PCE Working Group D. Wang
Internet-Draft Z. Wang
Intended status: Standards Track X. Fu
Expires: April 29, 2010 ZTE Corporation
October 26, 2009
Path Computation Element (PCE) Extensions for Inter-Layer Path
Computation
draft-wdj-pce-for-inter-layer-path-computation-01
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Abstract
This document mainly describes the extensions of multiple PCE inter-
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layer path computation with inter-PCE communication.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions Used in This Document . . . . . . . . . . . . 3
2. Scenario Statement and Requirements Overview . . . . . . . . . 3
2.1. Scenario Statement . . . . . . . . . . . . . . . . . . . . 3
2.2. Requirements Overview . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Inter-Layer Optimal Path Computation Procedure . . . . . . . . 6
4.1. Confirmation of The Topology Connectivity . . . . . . . . 6
4.2. Inter-layer TE Links . . . . . . . . . . . . . . . . . . . 6
4.3. Confirmation of Inter-Layer Border LSR . . . . . . . . . . 7
4.4. Discovery of Inter-layer PCEs . . . . . . . . . . . . . . 8
4.5. Communication of Inter-layer PCEs . . . . . . . . . . . . 9
4.6. Optimal Inter-layer Path Computation by BRPC . . . . . . . 9
5. Routing Protocol Extensions for Inter-Layer PCE Discovery . . 9
5.1. Extension of PATH-SCOPE Sub-TLV . . . . . . . . . . . . . 10
5.2. PCE-LAYER Sub-TLV . . . . . . . . . . . . . . . . . . . . 12
5.3. NEIG-PCE-LAYER Sub-TLV . . . . . . . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
8. Normative References . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
The Path Computation Element (PCE) defined in [RFC4655] is an entity
that is capable of computing a network path or route based on a
network graph and applying computational constraints.
A network may comprise multiple layers. In [PCE-INTER-LAYER-FRWK],
there are three inter-layer path computation models defined to
perform PCE-based inter-layer path computation, namely Single PCE
Computation, Multiple PCE Computation with inter-PCE communication,
and Multiple PCE Computation without inter-PCE communication. Mainly
by scalability, automation and confidentiality considerations,
multiple PCE computation instead of single PCE computation is more
concerned. In this mode, a PCE has the topology visibility of one or
more layers (but not all layers, in this document, only one layer
being considered).
This document mainly describes the extensions of multiple PCE inter-
layer path computation with inter-PCE communication.
1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
This document uses terminology from the PCE-based path computation
architecture [RFC4655] and also common terminology from Multi
Protocol Label Switching (MPLS) [RFC3031], Generalized MPLS (GMPLS)
[RFC3945], Framework for PCE-Based Inter-Layer MPLS and GMPLS Traffic
Engineering [PCE-INTER-LAYER-FRWK], OSPF Protocol Extensions for Path
Computation Element (PCE) Discovery [RFC5088], and Multi-Layer
Networks [RFC5212].
2. Scenario Statement and Requirements Overview
2.1. Scenario Statement
In the model of multiple PCE inter-layer path computation, there is
at least one PCE in each layer. Each PCE has the topology visibility
restricted to its own layer. When an ingress LSR tries to set up an
end-to-end LSP to an egress LSR is set up in the higher-layer
network, as a PCC it will select a PCE located in its layer and send
a path computation request to the PCE. At this time, the PCE will be
confronted with such secenarios:
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o As absence of essential TE link in the higher-layer network, the
network topology of the whole layer is divided into at least two
independent partitions.
o The border LSRs of each partition MAY be produced and a lower-
layer network exists between the pairs of border LSRs belonging to
two different partitions.
o The border LSRs MAY originate TE links connected to the lower-
layer network.
o The ingress LSR and the egress LSR MAY be located in different
partitions.
o When receiving a path computation request from the ingress LSR in
the higher-layer, this higher-layer PCE will select one border LSR
of the partition that the ingress LSR is located in and another
border LSR of the partition that the egress LSR is located in
respectively. This pair of LSRs will be taken as the head-end and
the tail-end nodes which are included in the inter-layer path
computation request sent to the lower-layer PCE. As the number of
the border LSRs in each partition is usually more than one,
higher-layer PCE will produce such pairs of border LSRs.
o As there can be at least one PCE in each layer,,the higher-layer
PCE SHOULD select one from the lower-layer PCEs according to the
information advertised by them and send a inter-layer path
computation request about the pairs of border LSRs to the selected
lower-layer PCE.
o In order to allow for effective PCE selection by PCCs,
furthermore, a PCC needs to know the layer that the PCE is located
in and the neighbor layer toward which the PCE can compute paths.
