Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

Site-to-Site CMEs via Public Internet - Viable ?

hi folks,

my customers has on several occasions posed this question to me on the viability of having Site-Site CME communications using the public Internet infrastructure, together with VPN. I understd cisco's recommendations are for pt-2-pt dedicated WAN link.

as such, if such an implementation were to be rolled out, what will be the most likely issues to occur ? What I can think of is lack of CAC & QOS, excessive hops, unable to use codec etc.

pls advise..thanks!


Re: Site-to-Site CMEs via Public Internet - Viable ?

The issue here is that you can only control QoS to the gateway. We have a centralized Callmanager deployment and I recently brought up a small remote site using a VPN over a 3Mb cable connection. When calling out to the PSTN or in from the PSTN at this location, only the call signaling goes across the VPN and everything works great. If you dial an extension at another location, both call signaling and the audio stream traverse the internet. Sometimes the call quality is good. Other times it's not so great. The biggest problem I've seen is delay causing one person to step on the other's conversation. So, it's viable, but you will see quality issues at least some of the time since the nature of the public internet is not to guarantee packet delivery, acceptable levels of delay, etc.

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


New Member

Re: Site-to-Site CMEs via Public Internet - Viable ?

I have worked on similar roll outs where where had 30 or so remote users on Call Manager. Using a VPN3020 concentrator to terminate the VPN tunnels at the main location and 831 routers with QoS at the remote connections. Some days the calls would work fine but othters there would be jitter, echo, and just poor call quality. The bottom line is yes it will work but you will never have guarenteed call quaility when using the internet for VoIP.

New Member

Re: Site-to-Site CMEs via Public Internet - Viable ?

You will have all the issues you mention, but they may be 'workable'. I have 2 small CME sites linked via the internet (ADSL) and as long as there are only a few calls going accross the VPN link then it works A OK.

I use QoS policies to prioritise the voice on the Outbound interface, and because there is a CME router at each side I use the g729 codec.

If you intend just putting IP phones without a local CME router then you'll have to use G711 so that gives bigger bandwidth problems - I have this at my home office but to be honest it's not failed yet (nearly a year working 100% via ADSL at both sides using GRE tunnels - not encrypting voice) so as long as you dont go crazy with calls I think it should be OK. (This is to quite a busy ADSL connection @ our office as well!)

Now if you want to try SIP (latest CME only) then I think you can use g729 for all remote phones, but I haven't tried this as yet.

good luck!

New Member

Re: Site-to-Site CMEs via Public Internet - Viable ?

Hi Peter,

thanks for the heads-up. Are u able to share your CME-CME configuration using VPN via Internet(ADSL)? I will like to know how I may have the QoS & VPN configured for such a scenario. my email is : . Thank you!

作成コンテンツを作成するには してください