VoIP White Paper
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© 2006 InSciTek Microsystems, Inc. All rights reserved. Allworx is a registered trademark of InSciTek Microsystems. All other names may be
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Revised: February 8, 2007
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13 Zoned Paging
Allworx system paging features use a special form of IP traffic routing called multicasting to direct zoned pages
from the Allworx server to all Allworx phones configured for a particular zone. Multicasting is used because
many phones need to receive the page simultaneously and this is exactly what Ethernet and IP multicasting
were designed for.
Phones subscribe to a multicast group to become a member of a particular paging zone, since each zone has
its own multicast address. Generally, this is all automatic and transparent to the end user, the administrator,
and even Ethernet switches. However, when a particular site is having trouble with pages reaching one or
more phones, understanding the configuration options and how Allworx transmits these pages should be
helpful in diagnosing site configuration problems.
Allworx zoned paging is configured on the Servers / VOIP Server page of the Allworx administrative Web
pages. In particular, there are three parameters used to determine where Allworx transmits zoned pages:
Configuration Item Description
Paging Base Multicast IP
Address
This is the multicast base IP address (zone 0 - the overhead
zone) of the system. Follow-on zones are numbered sequentially
from this base by adding the zone number to the base IP
address. For example, zone 5 is located at base + 5 multicast
address.
This setting is the UDP port number to which the server transmits
at the multicast IP address for the current zone. All zones use the
same port number, each with their own multicast address as
described in the above field. The actual UDP payload is RTP
packets of 20ms G.711 frames.
This value controls the time-to-live count value in the IP header
of all paging UDP/RTP frames. This value is usually set to one
(1) for a single LAN subnet, but if you have multiple LAN subnets
with phones on them, this value may need to be increased.
Generally speaking, pages are only implemented on a single site and a single LAN subnet. However, by
manipulation of the above parameters and through configuration of intermediate routers, it is possible for
Allworx pages to span multiple subnets and even to tunnel across a VPN between sites. What needs to be
configured on the site is a way for Allworx server-sourced multicast packets to be routed between subnets
using the normal router-specific configuration mechanisms. A full discussion of routing multicast IP packets
and how this is configured into different brand routers is beyond the scope of this document.
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