Here, the neighbor layer is usually lower than its own layer
according to multi-layer technology.
2.2. Requirements Overview
The multiple PCE inter-layer path computation mechanism MUST satisfy
the following requirements.
For the higher-layer PCE, it MUST identify connectivity of its own
layer topology by some algorithm. When the topology is no-connected,
if the head-end node and the tail-end node lie in two independent
partitions respectively, inter-layer path solution will have to be
considered.
As there is no direct TE link between partitions in non-connected
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topology, the higher-layer PCE SHOULD designate border LSRs to the
lower-layer. Generally in one partition, obtainment of border LSR
lies in whether the LSR has a TE link connected to the lower-layer
network. If so, this LSR will be considered as a border LSR of the
partition. An independent partition SHOULD usually have at least one
border LSR. Similarly, the lower-layer PCE should also designate
border LSRs which should have a TE link connected to the higher-layer
network.
In each layer, PCE discovery information should include the layer
into which the PCE has visibility.
In each layer, PCE discovery information should include the neighbor
layer to which the PCE can send path computation request. In this
case, the local-layer is usually higher, and the neighbor layer is
lower. Since a NE receives discovery information of PCEs in the
local-layer, as a PCC, it should know about which PCEs are in the
same layer and which neighbor layer the PCEs can communicate with.
When a path computation request is originated from this NE, firstly
it should estimate the neighbor layer that the path passes through if
possible.
A PCE discovery mechanism MUST allow that PCEs in different layers
know about their discovery information each other, especially their
local layer, neighbor layer, and the computation capability. Such
information MAY be got by flooding mechanism of some routing
protocol. So PCE discovery mechanism permits PCEs belonging to
different layers get discovery information each other, especially the
information about local layer, adjacent layer, and PCE's computing
capability etc. Some of PCEs in different layers and with inter-
layer computing capability can be chosen and consist of a PCE
topology. Then in this PCE topology the PCEs' discovery information
can be gotten by starting an instance of some routing protocol with
flooding mechanism. According to the PCEs' discovery information, as
a PCC, a higher-layer PCE may choose a suitable one from many
adjacent lower-layer PCEs with inter-layer path computing capability
in the PCE topology to compute an inter-layer path.
3. Terminology
BRPC: Backward-Recursive PCE-Based Computation.
FSC: Fiber Switching Capability.
GMPLS: Generalized Multi-Protocol Label Switching.
LSC: Lambda Switching Capability.
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L2SC: Layer2 Switching Capability.
LSP: Label Switched Path.
LSR: Label Switching Router.
MPLS: Multi-Protocol Label Switching.
PCC: Path Computation Client.
PCE: Path Computation Element.
PCReq: Path Computation Request.
PCRsp: Path Computation Respond.
PSC: Packet Switching Capability.
TDM: Time Division Multiplex.
TE: Traffic Engineering.
4. Inter-Layer Optimal Path Computation Procedure
4.1. Confirmation of The Topology Connectivity
The PCE in the local layer will compute the optimal path from the
ingress LSR to the egress LSR according to the information included
by the PCReq message belonging to PCEP.
Generally, only when the network topology of the whole layer is
divided into two or more partitions resulting from lack of TE links,
and the ingress LSR and the egress LSR are respectively located in
the different partitions, inter-layer path computation will be
considered by the PCE.
4.2. Inter-layer TE Links
Whether it is higher-layer or lower-layer PCE needs to get the TE
attribute of inter-layer TE links during the process of inter-layer
TE LSP computation.
Between the local port belonging to one inter-layer border LSR in the
side of higher-layer and the remote port belonging to the other one
in the side of lower-layer, one-way inter-layer TE links usually
appear in pairs. Among them, one is form the local port to the
remote port, and the other is in the opposite direction. In other
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words, both of them consist of a bidirectional TE link. The former
is originated from an inter-layer border LSR in the higher-layer, and
it belongs to the scope of higher-layer topology into which only the
higher-layer PCEs have visibility. Similarly the latter is
originated from an inter-layer border LSR in the lower-layer, and it
belongs to the scope of lower-layer topology into which only the
lower-layer PCEs have visibility.
By an inter-layer TE link, an adaptation is completed from one type
of switch capability to another one(e.g., electrical switching to
optical switching, etc.).
