U.S. patent application number 13/864863 was filed with the patent office on 2013-09-05 for method and apparatus for internetworking ethernet and mpls networks.
This patent application is currently assigned to Rockstar Consortium US LP. The applicant listed for this patent is ROCKSTAR CONSORTIUM US LP. Invention is credited to Nigel BRAGG, Dinesh MOHAN, Gerald SMALLEGANGE, Paul UNBEHAGEN.
Application Number | 20130230050 13/864863 |
Document ID | / |
Family ID | 39618623 |
Filed Date | 2013-09-05 |
United States Patent
Application |
20130230050 |
Kind Code |
A1 |
MOHAN; Dinesh ; et
al. |
September 5, 2013 |
METHOD AND APPARATUS FOR INTERNETWORKING ETHERNET AND MPLS
NETWORKS
Abstract
MPLS networks offering PW or VPLS services may be interconnected
with Ethernet networks implemented according to 802.1ah or
802.1Qay. The MPLS network may be a core and offer services to the
Ethernet access networks, or vise-versa. Additionally, a mixture of
different types of access networks may be interconnected by an MPLS
core or an Ethernet core. Both network interworking and service
interworking are provided. OAM fault detection may be implemented
via maintenance entities extending across the network or end to end
depending on the combination of networks and services offered by
the networks.
Inventors: |
MOHAN; Dinesh; (Kanata,
CA) ; SMALLEGANGE; Gerald; (Stittsville, CA) ;
UNBEHAGEN; Paul; (Apex, NC) ; BRAGG; Nigel;
(Weston Colville, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ROCKSTAR CONSORTIUM US LP |
Plano |
TX |
US |
|
|
Assignee: |
Rockstar Consortium US LP
Plano
TX
|
Family ID: |
39618623 |
Appl. No.: |
13/864863 |
Filed: |
April 17, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12016190 |
Jan 17, 2008 |
|
|
|
13864863 |
|
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|
|
60880816 |
Jan 17, 2007 |
|
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Current U.S.
Class: |
370/392 |
Current CPC
Class: |
H04L 12/4633 20130101;
H04L 12/4616 20130101; H04L 12/66 20130101; H04L 45/502 20130101;
H04L 12/4662 20130101; H04L 2212/00 20130101; H04L 12/4658
20130101 |
Class at
Publication: |
370/392 |
International
Class: |
H04L 12/56 20060101
H04L012/56 |
Claims
1. A method of transporting customer Ethernet frames over a
Multi-Protocol Label Switching (MPLS) network implementing a
pseudo-wire service, the method comprising: receiving a customer
frame on a network port, the customer frame including a customer
destination MAC address (C-DA) and a customer source MAC address
(C-SA); identifying a customer service instance based on at least
one of the network port and a VLAN associated with the frame;
encapsulating the customer frame with a backbone destination MAC
address (B-DA), a backbone source MAC address (B-SA), and
information identifying the customer service instance associated
with the frame, the B-DA being selected based on the customer
service instance; further encapsulating the customer frame with a
Label Switched Path (LSP) label and a pseudo-wire label, the
pseudo-wire label being selected based on the information
identifying the customer service instance and the LSP label being
selected based on the B-DA; and forwarding the encapsulated frame
toward a network node associated with the B-DA based on the LSP
label.
2. The method of claim 1, wherein encapsulating the customer frame
with the B-DA, the B-SA and the information identifying the
customer service instance comprises MAC-in-MAC encapsulation.
3. The method of claim 1, wherein the information identifying the
customer service instance comprises an I-SID.
4. The method of claim 1, wherein the information identifying the
customer service instance comprises a Virtual Local Area Network
identifier (VLAN-ID).
5. The method of claim 1, wherein the VLAN-ID is part of a
B-Tag.
6. The method of claim 1, wherein: receiving the customer frame on
the network port comprises receiving the customer frame at an edge
node of a first access network; encapsulating the customer frame
with the B-DA, B-SA and information identifying the customer
service instance comprises encapsulating the customer frame at the
edge node for forwarding over the first access network; and further
encapsulating the customer frame with an LSP label and a
pseudo-wire label comprises further encapsulating the customer
frame at an edge node of a core network for forwarding over the
core network to a second access network.
7. The method of claim 6, wherein the information identifying the
customer service instance comprises an I-SID.
8. The method of claim 6, wherein the edge node of the first access
network identifies the I-SID based on a Virtual Local Area Network
identifier (VLAN-ID) of the customer frame.
9. The method of claim 8, wherein the VLAN-ID is part of a
B-Tag.
10. The method of claim 6, further comprising forwarding the
customer frame over the second access network toward its
destination.
11. The method of claim 10, further comprising: decapsulating the
further encapsulated customer frame by removing the LSP label, the
pseudo-wire label, the B-DA, the B-SA, the information identifying
the customer service instance; and forwarding the customer frame
toward its destination over the second access network based at
least on the C-DA.
12. The method of claim 11, wherein: the frame comprises a customer
Virtual Local Area Network identifier (C-VLAN); and forwarding the
customer frame toward its destination over the second access
network based at least on the C-DA comprises forwarding the
customer frame based on its C-DA and its C-VLAN.
13. The method of claim 6, wherein the first access network
comprises a Provider Backbone Transport (PBT) network.
14. The method of claim 6, wherein the first access network is a
Provider Backbone Bridging (PBB) network.
15. The method of claim 6, wherein the first access network is a
Provider Link State Bridging (PLSB) network.
16. The method of claim 6, wherein the second access network
comprises a Provider Backbone Transport (PBT) network.
17. The method of claim 6, wherein the second access network is a
Provider Backbone Bridging (PBB) network.
18. The method of claim 6, wherein the second access network is a
Provider Link State Bridging (PLSB) network.
19. The method of claim 6, wherein the second access network is an
MPLS network.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/016,190, filed Jan. 17, 2008, entitled
METHOD AND APPARATUS FOR INTERNETWORKING ETHERNET AND MPLS
NETWORKS, which claims the benefit of and priority from U.S.
Provisional Patent Application No. 60/880,816, filed Jan. 17, 2007
entitled PBB/PBT MPLS INTERWORKING, the contents of which both are
hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to communication networks and,
more particularly, to a method and apparatus for interworking
Ethernet and MPLS networks.
[0004] 2. Description of the Related Art
[0005] The various network elements on the communication network
communicate with each other using predefined sets of rules,
referred to herein as protocols. Different protocols are used to
govern different aspects of the communication, such as how signals
should be formed for transmission between network elements, various
aspects of what the protocol data units should look like, how
packets should be handled or routed through the network by the
network elements, and how information associated with routing
information should be exchanged between the network elements.
[0006] Ethernet is a well known networking protocol that has been
defined by the Institute of Electrical and Electronics Engineers
(IEEE) as standard 802.1. Conventionally, Ethernet has been used to
implement networks in enterprises such as businesses and campuses,
and other technologies have been used to transport network traffic
over longer distances. As the Ethernet standards have evolved over
time, Ethernet has become more viable as a long distance transport
technology as well.
[0007] The original Ethernet standard allowed a source address (SA)
and Destination Address (DA) to be specified. Over time, several
additional fields have been added to allow other values to be
designated with respect to a particular Ethernet frame. The
original Ethernet frame format specified by IEEE 802.1 includes a
source address (C-SA) and a destination address (C-DA). IEEE 802.1Q
added a Customer VLAN tag (C-Tag) which includes an Ethertype, TCI
information, and customer VLAN ID. IEEE 802.1ad added a provider
VLAN tag (S-Tag), which also includes an Ethertype, TCI
information, and subscriber VLAN ID. The C-Tag allows the customer
to specify a VLAN, while the S-Tag allows the service provider to
specify a VLAN on the service provider's network for the frame.
These tags also allow the customer and subscriber to specify other
aspects which are not relevant to an understanding of the
contribution disclosed herein. When a network is implemented using
802.1ad it may be referred to as Q in Q encapsulation or Provider
Bridging (PB). A domain implemented using this Ethernet standard
will be referred to as a Provider Bridging (PB) domain.
[0008] The Ethernet standard has evolved to also allow for a second
encapsulation process to take place as specified in IEEE 802.1ah.
Specifically, an ingress network element to a service provider's
network may encapsulate the original Ethernet frame with an outer
MAC header including a destination address on the service
provider's network (B-DA), a source address on the service
provider's network (B-SA), a VLAN ID (B-VID) and a service instance
tag (I-SID). The combination of customer MAC addresses C-SA and
C-DA with the I-SID are commonly referred to as the I-Tag. A domain
implemented using this Ethernet standard will be referred to as a
Provider Backbone Bridging (PBB) domain.
[0009] There are also two other Ethernet standards that have been
developed or which are in the process of being developed that may
be used in one or more of the domains. Specifically, IEEE 802.1Qay
specifies a way for the network elements to switch traffic based on
the B-DA and B-VID rather than just forwarding the traffic
according to the B-DA. The header of the frames forwarded on an
Ethernet network established using this technology is not changed,
but the manner in which the information is used is changed to allow
forwarding to take place in a different manner. A network domain
that forward traffic using this forwarding paradigm will be
referred to as Provider Backbone Trunking (PBT). In IEEE 802.1Qay,
PBT is commonly referred to as Provider Backbone Bridges--Traffic
Engineering (PBB-TE). Thus, the term PBT will be used herein to
refer to a network implemented according to this standard.
[0010] PBB, PB, and the original Ethernet standard use a spanning
tree protocol to determine which links should be used to broadcast
traffic on the network and which links should be used to forward
unicast traffic on the network. To overcome some of the
shortcomings of using spanning trees, another Ethernet control
plane is in the process of being developed as IEEE 802.1aq, in
which a shortest path routing protocol such as Intermediate System
to Intermediate System (IS-IS) or Open Shortest Path First (OSPF)
is used in the control plane to establish forwarding paths through
the network. Traffic on the domain may then be forwarded based on
the B-DA and B-VID in a manner similar to PBT, but from a control
perspective a shortest path routing protocol is used instead of a
spanning tree to define routes through the network. A domain
implemented in this manner will be referred to herein as a Provider
Link State Bridging (PLSB) domain. PLSB is described in greater
detail in U.S. patent Ser. No. 11/537,775, filed Oct. 2, 2006,
entitled "Provider Link State Bridging," the content of which is
hereby incorporated herein by reference. Since PLSB refers to the
control plane, it may be used to control forwarding of packets
while allowing encapsulation of the packets using PB, PBB, or PBT
as described above.
[0011] MPLS is another commonly used networking protocol. MPLS
specifies a way in which a label switched path may be established
through a network. When a packet is received at an MPLS Label Edge
Router (LER) the LER will determine the destination LER for the
packet, attach a label to the packet, and forward the packet to a
first Label Switch Router (LSR) on the path to the destination LER.
The LSR will strip the label from the packet, look up the label to
determine the next label to be applied to the packet and the next
hop for the path, and forward the packet onward to the next hop.
