CCIE Collab – Gateways and Trunks in CUCM

Hi there, so today I wanted to bring up something that was very confusing to me long time ago. The concept of MGCP, H.323 and SIP.

these 3 are very big and there is a lot of information about them, I just want to explain with my own words what every single protocol means for me and the way I had to put it in my head before I was able to understand the technology behind it.

H.323 Gateways :


– So an H.323 gateway acts as a point to point protocol between the CUCM and the Router.

– Dial Plan is managed directly on the router.

– Dial Plan is also managed on CUCM and points to the router to be able to dial out.

– H225 and H245 are used for signal and for the setup messages between the router and CUCM.

– Provides SRST capabilities



– Is also a point to point protocol between the router and CUCM.

– Dial Plan is directly managed on the Router and on CUCM as well.

– It uses SIP messages from the provider in order to set up calls.

– Troubleshooting is so easy ! – no weird stuff on it (In my opinion).

– Uses SIP protocol to connect back to CUCM.

– Provides SRST capabilities



– Quick Configuration from the Voice gateway (In my opinion is my least preferred, I don’t use it unless I can’t convince my customer not to use it).

– Dial Plan is managed on CUCM only

– Gateway is just the connection to the PSTN (I think a waste of money unless in SRST mode)

– Provides SRST capabilities

I know there is so much more information about these protocols, but this is what helped me to understand the basics.

Please feel free to comment and debate about them, and if you see anything wrong please let me know!!


Images captured from CCIE Voice Advanced Technology Class Video video 20 – Unified CM – Gateways and Trunks – Concepts & Slides

About the Author:

Andres Sarmiento, CCIE # 53520 (Collaboration)
With more than 13 years of experience, Andres is specialized in the Unified Communications and Collaboration technologies. Consulted for several companies in South Florida, also Financial Institutions on behalf of Cisco Systems. Andres has been involved in high-profile implementations including Cisco technologies; such as Data Center, UC & Collaboration, Contact Center Express, Routing & Switching, Security and Hosted IPT Service provider infrastructures.

You can follow Andres using Twitter, LinkedIn or Facebook

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top