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White Paper
Service delivery technologies for Metro Ethernet Networks
Introduction
Ethernet had its origins in providing
network connectivity for a single organ-
ization. With the introduction of
metropolitan and wide area Ethernet
services, providers started using this
Ethernet “connectivity” technology to
provide Ethernet “services.” While the
standard IEEE 802.3 Ethernet LAN
protocol is still used, service delivery
technologies needed to be added in
order to create an Ethernet service.
Three service delivery technologies can
be used to provide Ethernet services —
namely, IEEE 802.1Q Virtual LANs
(VLANs), Q-in-Q (stacked VLANs)
and MAC-in-MAC (or M-in-M). This
paper describes the capabilities and
usage of each technology.
This paper, intended for service
provider network architects and tech-
nologists, provides a holistic view of
different Ethernet technologies used for
service delivery over Ethernet networks.
The terms “subscriber” and “customer”
are used interchangeably in this docu-
ment and refer to the users and buyers
of Ethernet services. Service Frame fields
preceded with a “C-“, e.g., C-VLAN
ID, refer to customer-created fields.
Service Frame fields preceded with a
“P-“, e.g., P-VLAN ID, refer to provider-added fields. Ethernet-Line (E-Line)
and Ethernet–LAN (E-LAN) services,
promulgated by the Metro Ethernet
Forum and used in this document, refer
to point-to-point and multipoint-to-
multipoint (“any-to-any”) Ethernet
connectivity services, respectively. The
Metro Access Network connects the
subscriber Ethernet User-to-Network
Interfaces (UNIs) to the provider’s
network. The Metro AggregationNetwork is a collector of Metro Access
Networks for a given metro region. This
network performs the switching func-
tion within the metro network, connects
to a WAN or connects to other service
networks, e.g., an ISP network.
IEEE 802.1Q Virtual LAN(VLAN)
The IEEE 802.1Q standard adds four
additional bytes to the standard IEEE
802.3 Ethernet frame and is referred to
as the VLAN tag. For Ethernet, the
EtherType is always 8100h and the CFI
(Canonical Field Indicator) is always set
to zero. Refer to Figure 1.
From a service perspective, the fields of
most interest in the VLAN tag are the
VLAN ID and User Priorities. Enterprises
use VLANs to engineer traffic in their
networks where their internal network’s
MAC DA
MAC SA
VLAN Tag
EtherType
Payload
User Priority
CFI = 0
VLAN ID
EtherType(8100h)
Figure 1. 802.1Q extensions to
802.3 Ethernet Frame
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Ethernet frames can be uniquely identi-
fied and prioritized via the VLAN ID
and User Priority, respectively. The
remainder of this document will use the
terms C-VLAN CoS to identify the
subscriber Service Frame’s User Priority,
C-VLAN ID to identify the subscriber
Service Frame’s VLAN ID, and C-VLAN
Tag to identify the subscriber Service
Frame’s VLAN tag, respectively. The
importance and use of the VLAN tag in
Ethernet service delivery will be illus-
trated in the subsequent sections.
Q-in-Q (Stacked VLANs)
In a Q-in-Q network, the service
provider adds an additional VLAN tag
or P-VLAN Tag to the subscriber’sIEEE 802.1Q tagged Ethernet frame,
as illustrated in Figure 2 . While not
standardized, this solution is available
from several Ethernet switch vendors,
including Nortel. Q-in-Q’s appeal is
its simplicity. The 802.1ad “Provider
Bridges” working group within the
IEEE is working to fully define Q-in-Q
technology.
The P-VLAN Tag is added after the
Ethernet Source MAC address. The
P-VLAN Tag includes a Provider VLAN
ID (P-VLAN ID) supporting up to
4,096 service instances. The three bit
P-VLAN CoS field provides up to eight
classes of service for each P-VLAN ID.
The Provider EtherType (P-Ethertype)
often uses a value other than 8100h,
indicating that this P-VLAN Tag is not
a standard IEEE 802.1Q VLAN Tag.
The P-CFI is also set to zero for Ethernet.
Refer to Figure 3 for a summary of the
Q-in-Q P-VLAN Tag fields and their
usage.
The P-VLAN Tag is used to identify the
service as illustrated in Figure 4 . The
subscriber’s VLAN Tag (C-VLAN Tag)
remains intact and is not altered by the
service provider’s anywhere within the
provider’s network.