This proceeds hop by hop across the network to cause the packet to
be forwarded across the Label Switched Path (LSP) through the MPLS
network.
[0012] The LSP connects a pair of nodes on the MPLS Network. Since
more than one customer may need to transmit traffic between the
pair of endpoints, it is desirable to allow multiple customers to
share one LSP rather than creating a new LSP for each customer. In
MPLS, this is accomplished through the use of Pseudowires.
Pseudowires allow traffic for different VLANs to be tagged with a
service label, so that traffic from multiple customers, VPNs, etc.,
can use a common LSP and be differentiated by the egress LER. A
service that utilizes a pseudowire will be referred to as a Virtual
Private Wire Service (VPWS).
[0013] In addition to pseudowires, a branching mechanism was
developed for MPLS that will allow a given packet that is received
at a label switch router (LSR) to be duplicated and passed out of
more than one forwarder. A service that utilizes this feature of an
MPLS network will be referred to as a Virtual Private LAN Service
(VPLS). VPLS uses pseudowires to set up the paths through the
network but allows the paths defined by the pseudowires to branch
to emulate a Local Area Network (LAN).
[0014] VPLS uses the signaling protocol described in
draft-ietf-12vpn-signaling-08.txt and IETF RFC 4447 to set up
pseudowires. The content of each of these protocols is hereby
incorporated herein by reference. RFC 4447 introduces the concept
of an Attachment Group Identifier (AGI) that may be conceptualized
as a VPN identifier or VLAN identifier. The AGI specifies a logical
group of forwarders at the egress node, rather than a particular
individual forwarder. When implemented in this manner, an
attachment circuit associated with a particular VPLS or pseudowire
is constructed to include the Attachment Group Identifier (AGI)
that identifies the group of forwarders, and an Attachment
Individual Identifier (AII) that identifies a particular forwarder
within the group.
[0015] In operation, the MPLS network will establish label switched
paths through the network using a Label Distribution Protocol
(LDP). As part of this process, the LDP will allow the Label Edge
Routers (LERs) to exchange AGI/AII pairs that will allow the
network to setup the dataplane for the pseudowires. This will set
up the forwarders at the nodes to cause the packets to be forward
in a specified manner. When a frame arrives at the ingress LER, the
ingress LER will check the signaled value of AGI/AII pairs with
local information and apply a service label as well as a tunnel
label. The tunnel label will be used to forward the frame along the
LSP through the MPLS network, while the service label will be used
by the egress node to obtain the context of the pseudowire at the
egress so that the frame may be sent to the correct set of
forwarders. The forwarders will then be used to forward the traffic
to the correct customer/VPN as the traffic exits the MPLS network.
The AGI/AII pairs are thus used in the signaling phase of
establishing the VPLS service by the ingress/egress LERs to
coordinate how frames should be handled at the egress to cause the
frames to be forwarded to the correct customers.
[0016] To monitor how a network is operating, such as to perform
fault detection, fault isolation, fault confirmation, and other
types of fault detection and remediation, an operator may want to
send Operation, Administration, and Maintenance (OAM) service
frames across the network. Different OAM flows may be used to
monitor different aspects or segments of a connection on the
network. For example, an OAM flow may be used end-to-end across the
network, may be used to monitor the connection within a particular
domain, or may be used to monitor other aspects of the connection
on the network. A particular OAM flow will be referred to herein as
a Management Entity (ME). By monitoring a particular ME the network
manager may determine whether connectivity exists across that
portion of the network, and if connectivity does not exist, may
enable the network manager to isolate the fault on the network.
When Ethernet networks and MPLS networks are required to connect
together, a network manager may need to be able to define
Maintenance Entities across a combined MPLS/Ethernet network
[0017] As discussed above, both Ethernet networks and MPLS networks
have implemented features that will allow traffic from different
VLANs to be identified, and which will also allow traffic
associated with particular service instances within a VLAN to be
identified. When the networks are interconnected, it would be
advantageous to allow interworking to occur, either at the network
level or service level, so that particular services may be offered
end-to-end across the interconnected network. Additionally, from a
management perspective, it would be advantageous to enable OAM
Maintenance Entities to be defined to monitor aspects of the
MPLS/Ethernet network.
SUMMARY OF THE INVENTION
[0018] MPLS networks offering PW or VPLS services may be
interconnected with Ethernet networks implemented according to
802.1ah or 802.1Qay. The MPLS network may be a core and offer
services to the Ethernet access networks, or vise-versa.
Additionally, a mixture of different types of access networks may
be interconnected by an MPLS core or an Ethernet core. Where
service frames are to be mapped from an ingress Ethernet network to
an egress Ethernet network across an MPLS network, the VLAN ID
value will be set to correspond to a PW through the MPLS core to
reach the particular egress Ethernet network. Where the MPLS core
implements VPLS, the destination address may be selected to allow
the Ethernet network to select the correct VPLS instance. Where an
Ethernet core is used, the Ethernet core may select a tunnel based
on the pseudowire label associated with the service frame or based
on the B-VID, I-SID, or B-VID and B-DA associated with the service
frame.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Aspects of the present invention are pointed out with
particularity in the appended claims. The present invention is
illustrated by way of example in the following drawings in which
like references indicate similar elements. The following drawings
disclose various embodiments of the present invention for purposes
of illustration only and are not intended to limit the scope of the
invention. For purposes of clarity, not every component may be
labeled in every figure. In the figures:
[0020] FIGS. 1-3 are functional block diagrams of communication
networks showing three example ways in which Ethernet and MPLS
network domains may be connected;
[0021] FIG. 4 is a functional block diagrams of a reference view of
a network including MPLS networks and an Ethernet (PBT) core
network;
[0022] FIG. 5 is a functional block diagram of a path through the
reference network of FIG. 4 illustrating the format of the headers
applied to the data as it traverses the network according to an
embodiment of the invention;
[0023] FIG. 6 is a functional block diagrams of a reference view of
a network including MPLS networks and an Ethernet (PBB) core
network;
[0024] FIG. 7 is a functional block diagram of a path through the
reference network of FIG. 6 illustrating the format of the headers
applied to the data as it traverses the network according to an
embodiment of the invention;
[0025] FIG. 8 is a functional block diagrams of a reference view of
a network including MPLS networks and an Ethernet (PBT/PBB) core
network;
[0026] FIG. 9 is a functional block diagrams of a reference view of
a network including Ethernet (PBT) networks and an MPLS (PW) core
network;
[0027] FIG. 10 is a functional block diagram of a path through the
reference network of FIG. 9 illustrating the format of the headers
applied to the data as it traverses the network according to an
embodiment of the invention;
[0028] FIG. 11 is a functional block diagram of path through the
reference network of FIG. 9 illustrating another format of the
headers applied to the data as it traverses the network according
to an embodiment of the invention;
[0029] FIG. 12 is a functional block diagram showing example
maintenance entities that may be implemented in the network of FIG.
9 according to an embodiment of the invention;
[0030] FIG. 13 is a functional block diagrams of a reference view
of a network including Ethernet (PBT) networks belonging to
different domains and an MPLS (PW) core network;
[0031] FIG. 14 is a functional block diagram of a path through the
reference network of FIG. 13 illustrating the format of the headers
applied to the data as it traverses the network according to an
embodiment of the invention;
[0032] FIG. 15 is a functional block diagram showing PBT trunk
segments in the network of FIG. 13 according to an embodiment of
the invention;
[0033] FIG. 16 is a functional block diagram showing example
maintenance entities that may be implemented in the network of FIG.
15 according to an embodiment of the invention;
[0034] FIGS. 17-19 are functional block diagrams showing several
different interconnects that may be used to interconnect the PBT
and MPLS networks;
[0035] FIG. 20 is a functional block diagrams of a reference view
of a network including Ethernet (PBB) networks belonging to
different domains and an MPLS (PW) core network;
[0036] FIG. 21 is a functional block diagram of a path through the
reference network of FIG. 20 illustrating the format of the headers
applied to the data as it traverses the network according to an
embodiment of the invention;
[0037] FIG. 22 is a functional block diagrams of a reference view
of a network including Ethernet (PBB/PBT) networks and MPLS
networks interconnected over an MPLS (VPLS) core network;
[0038] FIG. 23 is a functional block diagram of a path through the
reference network of FIG. 22 illustrating the format of the headers
applied to the data as it traverses the network according to an
embodiment of the invention;
[0039] FIG. 24 is a functional block diagrams of a reference view
of a network including Ethernet (PBB/PBT) networks and MPLS
networks interconnected over an MPLS (PW) core network;
[0040] FIG. 25 is a functional block diagram of a path through the
reference network of FIG. 24 illustrating the format of the headers
applied to the data as it traverses the network according to an
embodiment of the invention; and
[0041] FIG. 25A is a functional block diagram of a path through the
reference network of FIG. 24 illustrating another format of the
headers applied to the data as it traverses the network according
to an embodiment of the invention.
DETAILED DESCRIPTION
[0042] The following detailed description sets forth numerous
specific details to provide a thorough understanding of the
invention. However, those skilled in the art will appreciate that
the invention may be practiced without these specific details. In
other instances, well-known methods, procedures, components,
protocols, algorithms, and circuits have not been described in
detail so as not to obscure the invention.
[0043] When an Ethernet network and an MPLS network are
interconnected, the two networks will pass protocol data units
between each other. Depending on how the networks are connected,
service instances on one network may be translated to service
instances on the other network. A system that interconnects
networks of different types in this manner will be referred to
herein as "service interworking." Service interworking implies that
a handoff to another domain is such that the other domain
identifies its service instance (e.g. PW/VPLS) from service frames,
translates service frames to its service instance, and transports
them. Transformation of service frames is expected inside the other
domain in this case. In an Ethernet/MPLS context, service
interworking may occur in various ways. For example, service
interworking may occur where the MPLS network identifies its
service instance such as PW or VPLS from the I-SID or other service
identifier in use on the Ethernet network.
[0044] Another way of interconnecting two domains is for the two
domains to encapsulate service frames for transport without
transforming the service frames. An interconnection of this nature
will be referred to herein as network interworking. In an Ethernet
to MPLS context, Network Interworking may occur in various ways.
For example, network interworking may occur where the MPLS network
identifies its service instance such as PW or VPLS from the VLAN ID
in use on the Ethernet network.
[0045] There are many interworking cases that are possible, due to
the myriad different types of Ethernet and the several different
ways in which an MPLS network may be instantiated. Several ways of
interworking MPLS and Ethernet networks are set forth below. Since
there is a large deployed base of MPLS networking gear, an emphasis
on selecting ways to interwork MPLS and Ethernet networks has been
provided that will minimize the amount of modification required on
the MPLS networking gear.
