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LAN
Network
VLAN 1
VLAN 2
VLAN x
LAN
Network
Stacked
VLAN 2
VLAN 1
VLAN x
Stacked
VLAN 1
VLAN 1
VLAN x
Application Note
VLAN Stacking or Q-in-Q
Where is it and why?
MT9090A/MU909060A
Network Master GigE
By Stuart Whitehead
Background
Telecom operators test their networks in many different ways for many different reasons.
When testing an Ethernet network it’s important to note what type of testing is required and where it’s required, this document
aims to explain if testing VLAN Stacking is required in the Access network.
In order to do this the document will also overview the technologies involved and the reasons why people test in different areas.
Q-in-Q or VLAN Stacking are common terms used by today’s telecom operators which are the same thing. For convenience
we will reference it as “VLAN Stacking” for the rest of this document.
First let’s quickly look at the difference between VLAN and VLAN stacking.
VLAN
Where does a VLAN come from?
The IEEE standard 802.1Q which was first standardized in Dec 1998 and has since been revised and referenced many times.
The full standard can be downloaded from the IEEE website at http://www.ieee.org and there are many websites which explain
the standard in details including http://en.wikipedia.org/wiki/IEEE_802.1Q, for comprehensive and definitive details you
should always reference the standard itself.
What is a VLAN?
A VLAN is a Virtual Local Area Network which allows the network LAN to be broken
down into more logical networks simplifying management of the network and allowing
configuration and traffic priority across the network. It also has the effect of increasing
security, reducing broadcast traffic and better management of areas such as traffic flow.
VLAN Stacking
Where does VLAN Stacking come from?
VLAN Stacking comes from the IEEE Standard 802.1.ad which was first standardized in Dec 2005. The full standard can be
downloaded from the IEEE website at http://www.ieee.org and there are also many other websites that offer an overview such
as http://en.wikipedia.org/wiki/QinQ. Once again the definitive reference point should be the standard itself. This standard is
very closely related to the VLAN standard as it is all about placing one VLAN inside another (or on top of). This is why the
name VLAN Stacking is often used and because the VLAN standard ends in the letter “q” it is often called Q-in-Q.
What is VLAN Stacking?
VLAN allows the user to better manage his network and prioritize this traffic
though the network but for the service provider or telecom operator this
meant multiple connections from one customer. The telecom operator is
normally interested in having a single connection for each user. VLAN
Stacking allows all traffic from a single user to transfer the telecom network
combined in one logical group.
Figure 1. LAN with 3 VLAN’s inside.
Figure 2. LAN with 2 Staked VLAN’s each with 2
VLAN’s inside.
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Anritsu MU909060A-E-F-1
The VLAN Stacking allows the telecom operator to place all traffic from a single customer (which could be multiple VLAN’s)
into a single VLAN simplifying management across his network.
Next, let’s look at the differences in the Ethernet network. How a network is divided and where VLAN Stacking is in the
network.
How is an Ethernet Network divided?
Many telecom operators divide their network in different ways thus the below should be considered a broad guideline or
reference only. Some common terms used in dividing the networks are as follows,
- Access Network,
o From the customer premises to the Telecom network.
- Metro Network,
o The network confined to a region only (City, Suburb, Campus etc).
- Core Network,
o The backbone of the telecom operator’s network connecting all major areas.
- Point of Demarcation,
o Where the network changes from telecom operator control to customer control.
On the left is an example of a telecom operator’s network and
below are examples of where the network is commonly divided,
- Customer Network,
o From the left side to the Customers Router,
- Access Network,
o From the Customer Router to the Edge Router,
The Customers Router may be managed by the telecom
operator if so it’s often called a “Managed Service”.
The difference between the two above areas is often referred as the “Point of Demarcation”.
- Metro and Core Network,
o From the Edge Router into the cloud.
Where is there VLAN Stacking on the network and why?
Often customers are working with the telecom operators to reduce the cost of running their network. One way some telecom
operators are assisting their customers with this is offering different levels of service at different price plans. For example,
- Higher priority traffic,
o Higher cost.
- Non guarantee or lower priority traffic,
o Lower cost.
Figure 3. Example basic network.
Customer Network
Edge
Router
Telecom Operator Core
Network Cloud
Customer LAN
Access Network
Edge
Router
Core
Network