Metro Ethernet Networks

7/21/2019 Metro Ethernet Networks

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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



2

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



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



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



4

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


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


Ethernet framesC-VLAN IDs 50-69

Ethernet framesC-VLAN IDs 70-79


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



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



6

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(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


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



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



8

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


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


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



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.



N N 1 0 5 6 0 0 - 0 7 2 3 0 7

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