[0046] FIGS. 1-3 illustrate three example communication networks
and show three example ways in which Ethernet and MPLS network
domains may be connected. In FIG. 1, Customer Edge (CE) devices 10
connect via an Ethernet Access Switch 12 to an aggregation network
14 such as a metropolitan (Metro) area network. The use of an
Ethernet Access Switch is optional, and the invention is not
limited by the manner in which the Customer Edge devices 10 connect
to the aggregation network. Additionally, Ethernet Access Switches
have many common names, such as Network Interface Demarcation (NID)
and thus many different ways may be used to access the networks
described herein. Additionally, throughout this description the
term "metro" network will be used to refer to an aggregation
network. The invention is not limited to an implementation that
interworks a metropolitan area network with a core network,
however, as embodiments of the invention may be utilized to
interwork Ethernet and MPLS domains of any desired size and in any
desired context. The metro network is connected to a core network
16, which may be connected to other metro networks.
[0047] The metro networks may be implemented using MPLS and the
core network may be implemented using Ethernet, as shown in FIG. 1.
Alternatively, the core network may be implemented using MPLS and
the metro networks may be implemented using Ethernet as shown in
FIG. 2. Still alternatively, a mixture of Ethernet and MPLS
networks may be used to implement the metro networks and MPLS or
Ethernet may be used in the core as shown in FIG. 3. The Ethernet
and MPLS networks thus may be connected together in many different
ways and, accordingly, it may be desirable to interwork the
networks differently depending on the particular context.
[0048] Additionally, two or more of the metro networks may be
implemented using a common control plane, so that the two metro
networks are to be considered to be one logical network.
Interworking another network with the common metro networks may
need to take into account the fact that the two metro networks are
implemented using a common control plane so that flows of data may
be commonly implemented by the metro networks without alteration by
the intervening core network. Thus, many different network
scenarios are possible and, depending on the particular
implementation, the manner in which the networks are interworked
may vary as well.
[0049] In FIG. 1, the Customer Edge (CE) 10 will pass a
packet/frame to the Ethernet Access Switch (EAS) 12. The EAS will
pass the packet to a Multi-Service Edge (MSE) 18 on the MPLS
network which will place the packet on a Label Switched Path (LSP)
across the metro network. The MPLS network may implement
pseudo-wires (PW) or Virtual Private LAN Service (VPLS) depending
on whether the Label for the packet is selected based on the
packet's IP address or IP address and VLAN ID. The packet will be
received by another MSE on the edge of the metro network and passed
to a Switching--Provider Edge (S-PE) 20 on the core network.
[0050] The metro network 14 in FIG. 1 is an MPLS network having a
plurality of Multi-Service Edge (MSE) network elements configured
to receive traffic and put the traffic onto Label Switch Paths
(LSP) through the network. The MSE network elements act as Label
Edge Routers (LERs) that assign labels to packets according to the
path the packet is to take through the MPLS network. The MSE also
adds one or more PseudoWire (PW) tags to enable traffic from
multiple customers to be multiplexed across a given LSP through the
network. In operation, a MSE will receive a frame from the S-PE and
assign label and PW tag. The label will be used to forward the
frame across the MPLS network and the PW tag will be used to
demultiplex the frame to identify the customer flow associated with
the tag.
[0051] The core network in the embodiment of FIG. 1 is an Ethernet
network configured to operate using Provider Backbone Bridging
(PBB) defined by IEEE 802.1ah (Mac in Mac) or Provider Backbone
Transport (PBT) defined by IEEE 802.1Qay. In a PBB network, packets
are forwarded across the network based on the destination MAC
address in the outer header of the packet. PBT networks allow
traffic engineering to take place on the network to allow explicit
paths to be set up across the network based on VLAN ID (VID), and
forwarding takes place within the network based on both the
destination address and VLAN ID. Optionally, within the same
network a range of VIDs may be used to implement PBT while other
VIDs can be used to implement PBB. Thus, the two types of networks
may coexist. In the following description, particular reference may
be made to particular types of Ethernet networks being interworked
with MPLS networks. This description is not to be construed as an
indication that only one type of Ethernet network exists, but
rather is to be construed as referring to how a particular type of
Ethernet technology may be adapted to interwork with an MPLS
network. Other Ethernet standards may be implemented as well, and
as new standards are developed the concepts disclosed herein may be
extended to interoperate with those new standards where
applicable.
[0052] In the example shown in FIG. 1, the metro network has a
plurality of MSEs 18 configured to implement user to network
interface (UNI) interfaces to enable customers (e.g. CE 10 or EAS
12) to connect to the metro network. On the boundary between the
metro network 14 and the core network 16 the network elements will
implement Network to Network Interfaces (NNIs) to enable the
network element to connect to other network elements.
[0053] FIG. 2 is similar to FIG. 1, except that the Metro networks
are implemented as Ethernet networks (either PBB, PBT) and the core
network is an MPLS network (PW or VPLS). FIG. 3 is also similar
except that the metro networks are a mixture of Ethernet and MPLS,
and the core is an MPLS network. Other network scenarios are also
likewise possible.
[0054] FIG. 4 shows an example network 400 where three MPLS access
networks 410, 420, 430 (metro networks) are interconnected by a PBT
core network 450. FIG. 6 shows a similar embodiment in which a PBB
core network 650 is used to interconnect MPLS metro networks. As
mentioned above, as used herein the term Provider Backbone Trunking
(PBT) refers to a network that is implemented using Ethernet
standard IEEE 802.1Qay, which allows traffic engineered paths to be
established through the network. The manner in which PBT operates
is specified in IEEE 802.1Qay, the content of which is hereby
incorporated herein by reference. The term Provider Backbone
Bridging (PBB) refers to an Ethernet network that is established
using Mac in Mac encapsulation to allow forwarding within the
network to occur based on provider MAC addressing rather than
customer MAC addressing. The manner in which PBB operates is
specified in IEEE 802.1ah, the content of which is hereby
incorporated herein by reference.
[0055] In the embodiment shown in FIG. 4, MPLS access networks
include Network Provider Edge (N-PE) network elements 402 that
interface with customers, such as Customer Edge (CE) 404 or
User-Provider Edge (U-PE) 406. The MPLS access networks also
include Switching Provider Edge (S-PE) 408 that connect to the core
network 450. The PBT core network includes Provider Edge (PE)
network elements 452 that interconnect the core network with the
access networks.
[0056] In a scenario such as the one shown in FIG. 4, the MPLS
access networks and PBB or PBT core network may be interworked at
the network level or the service level. If the networks are
interworked at the network level, the MPLS domain will consider the
PBB/PBT domain as a server domain and will not peer with it. The
MPLS domain nodes will peer on either side of the PBB/PBT domain,
however. The MPLS domain will transmit and receive Ethernet
encapsulated frames containing LSP payloads, where Ethernet
encapsulation is link local (link here is represented as between
two MPLS peer nodes, which is virtualized over the PBB/PBT domain).
The PBB/PBT domain would therefore receive Ethernet frames which
would need to be mapped to PBB/PBT service instances.
[0057] Accordingly, from a network interworking standpoint, the PBT
domain requires the MPLS domains to use virtual links (i.e. VLANs)
such that an MPLS node only uses a virtual link such that it is
dedicated for a single peer MPLS domain only. By causing a
particular MPLS domains to use a different VLAN value or set of
VLAN values for each of the other MPLS domains, the ingress nodes
on the PBT core may map the VLAN values to PBT trunks in the PBT
core to cause the frames to be forwarded to the correct MPLS
domain. Thus, for example, assume that VLAN 1 was used by MPLS
domain X for traffic intended for MPLS domain Y, and that VLAN 2
was used by MPLS domain X for traffic intended for MPLS domain Z.
By using a different VLAN ID for each of the destination MPLS
domains, the ingress node on the PBT core may select a trunk to
carry the traffic to either MPLS domain Y or MPLS domain Z by
looking at the VLAN ID associated with the frame.
[0058] Where different PBT trunks are required to have different
traffic engineering requirements, more than one PBT trunk may be
implemented between the same set of metros. Thus, optionally, a set
of VLAN values may be used to designate a set of PBT trunks
extending between the pair of metros. If the MPLS domains are not
able to implement virtual interfaces, i.e. implement different VLAN
IDs for different destination MPLS domains, then a PBB core network
should be used instead of a PBT core network. Alternatively, the
S-PEs may use different ports (physical interface) for each metro
such that the PE is able to map traffic to different PBT trunks to
different metros based on the ingress physical interface.
[0059] If the networks shown in FIG. 4 are to be interworked at a
service level, then the MPLS domains will consider the PBB/PBT
domain as a peer domain. The MPLS domain will transmit and receive
Ethernet encapsulated frames containing a pseudowire payload.
Ethernet encapsulation, in this instance, will be link local for
the link between the MPLS and PBB/PBT nodes. The PBB/PBT domain
will receive Ethernet frames, de-encapsulate the frames to obtain
access to the PW encapsulated frames. Thus, where the networks are
to be interworked at the service level, the PBB/PBT domain will
preferably support Pseudo Wire signaling in line with MS-PW.
Alternatively, static configuration may be used as well. Additional
details of this type of interworking will be described below in
connection with FIGS. 9-12.
[0060] In the Example shown in FIG. 4, the access switch (U-PE) 406
hands off native service frames to the MPLS access switch (N-PE)
402 to be carried transparently over a PseudoWire (PW) service. The
N-PE 402 encapsulates different native services (e.g. TDM) over
PWs. The N-PEs establish end-to-end PWs. The S-PEs may optionally
run directed LDP sessions between them. The PBT core appears as a
single Ethernet link between the S-PEs. The S-PEs also establish
LSPs among each other. The PBT core provides transport of LSP
tunnels. Thus, for example in FIG. 4, S-PE1 will establish an LSP
with S-PE3 that spans the PBT core. The PBT core will provide
transport service for packets passed along the LSP between S-PE1
and S-PE3. Within each MPLS network, an LSP will also be set up
between the N-PE and S-PE. Thus, for example, an LSP may be set up
between N-PE 2 and S-PE1 in MPLS network X, and similarly between
S-PE3 and N-PE 4 in MPLS network Y. The LSP may be one LSP across
both MPLS domains and the PBT domain, or may be individual LSPs in
each of the three segments.
[0061] The PEs offer PBT trunks, such that frames entering the PBT
network either carry tags that are dedicated to connection a MPLS
domain with only a single other domain (i.e. dedicated virtual
interfaces as described above) or carry the S-PE's DA with a common
tag. The PE will map frames received from the S-PE to a PBT trunk
based on the tag associated with the frame, or uses the VLAN and DA
to identify the PBT trunk. For resiliency and loop avoidance, the
PEs may establish both primary and backup trunks.
