06/2006 - 06:33
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Thanks for your help,

I'm still having difficulty understanding what callmanager does in an h323 deployment. If the gateways have most of the intelligence, then what does callmanager do in a basic setup?

Also, is there a decent feature comparison out there that i can look at to see most of the differences?

Thanks again!

jconi Mon, 03/06/2006 - 07:55
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As from today, it's no more right, because, with CCM 4.2, overlap sending in now supported in H323


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