4.3. Confirmation of Inter-Layer Border LSR
Inter-layer border LSRs are respectively located on the boundary of
the high-layer and lower-layer networks. Each of them has at least
one unidirectional TE link connected to the other inter-layer border
LSR in the adjacent layer.
Before a higher-layer PCE begins to compute an inter-layer path, it
SHOULD collect the information about all of inter-layer border LSRs
in its local layer. And it MAY combine the inter-layer border LSRs
belonging to the partition in which the ingress LSR is located with
the inter-layer border LSRs belonging to the partition in which the
egress LSR is located into many pairs of inter-layer border LSRs. By
this combination, many pairs of inter-layer border LSRs are formed
and as end LSRs provided for the lower-layer PCE to compute end-to-
end paths across the lower-layer network. That is, a PCReq message
which is sent to lower-layer PCE and is used to do inter-layer path
computation will include many pairs of ingress and egress LSRs.
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----- ----- ----- ----- -----
| LSR |...| LSR | | PCE | | LSR |...| LSR |
| H1 | | H2 | | Hi | | H'1 | | H'2 |
/----- . -----\ --+-- /----- -----\
/ . \ | / \
-----/ ----- ... \----- | -----/ ----- ... \-----
| LSR | |LSP | | LSR | | | LSR | |LSP | | LSR |
| H6 | |Head | | H3 | | | H'6 | |End | | H'3 |
-----\ ----- . /----- | -----\ .----- . /-----
\ . / | \ . . /
\----- -----/ | \----- -----/
| LSR |...| LSR | --+-- | LSR |...| LSR |
| H5 | | H4 | | PCE | | H'5 | | H'4 |
-----\ -----\ | Lo | /----- /-----
\ . . \ ----- / . ./
\ . . \ / . ./
\ . . \----- -----/ . ./
\ | LSR |...| LSR | /
\ | L1 | | L2 | /
\ /----- -----\ /
\ / \ /
-----/ \-----
| LSR | | LSR |
| L6 | | L3 |
-----\ /-----
\ /
\----- -----/
| LSR |...| LSR |
| L5 | | L4 |
----- -----
4.4. Discovery of Inter-layer PCEs
From PCEP's point of view, inter-layer PCE communication is also a
kind of communication between PCC and PCE. The requesting entity
will be looked as a PCC, and the requested entity will be looked as a
PCE.
So PCE discovery mechanism permits PCEs belonging to different layers
get discovery information each other, especially the information
about local layer, adjacent layer, and PCE's computing capability
etc. Some of PCEs in different layers and with inter-layer computing
capability can be chosen and consist of a PCE topology. Then in this
PCE topology the PCEs' discovery information can be gotten by
starting an instance of some routing protocol with flooding
mechanism. Only in this PCE topology can this routing protocol
instance run. Its flooding contents are limited to the discovery
information of those PCEs that are added to the PCE topology and can
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not be beyond the scope of the PCE topology. According to the PCEs'
discovery information, as a PCC, a higher-layer PCE may choose a
suitable one from many adjacent lower-layer PCEs with inter-layer
path computing capability in the PCE topology to compute an inter-
layer path.
4.5. Communication of Inter-layer PCEs
If the higher-layer PCE decides to start inter-layer path
computation, it will confirm as many pairs of end inter-layer LSRs as
possible firstly. Then as a PCC, the higher-layer PCE will choose a
suitable lower layer PCE according to the discovery information
flooded by the lower layer PCEs and send a request to it for
computing paths of the pairs of end inter-layer LSRs.
Since a inter-layer TE link includes the information about inter-
layer LSRs on the both ends of it, when the lower-layer PCE receives
the PCReq message, it can find the correspondent inter-layer TE links
in its local-layer topology according to the message which includes
many pairs of end inter-layer LSRs in the side of the higher-layer.
By each inter-layer TE link, pairs of end inter-layer LSRs in the
side of the lower-layer can be found.
Thus the lower-layer PCE can compute at least one inter-layer path by
the above information and respond the computation result to the
higher-layer PCE.
4.6. Optimal Inter-layer Path Computation by BRPC
In [PCE-INTER-LAYER-FRWK], BRPC is recommended to solve the problem
of multiple PCE inter-layer path computation by considering layers as
separate domains. BRPC is always started by the higher-layer PCE
according to the response of lower-layer PCE about lower-layer path
computation results. In addition, if multiple paths about a common
pair of end LSRs are needed, all the complete paths will be ordered
in some optimal strategy(e.g., minimum hops number, minimum aggregate
te-metrics, etc.).