[0062] A packet may be provided with a particular quality of
service in the MPLS network. For example, the access switch U-PE or
MPLS access switch (N-PE) may set the LSP Exp bits in the MPLS
header to indicate a particular class of service. To allow the
Ethernet network to afford the same quality of service to the
packet as it traverses the core network, it may be desirable to map
the LSP Exp bits to the B-Tag p-bits in the Ethernet header. The
p-bits are three bits specified in the B-Tag which are defined by
IEEE 802.1p to be used to indicate a quality of service. Optionally
the p-bits associated with the Ethernet header that is applied to
the packet as it traverses the PBT network may be set to provide a
quality of service akin to that associated with the packet in the
MPLS network.
[0063] FIG. 5 shows encapsulations that may occur to a packet as it
traverses the network of FIG. 4. In the example shown in FIG. 5, it
will be assumed that the packet is received at U-PE2 on MPLS access
network X from CE2, and is addressed to CE4 connected to U-PE4 on
MPLS access network Y.
[0064] As shown in FIG. 5, the U-PE2 will output a service frame
500 which, when received by N-PE2 will be mapped to a LSP to N-PE4.
The LSP to be used to carry the packet from N-PE 2 to N-PE 4 may
extend end-to-end between the two MPLS networks or may terminate in
each MPLS network. For example, a first LSP may extend from N-PE2
to S-PE1, a second LSP may extend from S-PE1 to SPE3, and a third
LSP may extend from S-PE3 to N-PE4. Alternatively, a single LSP may
extend from N-PE2 to N-PE4. Where more than one LSP segment is
involved, the end point between the two segments will separately
signal the LSPs and map traffic from one to the next to complete a
path through the network. Similarly, the network element in this
instance may also map PWs on the different LSP segments to allow PW
service to extend end-to-end across the network.
[0065] In the example shown in FIG. 5, when N-PE2 receives a packet
it will assign a LSP label 502 to the packet and a PW label 504 to
the packet. The LSP in this instance identifies the path through
the network, while the PW label allows traffic from multiple
customers to be multiplexed on the same LSP and discerned by the
end router so that the different traffic may be forwarded to the
correct customer on the egress from the network.
[0066] In addition to the LSP label and PW label, the N-PE will
assign a link layer Ethernet header (transport header 506) that
will be used by the network element to forward the packet toward
the next hop on the MPLS network. Each hop on the MPLS network will
remove the transport header, read the LSP label, swap the LSP label
with a new LSP label, and forward the packet toward the next hop on
the MPLS network. The manner in which the MPLS network operates is
not intended to deviate from standard practice.
[0067] When the S-PE receives the packet it will perform a label
swap as normal and forward the packet over the LSP that passes
through the PBT core network. The PE, upon receipt of the packet,
will determine the PBT trunk to be used to carry the packet as
described in greater detail above. For example, the PE may read the
B-DA associated with the transport header or the B-VID contained in
the B-TAG to determine the PBT trunk to be used to carry the packet
across the PBT core network. The PE will then encapsulate the
packet with a header 508 that will be used to transport the packet
across the PBT core network. The header, may be a standard 802.1ah
PBB encapsulation header that will be used to transport the packet
across the PBT trunk on the PBT core network.
[0068] When the packet is received at the egress from the PBT
network, the PE will strip off the header 508 and forward the
packet to the S-PE3. The S-PE 3 will strip off the transport header
506, read the LSP label, and forward the packet toward N-PE4. Where
the LSP over the PBT core and the LSP over the MPLS access network
Y are different LSPs, the S-PE3 will map the packet from one LSP to
the next before forwarding the packet toward the LPS on MPLS access
network Y.
[0069] From a resiliency standpoint, the PBT network may implement
primary and backup PBT trunks, so that the PBT trunks may be
considered resilient. The MPLS domain can run its own resilient
PWs, which are transparent to the PBT core. The nature of the
interconnect determines the level of visibility and impact of any
failure.
[0070] The solution described herein, in connection with FIGS. 4-5,
allows the PEs to operate without reference to the PW labels. When
dedicated virtual interfaces (i.e. VLAN IDs) are used by the S-PEs
to forward traffic to different MPLS networks, the PEs may operate
in a normal manner by using the VID to identify the I-SID and PBT
trunk that are to be used to create the header 508 for use in
transporting the packet across the PBT network. Additionally, the
S-PE is not required to treat the link through the PBT network as
anything other than a regular Ethernet link. However, this solution
does require an additional 22 byte overhead for each frame passed
across the PBT network, since as shown in FIG. 5 the encapsulation
process performed by the ingress PE to the PBT network will result
in an 802.1ah MAC header 508 to be applied to the frames as they
enter the PBT network. Additionally, if the MPLS networks do not
use virtual interfaces, and hence use the same VID to identify more
than one other MPLS network, the PE may be required to use other
fields to map incoming frames to PBT trunks. For example, the PE
may be required in this instance to determine the I-SID and PBT
trunk based on the DA rather than only the VID.
[0071] FIG. 6 shows another example in which a PBB core network
implemented using 802.1ah is used to interconnect MPLS access
networks. As shown in FIG. 6, the access switch (U-PE) hands off
native service frames to the MPLS access switch (N-PE) to be
carried transparently over a PW service. The N-PE encapsulates
different native services over pseudowires. The N-PEs may establish
end-to-end PWs or may establish PWs with the S-PEs, and the S-PEs
may establish PWs. Thus, the LSP and PWs may extend end-to-end
between the N-PEs or may be segmented as described above in
connection with FIGS. 4-5. As with the previous example, the PBB
network will appear as a single Ethernet link between S-PEs on
different MPLS access networks, and the PBB core will thus provide
transport for the LSP tunnels.
[0072] The PEs offer E-LAN service connectivity across the PBB
core. E-Line may be considered a special case of point-to-point
E-LAN connectivity across the PBB core. Frames entering the PBB
network carry the S-PE's DA and possibly a tag. PEs offer E-LAN
service corresponding to the tag. One example of the tag that may
be used in connection with this is the B-VID contained in the
B-Tag.
[0073] When a packet arrives at the PE, the PE will use the B-VID
and B-DA (indicating S-PE DA) from the transport header 606 to
identify a service instance associated with the packet, and then
encapsulate the packet for transport across a PBB tunnel through
the PBB core network. As mentioned above with respect to the PBT
core network, when a PE receives a packet it may be desirable to
map the LSP Exp bits to the B-tag p-bits. This mapping is
advantageous as both the EXP bit field and the p-bit field are
three bits long, so that each accommodates 8 classes of
service.
[0074] The PBB network may implement either a spanning tree or a
link state protocol to control the PBB network. For example, it is
common for PBB networks to implement a spanning tree protocol to
implement resiliency and loop avoidance. Alternatively, a link
state protocol such as OSPF or IS-IS may be used to control the
network and provide resiliency and loop avoidance.
[0075] FIG. 7 shows the encapsulation that may occur as a packet
traverses the interworked MPLS networks and PBB core network. As
shown in FIG. 7, the encapsulation process is very similar to the
process described above in connection with FIG. 5. For example, as
a service frame enters the MPLS network it will be mapped to an LSP
and PW, and encapsulated using a LSP label and PW Label. A
transport header will be applied to transport the packet across the
MPLS network. The transport headers are mostly link specific.
[0076] When the packet is received at the S-PE the S-PE will either
forward the packet along the LSP onto the PBB network (where the
LSP exists end-to-end between the N-PEs) or will translate the LSP
from an LSP segment on the MPLS access network to an LSP that
extends across the PBB core network. Similarly, the PW label may
remain the same on the various LSP segments or may be translated by
the S-PE if the packet is put onto a new LSP segment at the S-PE.
The S-PE will then apply a link header to transport the packet to
PE1.
[0077] From the S-PE standpoint, regardless of whether the LSP
extends from end-to-end or there are multiple LSP segments, the
next hop on the LSP as seen by the S-PE on the first MPLS network
is the S-PE on the second MPLS network. For example, on the path
shown in FIG. 7, the next hop for S-PE1 on MPLS access network X is
S-PE3 on MPLS access network Y. Thus, the transport header applied
by S-PE1 to the packet will point to S-PE3. Upon receipt, the PE
will use the data contained in the transport header to map the
packet to a PBB tunnel and apply a PBB header that will be used to
forward the packet through the IP network.
[0078] From a resiliency standpoint, the PBB tunnels are resilient
assuming that the PBB core is running either xSTP or a link state
protocol on the control plane. Similarly, the MPLS domain can run
its own resilient PWs which are transparent to the PBB core. The
nature of the interconnect between the MPLS networks and the PBB
core will determine the level of visibility and impact of a failure
on the network.
[0079] One benefit of using a PBB core to interconnect multiple
MPLS domains is that the PEs on the PBB core are transparent to the
PW labels. Stated another way, the MPLS network is not aware of the
PBB core and can implement PWs that span across the PBB core
without requiring modification to the manner in which the S-PEs
operate. Additionally, the PEs on the PBB core are not required to
operate differently but rather can implement normal forwarding
behavior and use the VID and DA of the transport header applied to
incoming packets to identify the I-SID and PBB tunnel to be used to
transport the packet across the PBB network.
[0080] Like the previous example, however, the PE will add a 22
byte header to each frame of the packet which increases the
overhead associated with transmitting the packet across the PBB
network. Depending on the nature of the traffic this may or may not
be a concern. Additionally, the PBB network is still required to
implement one or more spanning tree instances or a link state
protocol to avoid loop formation and for resiliency.
[0081] The previous two examples, shown in FIGS. 4-5 and 6-7,
assumed that the MPLS network was implementing PseudoWires (PWs).
It is also possible for the MPLS network to offer Virtual Private
LAN Service (VPLS) to customers. Where the MPLS network implements
VPLS rather than PWs, the access switch (U-PE) will hand off native
service frames to the MPLS access switch (N-PE) to be carried
transparently over a VPLS service.
[0082] To implement VPLS services, the N-PEs will establish a mesh
of PWs interconnecting all of the N-PEs with all of the S-PEs. The
S-PEs will also support spokes to all other S-PEs on all other
metros. FIG. 8 shows an example of this in which a mesh of PWs 802
has been established in the MPLS access network X, and a mesh of
PWs 804 to other S-PEs on other MPLS access networks.
[0083] When the N-PE receives a packet, it will encapsulate the
frame with a PW label and LSP label and forward the packet across
the PW to the S-PE. The S-PE replicates the frame at handoff, if
the service instance spans more than one remote metro, and forwards
multiple copies of the frame across the PWs to each of the S-PEs on
each of the remote metros.
[0084] The PEs on the PBB/PBT network offer E-LINE/E-LAN service
for connectivity across the PBB/PBT core. Frames entering the
PBT/PBB core have a link level transport header including the DA of
the intended S-PE on the remote metro network. The transport header
may also include a VLAN ID or other tag. The PE uses the VLAN or
the VLAN and MAC (DA) to identify the service instance in the
PBB/PBT network that should be used to transport the packet across
the PBB/PBT network. The PE will encapsulate the packet in a
PBB/PBT tunnel (using the PBB encapsulation process of 802.1ah, as
described above in greater detail) and forward the packet across
the network. Thus, the interworking between PBB/PBT networks and
the MPLS network may be implemented, from a PE standpoint, in the
same manner regardless of whether the MPLS network is offering a PW
service or VPLS service.