Next, the significant service attributes
and capabilities addressed by Q-in-Q
are described.
Subscriber VLAN administration
In a Q-in-Q network, the service provider
assigns a P-VLAN ID for each service
instance. The provider then maps the
agreed-upon subscriber C-VLAN IDs to
the service instance identified by that
particular P-VLAN ID. Thus, the
subscriber’s C-VLAN IDs are preserved.
For example, suppose a subscriber wants
to use C-VLAN IDs 50, 51 and 52 over
an E-Line service to another subscriber
location. Assume that the provider
assigns P-VLAN ID 100 for this E-Line
service. The provider would map C-
VLAN IDs 50, 51 and 52 to P-VLANID 100, as shown in Figure 5 .
As a result, subscribers are free to assign
C-VLAN IDs and C-VLAN CoS values
to meet their needs without concern
that they will be altered by the service
provider.
Subscriber/provider MAC
address separation and learning
Q-in-Q networks do not provide any separation between the provider’s and
subscribers’ MAC addresses. Therefore,
when using Q-in-Q for E-LAN (any-to-
any switched) services, provider switches
must learn all MAC addresses in the
network, regardless of whether they
belong to the service provider or to the
subscriber.
C-MAC DA
C-MAC SA
C-VLAN Tag
C-EtherType
C-Payload
C-MAC DA
C-MAC SA
C-VLAN Tag
C-EtherType
C-Payload
C-MAC DA
C-MAC SA
P-VLAN Tag
C-VLAN Tag
C-EtherType
C-Payload
P-VLAN Tagadded
Subscribernetwork
Subscribernetwork
Providernetwork
P-VLAN Tagremoved
UNI UNI
Service provider usage Q-in-Q field
Service identification P-VLAN ID
Traffic engineering P-VLAN CoS
Figure 3. Summary of Q-in-Q fields
and their usage
Figure 4. P-VLAN Tag added to subscriber Service Frame
C-MAC DA
C-MAC SA
P-VLAN Tag
C-VLAN Tag
C-EtherType
C-Payload
P-EtherType
P-VLAN CoS
P-CFI
P-VLAN ID
Figure 2. Q-in-Q stacked VLAN tag
fields
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Each time a new host is added in the
subscriber’s network, the new MAC
address must be learned by the provider’s
network switches. This makes the
provider and subscriber networks appear
as one large network to the provider’s
switches. Refer to Figure 6 .
Subscriber/provider control
protocol transparency
Most Ethernet control protocols (i.e.,
Bridged Protocol Data Units or BPDUs)
used by subscribers’ networks must not
interact with the provider’s networking
equipment. For example, Spanning Tree
Protocol (STP) instances used in the
subscriber network must not interact
with STP instances used in the provider
network. In this case, the provider needsto “tunnel” the subscriber’s STP BPDUs
through the network.
BPDUs are identified by their destina-
tion MAC address and do not have a
VLAN tag associated with them. For
example, the Spanning Tree Protocol is
identified by destination MAC address
01-80-C2-00-00-00. Q-in-Q cannot
provide differentiation between subscriber
and provider BPDUs because each
entity’s BPDUs have the same MAC
address, and duplicate MAC addresses
cannot be supported. This will cause
unpredictable network behavior because
the provider’s networking equipment
cannot distinguish between subscriber
and provider BPDUs. The IEEE is
proposing a solution to this limitation,
in which the provider’s network would
use a different set of destination MAC
addresses for its own BPDUs. However,
to support these new provider BPDU
MAC addresses, the provider must replace
the existing Ethernet switches , because
BPDU MAC addresses, in general, are
not configurable. Because of this, Q-in-
Q technology has significant limitations
for E-LAN Services that must support
multiple subscriber control protocols
(BPDUs).
For some E-Line (point-to-point) services
such as Ethernet access to the Internet,
no control protocols are required. Since
control protocol transparency is not anissue, Q-in-Q is suitable for these services.
