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MCU SIP Proxy Address

What does the "SIP proxy address" do on an MCU, for example the MSE8510?  I read the online help, but I'm still not clear on what it does, or can do when calls are placed.  What is the prefeered setting, blank or insert an address such as the VCS?

Thanks, Patrick

8 Replies 8

Alok Jaiswal
Cisco Employee
Cisco Employee

Hi Patrick,

you can register the MCU as a H.323 or SIP to a Gatekeeper (h.323) and SIP registrar (SIP). and it depends on the deployment you have and whether you want to use the SIP or H.323.

so if you want to register the MCU probably on a VCS and want to use the SIP as a protocol type then you can put the VCS ip as sip proxy address.



Currently our MCU is configured both for H323 and SIP, however up until to this point I never thought of or realized the proxy address field and it's use.

From what I'm understanding from your message, if I put in the address of our VCS, than any SIP call from the MCU will go through the VCS?  Wouldn't just registering to the VCS be enough?


I didn't get the exact question. You can choose MCU to register with H.323 as well as SIP both. It all depends..

yes, thats right if you register the MCU as SIP to VCS then the SIP calls from MCU will go through the VCS only, and that's what we want isn't it ?? That's the whole point of having a SIP proxy in the network.

Apart from MCU registeration you can also register the specific conf to the VCS with SIP or H.323 depending on the deployment.

Also please keep in mind if the endpoint protocol in use is SIP and MCU registration is only H.323 then in that case the VCS will do a interwork and uses a traversal license which i think no one wants.!!



Sorry, we have our MCU registered in both protocols, was just trying to figure out what that particular settings does when registered as SIP to a VCS.  Still don't understand though, we've been running our MCU registered to the VCS, but the SIP proxy address in the bottom of the SIP settings page has been empty, should it remain empty or put in our VCS address?


if the SIP proxy address field is empty that means its not registered to VCS as SIP. 

does it show registered on the SIP settings under MCU ?? if the sip registrar usage is enabled and you didn't put the sip proxy address then it won't register.

how you dial to MCU currently ??? using a conf alias or via ip-addres ??

As i said i won't prefer to use interworking on VCS and use traversal call license. so obviously if my endpoint is a SIP then i will register the MCU as SIP.




I happen to be looking for a answer in a similar issue. You answer is what I am looking for but need a bit more direction.

I have cisco c20 endpoints. Currently our default calls both point to point and to MCU is h323. Keeping in mind MCU is registered to VCS as both H323 and SIP.

What I am trying to achieve is being able to make the endpoints call the MCU via SIP but doing that makes the MCU use a traversal license, which like you said I don't want.

Should I unregister the MCU as h323 from the vcs and keep only SIP?

Hi Mohammed,

As pointed by Tomo, VCS always try to use the same protocol type for the call and if fails it falls back to different protocol and do a interworking.

if you want you can register the conf alias with both h.323 and SIP.



Tomonori Taniguchi
Cisco Employee
Cisco Employee

I’m not fully understand what need to be archive here, but important to understand that VCS always trying to establish native call before trying to interworking call within same priority.

If looking the way to force to make interworking call, MCU should not register, should not use same search rule(s), or multiple search rules with same priority that matching MCU both SIP/H.323 as call protocol.

There is similar discussion for transforming MCU prefix to SIP call at

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