U.S. patent application number 09/908752 was filed with the patent office on 2002-05-30 for joint ip/optical layer restoration after a router failure.
Invention is credited to Chiu, Angela L., Strand, John Lester.
Application Number | 20020063916 09/908752 |
Document ID | / |
Family ID | 22820739 |
Filed Date | 2002-05-30 |
United States Patent
Application |
20020063916 |
Kind Code |
A1 |
Chiu, Angela L. ; et
al. |
May 30, 2002 |
Joint IP/optical layer restoration after a router failure
Abstract
A method and system for providing joint IP/Optical Layer
restoration mechanisms for the IP over Optical Layer architecture,
particularly for protecting against router failure within such
architecture, includes any one of plural node elements
participating in the detection and restoration of the joint
IP/Optical Layer architecture upon the failure of a router in one
of the nodes. The plural node elements may include, but are not
limited to, one of plural routers and an optical cross-connect.
Inventors: |
Chiu, Angela L.; (Holmdel,
NJ) ; Strand, John Lester; (Holmdel, NJ) |
Correspondence
Address: |
BANNER & WITCOFF LTD.,
ATTORNEYS FOR AT & T CORP
1001 G STREET , N.W.
ELEVENTH STREET
WASHINGTON
DC
20001-4597
US
|
Family ID: |
22820739 |
Appl. No.: |
09/908752 |
Filed: |
July 20, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60219777 |
Jul 20, 2000 |
|
|
|
Current U.S.
Class: |
398/2 ;
398/5 |
Current CPC
Class: |
H04Q 11/0066 20130101;
H04Q 2011/0064 20130101; H04Q 2011/0081 20130101; H04Q 11/0062
20130101; H04L 45/00 20130101; H04L 49/557 20130101; H04B 10/038
20130101; H04L 45/58 20130101; H04L 45/28 20130101; H04Q 11/0071
20130101; H04L 45/62 20130101 |
Class at
Publication: |
359/110 ;
359/118 |
International
Class: |
H04B 010/08; H04B
010/20; H04J 014/00 |
Claims
We claim:
1. A node method of restoring an IP/Optical Layer after failure of
a router in one of a plurality of nodes, said method comprising the
steps of: detecting a failure in a path to a first node;
transmitting a request to an optical network to re-establish the
path; and reestablishing the failed path using a redundant router
in place of a failed router.
2. The method of claim 1, wherein the path is a light path between
the first node and a second node.
3. The method of claim 2, wherein the failure in the path to the
other of the plurality of nodes is detected by a router at a second
node, and wherein the failed router and the redundant router are at
the first node.
4. The method of claim 2, wherein the failure in the path to the
other of the plurality of nodes is detected by the redundant router
at the first node, and wherein the failed router is at the first
node.
5. The method of claim 2, wherein the failure in the path to the
first node is detected by an optical cross-connect at the first
node, and wherein the failed router and the redundant router are at
the first node.
6. The method of claim 3, wherein said transmitting step includes
the router at the second node transmitting the request to an
optical cross-connect at the second node to reestablish the path to
the first node by using the redundant router in place of the failed
router.
7. The method of claim 6, wherein said transmitting step further
includes the optical cross-connect at the second node transmitting
the request to an optical cross-connect at the first node.
8. The method of claim 4, wherein said transmitting step includes
the redundant router transmitting the request to an optical
cross-connect at the first node to re-establish the path by using
the redundant router in place of the failed router.
9. The method of claim 5, wherein said transmitting step includes
the optical cross-connect at the first node transmitting the
request to an optical cross-connect at another node to re-establish
the path by using the redundant router in place of the failed
router at the first node.
10. A method of restoring an IP/Optical Layer after failure of one
of plural routers at a first node that further includes an optical
cross-connect, said method comprising the steps of: a router at a
second node detecting a failure in a path between the router at the
second node and a router at the first node; transmitting a request
to an optical network to re-establish the path; and reestablishing
the path using a redundant router in place of the failed router at
the first node.
11. The method of claim 10, wherein the path is a light path
between the first node and the second node.
12. The method of claim 11, wherein said transmitting step includes
the router at the second node transmitting the request to an
optical cross-connect at the second node to reestablish the
path.