Service identification
and scalability
Recall that, with Q-in-Q, the P-VLAN
ID identifies the service to which a
subscriber’s Ethernet frames are associ-
ated. Therefore, each service instance
requires a separate P-VLAN ID. Because
the P-VLAN ID consists of twelve bits
3
C-MAC DA
C-MAC SA
C-VLAN Tag
C-EtherType
C-Payload
C-MAC DA
C-MAC SA
P-VLAN Tag
C-VLAN Tag
C-EtherType
C-Payload
Subscriber network Provider network
(C-VLAN IDs50, 51, 52)
(P-VLAN ID 100)
UNI P-VLAN ID 100
E-Line service
Ethernet framesC-VLAN ID 50
Ethernet framesC-VLAN ID 51
Ethernet framesC-VLAN ID 52
Figure 5. Mapping C-VLAN IDs to E-Line VPN Service
Provider network
using Q-in-Q
Subscribernetwork
Subscribernetwork
Subscribernetwork
Subscribernetwork
Figure 6. Provider’s and subscribers’ MAC addresses visible to all networks
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of the P-VLAN Tag, up to 4,096
possible service instances can be created.
To increase scalability in the metro
network, a tunneling technology must
be used to support overlapping Q-in-Q
P-VLAN IDs. With such an approach,
each Q-in-Q “island” of 4,096 service
instances is tunneled across the aggre-
gation network. In such a network
configuration, OAM tools are needed
to properly manage the overlapping
P-VLAN IDs.
Figure 7 illustrates three example serv-
ices provided to a subscriber using a
single UNI. The subscriber determines
which Service Frames, identified by the
C-VLAN ID, they want mapped to
each service instance, and the providermaps these C-VLAN IDs to the appro-
priate P-VLAN ID for the service. In this
example, P-VLAN IDs 3000, 3001 and
4000 identify a Metro E-Line Service, a
WAN E-Line Service and an Internet
Access E-Line Service, respectively. Each
service instance requires a separate P-
VLAN ID.
Suppose multiple E-Line Services are
offered between the same provider’s
POPs. In this case, each service instance
requires a separate P-VLAN ID, as
illustrated in Figure 8 . Three service
instances need to be provisioned even
if they use the same physical transport
between the two POPs.
Traffic engineering
The provider uses the P-VLAN CoS
field to identify the class of service.
Using the P-VLAN CoS, the provider’s
network can support up to eight classes
of service.
C-VLAN Tag preservation
and mapping
A Q-in-Q network preserves the
C-VLAN Tags. The provider maps the
subscriber-specified C-VLAN IDs and
C-VLAN CoS to the provider assigned
the P-VLAN ID and P-VLAN CoS
used to identify the service and the
service performance (CoS), respectively.
Figure 9 illustrates different subscriber
Service Frames mapped to the three
services provided at the UNI.
In this example, the subscriber wants to
use C-VLAN IDs 50-69 for the Metro
E-Line Service and the provider maps
these to P-VLAN ID 3000. The
subscriber wants to use C-VLAN IDs
70-79 for the WAN E-Line Service and
the provider maps these to P-VLAN ID
3001. Finally, the subscriber wants to
use C-VLAN ID 100 for the Internet
Access E-Line Service and the provider
maps this to P-VLAN ID 4000.
The C-VLAN ID to P-VLAN ID
mapping for this example is summa-
rized in Figure 10 .
The C-VLAN CoS values can also be
preserved and would be mapped to the
P-VLAN CoS values. For example,suppose the WAN E-Line Service
provides three classes of service —
Premium, Gold and Standard indicated
by P-VLAN CoS values 6, 4 and 2,
respectively. The subscriber may also use
three classes of service in their network
but with different C-VLAN CoS values.
Therefore, the mapping table illustrated
in Figure 11 would be used.
UNI
3000
3001
4000
MetroE-Line Service
WANE-Line Service
Internet AccessE-Line Service
P-VLAN IDs
Figure 7. Service identification via
Q-in-Q P-VLAN IDs
Providernetwork
E-Line Service 2(P-VLAN ID 11)
E-Line Service 3(P-VLAN ID 12) POPPOP
E-Line Service 1(P-VLAN ID 10)
UNI
UNI
UNI
UNI
UNI
UNI
Figure 8. Separate P-VLANs per
service instance
Subscriber
network
UNI
3000
3001
4000
MetroE-Line Service
WANE-Line Service
Internet AccessE-Line Service
Ethernet framesC-VLAN IDs 50-69
Ethernet framesC-VLAN IDs 70-79
Ethernet framesC-VLAN ID 100
P-VLAN IDs
Figure 9. Service identification via Q-in-Q P-VLAN IDs
Metro WAN InternetE-Line E-Line Access E-LineService Service Service
P-VLAN ID 3000 3001 4000
MappedC-VLAN IDs 50-69 70-79 100
Figure 10. C-VLAN ID to P-VLAN ID
mapping
WAN E-Line Service
Premium Gold Standard
P-VLAN 6 4 2CoS
Mapped 5 3 0C-VLAN CoS
Figure 11. C-VLAN CoS to P-VLAN
CoS mapping
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Note that multiple C-VLAN CoS
values may be configured to map to the
same CoS identified via the P-VLAN
CoS. Figure 12 illustrates this using the
previously discussed example with three
classes of service.