[0085] Within the MPLS networks, a reservation protocol such as
RSVP may be run to implement redundant spokes between each pair of
metros. RSVP allows traffic engineered paths to be established
through a network. Hence, RSVP may be used to create two separate
paths between each pair of N-PE/SPE to allow for redundant paths to
be created within the MPLS networks. The resilient paths within the
metro are transparent to the PBB/PBT core.
[0086] As a summary, when a PBB or PBT network is implemented as
the core network, and MPLS networks are used to implement the metro
networks, the PE must recognize Ethernet frames encapsulating the
MPLS payload from the MPLS networks. The PE may use the VLAN or the
VLAN and DA from the transport header applied by the S-PE to map
the packets to appropriate PBB or PBT tunnels through the network.
Where the SPEs are able to implement VLAN sets containing one or
more VLAN per remote metro, the PE may identify the PBB/PBT tunnel
from the VLAN and map the packets to the appropriate PBB/PBT tunnel
according to the VLAN. Where the SPEs are not able to implement one
VLAN per remote metro, the PE may use the DA along with the VLAN to
map the packets to the appropriate PBB/PBT tunnel. Optionally, the
PE may also map the LSP EXP bits to PBB/PBT tunnel p-bits to allow
the same quality of service features to be provided end-to-end
across the MPLS/PBB/MPLS or MPLS/PBT/MPLS network.
[0087] When a PBB/PBT trunk fails, an alarm indication signal (AIS)
may be transmitted toward the MPLS domain on a per-VLAN basis. This
will allow the alarm indication signal to be propagated to the MPLS
domain on the virtualized links to enable the MPLS domain to
failover traffic to a backup path. By implementing AIS signaling
from the PBB/PBT domain to the MPLS domain, the MPLS domain is not
required to run end-to-end maintenance entities over the PBB/PBT
domain, and may thus treat the PBB/PBT tunnels as a link.
Implementation of this feature would require the S-PEs to be
configured to implement Ethernet OAM signaling to allow the S-PEs
to interpreted receipt of an AIS as a failure indication rather
than a generic Ethernet frame. Accordingly, implementation of this
feature may require modification of the S-PE to enable it to be
implemented on the network.
[0088] FIGS. 9 and 10 show an example network in which Ethernet
access (Metro) networks 910, 920, 930, are interconnected by an
MPLS core network 950. As shown in FIG. 9, Ethernet network
includes a Provider Edge (PE) that receives traffic from customers
and places the traffic onto the Ethernet network. Switching PEs
(S-PE) 904 forward the traffic from the Ethernet network to the
MPLS core network. The MPLS core network implements Multi-Service
Edge (MSE) network elements 906 which receives traffic from the
Ethernet network and puts the traffic onto Label Switched Paths
(LSPs) through the MPLS core. The MPLS core may implement
PseudoWire (PW) or Virtual Private LAN Service (VPLS) service.
[0089] From a network interworking perspective, the Ethernet domain
would consider the MPLS domain as a server domain and would not
peer with it. Ethernet domain nodes would peer on either side of
the MPLS domain. The Ethernet domain would transmit and receive
Ethernet encapsulated frames containing native payload. Optionally,
the S-PE nodes may transmit PW encapsulated frames.
[0090] MSEs on the MPLS domain would receive Ethernet frames which
would need to be mapped to PW or VPLS service instances. If the
MPLS domain implements PW service, interworking can be accomplished
by requiring the Ethernet domains to use correct B-VIDs to identify
egress Metro domains, since the MSE is not able to map B-MAC
addresses into PWs. Where the MPLS domain implements VPLS service,
the MSE similarly determines the VPLS service instance based on the
B-VID in the case of network interworking.
[0091] Where the networks are to be interworked at the service
level, the Ethernet domain will consider the MPSL domain as a peer
domain. The Ethernet domain transmits and receive Ethernet
encapsulated frames. The MPLS domain receives Ethernet frames and
de-encapsulates the frames to have visibility to the native service
payload. Accordingly, service interworking requires the Ethernet
domain to support PW signaling, unless static configurations are
allowed at the edge of the domains.
[0092] FIGS. 9-10 show a single PBT implemented across a MPLS PW
core. As shown in FIG. 9, the Ethernet access switch (U-PE) hands
off Ethernet frames to the metro access switch (PE) to be carried
transparently over an E-line service. The U-PE may encapsulate
different native services, however the PE does not have visibility
to these native services, but rather simply sees Ethernet
frames.
[0093] The PE offers either a port-based E-line or a tagged E-line
service. A port-based E-line service encapsulates all frames
received on a particular port as a particular service instance.
Tagged E-line service, by contrast, encapsulates frames received
with a particular VLAN set, including one or more VLAN IDs, into a
particular service instance for transmission over the PBT network.
The PE will then encapsulate the frames into a PBT trunk for
transmission across the PBT network. The I-SID is end-to-end unique
across the combined Metro domains and, hence, the I-SID may be used
end to end to identify the service instance associated with the
frame.
[0094] According to an embodiment of the invention, the B-VIDs
assigned to frames are allocated as belonging to a particular metro
pair. Thus, in FIG. 9, traffic from PBT metro X with a destination
of PBT metro Y would be assigned a first B-VID, traffic from PBT
metro X to PBT metro Z would be assigned a second B-VID, etc. Each
pair would thus use one particular B-VID. Optionally, traffic in
the reverse direction (i.e. from Y to X or from Z to X) would use
different B-VIDs. For resiliency, PE pairs maintain primary and
secondary PBT trunks which are monitored via connectivity check
messages (CCMs).
[0095] The MPLS core provides PW instances interconnecting each
pair of metros. A PW instance is created per PBT B-VID PW instances
can provide the same traffic profile as the PBT trunks, which
allows the same QoS to be implemented in the core network as in the
metro networks.
[0096] For example, as shown in FIG. 9, assume that PE 2 is
required to transmit frames to PE4 on PBT metro Y and is also
required to transmit frames to PE 5 on PBT metro Z. If the MPLS
core implements one PW per B-VID, S-PE1 may transmit frames to MSE1
intended for PE4 using (VID1, PE4) and may transmit frames to MSE1
intended for (VID2, PE5). The MSE is unaware where the PEs reside
on the network but has a PW implemented per B-VID. Accordingly, the
MSE may encapsulate the frames with B-VID=VID1 onto a PW to metro Y
and may encapsulate the frames with B-VID=VID2 onto a PW to metro
Z. Other MSEs would see different VIDs and associate those VIDs
with different PWs, which allows BVIDs to be reused between
different disjoint pairs of Metro networks. Additionally, the S-PEs
do not need to add more information to the PBT frames at the
handoff to the MPLS network.
[0097] According to an embodiment, the MPLS core implements a PW
for each PBT VID. The S-PE does not need to maintain any additional
mappings and forwards regular PBT frames to the MPLS core. For each
metro, each PBT B-VID is allocated such that it connects to a
single other metro. Within the MPLS core PWs are implemented
between each metro such that traffic may be mapped according to the
PBT B-VID to a PW in the MPLS core.
[0098] FIG. 10 shows an example encapsulation process that may be
used to encapsulate traffic as it traverses a network having a
single PBT domain implemented across multiple PBT metro networks,
with an MPLS core. As shown in FIG. 10, when the U-PE transmits a
frame to the PE it will be encapsulated with an Ethernet header
1002. The service frame includes a C-SA and A C-DA which are the
MAC addresses associated with the service frame. Optionally, the
service frame may include a C-Tag specified in 802.1Q and an S-Tag
specified in 802.1ad, although these tags are not required and will
depend on the particular implementation of the customer network.
The service tag will not change as the frame is transmitted across
the network.
[0099] When the frame is received at the PE, the PE will perform
PBB encapsulation specified in 802.1ah to add an I-SID, Ethertype,
B-TAG, Ethertype, B-SA and B-DA. The B-SA is the MAC address of the
PE that received the frame from the customer, and the B-DA is the
destination MAC address of the PE on the PBT domain. According to
an embodiment, the B-TAG may be selected to include a B-VID that
specifies the destination Metro network where the destination
network element is located. Selecting the B-VID corresponding to
the destination network allows the MPLS network to select a PW for
the frame for use in transporting the frame across the MPLS
network.
[0100] The PE will perform the PBB encapsulation and forward the
frame across a PBT tunnel to the S-PE, which will forward the frame
to the MSE on the edge of the MPLS network. The MSE will read the
B-VID and use the B-VID to select a PW for the frame. The MSE will
then attach a PW label and LSP label and forward the frame across
the MPLS network. The MSE may also apply a further link-layer
Ethernet header to the frame which will be stripped and replaced at
each hop through the network.
[0101] FIG. 11 shows another embodiment in which PseudoWire (PW)
signaling is supported end-to-end across the Ethernet network. In
this embodiment, the service frame is considered the PW payload,
and the U-PE or PE will attach a PW label 1102 to the PW payload
for transmission across the network. The PW label 1102 may also be
referred to as a Virtual Channel (VC) label. The U-PE will also
attach an Ethertype 1104 to allow the frame to be identified as PW
encapsulated. The U-PE will also attach a link layer Ethernet
header 1106 identifying the PE as the destination of the frame and
the U-PE as the source of the frame. The Ethernet header may also
include one or more tags such as a C-Tag or an S-Tag (not
shown).
[0102] When the PE receives the packet, it will strip off the
customer header 1106 and add a provider header 1108. The provider
header 1108 includes a B-TAG (which includes a B-VID), an
Ethertype, and the provider source and destination MAC Address
(B-SA and B-DA). The B-VID will be selected in this embodiment, as
with the last embodiment, to identify the egress Metro network that
contains the destination network element. The ingress PE on the PBT
network will then forward the frame across a PBT trunk to the
S-PE.
[0103] The S-PE will forward the frame to the MSE, which will use
the B-VID 1110 to identify the PW, and attach a PW label 1112 and
LSP label 1114 to the packet. The MSE will then forward the packet
across the LSP to the destination metro network. Alternatively,
where the MPLS network is implementing VPLS, the MPLS network would
implement a VPLS per B-VID, and make forwarding decisions based on
B-DA. The egress MSE will strip the PW and LSP labels off the
packet and forward the packet to the S-PE of the egress metro. The
Egress metro will forward the packet across the PBT trunk in the
PBT network to the destination.
[0104] From an OAM standpoint, PBT trunk OAM maintenance entities
may be monitored on an end-to-end basis. When a PBT trunk fails,
the head-end can switch the services, represented by I-SIDs onto
backup PBT trunks. When a PW fails, the MSE can notify via MS on
the PBT trunk, if the MSE supports Ethernet OAM. FIG. 12 shows some
of the OAM maintenance entities that may be implemented to support
end to end OAM on the PBT trunks within the network of FIGS.