13. The method of claim 12, wherein said transmitting step further
includes the optical cross-connect at the second node transmitting
the request to the optical cross-connect at the first node.
14. A method of restoring an IP/Optical Layer after failure of one
of plural routers in a first node that further includes an optical
cross-connect, said method comprising the steps of: a first router
at the first node detecting a failure in a path between a second
router at the first node and a router at a second node;
transmitting a request to an optical network to re-establish the
path; and reestablishing the path using the first router in place
of the second router.
15. The method of claim 14, wherein the path is a light path.
16. The method of claim 15, wherein said transmitting step includes
the first router transmitting the request to an optical
cross-connect at the first node to re-establish the path by using
the first router in place of the second router.
17. A method of restoring an IP/Optical Layer after failure of one
of plural routers in a first node, said method comprising the steps
of: an optical cross-connect at the first node detecting a failure
in a path between a first router at the first node and a router at
a second node; and reestablishing the path using a second router in
place of the first router at the first node.
18. A computer-readable medium at a node method of an IP/Optical
Layer, said computer-readable medium having computer-executable
instructions for performing, after failure of a router in one of a
plurality of nodes, the steps of: detecting a failure in a path to
a first node; transmitting a request to an optical network to
re-establish the path; and reestablishing the failed path using a
redundant router in place of a failed router.
19. The computer-readable medium having computer-executable
instructions according to claim 18, wherein the path is a light
path between the first node and a second node.
20. The computer-readable medium having computer-executable
instructions according to claim 19, wherein the failure in the path
to the other of the plurality of nodes is detected at a router at a
second node, and wherein the failed router and the redundant router
are at the first node.
21. The computer-readable medium having computer-executable
instructions according to claim 19, wherein the failure in the path
to the other of the plurality of nodes is detected at the redundant
router at the first node, and wherein the failed router is at the
first node.
22. The computer-readable medium having computer-executable
instructions according to claim 19, wherein the failure in the path
to the first node is detected by an optical cross-connect at the
first node, and wherein the failed router and the redundant router
are at the first node.
23. The computer-readable medium having computer-executable
instructions according to claim 20, wherein said transmitting step
includes the router at the second node transmitting the request to
an optical cross-connect at the second node to re-establish the
path to the first node by using the redundant router in place of
the failed router.
24. The computer-readable medium having computer-executable
instructions according to claim 23, wherein said transmitting step
further includes the optical cross-connect at the second node
transmitting the request to an optical cross-connect at the first
node.
25. The computer-readable medium having computer-executable
instructions according to claim 21, wherein said transmitting step
includes the redundant router transmitting the request to an
optical cross-connect at the first node to re-establish the path by
using the redundant router in place of the failed router.
26. The computer-readable medium having computer-executable
instructions according to claim 22, wherein said transmitting step
includes the optical cross-connect at the first node transmitting
the request to an optical cross-connect at another node to
reestablish the path by using the redundant router in place of the
failed router at the first node.
27. An IP/Optical Layer system, comprising: a first router at a
first node; a second router at a second node that receives a light
path transmitted from said first router; an optical network that
receives a request to re-establish the light path transmitted from
said first router, when said first router determines that the light
path has failed, and reestablishes the light path using a third
router in place of said second router at the second node.
28. An IP/Optical Layer system according to claim 27, wherein the
first router determines that the light path has failed when the
second router fails.
29. An IP/Optical Layer system according to claim 28, wherein said
optical network includes an optical cross-connect at the first
node, and said optical-cross connect at the first node transmits
the request to re-establish the light path to a cross-connect at
the second node.
30. An IP/Optical Layer system, comprising: a first router at a
first node; a second router at the first node; a third router at a
second node that receives a light path transmitted from said second
router; an optical network that receives a request to re-establish
the light path transmitted from said first router, when said first
router determines that the light path between said second router
and said third router has failed, and re-establishes the light path
using said first router in place of said second router at the first
node.
31. An IP/Optical Layer system according to claim 30, wherein the
first router determines that the light path has failed when the
second router fails.
