Showing results for 
Search instead for 
Did you mean: 


SIP domain, where does it come from?

I've been doing video conferencing for years either over our network between sites or via ISDN to the world. We are now installing a system with a VCS Control, a VCS Expressway, a MCU 4501, and soon TMS to run the whole show.

During the initial configuration, I am to enter our SIP domain in both the Control and the Express. Where does this come from and how do I get one? I can't imagine that I just make it up out of thin air and hope for the best.

Yes, I know the rest of the world has been using this for years, but this is entirely new to us and I'm mostly in the dark as to how to make this work.

And I probably sound like some old codger that hates change, but I'm not really. I'm just lost.

Alok Jaiswal
Cisco Employee

Hi Smith,

the SIP domain could be the original organization domain like we have "" or it could be something specific for e.g. "" only for video service but this sip domains should be rosolvable.

for this this sip domain needs to be configured with the srv records so that if some one query to your domain it should resolve based on the service user is trying to access.

this srv records used for registration and calling purpose, plus it is also a recomended for the VCS clustering.

check the below link for more information on srv records requirement for the expressway and control.

Appendix 2, page 50.



Thank you for the quick response. Am I correct then that this means that I can't register an endpoint with SIP or make SIP calls between two internal endpoints until I have a public IP registered with a name that I can then use for my SIP domain?

Step 5 of the deployment guide has me entering the same SIP domain on both the Control and the Express, and it appears that this would be a publicly resolvable name.

No, that is not entirely correct for the internal calls - as long as you have DNS records corectly resolving the SIP domain name (for calls, presence , phone books, etc.) you don't need public registered domain name . The picture is changing however if you want your SIP registered endpoints to be reached out from the public internet - then proper srv dns records should be in place , pointing to the SIP registrar (expressway in your case).


SIP domain configuration in deployment guide is to ensure to configured SIP domain on VCS which will handle SIP UA registration.

The list SIP domain(s) for VCS is authoritative.

The VCS will act as a SIP register and Presence server for SIP domain(s) listed in domain configuration and will accept registration request from any SIP UAs attempting to register with an alias that include these domains.

So if deployment is internal only and just for registration and making a call, no DNS registration is necessary.

However to use of full SIP feature, highly recommend to configure DNS SRV (even deploy single VCS only) to define call protocol and priority.

Recognize Your Peers
Content for Community-Ad