5. Routing Protocol Extensions for Inter-Layer PCE Discovery
In a multi-layer network model, multiple PCEs MAY have the function
of inter-layer path computation. It may be necessary or desirable
for a higher-layer PCE to choose a lower-layer PCE by the PCE
discovery information originated from the lower-layer PCE.
Since the number of local-layer PCEs may be usually more than one,
the PCEs' discovery information to which now is added local-layer and
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adjacent layer information needs to be flooded through all the layers
unless safety is considered. By this way, as a PCC, when a higher-
layer PCE needs to send a path computation request to a lower-layer
PCE, it can dynamically choose a suitable one but not be allocated a
fixed one according to the flooded layers' information from all the
PCEs in the lower-layer. That is, all the PCEs belonging to all
different layers will form a PCE topology and MAY participate in an
independent IGP (OSPF or IS-IS) instance. This PCE topology's
visibility MUST be opened only for these PCEs.
In [RFC5088] and [RFC5089], PCE discovery information is referred to.
It is usually composed of the PCE location, the PCE path computation
scope, the set of PCE-Domain(s), the set of neighbor PCE-Domain(s),
and the set of communication capabilities etc. Here according to the
above description, for the purpose of layer information automatic
discovery and dynamically choosing among PCEs from different layers,
the set of PCE-Layer(s) and the set of neighbor PCE Layer(s) SHOULD
be added to the PCE discovery information.
Considering the two new types of PCE discovery information, the sub-
TLVs that may be carried within the PCED TLV will be extended. The
following sections describe the new extended sub-TLVs.
5.1. Extension of PATH-SCOPE Sub-TLV
In view of layer information discovery, here PATH-SCOPE Sub-TLV in
[RFC5088] and [RFC5089] is extended. Yd bit is added to PATH-SCOPE
Sub-TLV and the new sub-TLV has the following format:
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1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|1|2|3|4|5|6| Reserved |PrefL|PrefR|PrefS|PrefY| Res |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 2
Length: 4
Value: This comprises a 2-octet flags field where each bit
represents a supported path scope, as well as four
preference fields used to specify PCE preferences.
The following bits are defined:
Bit Path Scope
0 L bit: Can compute intra-area paths.
1 R bit: Can act as PCE for inter-area TE LSP
computation.
2 Rd bit: Can act as a default PCE for inter-area TE LSP
computation.
3 S bit: Can act as PCE for inter-AS TE LSP computation.
4 Sd bit: Can act as a default PCE for inter-AS TE LSP
computation.
5 Y bit: Can act as PCE for inter-layer TE LSP
computation.
6 Yd bit: Can act as a default PCE for inter-layer TE LSP
computation.
PrefL field: PCE's preference for intra-area TE LSP computation.
PrefR field: PCE's preference for inter-area TE LSP computation.
PrefS field: PCE's preference for inter-AS TE LSP computation.
PrefY field: PCE's preference for inter-layer TE LSP computation.
Res: Reserved for future use.
The L, R, S, and Y bits are set when the PCE can act as a PCE for
intra-area, inter-area, inter-AS, or inter-layer TE LSP computation,
respectively. These bits are non-exclusive.
Similarly, when set, the Yd bit indicates that the PCE can act as a
default PCE for inter-layer TE LSP computation (that is, the PCE can
compute a path toward an adjacent layer). When the Yd bit is set,
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the PCED TLV MUST NOT contain a NEIG-PCE-LAYER sub-TLV.
When the Y bit is clear, the Yd bit SHOULD be clear on transmission
and MUST be ignored on receipt.
5.2. PCE-LAYER Sub-TLV
The PCE-LAYER sub-TLV specifies a PCE-LAYER into which the PCE has
topology visibility and through which the PCE can compute paths. The
PCE-LAYER sub-TLV SHOULD be present when PCE-Layers for which the PCE
can operate cannot be inferred by other IGP information: for
instance, when the PCE is inter-layer capable (i.e., when the Y bit
is set) and the flooding scope is the entire visible layer topology
and the entire PCE topology that is composed of all the PCEs from all
of layers. A PCED TLV may include multiple PCE-LAYER sub-TLVs when
the PCE has visibility into multiple PCE-Layers.
