This may help.
The network switches need to support Multicasting
Generally only IP phones on the local LAN can use the Multicast feature.
IP Phones across a WAN network may still require an individual MGI resource.
Where the Routers that support the WAN are Multicast compliant,
the Multicast functions of the OfficeServ can be used.
First you must enable Multicast paging per IP phone • MMC 840/DM 2.7.1
You must then set the Multicast address
list your network will use.
Multicast IP addresses are a Class D, you can use: • 224.0.1.0 to 239.255.255.254 • MMC 874/DM 5.2.25
Then configure your Page groups • MMC 604-605/DM 4.1.3
Then add this multicast address to: • MMC 874/DM 5.2.25 try using 228.228.228.288
and add the extn numbers
Now make a page, in default 55 + page group • During the page check port connection status DM 6.2.1