Specifications

VoIP and VLANs
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VoIP Installation and VLAN Configurations
Although this section refers to VLAN configurations, it can also be used to consider whether or
not VLANs are needed for a particular installation.
There are, currently, six configurations that have been identified. These are not expected to
cover all possible configurations, there will always be exceptions, but as a guideline for the
more general installations. The number of configuration variations has arisen because of the
introduction of the CXi product, which includes a VoIP capable Layer 2 switch. In effect the CXi
is now an integral part of the network, whereas the MX is considered more as an end point or
server within the network.
The main installations that are likely to be encountered are:
• A standalone CXi, voice-only devices, including expansion Layer 2 switch.
• Segregation of data and voice networks, with a router connecting the two. (In effect this is
a physical solution, rather than the logical solution through use of VLAN.)
• Standalone CXi unit with dedicated ports for voice and data devices, no expansion switch.
• CXi with expansion Layer 2 switch, voice and data using dedicated ports on both CXi and
expansion switch
• Data devices using second port of voice devices, i.e. both devices share a common
connection
• CXi is more a server and connects to a larger network infrastructure. The voice and data
devices are connected elsewhere within the network. (This is also the connection scenario
for the MX.)
When to use VLANs?
VLANs are used to provide a level of logical separation between voice devices and other devices
in the network. The main requirement is to ensure that there is adequate priority setting at the
various network egress points, and that priority queues are enabled at these points. Layer 2
priority setting can only be provided in conjunction with VLAN settings.
The simple question to ask is probably, “Will the voice information need to share a common
connection with other data?” If it does, then priority schemes are needed at that point, which
implies VLANs are needed, at that point. Larger networks will also tend to use VLANs to provide
a level of isolation and security between different services. However, the main requirement with
voice is to get access to the priority settings and information.
Network Configurations
The following is a brief description of the different network configurations and whether VLANs
are needed.