Network interconnection
Q-in-Q can be used for point-to-point
connections between networks as illus-trated in Figure 13 .
At the UNI, Q-in-Q adds an additional
P-VLAN Tag to the subscriber’s Service
Frames and preserves the C-VLAN Tag.
Assuming that there are less than 4,096
service instances, the Service Frames are
relayed through the Metro Aggregation
Network based on the P-VLAN ID
(service identifier) to the Network-to-
Network Interface (NNI). At the NNI,
the Service Frames may be tunneled
across the WAN using, for example,
MPLS, to connect to another Metro
Aggregation Network. Alternatively,
Service Frames may be terminated and
mapped to another Layer 2 WAN
service, such as Frame Relay.
MAC-in-MAC (M-in-M)
An alternative tunneling technology
called MAC-in-MAC (M-in-M) provides
capabilities that address the Q-in-Q
technology limitations previously
described, including subscriber/provider
MAC address separation, subscribercontrol protocol transparency, and
service identification and scalability.
M-in-M also enables additional traffic
engineering capabilities. M-in-M
prepends a Provider source and destina-
tion MAC address, a Provider VLAN
Tag (P-VLAN Tag) and a Provider
Service Label to the subscriber’s Ethernet
frame at the NNI, as illustrated in
Figure 14 .
The M-in-M P-VLAN Tag is identical
in format to the Q-in-Q P-VLAN Tag.
However, with M-in-M, the P-VLAN
ID within the P-VLAN Tag identifies
the Provider VLAN over which the
subscribers’ Service Frames traverse. The
P-VLAN CoS determines the service
class and is used for traffic engineering.
Finally, the Service ID identifies the
service instance in the provider’s
network. M-in-M provides up to 16
million service instances. Figure 15
provides a summary of the M-in-M
fields and their usage.
With M-in-M, the provider switches
traffic based on the provider’s MAC
addresses. This solution allows the
subscribers’ MAC addresses to overlap
with the provider’s MAC addresses,
because the subscribers’ Service Frames
are tunneled by M-in-M and are notused when switching frames inside the
provider’s network. Since the subscribers’
Service Frames are tunneled, the
subscriber and provider networks are
separate and isolated, as illustrated in
Figure 16 .
The following sections of this paper
describe the significant service attributes
and capabilities addressed by M-in-M.
P-EtherType
P-VLAN CoS
P-CFI
P-VLAN ID
Provider MAC DA
Provider MAC SA
Provider EtherType
Provider VLAN Tag
Provider Service Label
Customer MAC DA
Customer MAC SA
Customer VLAN Tag
Customer EtherType
Customer Payload
P-EtherType
Service ID
Inter-MetroWAN
SubscriberNetwork
Q-in-Q
MetroAggregation
Network
MetroAccess
Network
Subscriber
Service FrameTerminate L2
NNIUNI
WAN Tunnel
Figure 13. Q-in-Q usage at inter-network connections
Figure 14. M-in-M frame fields
Service provider usage M-in-M field
Provider network addressing Provider MAC header
Service identification Service ID
Provider VLAN identification P-VLAN ID
Traffic engineering P-VLAN CoS
Figure 15. Summary of M-in-M
fields and their usage
WAN E-Line ServicePremium Gold Standard
P-VLAN 6 4 2CoS
Mapped 5, 6, 7 3, 4 0, 1, 2C-VLAN CoS
Figure 12. Multiple C-VLAN CoS
values mapped to
P-VLAN CoS
5
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Subscriber VLAN administration
M-in-M transparently tunnels subscribers’
Ethernet Service Frames through the
provider’s network. At the UNI, the
provider maps the subscriber’s C-VLAN
ID and C-VLAN CoS values to the
Service ID and P-VLAN CoS value
specified for the particular service
instance. As a result, subscribers are free
to assign C-VLAN IDs and C-VLAN
CoS values to meet their needs without
concern that they will be altered by the
service provider. Providers need not
worry about VLAN ID coordination
with their enterprise customers.
