Cisco E20 - Understanding Cisco Discovery Protocol on the Former TANDBERG Endpoints

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Cisco IP Video Phone E20 Administrator guide
D143 30.12 Administrator guide Cisco IP Video Phone E20, TE4.1 November 2011.
All contents are Copyright © 2010–2011, Cisco Systems, Inc. All rights reserved.
Introduction
Cisco Discovery Protocol (CDP) is a proprietary layer-2
management protocol developed by Cisco in the early
1990s to provide enhanced automation of network discov-
ery and management. It is broadly deployed on millions of
existing Cisco products and provides countless benets
to network administrators for managing router and switch
interfaces. With the introduction of IP Telephony in the late
1990s and early 2000s, CDP was enhanced to provide
additional automation capabilities for IP-based telephones,
including automatic VLAN discovery, Power over Ether-
net (POE) negotiation, Quality of Service (QoS) automa-
tion, location awareness (to automate the discovery of
the physical location of an IP telephone for management
and emergency services purposes), Ethernet speed and
duplex mismatch detection, and more.
Note: The IETF, IEEE and TIA, in cooperation with Cisco
and numerous other networking vendors, have since
created the IEEE 802.1AB standard, known as Link-Layer
Discovery Protocol (LLDP), with extensions developed
for Media Endpoint Discovery (LLDP-MED) for voice and
video endpoints. LLDP-MED will eventually subsume CDP,
but this may take years to unfold due to the enormous
installed-base and widespread use of CDP.
Cisco acquired TANDBERG in April 2010. The TANDBERG
portfolio of video endpoints compliments Cisco’s existing
Telepresence and Unied Communications solutions. With
TANDBERG now a part of Cisco, one of the rst
steps towards integrating the portfolios is to add
CDP support to the former TANDBERG products.
CDP support is introduced on the Cisco E20 IP
Video Phone in release TE4.0. Similar support is
planned for the Cisco Telepresence EX series,
Quick Set 20, C40/C60/C90 stand-alone inte-
grator codecs, and the C-Series based Prole
Systems, in release TC4.2.
However, because there is already an installed-
base of these endpoint models (prior to the Cisco
acquisition) that are not running CDP, introducing
CDP in a software release requires careful con-
sideration of how the new automation functional-
ity will aect that existing installed-base. Enabling
CDP by default could cause undesired behavior
for those existing deployments when they up-
grade to a CDP-enabled release and the devices
suddenly begin using VLAN automation, so CDP
is being introduced in a phased approach.
This document briey highlights the benets of
CDP, and the behavior of the Cisco E20 in release
TE4.0. A similar approach will be taken when in-
troducing CDP support in the TC4.2 software that
runs on the EX and C-Series products.
Benets Provided by CDP
As mentioned in the introduction above, CDP provides
numerous automation benets for network administra-
tors deploying IP-based voice and video endpoints on their
networks. This section briey highlights some of the most
pertinent benets for IP-based voice/video endpoints like
the Cisco E20.
Automatic VLAN discovery
Virtual LANs (VLANs) allow a network administrator to in-
troduce IP-based telephones and video terminals onto their
network without the need for re-addressing their existing
data subnets, or adding additional ethernet ports to their
switches. Leveraging the 802.1Q standard, a device such
as a Cisco E20 can tag its Ethernet frames with the VLAN
ID that its trac belongs to, placing its trac into the voice /
video VLAN (known as the auxiliary VLAN); while Ethernet
frames sent by a PC are not tagged, and therefore end up
in the data VLAN (known as the native VLAN). This allows
the E20 to be inserted in between an existing PC and the
Ethernet switch to which it is attached, allowing for a single
Ethernet port per user, thereby eliminating the need to add
additional ports in the wiring closet, and allowing the E20 to
be assigned to a dierent (new) IP subnet rather than con-
suming IP addresses in the existing PC VLAN. VLANs also
allow the network administrator to apply dierent security
and Quality of Service (QoS) policies on a per-VLAN basis.
Figures 1 and 2 illustrate these concepts.
Without CDP (or LLDP-MED), the user must manually con-
gure each endpoint with the 802.1Q VLAN ID it should
use. CDP automates this task, allowing the Ethernet
switch to advertise to the endpoint the ID of the VLAN it
should belong to.
Appendix: Understanding Cisco Discovery Protocol on the former TANDBERG endpoints
Figure 1: Without VLANs
Figure 2: With VLANs