32. An IP/Optical Layer system according to claim 31, wherein said
optical network includes an optical cross-connect at the first
node, and said optical-cross connect at the first node transmits
the request to re-establish the light path to a cross-connect at
the second node.
33. An IP/Optical Layer system, comprising: a first node having
plural routers; a second node having plural routers; and an optical
cross-connect disposed at said first router that detects a failure
in a light path between a first router in said first node and a
first router in said second node, and reestablishes the light path
by using a second router at said first node in place of said first
router at said first node.
Description
FIELD OF THE INVENTION
[0001] The invention generally relates to optical communications
and particularly a method for the restoration of a joint IP/optical
layer after failure of a router therein.
BACKGROUND OF THE INVENTION
[0002] With the Internet rapidly replacing traditional telephone
networks as the ubiquitous network infrastructure, there is
ever-increasing consumer demand for greater bandwidth, which
translates to a need for increased system performance. Coping with
the continuing high growth rate of Internet traffic volume is a
significantly challenging scalability problem. Fiber optics using
Wavelength Division Multiplexing (WDM) offers the enormous capacity
that the Internet requires to continue to grow at its present and
projected future rates. In addition, the increasing agility of the
latest Optical Layer Cross-Connects (OLXCs) offers the ability to
dynamically change the optical layer connectivity on small time
scales. OLXCs have the ability to convert the wavelength of any
incoming channel to any outgoing wavelength (i.e. have wavelength
conversion).
[0003] Internet Protocol (IP) network connectivity is more often
being provided by optical circuits, including OC-48/192, for
example. Thus, FIG. 1(a) is a schematic diagram showing the
connectivity of IP layer 5 to an optical layer 10. FIG. 1(b) shows
a more specific schematic diagram in which IP router 15 may be
either hard-wired to Dense Wave Division Multiplexer (DWDM) 20 for
transport, or it may be connected to OLXC 25.
[0004] There is an underlying conflict, however, between the
typical datagram (connectionless) service that supports the
best-effort data delivery of the Internet and virtual circuit
(connection-based) service. This conflict is exacerbated in the
world of optical networks, due to the fixed nature of the
wavelengths available and the restoration of service in optical
networks.
[0005] Optical networks are connection oriented and designed for
fixed rate bit streaming with very low error rates. Whereas the
Internet employs soft state where possible, the state of the
optical infrastructure that is encoded in its OLXCs is hard and
must be explicitly removed. The key elements in the success of the
Internet have been its simplicity and the flexibility of the
Internet service model, and therefore a significant challenge in
leveraging the new optical capabilities to enhance the Internet and
other services is to manage the optical resources efficiently,
without sacrificing the simplicity and flexibility of the
Internet.
[0006] In spite of most traffic and media types becoming internet
protocol (IP) based, multiple-hop high-bandwidth optical
connections referred to as lightpaths will continue to be of value.
Aggregate loads between major metropolitan areas are rather stable,
with most of the achievable statistical multiplexing already
attained in the regional and collection (distribution) portion of
the network. With electronic switching systems coping with
substantial regional network volumes, this load can conveniently be
assigned to point-to-point lightpaths that bypass intermediate
backbone routers, reducing their load and reducing end-to-end delay
and delay variation. Traffic engineering, i.e., load and quality
management, is increasingly performed by adjusting connectivity and
capacity between major backbone gateways on a relatively large
time-scale, still small compared to the time-scale of
provisioning.
[0007] This is both a primary function of, and a significant reason
that, ATM or Multi-Protocol Label Switching (MPLS) is employed
below the IP layer by most network operators. Agile, dynamically
configurable OLXCs allow the use of the optical layer directly to
implement these functions, avoiding having ATM or MPLS as
intermediate layers in future networks. Lightpaths carrying transit
traffic, or non-IP traffic, may remain a significant source of
revenue for network operators for the foreseeable future. Whereas
much of the transit capacity may carry IP traffic, operators
leasing optical capacity may choose not to disclose this.
[0008] There are issues involving networks in general as they
relate to where particular service and intelligence are provided.
Functions previously provided by a SONET/SDH layer.