Provider VLANs
The M-in-M P-VLAN ID enables the
provider to segregate their network into
regions or “zones” to simplify traffic
engineering. Provider VLANs enable
the support of multiple subscriber serv-
ices instances. For example, suppose a P-
VLAN is engineered to support one
thousand 10 Mbps E-Line Services
between POPs. Up to one thousand E-
Line service instances can be activated
using the one initial P-VLAN setup.
Refer to Figure 17 .
When using M-in-M P-VLANs, the
service provider engineers the network
once during the network- and service-
planning phases. Later, services can be
simply activated and supported over the
P-VLAN up to its engineered limits.
Subscriber/provider MAC
address separation and learning
M-in-M tunneling provides isolation
and separation of subscriber and provider
MAC addresses. Therefore, only the
provider’s MAC addresses need to be
learned by the network. MAC addresslearning only occurs as the provider
adds new Ethernet interfaces to existing
switches or new switches in the network.
However, this method is more predictable
(new UNIs are scheduled) when
compared to randomly learning new
MAC addresses whenever a subscriber
connects additional hosts (MAC
addresses) in their network. This leads
to a more stable provider network with
significantly fewer broadcast frames,resulting in more bandwidth available
for subscriber traffic.
Service identification
and scalability
M-in-M identifies the service from two
perspectives. One part is the service
instance at the UNI, which is identified
by the Service ID. This is where one or
more of the subscriber’s C-VLAN IDs
map to a particular service. The otherpart is the P-VLAN ID, identifying the
Provider VLAN over which the service is
transported. M-in-M supports up to
4,096 P-VLANs and up to one million
Providernetwork
E-Line Service 2(P-VLAN ID 11)
E-Line Service(s)(P-VLAN 10)
POPPOP
UNI
UNI
UNI
UNI
UNI
UNI
Figure 17. Single P-VLAN for
multiple service instances
UNI
Service ID 10
MetroE-LAN Service
MetroE-Line Service
Internet AccessE-Line Service
Service ID 11
Service ID 12
P-VLAN 1000
P-VLAN 3000
P-VLAN 4000
Other subscribers ofInternet AccessE-Line Service
Other subscribers ofMetro E-Line Service
Other subscribers of
Metro E-LAN Service
Figure 18. Service identification at UNI and mapping to P-VLANs
SubscriberNetwork
SubscriberNetwork
ProviderNetwork
SubscriberNetwork
SubscriberNetwork
UNIUNI
UNI
UNI
Figure 16. Provider/subscriber MAC address separation at the UNI
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service instances. Figure 18 illustrates
Provider VLANs engineered for three
different services.
Provider VLAN 1000 provides metro
E-LAN Services, Provider VLAN 3000
provides metro E-Line Services and
Provider VLAN 4000 provides Internet Access E-Line Services. Each subscriber
is assigned a Service ID for each service
instance and each subscriber has C-VLAN
IDs that they want to map to the
particular service. Figure 22 provides a
sample mapping table for a subscriber
using all three services in Figure 19 .
Traffic engineering
M-in-M uses the P-VLAN Tag for traffic
engineering. M-in-M, via the P-VLANID and P-VLAN CoS, enables the
provider to engineer the network for the
services to be supported prior to service
activation. Each P-VLAN is engineered
to support the service requirements.
Therefore, service activation is decou-
pled from network engineering. This
simplifies network operations and
enables quicker service activation.
For example, one P-VLAN could beengineered for an Internet access service.
Another P-VLAN could be engineered
to support a CoS-based VPN with three
classes of service. Each P-VLAN is iden-
tified via the P-VLAN ID and each class
of service is identified via the P-VLAN
CoS value. P-VLANs allow each service
to be engineered for different service
performance levels.
C-VLAN Tag preservation
and mapping
M-in-M preserves the C-VLAN Tag
because the subscriber’s Service Frames
are simply tunneled across a network.
The provider therefore can transport the
Service Frames transparently. Theprovider specifies the Service ID used
for a given service instance and the
provider maps the subscriber-provided
C-VLAN IDs to the Service ID and
C-VLAN CoS to P-VLAN CoS values.
