Cisco 8851, Administration Manual

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Usage notes Purpose Network protocol
UDP is used only for RTP streams.
SIP signaling on the phones do not
support UDP. UDP is a connectionless messaging protocol for delivery of
data packets. User Datagram Protocol (UDP)
VLAN Interaction
The Cisco IP Phone contains an internal Ethernet switch, enabling forwarding of packets to the phone, and
to the computer (access) port and the network port on the back of the phone.
If a computer is connected to the computer (access) port, the computer and the phone share the same physical
link to the switch and share the same port on the switch. This shared physical link has the following implications
for the VLAN configuration on the network:
• The current VLANs might be configured on an IP subnet basis. However, additional IP addresses might
not be available to assign the phone to the same subnet as other devices that connect to the same port.
• Data traffic present on the VLAN supporting phones might reduce the quality of VoIP traffic.
• Network security may indicate a need to isolate the VLAN voice traffic from the VLAN data traffic.
You can resolve these issues by isolating the voice traffic onto a separate VLAN. The switch port to which
the phone connects would be configured for separate VLANs for carrying:
• Voice traffic to and from the IP phone (auxiliary VLAN on the Cisco Catalyst 6000 series, for example)
• Data traffic to and from the PC that connects to the switch through the computer (access) port of the IP
phone (native VLAN)
Isolating the phones on a separate, auxiliary VLAN increases the quality of the voice traffic and allows a large
number of phones to be added to an existing network that does not have enough IP addresses for each phone.
For more information, see the documentation that is included with a Cisco switch. You can also access switch
information at this URL:
http://cisco.com/en/US/products/hw/switches/index.html
External Devices
We recommend that you use good-quality external devices that are shielded against unwanted radio frequency
(RF) and audio frequency (AF) signals. External devices include headsets, cables, and connectors.
Depending on the quality of these devices and their proximity to other devices, such as mobile phones or
two-way radios, some audio noise may still occur. In these cases, we recommend that you take one or more
of these actions:
• Move the external device away from the source of the RF or AF signals.
• Route the external device cables away from the source of the RF or AF signals.
• Use shielded cables for the external device, or use cables with a better shield and connector.
• Shorten the length of the external device cable.
Cisco IP Phone 8800 Series Multiplatform Phones Administration Guide
18
VLAN Interaction