9-11.
[0105] One of the advantages of interworking PBT metro networks
with an MPLS network are that the S-PEs are not required to
introduce modifications into the data path to implement the handoff
to the MPLS network. Additionally, the S-PEs do not need to
maintain visibility to the I-SIDs or individual service instances.
End-to-end trunk level OAM is possible and is independent of the
MPLS core. Additionally, end-to-end service level OAM is also
possible.
[0106] On the other hand, the end-to-end PBT OAM does not scale
well. The metros are also not autonomous, and need to have
visibility into each other's address space. OAM scaling issues,
e.g. via AIS, can be addressed but require Ethernet OAM support in
the MSEs. Additionally, when the MPLS network is implementing VPLS,
a MSE Virtual Switch Instance (VSI) is required on a per-port
basis, and the MSE will make forwarding decisions based on the
B-DA.
[0107] In the previous description it was assumed that the S-PE
would forward the packets from the PBT network to the MPLS network
without performing B-VID translation. It is possible to implement a
mapping at the S-PE that would allow B-VIDs to be translated so
that the B-VID in use on the PBT network is not the same as the
B-VID used on the MPLS network. This has implications with
connectivity fault management, however, the reverse VLAN ID may be
carried in the CFM payload. Thus, if the S-PE is performing B-VID
translation, the mapping would need to take place within the CFM
payload or another mechanism would need to be implemented to cause
the correct B-VID for the reverse path to be carried in the CFM
payload.
[0108] The PBT networks may be part of the same domain or,
alternatively may be separate domains. Where the PBT networks are
separate domains, for example if PBT metro X and PBT metro Y
implement separate control planes, then the PBT trunk segments will
not extend end-to-end across the network. Rather, the S-PEs will
maintain a mapping on a per-ISID basis to map traffic between trunk
segments.
[0109] For example, as shown in FIGS. 13-14, the Ethernet access
switch (U-PE) will hand off Ethernet frames (which may be
encapsulated native service frames) to the PE. The PE offers an
Ethernet UNI and either port-based E-line service or tagged E-line
service. The PE will thus use either the port, VLAN, or both to
identify the service instance. The PE will encapsulate the frame in
a PBT trunk within the metro, as shown in FIG. 14, by assigning a
service identifier (I-SID), B-Tag, and destination MAC address
(DA). The DA in this instance will be the DA of the S-PE that will
forward the traffic out of the metro network. The I-SID is
recommended to be end-to-end unique, but may be locally significant
only within each metro.
[0110] When the S-PE receives the frame it will determine the PBT
segment across the MPLS core. As with the example discussed above,
each metro allocates B-VIDs such that a particular B-VID is used
only to connect to one other metro. The S-PE maintains a mapping of
PBT segments and maps the traffic to the next PBT segment. The
B-VID used for the segment is selected such that the B-VID will
cause the frame to be forwarded across the MPLS core to the correct
metro.
[0111] When the MSE receives the frame, it will read the B-VID and
place the frame onto a LSP/PW through the core to the correct metro
by assigning a PW label and LSP label. The egress MSE will strip
off the PW and LSP labels and forward the frame to the S-PE on the
metro. The S-PE will either perform a second mapping to map the
frame to a PBT trunk within the second metro or will directly
forward the frame onto the trunk within the metro. This second
option may exist where the PBT trunk segment extends from the
second metro across the MPLS core. Where the frame is mapped to
different trunk segments, the PBB header or portions of the PBB
header such as the B-DA and B-SA, B-VID, and I-SID may be changed
so that these values are unique within each PBT tunnel.
[0112] FIG. 15 shows multiple trunk segments extending end to end
across a network having split PBT metro domains. The PBT trunk may
be implemented to include several segments. For example, a first
PBT trunk segment may exist in PBT metro X, a second PBT trunk
segment may extend between S-PEs on different metros across the
MPLS network, and a third PBT trunk segment may extend across the
PBT metro Y. Optionally, as mentioned above, a two segment PBT path
may be implemented such that either the first and second PBT trunk
segments or the second and third trunk segments are implemented as
a single trunk segment.
[0113] For resiliency, PE pairs maintain primary and secondary
trunks, which are monitored via connectivity check messages. The
S-PE at the edge of each metro provides the interworking function.
It is I-SID aware and maintains, on a per-I-SID basis, a mapping
between trunk segments that extend over the PBT metro and the MPLS
core. The mapping is maintained in both directions so that the S-PE
is able to map frames from a PBT trunk on the metro to a PBT trunk
on the core, and conversely from a trunk on the core to a trunk on
the metro. The S-PE thus provides a UNI functionality to map frames
to trunks on the PBT network. The MSEs will map frames to PWs on a
per-B-VID basis, so that the S-PE is not required to modify the
format of the frames when passed to the MSEs. Alternatively, the
S-PE may offer PW UNI to participate in PW signaling and apply PW
labels to frames before they are forwarded onto the MPLS core.
[0114] Encapsulation of frames with different PBT domains
interconnected with an MPLS core is the same as the encapsulation
process described above in connection with a unitary PBT domain
extending across an MPLS core. However, since the S-PEs are mapping
between PBT tunnels, the destination address of the packet on each
segment will be set to be the terminating device on that segment.
Thus, for example in FIG. 15, PE2 will create a header for use in
the PBT network and use the MAC address of S-PE1 as the destination
address. S-PE1 will remove the MAC header and create a new MAC
header using the MAC address of S-PE3 as the destination address.
As noted above, the B-VID that is applied to the MAC header by
S-PE1 will be the B-VID that allows the MSE to select a PW that
connects PBT metro X to PBT metro Y. Thus, although the
encapsulation does not change, the end points of the PBT trunk
segments will replace the values of the header with new values to
reflect associated with the new PBT trunk segment.
[0115] Each PBE trunk segment is monitored on an end-to-end basis
by an OAM Maintenance Entity (ME). As shown in FIG. 16, each trunk
segment whether it extends across a metro, the core, or across both
a metro and the core, is monitored by an OAM ME. The particular
resiliency strategy is dependent on the manner in which the PBT
domain and the MPLS core are interconnected. FIGS. 17-19 show three
example ways in which the domains may be interconnected. In these
Figs., FIG. 17 illustrates a full mesh interconnect, FIG. 18
illustrates a dual homed interconnect, and FIG. 19 illustrates a
square split multi-link trunking interconnect. The interconnect
shown in FIG. 19 differs from that of FIG. 18 in that the two S-PEs
in the interconnect of FIG. 19 share state and treat the links
extending between the network domains as a common link.
[0116] If a full mesh interconnect is in use (see FIG. 17), and a
PBT trunk fails within a metro, the PE can detect it and switch
over to another PBT trunk. None of the other domains are impacted
by this type of failure. Similarly, if the PW in the MPLS domain
fails, restoration does not impact the metro domains since the MPLS
network may implement a route around the failure in the MPLS
network. If the S-PE fails, the PE needs to switch the traffic to a
different PBT trunk that should terminate at another S-PE. This
requires the PE to switch to another PBT trunk with potentially
different VIDs and MAC DA.
[0117] If a dual homed interconnect is used, as shown in FIG. 18 or
19, and a PBT trunk fails in the metro, the PE will detect it and
the S-PE can determine which I-SIDs are affected by the failure.
The S-PE can then send Alarm Indication Signals (AIS) at the I-SID
level on the PBT trunks across the WAN core associated with those
I-SIDs. If a PBT trunk across the MPLS core fails, the S-PE can
determine which I-SIDs are impacted and send Alarm Indication
Signals at the I-SID level on PBT trunks across the metro
associated with those I-SIDs. Upon detecting a PBT trunk failure or
receiving an I-SID AIS notification, the PE can switch the service
instance (I-SID) to a backup PBT trunk. This type of interconnect
thus requires the PE to switch to another PBT trunk with
potentially different VID and B-DA. The same behavior applies when
an S-PE fails.
[0118] Some of the advantages associated with interworking split
PBT metro domains with an MPLS core are that the S-PE is not
required to introduce any modifications to the data path. Thus, a
normal S-PE should be able to be used to implement an interworking
of this nature. Additionally, OAM scaling issues are not severe,
and end-to-end service level monitoring is possible. The metros are
also able to remain autonomous without visibility into each other's
address space, while a full mesh of connectivity between metros may
be implemented across the MPLS core.
[0119] On the other hand, S-PEs are required to be I-SID (service
instance) aware. The S-PEs need to change PBT trunks for I-SID
flows and the S-PEs need to be configured to map I-SIDs to PBT
trunks in the Metro and over the core. End-to-end trunk level OAM
is not possible, and requires notification at the I-SID level.
[0120] If the customer is implementing OAM as well, and is not
using S-tagged or C-tagged frames, or if the customer S-Tag or
C-Tag is removed during the 802.1ah encapsulation process, then the
ME level space may need to be split so that both the customer and
the provider may use the same ME level space.
[0121] In the previous example, the S-PE was described as mapping
PBT trunks on a per-I-SID basis. Optionally, where the I-SID is not
end-to-end unique, the S-PE may also map I-SIDs so that different
I-SID values may be used for the same flow in each of the trunk
segments. In this instance, the S-PE would receive a frame, read
the I-SID to determine the next PBT trunk segment, and also use the
I-SID to determine the I-SID to be used as a service identifier on
the next PBT trunk segment.
[0122] Similarly, the S-PE may map PW labels between domains, for
example where PW over PBT is being implemented (see FIG. 11) so
that different PW label management may be used in each of the
domains. The S-PE may therefore implement PW label translation
between PBT trunks as well as other types of mappings between PBT
trunks. Where the p-bits are used to provide a particular type of
service on the PBT network, the S-PE or MSE may map the p-bits to
LSP EXP bits on the MPLS network. Additionally, the S-PE may map
p-bits between PBT tunnels such that the same quality of service
(as determined by the p-bits) is implemented on both PBT tunnel
segments.
[0123] It is also possible to implement PBB metros interconnected
via an MPLS core. In this embodiment, the Ethernet access switch
(U-PE) hands off Ethernet frames to the metro access switch (PE).
The PE uses the VLAN ID (VID) to identify the service instance
(I-SID). The PE encapsulates the frame in a PBB tunnel and ships it
across the PBB network. The I-SID is end-to-end unique. The B-VID
and multicast address assignments that are used to create one or
more PBB tunnels may be implemented via traffic engineering.
[0124] Resiliency is provided by redundant interconnects and by
running xSTP across a single domain joining the several metros. The
MPLS core provides a VPLS service instance per B-VID that it is
exposed to, and forwards traffic based on the B-DA. When offering
VPLS, the MSE will provide bridged Virtual Switch Instance (VSI)
(not per port VSI) such that it can switch between different ports.
When replication needs to occur across the WAN, the MSE does so
similar to VPLS. The S-PE is not required to maintain a special
mapping in this case. Additional details associated with PBB metros
and an VPLS core are contained in U.S. patent application Ser. No.