[0009] SONET(Synchronous Optical NETwork)/SDH (Synchronous Digital
Hierachy) is an industry standard for broadband optical fiber
communications. It provides universal optical interfaces at
OC-N/STM-M rate. It also provides integrated OAM&P capabilities
within each network element which enables fast
protection/restoration. A good reference book is "Understanding
SONET/SDH, Standards and Applications" by Ming-Chwan Chow, Andan
Publisher, 1995.) interposed (not shown) above optical layer 10
must be distributed between IP layer 5 and Optical Layer 10 in the
architecture of FIGS. 1(a) and 1(b), including the recovery of
service after equipment failure.
[0010] Restoration may be provided by either the IP layer or the
optical layer 10. The optical layer 10 is able to independently
provide sub-second protection and/or restoration for link failures,
that is when a fiber is cut, and is the most cost-effective
solution therefore. However, when a router in the IP/Optical Layer
architecture fails, the optical layer has no independent awareness
of the router failure.
[0011] Thus, presently, it is the IP layer 5 that includes the
necessary functionality for protecting against router failure. In
addition, the IP layer 5 may include extra link capacity so that
the quality of service may be preserved in the event of a router
failure. As a result, it is then more cost-effective to use the
extra link capacity to protect against link failure, and thus there
is no incentive to utilize the protection/restoration function
provided by the optical layer 10. Accordingly, IP network operators
may choose a restoration strategy that depends solely upon the IP
layer 5.
[0012] However IP layer restoration systems have some
disadvantages. For instance, the failure of an unprotected link may
result in a mean-time-to-repair in the range of four to ten hours
although mean-time-to-repair for a router failure may be less than
one hour. Still, the excessive amount of down-time due to a link
failure may result in further router failures, which has the
potential for significant network congestion.
SUMMARY OF THE INVENTION
[0013] Accordingly, the present invention includes a method and
system for providing joint IP/Optical Layer restoration mechanisms
for the IP over Optical Layer architecture, particularly for
protecting against router failure within such architecture.
[0014] According to an example embodiment of the present invention,
any one of plural node elements may participate in the detection
and restoration of the joint IP/Optical Layer architecture upon the
failure of a router in one of the nodes. The plural node elements
may include, but are not limited to, one of plural routers and an
optical cross-connect (OXLC).
[0015] For example, a node element may detect a failure in a
lightpath to a node, transmit a request to an optical network to
re-establish the lightpath, and reestablish the lightpath using a
backup or redundant router in place of a failed router at the same
node thereof.
[0016] All routers at the nodes are used during normal operations,
though, for the purposes of this description, one router may be
deemed to be "redundant" since it backs up traffic for another
router that has failed at the same node. The node element that
detects the failed router may include a router, disposed at another
node, whereby the lightpath runs between the detecting router and
the failed router; a redundant router at the same node as the
failed router; or an OXC at the same node as the failed router.
[0017] If the router failure is detected by a router, at either a
remote node or at the same node as the failed router, the detecting
router transmits a request to an OXC at the respective node that
the lightpath be re-established using the redundant router in place
of the failed router. If the detecting router is at the remote
node, the OXC at the remote node transmits the request to the OXC
at the same node as the failed router.
[0018] Upon receiving the request for re-establishing the failed
lightpath by using the redundant router in place of the failed
router, the OXC at the same node as the failed router coordinates
the re-establishment of all links using the redundant router in
place of the failed router. Also, the OXC at the same node as the
failed router may also detect the failed router and re-establish
links using the redundant router in place of the failed router.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1(a) shows a schematic diagram of a joint IP/Optical
Layer architecture.
[0020] FIG. 1(b) shows a more detailed schematic diagram of a joint
IP/Optical layer architecture, including the interconnection
options therefore.
[0021] FIG. 2 shows an example IP architecture, as part of an
example embodiment of the present invention, in which a router has
failed.
[0022] FIG. 3 shows an example of the IP over Optical Layer
architecture, according to an example embodiment of the present
invention, in which a router has failed.
[0023] FIG. 4 shows an example IP architecture, as part of an
example embodiment of the present invention, in which a path has
been re-routed after a router has failed.
[0024] FIG. 5 is a flow chart showing an example method embodiment
according to the present invention for a router at a remote
node.
