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Community Member

Subnet for IP Phones registered to CME


When registering IP (SCCP) phones to CME, it is generally stated that the phones should be in the same local network.

I used to think that this meant the same IP subnet and VLAN as the CME, but found out that phones in subnet 192.168.5.x can register with CME on 192.168.1.x network, as long as inter-vlan routing is configured.

At the same time, I see posts about restrictions on IP phones registering to CME over a WAN.

Apart from speed, what is the difference between WAN and LAN at layer 3?

How would an IP phone on a WAN, be treated any differently than one on a different subnet on a local lan ?

VIP Purple

Re: Subnet for IP Phones registered to CME

Along with speed come other issues such as latency, jitter, and packet loss. In an environment where some portion of the WAN traverses the public internet, you have no control of and no guarantees for these factors. You can configure QoS on your equipment, but beyond that it's normally best effort. While not the best scenario, it is possible to register a phone with CME in this circumstance and may meet your needs. If the WAN is a connection for which you have control of QoS and SLAs from the provider, it is possible and very feasible to register a phone with CME over the WAN. One issue to be aware of in both cases is that all calls, including 911, will be routed out the CME gateway. This could pose a problem if a user in Seattle dials 911 and a truck rolls to the CME location in Chicago.

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


Hall of Fame Super Silver

Re: Subnet for IP Phones registered to CME

With CME 4.0 a new feaure "teleworker remote phone" is supported, where you can have home users register to CME via VPN. As Brandon stated this can cause some issues, such QoS and 911. Here is the link:


Community Member

Re: Subnet for IP Phones registered to CME

Thanks :-)

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