11/540,023, entitled Method And Apparatus For Transporting Ethernet
Services, filed Sep. 30, 2006, the content of which is hereby
incorporated herein by reference.
[0125] In a network including PBB metros and an MPLS core, the PBB
tunnels can be monitored on an end-to-end basis. When an S-PE or
MSE or NNI or link within a metro fails, the spanning tree in use
on the metro or the link state protocol (where the Ethernet metro
is a link state protocol controlled Ethernet network) can address
the failure via redundant paths. If the failure leads to network
segmentation, the PBB tunnel monitoring will be able to detects
this, however rectification of the problem and restoration would
require manual intervention.
[0126] Where failure occurs in the MPLS core, the MPLS network may
have no way to signal to the xSTP instance in the metro that the
failure has occurred. Thus, the xSTP will not be able to initiate
restoration/reconvergence for an unacceptably long period of time
or may have an unacceptable detection time. To mitigate this, a
monitoring domain may be implemented at the S-PEs to allow the
S-PEs to implement a PBB segment Maintenance Entity (ME) across the
segment of the PBB tunnel that extends across the MPLS core
network.
[0127] If a PBB segment ME indicates failure, the S-PE should
trigger xSTP convergence. Since the failure in the MPLS domain may
not be propagated into the PBB network, when the connectivity fault
management (CFM) being run across the PBB segment between the S-PEs
(which spans the MPLS domain) indicates a failure in the MPLS
domain, the S-PEs should initiate xSTP convergence assuming a
failure on the PBB segment. This allows the network to reconverge
quickly upon detection of a failure in the MPLS network to allow a
new set of PBB tunnels to be established that can span the MPLS
network and avoid the failed tunnel.
[0128] The S-PE is not required to be modified to enable PBB
networks to interconnect with MPLS core network and thus can
implement an NNI handoff to the MPLS core network. The S-PEs do not
need to maintain visibility to the I-SIDs or to individual service
instances. A full mesh of WAN connectivity may be implemented in
the MPLS core network between all pairs of metros. Additionally,
end-to-end service level monitoring is possible as is segment
monitoring across the MPLS core.
[0129] However, since the PBB networks are implemented as a single
large metro domain, running a single xSTP spanning instance or link
state protocol instance, the large domain may make multicast domain
difficult to manage. Additionally, the metros are not autonomous
and, thus, need to have visibility into each other's address space.
The metros are also required to implement some form of loop
avoidance technique, such as xSTP.
[0130] FIG. 20 illustrates an embodiment where the MPLS core
implements PWs. In this embodiment, the Ethernet access switch
(U-PE) will hand off Ethernet frames to the metro access switch
(PE). The PE uses the VLAN to identify the service instance
(I-SID), encapsulates the frame in a PBB tunnel, and transmits the
frame across the PBB network. The I-SID is end-to-end unique. The
B-VID and multicast address assignments are implemented via
engineering. At the S-PE, different physical interfaces are used to
connect to different peer PBB domains. If the number of interfaces
becomes a concern, aggregation structures may be employed.
[0131] By using a different physical interface on the S-PE for each
destination metro, the MSE can implement a PW service instance on a
per-port basis. Alternatively, the MSE may implement a PW service
instance on a per-B-VID basis. The S-PE implements the equivalent
of a Virtual Switch Instance, since the S-PE is responsible for
replicating frames to multiple ports or outputting the frame using
multiple B-VIDs. Thus, the MSE will receive the frame multiple
times (once for each destination Metro) and map the frames to PWs
through the MPLS core to the destination metros.
[0132] Where a link state protocol is in use on the PBB network,
the S-PE may view different interfaces as regular bridged ports and
may use inherent bridge replication. Resiliency, in this instance,
may be provided by implementing redundant interconnects from the
S-PE to the MPLS network and running a common link state protocol
instance across the several PBB networks.
[0133] From an encapsulation perspective, the service frame (which
may or may not contain the C-Tag and S-Tag) will be encapsulated
using 802.1ah by PE2. Since the various PBB metros are implementing
a common control plane, PE will have visibility into PBB metro Y's
address space and may create a provider MAC header that includes
the MAC address of PE4 as the destination MAC address (DA=PE4).
Thus, the 802.1ah MAC header need not be changed as the frame
traverses the network.
[0134] When the frame is passed to the MSE at the ingress to the
MPLS core network, the MSE will map the frame based on the port on
the S-PE over which it was sourced, or based on the B-VID, and
apply a PW label and an LSP label to transport the frame across the
MPLS network.
[0135] From a resiliency standpoint, the PBB tunnels can be
monitored on an end-to-end basis. when an S-PE, MSE, NNI, or link
within the metro fails, the link state protocol being run on the
PBB metro may address the failure in a normal manner (i.e. via a
redundant PBB tunnel). If the failure leads to network
segmentation, the failure will be detected by the end-to-end
Maintenance Entity, but correction will require manual
intervention.
[0136] If a failure occurs in the MPLS core, the MPLS network may
not be able to signal the failure to the PBB metro networks. This
may result in the PBB networks being unable to initiate
reconvergence/restoration within an acceptable period of time.
Accordingly, the S-PEs may implement a PBB segment ME across the
MPLS core to allow the S-PEs to detect a failure within the MPLS
network. Upon detection of a fault on the PBB segment ME extending
between the S-PEs across the MPLS core, the S-PEs may initiate xSTP
reconvergence or link state protocol reconvergence to allow the PBB
network to route traffic around the failure. Thus, if the PBB
segment ME indicates failure, the link state protocol should be
notified to trigger convergence. This allows reconvergence to be
initiated without explicit notification of the failure from the
MPLS network to the PBB networks.
[0137] The S-PE does not require modification to the data path to
implement handoffs to the MPLS network. The S-PEs also are not
required to maintain visibility to the I-SID or individual service
instances. A full mesh of connectivity between metros may be
implemented in the MPLS core, and end-to-end service level
monitoring is possible.
[0138] On the other-hand, implementing one big metro domain across
the several metro networks means that the multicast domain is
concomitantly large and, hence, difficult to manage. Metros are
also not autonomous, and need to have visibility into each other's
address space. A loop avoidance technique, such as reverse path
forwarding check implemented in connection with a link state
protocol such as Open Shortest Path First (OSPF) or Intermediate
System to Intermediate System (IS-IS) is also required.
[0139] In addition to implementing the PBB metros as one domain, it
is possible to run different xSTP or link state protocol control
instances in each of the PBB metros to allow the metros to be
independent. Where split PBB metros are interconnected across an
MPLS domain, the PBB metros will implement PBB tunnels between the
PEs and S-PEs. The I-SID in this case may be end-to-end unique or
may be metro-specific. Resiliency is provided by redundant
interconnects between the PBB metros and the PLSB core, and by
running xSTP within each domain--i.e. each PBB metro runs its own
xSTP instance.
[0140] The MPLS core provides VPLS service instance per B-VID that
it is exposed to. B-VLAN IDs are allocated based on
per-connectivity required across metros. Thus, if there are five
metros, 24 VPLS instances will be required to interconnect the
metros (10 connecting each metro pair, 9 connecting 3 each, 4
connecting 4 each, and 1 connecting all of the metros).
[0141] When a frame is received at the PE in metro X it will be
encapsulated using 802.1ah and mapped to a PBB tunnel within metro
X. If the C-DA of the frame that is received by the PE is unknown
to the PE, the PE will map the frame to a multicast MAC DA in the
B-VID tunnel (PBB tunnel). The S-PE terminates the B-VID tunnel,
and maps the B-VID tunnel across the WAN, which means that the S-PE
maintains a mapping between I-SID or C-DA and corresponding B-VID
tunnel and B-DA for use in across the MPLS core in a manner similar
to the mapping maintained by the PE. Additionally, the receiving
S-PE will map the received frame to a B-VID tunnel across Metro
Y.
[0142] Within the MPLS core, the MSE treats the frames like regular
Ethernet frames. Since the MPLS core has implemented VPLS service
instances on a per-B-VID basis, the MSE will map the frame using
the B-VID to a VPLS service instance and forward it across the MPLS
network. The Ethernet frames will be received by one or more egress
metros to be forwarded onto those metro networks.
[0143] Thus, in this embodiment, the S-PE maintains a mapping of
I-SID and C-DA to B-VID and B-MAC in both directions. The S-PEs
also run xSTP or a link state protocol in the control plane and in
the MPLS WAN using distinct V-LAN space. The S-PE will also
correlate failures between the Metro and MPLS core domains to
block/unblock forwarding states depending on the state of the
networks.
[0144] From a resiliency standpoint, the PBB domain will be able to
detect and correct for failures that occur within the PBB domain.
The MPLS domain may have no way of signaling failures that occur in
the MPLS core, however. Thus, the S-PEs may implement OAM
maintenance entities across the core to detect for failure in the
MPLS core and initiate reconvergence in the PBB network upon
detection of a failure on the PBB segment maintenance entity.
[0145] Since the PBB domains are separate domains, the S-PE is
required to map flows between PBB tunnels. Accordingly, the S-PE
will map flows from one PBB tunnel to the other PBB tunnel based on
the I-SID or the C-DA. Thus, the S-PE maintains a mapping to enable
it to perform the mapping between I-SID and target PBB Tunnels. The
S-PE may also translate other values, such as B-VID, to allow for
independent B-VID management in different domains. Similarly, the
S-PE may maintain a table of ingress multicast DA and egress
multicast DA to allow for translation of multicast DA between
domains. This may be particular useful where the metro domain
allocates multicast DAs using an algorithm different than that used
by the core PLSB domain, i.e. when the core uses an I-SID unique
multicast DA. The S-PE is also required to support control xSTP
instances, which allows the S-PE to block data forwarding for
particular sets of VIDs.
[0146] Split PBB domains may be implemented and interconnected by
an MPLS network providing PW service, where the S-PEs are not
configured to perform B-VID translation. In this instance, the
S-PEs would run a control instance such as xSTP or a link state
protocol, to enable the S-PEs to implement a common control plane.
This allows the S-PEs to block data forwarding for particular sets
of B-VIDs.
[0147] In this embodiment, the S-PE will switch flows from PBB NNI
to PBB NNI based on I-SID. The S-PE will thus maintain a mapping of
I-SIDs to PBB tunnels and maintain a table of ingress multicast DA
and egress multicast DA to allow translation of multicast DA
between tunnels. This is needed where the metro domain allocates
multicast DA using an algorithm that is different than the
algorithm used by the core domain, which uses I-SID unique
multicast DAs. Optionally, the S-PE may allow B-VID translation
between tunnels so that independent management of B-VID may occur
in the different domains. For resiliency, the S-PE should implement
segment PBB tunnel maintenance entities to detect faults on the
MPLS network, and trigger xSTP or link state protocol reconvergence
upon detection of a failure. Additionally, the S-PE may allow for
I-SID translation between PBB tunnels to allow for independent
management of I-SIDs in different domains.