[0025] FIG. 6 is a flow chart showing an example method embodiment
according to the present invention for a router at a home node.
[0026] FIG. 7 is a flow chart showing an example method embodiment
according to the present invention for an optical cross-connect at
a home node.
DETAILED DESCRIPTION OF THE INVENTION
[0027] As set forth above, FIG. 1(b) illustrates a joint IP/Optical
Layer network node with the optical layer cross-connect (OLXC) 25
connected to DWDM 20, to thereby be connected to other OLXCs. The
network node may further include IP router 15, along with
dynamically-reconfigurable OLXC 25. Optical lightpaths may be
established between network elements, via OLXCs, and the lightpaths
serve as a virtual circuit.
[0028] In order to facilitate the description of the present
invention the following network objects are defined.
[0029] A Wavelength Division Multiplexer (WDM) is a system that
converts multiple optical inputs into narrowly spaced wavelength
optical signals within an optical amplification band and couples
them onto a single fiber. At the receiving end, the amplified
signal may be de-multiplexed and converted to multiple channels of
standard wavelength to interface with other equipment. It may also
be possible to take the wavelength specific signals directly as the
inputs. In that case, no wavelength conversion may be necessary at
the WDM system. The WDM system may or may not be integrated with an
OLXC.
[0030] A channel is a unidirectional optical tributary connecting
two OLXCs. Multiple channels may be multiplexed optically at the
WDM system. One direction of an OC-48/192 connecting two
immediately neighboring OLXCs is an example of a channel. A single
direction of an Optical channel (Och) as defined in ITU-T G.872
between two OLXCs over a WDM system is another example of a
channel. A channel may generally be associated with a specific
wavelength in the WDM system. However, in a WDM system with
transponders, the interfaces to the OLXC may be a standard single
color (1310 or 1550 nm). Further, a single wavelength may transport
multiple channels multiplexed in the time domain. For example, an
OC-192 signal on a fiber may carry four STS-48 channels. For these
reasons, a channel may be defined separately from wavelength
although in most applications there is a one-to-one
correspondence.
[0031] An optical layer cross-connect (OLXC) is a switching element
that connects an optical channel from an input port to an output
port. An OLXC may also be referred to as an optical cross-connect
(OXC), and therefore shall be referred to as "OXC" hereafter.
[0032] A drop port is an OXC port that connects to the end client
network element (NE). The drop interface may connect the client
port to the OXC drop port. The OXC drop port is essentially a User
Network Interface (UNI) that connects end devices to the optical
layer. The drop port terminates the user network interface between
the client NE and the optical network. It is necessary to
distinguish this type of interface from others to identify network
requests originating from a client NE.
[0033] A network port is an OXC port that does not directly
interface with an end client NE. A Network Port in an OXC
interfaces with another Network Port via a WDM system or directly
via optical fibers.
[0034] A lightpath is an abstraction of optical layer connectivity
between two end points. A lightpath is a fixed bandwidth connection
(e.g. one direction of a STM-N/OC-M payload or an Och payload)
between two network elements (NEs) established via OXCs. A
bidirectional lightpath includes two associated lightpaths in
opposite directions routed over a same set of nodes.
[0035] A source may be a client router physically connected to an
OXC by one or more OC-48/192 interfaces. A source may also be a
non-IP NE connected to the OLXC via an OC-48/192 interface. In the
case of an IP router source, the router may have an IP address, and
the physical interfaces to the OXC are identified with some set of
addresses (potentially a single IP address or a unique address per
port). In the case of a non-IP NE, either the NE may be assigned an
IP address, or the OLXC port connecting the NE may have an IP
address. For non-IP aware equipment interfacing the OLXC, any
connection request must be originated externally via a proxy or
external OS interfaces. The destination is essentially the same as
the source from the physical interface perspective. When a request
is generated from one end, the other end client or end OXC
interface may become the destination.
[0036] A prominent feature of joint IP/Optical Layer network
architecture according to an example embodiment of the present
invention is that every office or node, A-F, in the network
includes multiple, or redundant, IP routers 100.sub.A -100.sub.F.
and a dynamically reconfigurable OXC 200.sub.A-200.sub.N, as shown
in FIG. 3, although the present invention is in no way limited
thereto. In FIG. 3, however, only office/node B is shown as having
multiple routers 100.sub.B1-100.sub.B2, though the present
invention is not limited thereto. Rather, it is intended, in the
present example embodiment of the invention, that all offices/nodes
have multiple, or redundant, IP routers 100.sub.N.