Refer to Figure 19 for an example of
C-VLAN ID preservation and mapping
to Service ID and P-VLAN ID.
For example, suppose the Metro E-Line
Service operating over P-VLAN 3000
provides three classes of service —
Premium, Gold and Standard, indicated
by P-VLAN CoS values 6, 4 and 2,
respectively. The subscriber may also use
three classes of service in their network,
but with different C-VLAN CoS values.
M-in-M would use a mapping table
such as the one illustrated in Figure 20 .
Subscriber control protocol
transparency
Since M-in-M tunnels subscribers’
Service Frames, all subscriber Ethernet
Control Protocols (BPDUs) are tunneled
transparently across the provider’s
network. This allows these EthernetControl Protocols to be used indepen-
dently by subscribers’ networks and the
provider’s network.
Recall that Spanning Tree Protocol
(STP) instances used in the subscribers’
networks must not interact with STP
instances used in the provider’s network.
In this case, the provider needs to “tunnel”
the subscribers’ STP BPDUs through
the network. The Spanning Tree Protocol
is identified by destination MAC
address 01-80-C2-00-00-00. With
M-in-M, the subscriber’s STP BPDUs
are tunneled through the provider’s
network. Therefore, both the provider
and subscribers can simultaneously use
the standard STP destination MAC
address with no additional provisioning
required on the provider’s switches. This
allows the provider to use the standard
BPDU MAC addresses on the existing
switches in the network.
Summary of MetroEthernet service deliverysolutions
Several Ethernet service delivery solutions
are possible, depending upon the services
being offered. Figure 21 provides a
summary of the service provider usage
of Q-in-Q and M-in-M fields.
7
Service provider usage Q-in-Q field M-in-M field
Provider network addressing - Provider MAC Header
Service identification P-VLAN ID Service ID
Traffic engineering P-VLAN CoS P-VLAN ID andP-VLAN CoS
Figure 21. Provider usage of Q-in-Q and M-in-M fields
Premium Gold Standard
P-VLAN 6 4 2CoS
Mapped 5, 6, 7 3, 4 0, 1, 2C-VLAN CoS
Metro E-Line Service over
P-VLAN ID 3000
Figure 20. C-VLAN CoS to P-VLANCoS mapping for allsubscribers using E-LineServices over P-VLAN3000
Metro Metro InternetE-LAN E-Line Access E-LineService Service Service
P-VLAN ID 1000 3000 4000
SubscriberService IDs 10 11 12
MappedC-VLAN IDs 50-69 70-79 100
Figure 19. Mapping table of
subscriber C-VLAN IDs
to Service IDs and
P-VLANs
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M-in-M solution
Because M-in-M is a tunneling tech-
nology, it provides the most flexible
solution to support service multiplexing
of any combination of service, including
E-Line, E-LAN, Internet Access and
WAN services. Refer to Figure 22 .
Q-in-Q solution
Q-in-Q is best suited for Internet
Access Services and E-Line services used
for WAN connectivity, which typically
use a router as the subscriber CPE
device connecting to the service. For
these services, the Service Frames are
terminated (for Internet access or to
other Layer 2 services, e.g., Frame
Relay) or tunneled via a WAN tech-nology (e.g., MPLS). Also, the router
discards all Layer 2 control protocols
(BPDUs), so provider/subscriber over-
lapping BPDU MAC addresses pose no
issues for these services. For an Internet
Access E-Line Service, a solution such as
the one illustrated in Figure 23 could be
used for service delivery.
Hybrid solution
A hybrid solution of Q-in-Q and M-in-M can be used as illustrated in Figure
24 . This solution takes advantage of the
simplicity of Q-in-Q in the Metro
Access Network (where there is only
multiplexing and no switching) and
M-in-M in the Metro Aggregation
Network where scalability and tunneling
(provider/subscriber MAC address sepa-
ration) are key requirements that cannot
be met with Q-in-Q. M-in-M can also
be used to interconnect Q-in-Q access
networks.
InternetSubscriber
network
Q-in-Q
MetroAggregation
network
MetroAccessnetwork
SubscriberService Frame
Terminate L2
NNIUNI
Ethernet header removed.Ethernet protocol
terminated.
