H.323 Telephone Installation
Page 59
15-601046 Issue 17e (Wednesday, November 14, 2012)
IP Office
Installation: Other Installation Options
2.11.2 VLAN and IP Phones
The use of VLAN allows separate collision domains to be created on Ethernet switches. In the case of IP Office and IP
Phones the advantages are:
1. It allows PCs to continue in the same IP subnet while IP Phones can use a new and separate IP addressing
scheme.
2. Broadcast traffic is not propagated between the PC data network and the IP Phones voice network. This helps
performance as otherwise broadcast traffic must be evaluated by all receivers.
3. VLAN networking and traffic prioritization at layer 2 are closely bound together in the same 802.2 standard. It is
therefore easier to maintain L2 QoS when using a VLAN.
The table below shows the three ways in which VLAN can be deployed with an Ethernet Switch. The first two methods
require only elementary configuration, and since this document assumes both PC and IP Phones share the same Ethernet
port, the focus will be the third method (overlapping).
Type
Description
Advantages
Disadvantages
No VLAN
Both Voice and Data occupy the
same collision domain
Simple configuration
PC broadcast traffic adverse effect on
Voice traffic
Requires two (2) ports per user; one
for IP Phone and one for PC)
Physical VLAN
Separate VLAN for data and voice Simple configuration
Requires two (2) ports on switch; one
for IP phone and one for PC
Overlapping
VLAN
A single port on the switch
carrying both the IP Phones as
well as the PC traffic
Requires only a single port
for both PC and IP Phone
PC broadcast traffic cannot
adversely effect Voice
traffic
Complex configuration