[0037] Each IP office/node may be connected to other offices/nodes
by one or more lightpaths. On each link within the network, one
channel/wavelength is assigned as the default routed (one hop)
lightpath. The routed lightpath may provide router-to-router
connectivity over this link. These routed lightpaths may reflect
(and are thus identical to) the physical topology. The assignment
of this default lightpath is by convention, e.g. the "first"
channel/wavelength. All traffic using this lightpath is IP traffic
and is forwarded by the router.
[0038] As shown in FIG. 3, IP routers 100.sub.N at the respective
offices/nodes may communicate with their respective OXCs 200.sub.N
through a logical interface (not shown). The logical interface
defines a set of basic primitives to configure the respective OXC
200.sub.N, and to enable the respective OXC 200.sub.N to convey
information to the respective router 100.sub.N. The mediation
device translates the logical primitives to and from the
proprietary controls of the OXC. A further embodiment may integrate
the routers and their respective OXC into a single box or component
and use a proprietary interface implementation, while still
providing equivalent functionality to the interface described
herein.
[0039] Beyond the node local mechanisms, signaling mechanisms may
be required to construct optical lightpaths. An Application
Programming Interface (API) call to create a path may require at
least five parameters including: destination, wavelength,
bandwidth, restoration flag, and a transparency flag. If the
restoration flag is set, the lightpath will be protected.
Lightpaths without the transparency flag are assumed to carry IP
services, and may be rerouted if needed. On completion, an explicit
tear down message is sent to remove the path.
[0040] Lightpath services may include lightpath requests between a
source and destination, such as an API call with the following
attributes:
[0041] As set forth above, restoration could be done at the IP
layer 5 and/or the Optical Layer 10, as shown in FIG. 1(a). The
present invention will be explained in the exemplary context of an
ISP central office, using the schematic diagrams of FIGS. 2-4. The
IP network of FIG. 2 includes, at each node therein, at least 2
backbone routers for redundancy, though the detailed office
architecture is shown for office B only. These routers, 100.sub.N,
aggregate all traffic to or from routers that connect to the
customers of the IP network.
[0042] Under current IP routing systems, for example, when router
100.sub.B1 at office/node B fails, IP traffic from office 100.sub.A
to 100.sub.B would go around offices 100.sub.D, 100.sub.E,
100.sub.F, and 100.sub.C to reach office 100.sub.B via router
100.sub.B2, the backup router for 100.sub.B1. Similarly, traffic
from office 100.sub.A to 100.sub.C, which originally went through
office 100.sub.B would need to go around offices 100.sub.D,
100.sub.E, 100.sub.F, and 100.sub.C to reach 100.sub.C. Additional
capacity may therefore be needed on all the inter-office links.
[0043] Under current IP rerouting systems, for example, when router
100.sub.B, at office/node B fails, IP traffic from office 100.sub.A
to 100.sub.B would go around offices 100.sub.D, 100.sub.E,
100.sub.F, and 1000.sub.C to reach office 100.sub.B via router
100.sub.B2, the backup router for 100.sub.B1. Similarly, traffic
from office 100.sub.A to office 100.sub.C , which originally went
through office 100.sub.B would need to go around offices 100.sub.D,
100.sub.E, 100.sub.F, and 100.sub.C to reach office 100.sub.C.
Additional capacity may therefore be needed on all the inter-office
links.
[0044] With the new IP over Optical Layer architecture shown in
FIG. 3, according to an embodiment of the present invention, each
office/node may be equipped with one OXC 200.sub.N, which connects
to the two backbone routers 100.sub.N1 and 100.sub.N2 at the same
office/node. Then all the OXCs 200.sub.N may be connected by a mesh
topology. Links between routers are provided by direct lightpaths
through the Optical Layer 10, which includes OXC's 200.sub.N. In
FIG. 3 solid lines represent physical layer connectivity, and the
dotted lines show the OC-48 links that may be used for the
transport of packets between the routers at offices 100.sub.N and
to the neighboring offices.
