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Cisco IP Video Phone E20
Contents
Introduction
Automatic Quality of Service
Quality of Service is essential for a well-performing
network, providing preferential service to latency, jitter or
loss sensitive applications like voice and video; deferential
service to misbehaving applications such as viruses and
other undesirable network traffic; and fair treatment to
routine, non-time sensitive traffic such as email or web
browsing. However, QoS can be complex to configure
and manage, and the administrator needs to be assured
that the traffic entering the network is marked with the
correct QoS values. For user-facing devices such as PCs,
IP-based telephones and video terminals, the administra-
tor must establish a demarcation point where QoS mark-
D14330.12
Administrator guide Cisco IP Video Phone E20, TE4.1 November 2011.
All contents are Copyright © 2010–2011, Cisco Systems, Inc. All rights reserved.
Deploying E20
Using E20
ings coming in from these devices are either not trusted—
and instead overwritten to an administratively configured
value—or trusted to set their own QoS values and the
Ethernet switch will honor those values. This demarcation
point, or trust boundary, ensures that if the user accidently,
or intentionally, tampers with the QoS values assigned to
these devices, those QoS values will be remarked by the
administrator as they ingress the network.
CDP provides a method of automatically extending this
trust boundary (at the administrators' discretion) so that
the phone or video terminal can mark its packets with
the desired QoS values, and the switch will trust the
phones packets (because the administrator knows that
the specific model of phone in question can
be trusted to behave properly and cannot be
tampered with) and forwards those pack-
Without
Fig. 3:
ets on into the network. This functionality is
CDP / AutoQoS
known as AutoQoS on the Cisco Catalyst line
of Ethernet switches. Figures 3 and 4 illustrate
the concept of AutoQoS. More information on
AutoQoS can be found at
http://www.cisco.com/en/US/docs/solutions/
Enterprise/WAN_and_MAN/QoS_SRND_40/
QoSCampus_40.html#wp1098057
Power over Ethernet (POE) nego-
tiation
The 802.3af standard provides for Power over
Ethernet to devices such as IP-based tele-
Fig. 4: With
phones and video terminals. CDP provides
AutoQoS
CDP /
additional benefit by allowing the endpoint
to indicate to the Ethernet switch how much
power it requires—and for the switch to ad-
vertise to the endpoint how much power is
available—thereby allowing more granular level
of negotiation between the switch and the
endpoint, and allowing the Ethernet switch to
more closely track its available power budget.
Note that POE is not used by the Cisco E20,
but is mentioned here as informational benefit
to the reader since POE is widely used by
many other models of Cisco Unified IP Phones,
The settings
Wireless Access Points, surveillance cameras, and myriad
other devices.
Location Awareness
With the introduction of IP-based telephones, a new level
of mobility was afforded in that an IP endpoints could be
plugged in anywhere in the network, obtain an IP address,
and start making calls, reducing the costs associated with
physically patching telephone cables when moving an
employee from one office to another. However, certain
management functions and emergency services rely on
knowing the precise location of a telephone. CDP al-
lows for network management applications to identify the
physical location of a phone (by detecting what Ethernet
port that phone is attached to, and hence, where it physi-
cally is located). This information is then leveraged by ap-
plications such as Cisco Emergency Responder to direct
telephone calls made to emergency services personnel to
the correct dispatch office. There are many other real and
potential uses for location information.
Ethernet Speed / Duplex Mismatch Detection
Ethernet devices use the 802.3 auto negotiation proce-
dure to automatically negotiate their speed and duplex
settings. However, a very common problem is that one
side or the other is accidently configured for the wrong
settings, resulting in packet loss. For example, the network
administrator has configured all the Gigabit Ethernet ports
on the switch for auto negotiation, but the user accidently
sets the port on his or her PC, IP phone or video terminal
to a manually configured value, such as 100 Mbps / Full
duplex. This can result in a mismatch between the switch
and the endpoint, resulting in a large percentage of loss
on that interface. CDP does not automate the resolution of
such a condition, but it does detect it and cause an alarm
to be generated on the switch, notifying the administra-
tor of the condition so that he or she may take steps to
resolve it.
32
Administrator guide
Advanced settings
Advanced settings
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