The PCE-LAYER sub-TLV has the following format:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 6 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Layer-type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Layer ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PCE-LAYER sub-TLV format
Type: 6
Length: 8
Current five layer-type values are defined:
1 PSC layer
2 L2SC layer
3 TDM layer
4 LSC layer
5 FSC layer
Layer ID: This indicates the 32-bit Layer ID of a layer where the
PCE has visibility and can compute paths.
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5.3. NEIG-PCE-LAYER Sub-TLV
The NEIG-PCE-LAYER sub-TLV specifies a neighbor PCE-Layer toward
which a PCE can compute paths. It means that the PCE can take part
in the computation of inter-layer TE LSPs with paths that transit
this neighbor PCE-Layer.
For each PCE-LAYER sub-TLV, this neighbor layer usually refers to the
lower adjacent layer.
The NEIG-PCE-LAYER sub-TLV has the following format:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 7 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Layer-type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Layer ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NEIG-PCE-LAYER sub-TLV format
Type: 7
Length: 8
Current five layer-type values are defined:
1 PSC layer
2 L2SC layer
3 TDM layer
4 LSC layer
5 FSC layer
Layer ID: This indicates the 32-bit Layer ID of a neighbor layer
toward which the PCE can compute paths.
The NEIG-PCE-LAYER sub-TLV MUST be present at least once if the Y bit
is set and the Yd bit is cleared.
6. Security Considerations
The inter-layer path computation procedure relies on the use of the
PCEP and as such is subjected to the potential attacks listed in
Section 10 of [RFC5440]. In addition to the security mechanisms
described in [RFC5440] with regards to spoofing, snooping,
falsification, and denial of service, an implementation MAY support a
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policy module governing the conditions under which a PCE should
participate in the inter-layer path computation.
In addition, each layer topology's confidentiality should be
especially considered.
For the purpose of network topology safety and confidentiality, the
following points should be paid attention to:
o For each PCE in the PCE topology, the flooding scope of its
discovery information is limited only to the local-layer topology
and the PCE topology.
o For the PCEs outside the PCE topology, the flooding scope of its
discovery information is limited only to the local-layer topology.
o For the PCEs of each layer, not all the PCEs can be added to the
PCE topology. Only those which have the capability of inter-layer
path computation are qualified for being added to the PCE
topology.
o For confidentiality consideration, users can add the PCEs to the
PCE topology or move them out of it dynamically. But if inter-
layer path computation need to be desired, in each layer at least
a PCE with the capability of inter-layer path computation should
be add to the PCE topology. As a result, some of the PCEs in each
layer are invisible to the PCEs in other layers, that is, the
PCEs' visibility in one layer is partially opened to other layers.
7. Acknowledgments
The RFC text was produced using Marshall Rose's xml2rfc tool.
The authors would like to extend their warmest thanks to the ZTE's
PCE software engineers.
8. Normative References
[ITUT-G709]
ITU-T, "Interface for the Optical Transport Network
(OTN)", G.709 Recommendation (and Amendment 1) ,
October 2001.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
September 2003.
[RFC4203] Kompella, K. and Y. Rekhter, "OSPF Extensions in Support
of Generalized Multi-Protocol Label Switching (GMPLS)",
RFC 4203, October 2005.
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
[RFC4328] Papadimitriou, D., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Extensions for G.709 Optical
Transport Networks Control", RFC 4328, January 2006.
[RFC5150] Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel,
"Label Switched Path Stitching with Generalized
Multiprotocol Label Switching Traffic Engineering (GMPLS
TE)", RFC 5150, February 2008.
Authors' Addresses
Dajiang Wang
ZTE Corporation
12F,ZTE Plaza,No.19,Huayuan East Road,Haidian District
Beijing 100191
P.R.China
Phone: +8613811795408
Email: wang.dajiang@zte.com.cn
URI: http://wwwen.zte.com.cn/
Zhenyu Wang
ZTE Corporation
12F,ZTE Plaza,No.19,Huayuan East Road,Haidian District
Beijing 100191
P.R.China
Phone: +8613911266628
Email: wang.zhenyu1@zte.com.cn
Wang, et al. Expires April 29, 2010 [Page 15]
Internet-Draft PCEP Ext for Inter-Layer Path Comp October 2009
Xihua Fu
ZTE Corporation
West District,ZTE Plaza,No.10,Tangyan South Road,Gaoxin District
Xi An 710065
P.R.China
Phone: +8613798412242
Email: fu.xihua@zte.com.cn
URI: http://wwwen.zte.com.cn/
Wang, et al. Expires April 29, 2010 [Page 16]