[0045] In the restoration scheme according to an embodiment of the
present invention, when router 100.sub.B1 at office B fails,
bringing down both inter-office lightpath link between routers
100.sub.A and 100.sub.B1 and the lightpath link between routers
100.sub.B1 and 100.sub.B2, router 100.sub.A may detect that router
100.sub.B1 has failed and may request a new connection to be set up
to the backup router, R.sub.B2. Further, OXC.sub.B that connects to
failed router 100.sub.B1 directly may detect the failure and
coordinate the setup of the new lightpath link between routers
100.sub.A and 100.sub.B2. This new link may use the same port for
the failed link between routers 100.sub.A and 100.sub.B1 on router
100.sub.A, and either the same port for the failed lightpath link
between routers 100.sub.B1 and 100.sub.B2 on router 100.sub.B2, or
a spare port on router 100.sub.B2. In addition, the bandwidth
originally used for the lightpath link between routers 100.sub.A
and 100.sub.B1 may be reused, as may the intra-office cabling from
router 100.sub.A to OXC.sub.A and the cabling from OXC.sub.B to
100.sub.B2. The restoration for router failures, described above,
is implemented in a time period of a couple of seconds.
[0046] More specifically, as shown in FIG. 5, the failure of router
100.sub.B1 at office/node B (step 500) may be detected by router
100.sub.A at office/node A, as in step 505. In step 510, router
100.sub.A may send a request to OXC.sub.A, also at node A, to
restore the link between routers 100.sub.A and 100.sub.B1 by
setting up a new link (i.e., lightpath) between router 100.sub.A
and 100.sub.B2. The signaling mechanism in the optical layer
coordinates the lightpath establishment. The request may be
transmitted from OXC.sub.A to other OXC's that are on the new
lightpath, i.e., OXC.sub.B in this case in step 515, and may
complete all necessary switching in OXC.sub.A to OXC.sub.B to
establish the new lightpath. Then, in step 525, upon restoration of
the lightpath links to office/node B, routing in the IP layer will
automatically discover the new link between 100.sub.A and
100.sub.B2, and router 100.sub.B1 may be replaced by router
100.sub.B2 for all IP traffic through office/node B, and
restoration may be complete at step 530.
[0047] The failure of router 100.sub.B1, at step 600, may also be
detected by the redundant router 100.sub.B2, which is at the same
node as the failed router, at step 605, as depicted in the
flowchart in FIG. 6. In step 610, router 100.sub.B2 sends a request
to OXC.sub.B that it connects to directly, also at node B, to
restore the connection to office A by setting up a new lightpath
link to routers 100.sub.A. In step 615, the signaling mechanism may
forward the request from OXC.sub.B to OXC.sub.A to complete all
necessary switching to establish the new lightpath. Then, in step
620, upon restoration of the lightpath link to office/node A,
routing in the IP layer will may automatically discover the new
link between 100.sub.A and 100.sub.B2, and router 100.sub.B1 will
be replaced by router 100.sub.B2 for all IP traffic through
office/node B, and restoration may be complete at step 625.
[0048] Further, as shown in the flowchart of FIG. 7, the failure of
router 100.sub.B1, at step 700, may be detected by the
cross-connect OXC.sub.B, which is disposed at the same office/node
B as the failed router 100.sub.B1 as in step 705. Since OXC.sub.B
controls connections for all routers at node B, in step 710,
OXC.sub.B may restore all inter-office links associated with failed
router 100.sub.B1 with router 100.sub.B2 via the signaling
mechanisms, thus ending restoration at step 715.
[0049] The IP layer topology resulting from the restoration
described in accordance with the example method embodiments of
FIGS. 5-7 above is shown in FIG. 4. As a result of the restoration
implementation described above, lightpath traffic, as shown in FIG.
4, may utilize lightpath link from router 100.sub.A to router
100.sub.B2 using the same number of hops with no additional
backbone capacity required.