[0148] Implementing split PBB domains reduces the size of the xSTP
or link state protocol domains, which makes the domains more
manageable from a control standpoint. Additionally, the metros are
autonomous, so that they do not need to have visibility into each
other's address space except at the S-PE. A full mesh of
connectivity may be supported in the core network between each
pairs of metros. Additionally, end-to-end service level monitoring
is possible.
[0149] However, the S-PEs are required to be I-SID aware and C-MAC
aware. The S-PE needs to provide a mapping between PBB tunnels and
B-MACs based on the I-SID and C-MAC. It also requires coordination
of failures within different instances of xSTP or link state
routing protocol at the S-PE. The solution also requires the use of
some loop avoidance technique, such as implementation of xSTP or
link state routing protocol in the control plane.
[0150] FIGS. 22 and 23 show another interconnection scenario in
which both PBB/PBT and MPLS metros are interconnected across an
MPLS core network implementing VPLS service. Services, in this
scenario, will be assumed to be driven from an MPLS
standpoint--what an MPLS network might be offering. For example, an
MPLS metro may offer VPLS service or PW service. For end-to-end PW
service, the PBT/PBB metro will offer PW over PBT, and the MPLS
metro may implement PWs. For end-to-end VPLS, the PBT/PBB metro
will implement PBB tunnels while the MPLS metro may implement VPLS
or PW spokes.
[0151] In the embodiment shown in FIG. 22, the access switch (U-PE)
hands off native service frames to the PBB/PBT access switch (PE)
to be carried transparently over a PW service. The PE may
encapsulate different native services using PW over PBT. In the
other direction, the access switch will hand off native service
frames to the MPLS access switch (N-PE) which will encapsulate the
native services to be carried transparently over a PW service. The
PE and N-PE establish an end-to-end PW. The PE and N-PE is not
necessarily aware of the other metro, however.
[0152] An end-to-end PW may be established manually via a network
management plane or via signaling in the control plane. If MS-PW
signaling is used, then the PE and N-PE would serve as terminating
PEs (T-PEs) and the S-PE and MS-PE would serve as switching PEs
(S-PEs). Optionally the MSE can also act as an S-PE.
[0153] FIG. 23 shows the encapsulation of traffic as it passes
across the network of FIG. 22. As shown in FIG. 23, when PE2
receives a packet it encapsulates the packet with a PW label. PE2
may provide encapsulation for different types of traffic, i.e.
different native type UNIs. The PE will also apply a MAC header to
the packet to place the packet onto a PBT trunk through the metro
network X.
[0154] When the S-PE receives the packet, it will remove the MAC
header and use the PW label to map the packet to a PBT trunk across
the MPLS core. The S-PE thus maintains a mapping between PBT trunks
in either direction based on PW label.
[0155] The MPLS core will provide VPLS instances for each B-VID
that it is exposed to, which would thus not require the metro to
make any modifications to frames across the NNI. Thus, the B-VID of
the PBT trunk across the MPLS core may be selected according to the
VPLS instance that is to be used to transport the packet to one or
more destination metros.
[0156] When the MPLS metro receives the packet, the MS-PE on the
MPLS metro (MS-PE3 in FIG. 23) would treat the frames as link local
tagged frames. Thus, the MS-PE will remove the Ethernet
encapsulation header and treat the frames as PW frames. The MS-PE
will thus read the PW label and apply a LSP label to forward the
packet across the MPLS network. The MS-PE is required, in this
instance, to support static PW UNI to enable it to read the PW and
select a LSP for the packet.
[0157] From a resiliency standpoint, each PBT trunk may be
monitored on an end-to-end basis by implementing a PBT trunk
maintenance entity. In the MPLS domain the path may be monitored
via an MPLS LSP maintenance entity. The end-to-end service may also
be monitored using a PW Virtual Circuit Connection Verification
(VCCV) or via MS-PW OAM.
[0158] Advantageously, no modifications are required to the data
path at handoff. Additionally, the PWs that are required to be set
up in the MPLS core scale on the order of O(n), where n is the
number of Metros connected to the MPLS core. Also, a full mesh of
connectivity may be implemented between the metros. The metros are
autonomous, and thus do not need to have visibility into each
other's address space. Additionally, end-to-end service level
monitoring is possible.
[0159] On the other hand, S-PEs are PW label (service instance)
aware. In addition to PBT trunk configurations, S-PEs need to be
configured to map PW labels to the PBT trunks in both directions
(into the PBT metro and into the MPLS core). End-to-end trunk level
OAM is not possible, and requires notification at the PW level. The
MS-PE will also be required to support a static PW UNI, if MS-PW
signaling is not used.
[0160] In summary, the S-PEs switch flows from PBT-NNI to PBT-NNI
(between PBT Trunks) based on the PW label (where PW over PBT is
used in the PBT network). The PE and S-PE also support VCCV OAM on
the PW to monitor the service on an end-to-end basis. When the S-PE
detects a failure of a PBT trunk, it will determine the PWs
affected by the failure and generate an Alarm Indication Signal
(AIS) at the PW level on the corresponding PBT trunk. Optionally,
trunks may be implemented as PBT trunk groups for monitoring
purposes.
[0161] The S-PE may implement several additional features to reduce
the amount of interdependence between the domains. For example, the
S-PE may allow PW label translation between PBT trunks, to allow
for independent management of I-SIDs in the different domains.
Additionally, the S-PE may implement B-VID translation between PBT
trunks and may also implement DA translation between PBT trunks.
This solution requires the MS-PE to support a static PW UNI.
[0162] FIGS. 24-25 show a scenario in which the MPLS core that
interconnects the PBT and MPLS metros is implements PWs rather than
VPLS service instances.
[0163] In the scenario shown in FIGS. 24-25, the access switch
(U-PE) will hand off native service frames to the MPLS/PBT access
switch (N-PE/PE) to be carried transparently over a PW service. The
N-PE may encapsulate different native services (e.g. TDM) over the
PW. The PE may encapsulate different native services over PWoPBT.
The N-PE and PEs establish end-to-end PWs to be used to carry the
traffic across the network. The PE and N-PE, however, are not
necessarily aware of the other metro.
[0164] End-to-end PWs may be established by manual provisioning at
the management plane or by PW signaling in the control plane. If
MS-PW signaling is used, then the PE and N-PE would serve as
terminating PEs and the S-PE and MS-PE would serve as switching PEs
(S-PEs). The MSE may also act as a switching PE if desired.
[0165] FIG. 25 shows the encapsulations that may be used to
transport the service frame (payload) across the network. As shown
in FIG. 25, when a PE receives a packet from the U-PE, it will
encapsulate it with a PW label and also apply a MAC header to place
the Packet onto a PBT tunnel across the PBT metro. When the S-PE
receives the packet, it terminates the PBT tunnel and removes the
MAC header. The S-PE provides a mapping of PW label to PBT trunks
in the metro direction, and maintains a mapping of PBT trunk to PW
label in the direction of the MPLS core.
[0166] The S-PE will remove the PBT trunk MAC header and apply a
link level MAC header and forward the packet to the MSE. The MSE
will strip off the link MAC header, read the PW label, and apply a
LSP label to forward the packet across the MPLS network. The egress
MSE will remove the LSP label, read the PW label, and apply a link
level MAC header to forward the packet to the MPLS metro Y. The
MS-PE will remove the link level MAC header, read the PW label, and
apply a LSP label to forward the packet across the MPLS metro
network Y. The egress N-PE will remove the PW label and forward the
packet to the U-PE.
[0167] From a resiliency standpoint, each PBT trunk ME may be
monitored on an end-to-end basis in each domain. In the MPLS
domain, the trunk may be monitored by monitoring the MPLS LSP. The
end-to-end service may also be monitored by using a PW Virtual
Circuit Connectivity Verification and MS-PW OAM.
[0168] The scenario has similar advantages/disadvantages as the
scenario described above with respect to FIGS. 22 and 23 in which
the MPLS core offered VPLS service rather than PW service. However,
in this instance MS-PW signaling is required to be implemented
across the PE, S-PE, MSE, and MS-PE.
[0169] FIG. 25A shows another encapsulation scenario in which the
U-PE implements PW encapsulation prior to forwarding the packet to
the PE. Thus, in this example the PW label is applied at the U-PE
before being transmitted to the PE, rather than having the ingress
PE apply the PW label to the frame. The other encapsulation
processes described above with respect to FIG. 25 may be used to
transport this frame across the network.
[0170] In the previous two scenarios, it was assumed that the PW
was maintained end-to-end. Optionally, the PW may be switched
(mapped) at one or more locations along the end-to-end path to
enable the domains to remain independent. For example, the S-PE may
map PW labels in addition to mapping packets to/from PBT tunnels on
a PW basis. This allows different PWs to be used in the PBB/PBT
metro X than are used in the MPLS core. Similarly, the MSE may map
PWs to allow different PW labels to be used in the interconnect
than are used in the MPLS core. Likewise, the MS-PE may map PW
labels to allow different PW labels to be used in the MPLS metro Y
than are used in the MPLS core. Thus, many different mappings may
occur depending on which nodes on the network are configured to map
parameters for the packet as the packet is passed along a path on
the network.
[0171] The network elements described above, such as the PE and
S-PE, as well as the MSE and N-PE, are all conventional network
elements. The network elements are programmed, however, or have
hardware implementations, that will enable them to perform the
functions described above to place traffic on tunnels through the
network and to switch traffic from tunnel segments. Similarly, the
network elements include software, hardware, and/or firmware that
will enable the network elements to participate in OAM maintenance
entities and other OAM flows to enable appropriate monitoring to
occur as described in greater detail above. Thus, the invention is
not limited to any particular hardware implementation as many
different network element hardware platforms have been created over
the years and are likely to be created in the future as network
elements continue to evolve.
[0172] Thus, it will be apparent to a skilled artisan that all
logic described herein can be embodied using discrete components,
integrated circuitry such as an Application Specific Integrated
Circuit (ASIC), programmable logic used in conjunction with a
programmable logic device such as a Field Programmable Gate Array
(FPGA) or microprocessor, or any other device including any
combination thereof. Programmable logic can be fixed temporarily or
permanently in a tangible medium such as a read-only memory chip, a
computer memory, a disk, or other storage medium. Programmable
logic can also be fixed in a computer data signal embodied in a
carrier wave, allowing the programmable logic to be transmitted
over an interface such as a computer bus or communication network.
All such embodiments are intended to fall within the scope of the
present invention.
[0173] It should be understood that various changes and
modifications of the embodiments shown in the drawings and
described in the specification may be made within the spirit and
scope of the present invention. Accordingly, it is intended that
all matter contained in the above description and shown in the
accompanying drawings be interpreted in an illustrative and not in
a limiting sense. The invention is limited only as defined in the
following claims and the equivalents thereto.
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