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IP Phone communication

Hi, We have 4 overseas Location including HO. Lets Name is HO Location – A & rest of branch location is B, C & D B, C & D are connected with A via Site to site VPN (IPSec Tunnel) over internet as a star topology. If B wants to reach C then its connectivity is via A & same for all location. A to B --- Latency 250 ms A to C --- Latency 260 ms A to D --- Latency 275 ms B to C – Latency will be 250+260=510 ms We are planning to deploy IP Phone at B & C Location for communication. But we are suspecting Latency issue. For your information we have Microsoft Lync 2010 at A location & all B,C & D location’s users are voice/chat etc. Could you please suggest us how we should go forward? Or any topology change
8 Replies 8

Sreekanth Narayanan
Cisco Employee
Cisco Employee

We have seen voice calls being able to handle latencies of ~600 ms because of satellite links when the routers and phones are located on ships. So you should be able to make calls. However, registration is another matter. Where are the phones of locations B,C and D registered? If they are registered to CMEs located in locations B, C and D respectively, it should be ok, but registering phones over VPN with high latency is not possible. The keepalives will timeout and phones will get unregistered frequently.

if B,C & D have voice gateway with CME & we create additional B to C site to site VPN.

A to B & A to C site to site VPN remain same & we remove the B to C permission from Access List for reachability  between B to C via A.

doing above task, I am going correct way or suggest any other solution.

Please help us.



I am colleague of above member of this community

Although latency is 600 ms is possible for voice calling.But Here i have some concerns

1. Either we should go for deploying CME at Hub Site and all voice communication happen   through hub site of 2 spoke sites and latency will be around 600 ms

2.other point is whether we should go for individual CME for spoke sites and create vpn between spoke sites and minimize latency.
3. other point is we should deploy CME box at single spoke site and both sites IP phone register with single CME.

is it necessary to go with voice gateway solution at each site

Please suggest best and standard practices for CME and IP phone for spoke sites


All suggestions will be appreciated.




CME at each site to minimize the possibility of phone registration issue which may occur in hub-spoke topology and VPN tunnel between B to C will be best possible solution I can see. 


You should proceed with it.


Thanks !!

Anas Abueideh


Deploy DMVPN topology for your vpn connection. in DMVPN you will create dynamically vpn tunnel between B and C, instead of passing HQ.



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A,B,C & D locations have Cisco ASA. & we have created site to site VPN over internet between ASA to ASA. B Location's users accessing mail, sap & intranet application from A (HO ) Location. & same as C & D Location also.

you mean to say that A to B & A to C site to site VPN will remain intact(no change). as per your recommendation, need to create new DMVPN between B & C.

if yes then please share the DMVPN document.






Unfortunately, DMVPN is not supported on ASA



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any help ?

How should go forward.  Please help us.

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