[0050] As set forth above, intra-office capacity from cross-connect
OXC.sub.B to router 100.sub.B2, for example, that was formerly used
for the intra-office link between routers 100.sub.B1 and 100.sub.B2
may be reused. Both intra-office lightpath links may require the
same amount of additional intra-office capacity from the backup
router 100.sub.B2 to all provider edge routers. With the
restoration scheme described above, lightpath traffic between
router 100.sub.A and router 100.sub.C, via router 100.sub.B, now
may use the new link between router 100.sub.A and router
100.sub.B2, with one intra-office hop less than an original path to
go across office B and with no additional backbone capacity
required. In comparison, IP rerouting would send the traffic via
another route, thus potentially requiring additional backbone link
capacity and very likely increasing the hop count.
[0051] Thus, in this example restoration against the failure of
router 100.sub.B1 has been achieved with no requirement for
additional backbone bandwidth, OXC ports, or router ports.
[0052] In other cases with different topology, additional ports may
be required on the backup router. For example, if one more backbone
link is added to router 100.sub.B1 in the original network shown in
FIG. 2, for example a lightpath link between routers 100.sub.E and
100.sub.B1, in addition to restoring the lightpath link between
routers 100.sub.A and 100.sub.B1 using the new lightpath link
between routers 100.sub.A and 100.sub.B2, the lightpath link
between routers 100.sub.E and 100.sub.B1 may be replaced by new
lightpath link between routers 100.sub.E and 100.sub.B2. Since
there is only one port on router 100.sub.B2, e.g., the port used by
the failed intra-office lightpath link between routers 100.sub.B
and 100.sub.B2, reusable taken by the lightpath link between
routers 100.sub.A and 100.sub.B2, an port may be required on router
100.sub.B2 for the further required lightpath link between routers
100.sub.E and 100.sub.B2. In general, the minimum number of
additional ports needed on the backup router equals the total
number of inter-office links on the failed router reduced by the
number of re-usable ports (i.e., same type of ports) on the backup
router that can be used by the failed intra-office links between
the failed router and its backup router.
[0053] After a router failure is repaired, it is desirable to
revert back to the normal connections. We describe the details in
the following three cases:
[0054] No re-use of the wavelength(s) and port(s) of the replaced
lightpath
[0055] When a neighbor of the failed router detects that the
failure has been repaired, it may first request the replaced
lightpath to be re-established using the original wavelength(s) and
port(s). After the original lightpath has been restored, it may
then request the recovery lightpath to be torn down. This case
results in minimum interruption of the traffic.
[0056] Re-use of the wavelength(s) without the re-use of the
port(s) of the replaced lightpath
[0057] When a neighbor of the failed router detects that the
failure has been repaired, it may first request the replaced
lightpath to be re-established using the original port(s) and new
wavelength(s) if feasible. After the replaced lightpath has been
restored, it may then request the recovery lightpath to be torn
down. However, if additional wavelength(s) are not available or if
it is required to revert back to the same wavelength(s) as the
one(s) used in the normal condition, the recovery lightpath may
need to be torn down first before the original one gets restored
using the original port(s) and wavelength(s). This may result in
some traffic loss during the reversion process.
[0058] Re-use of the wavelength(s) or port(s) of the replaced
lightpath
[0059] When a neighbor of the failed router detects that the
failure has been repaired, it may first request the replaced
lightpath to be re-established using new port(s) and wavelength(s)
if feasible. After the replaced lightpath has been restored, it may
then request the recovery lightpath to be torn down. However, if
additional wavelength(s) or port(s) is not available or if it is
required to revert back to the same port(s) and wavelength(s) as
the ones used in the normal condition, the recovery lightpath needs
to be torn down first before the original one gets restored using
the original port(s) and wavelength(s). This may result in some
traffic loss during the reversion process.
[0060] Note that the restoration mechanisms proposed here are
applicable to failure restoration for router interfaces. It is also
applicable to cases without backup routers in the same office.
Instead, a router in a neighboring office can be used as the backup
router.
[0061] While the invention has been described with respect to
specific examples including presently preferred modes of carrying
out the invention, those skilled in the art will appreciate that
there are numerous variations and permutations of the above
described systems and techniques that fall within the spirit and
scope of the invention as set forth in the appended claims.
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