P-VLAN Tag added.C-VLAN ID mapped to
P-VLAN ID
WANInter-Metro
VPNSubscribernetwork
M-in-MTunnel
MetroAggregation
network
MetroAccessnetwork
SubscriberService Frame
Terminate L2
NNIUNI
InternetNNI
M-in-M header mapped toWAN header fields orL2 service terminated
M-in-M header added.P-VLAN ID mapped to
Service ID.
Q-in-Q
P-VLAN Tag added
WAN Tunnel
Figure 23. Q-in-Q Internet Access Solution
Figure 24. Hybrid Multi-Service Delivery Solution
WANInter-Metro
VPNSubscribernetwork
M-in-Mtunnel
MetroAggregation
network
MetroAccessnetwork
SubscriberService Frame
Terminate L2
NNIUNI
InternetNNI
M-in-M header fieldsmapped to WAN header
fields or L2 service terminated
M-in-M header added.C-VLAN ID mapped to
Service ID.
WAN Tunnel
Figure 22. Multi-service delivery using M-in-M
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References
• “Metro Ethernet Services – A Technical Overview”, http://www.metroethernetforum.org/metro-ethernet-services.pdf MetroEthernet Forum, Ralph Santitoro, June 2003
• “Virtual Bridged Local Area Networks”, IEEE 802.1Q, December 1998http://standards.ieee.org/reading/ieee/std/lanman/restricted/802.1Q-2003.pdf
• IEEE 802.1ad Provider Bridges Working Group, http://grouper.ieee.org/groups/802/1/pages/802.1ad.html
9
Definition
Customer Premises Equipment. The equipment that connects the subscriber’s network to the provider’s network
at the UNI.
Customer VLAN Class of Service. The 802.1p user priority value used in the customer’s Ethernet Service Frame.
Customer VLAN Identifier. The VLAN ID used in the customer’s Ethernet Service Frame.
Customer VLAN Tag. The IEEE 802.1Q VLAN tag added by the customer to the Ethernet Service Frame.
An Ethernet service providing multipoint-to-multipoint (any-to-any) connectivity. Also referred to as a switched
Ethernet service.
An Ethernet service providing point-to-point connectivity.
Internet Service Provider.
A service delivery technology whereby the provider adds an additional Ethernet header to the customer’s
Ethernet Service Frame. This header includes a Source and Destination MAC address, a P-VLAN Tag and a Provider
Service Label. Abbreviated M-in-M.
The network which connects the UNI to the provider’s network. May be a direct or indirect (UNIs multiplexed to a
single uplink) connection to the Metro Aggregation Network.
The network that is the collector of Metro Access Networks for a given metro region. This network performs the
switching function to other metro networks, WANs and other service provider networks, e.g., ISP.
Network-to-Network Interface. The demarcation point between two different networks of the same or different
administrative domains.
Provider VLAN ID. The VLAN ID added by the provider to the subscriber’s Ethernet Service Frame as part of the
P-VLAN Tag. Note that the P-VLAN ID is used for different purposes in M-in-M and Q-in-Q.
Provider VLAN Class of Service. The CoS field added by the provider to the customer’s Ethernet Service Frame as
part of the P-VLAN Tag to indicate the service class.
Provider VLAN Tag. The VLAN added to the customer’s Ethernet Service Frame by the provider. Both Q-in-Q and
M-in-M service delivery technologies insert a P-VLAN Tag although it is used for different purposes in each tech-
nology.
Point of Presence.
A service delivery technology whereby the provider adds a second VLAN tag (called P-VLAN Tag) to the
customer’s Service Frame. Also referred to as Stacked VLANs.
The identifier in M-in-M used to indicate the service instance at a UNI.
An Ethernet frame transmitted across the UNI toward the service provider or an Ethernet frame transmitted
across the UNI toward the subscriber.
The network of the purchasing entity of a retail service.
User-to-Network Interface. The demarcation point between the provider and subscriber
administrative domains.
Term
CPE
C-VLAN CoS
C-VLAN ID
C-VLAN Tag
E-LAN Service
E-Line Service
ISP
MAC-in-MAC or
M-in-M
Metro Access
Network
Metro
Aggregation
Network
NNI
P-VLAN ID
P-VLAN CoS
P-VLAN Tag
POP
Q-in-Q
Service ID
Service Frame
Subscriber
Network
UNI
Terminology
Note that some of these terms have been defined by the Metro Ethernet Forum and IEEE standards organizations.
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