CCAMP and PCE Working Group X. Lin
Internet-Draft G. Xie
Intended status: Standards Track G. Xiang
Expires: April 22, 2010 X. Fu
ZTE Corporation
October 19, 2009
A Path Computation Element (PCE) Solution for multilayer lsp
draft-lin-pce-ccamp-multilayer-lsp-00
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Abstract
This document mainly describes the extensions of single PCE inter-
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layer path computation for multiple FA-LSP.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Description of Question . . . . . . . . . . . . . . . . . . . 4
3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Explicit Control of FA-LSP . . . . . . . . . . . . . . . . 5
3.2. Process of multiple FA-LSPs in multiple layers . . . . . . 6
3.3. Process of multiple FA-LSPs in the same layer . . . . . . 7
4. Updated Message Formats . . . . . . . . . . . . . . . . . . . 8
4.1. Updated PCEP Message Formats . . . . . . . . . . . . . . . 9
4.2. Updated RSVP Message Formats . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6.1. SERO Object-Class in PCEP . . . . . . . . . . . . . . . . 10
6.2. SERO Object-Type in RSVP . . . . . . . . . . . . . . . . . 10
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
8. Normative References . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
Generalized MPLS (GMPLS) extends MPLS to handle multiple switching
technologies. For example: packet switching(PSC), Layer-2 switching
(L2SC), Time-Division Multiplexing switching(TDM) , wavelength
switching(LSC), and fiber switching(FSC) (see [RFC3945]). GMPLS is
not designed for a particular layer network design, so it can be
unified management of the network with multiple switching capability.
A MRN/MLN is defined as a TE domain supporting at least two different
switching types (e.g.,TDM and LSC), and under the control of a single
GMPLS control plane instance.In MRN TE links are consolidated into a
single Traffic Engineering Database (TED). Since this TED contains
the information relative to all the different regions and layers
existing in the network, a path across multiple regions or layers can
be computed using this TED. Thus, optimization of network resources
can be achieved across the whole MLN/MRN.
Path computation in large, multi-domain networks is complex and may
require special computational components and cooperation between the
elements in different domains. IETF PCE group specifies the
architecture for a Path Computation Element PCE)-based model to
address this problem space. A Path Computation Element (PCE) is an
entity that is capable of computing a network path or route based on
a network graph, and of applying computational constraints during the
computation.
In [draft-ietf-pce-inter-layer-frwk-10] two models are defined to
perform PCE-based inter-layer path computation, mainly including:
o Single PCE Inter-Layer Path Computation
In this model inter-layer path computation is performed by a single
PCE that has topology visibility to all layers.
o Multiple PCE Inter-Layer Path Computation
In this model there is at least one PCE per layer, and each PCE has
topology visibility restricted to its own layer
A set of one or more lower-layer LSPs provides information for
efficient path handling in higher layer(s) of the MLN, in other
words, provides a virtual network topology (VNT) to the higher
layers.A VNT Manager (VNTM) is defined as a functional element that
manages and controls the VNT. PCE and VNT Manager are distinct
functional elements that may or may not be co-located.There are three
Inter-Layer Path Control Models:
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o PCE-VNTM Cooperation Model
o Higher-Layer Signaling Trigger Model
o NMS-VNTM Cooperation Model
A MRN/MLN is a traffic engineering domain, so TE topology for all
layer networks is visible within this routing
domain.[draft-ietf-pce-inter-layer-frwk-10] suggest that the single
PCE inter-layer path computation model may be adopted because a PCE
is able to collect all layers' TE topologies by participating in only
one routing domain. However, in the above scenario, if Higher-Layer
Signaling Trigger Model is used to establish FA-LSP there are some
flaws.
2. Description of Question
In Single PCE Inter-Layer Path Computation model, the PCE know the TE
information of all the layers, so PCE can calculate a complete
path,which include the higher path and the lower path.
In [RFC4606], the information carried in the Interface Switching
Capabilities is used to construct LSP regions and to determine
regions' boundaries as follows:
o Define an ordering among interface switching capabilities as
follows: PSC-1 < PSC-2 < PSC-3 < PSC-4 < TDM < LSC < FSC. Given
two interfaces if-1 and if-2 with interface switching capabilities
isc-1 and isc-2 respectively, say that if-1 < if-2 iff isc-1 <
isc-2 or isc-1 == isc-2, and if-1's max LSP bandwidth is less than
if-2's max LSP bandwidth.
For a LSP, if two adjacent interfaces if-(i-1) < if-i, then we say
the LSP has crossed a region boundary at the node where if-(i-1)
locate.This node is the source node of lower FA-LSP. If two adjacent
interfaces if-(k-1)> if-k, then the node where if-k locate is the
destination node of the lower FA-LSP.
In Section 6.2 further shows that when RSVP-TE is as a signaling
protocol, how to establish the FA-LSP automatically, briefly
described as follows:
o when a region boundary node receives a Path message, the node
determines whether or not it is at the edge of an LSP region with
respect to the ERO carried in the message. If the node is at the
edge of a region, it must then determine the other edge of the
region with respect to the ERO,using the IGP database. The node
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then extracts from the ERO the sub-sequence of hops from itself to
the other end of the region.
o Then the LSR establish a new FA-LSP, and this FA-LSP is as a
higher FA.
However, in Single PCE Inter-Layer Path Computation model, the above
method has some defects:
o Because TED is centralized management, each node may not have the
IGP database, it PCE needs to determine the region boundary.
o When there are multi-nested FA-LSP exists, PCE already know the
region boundary nodes ,so it is not necessary to use IGP database
to determine the region boundary.
In a word, in Single PCE Inter-Layer Path Computation model, using
signaling explicitly specify the FA-LSP can simplify the process of
FA-LSP esstablishment.
3. Solution
When PCE computes the route,it can determine the regions' boundaries
and the initiator and the terminator of the FA-LSP via the
description in [RFC4206] section 5.1.
3.1. Explicit Control of FA-LSP
In[RFC4873],the Secondary Explicit Route objects( SEROs) is used to
indicate the protected path of the LSP!_s segment recovery. When
service path includes one layer or multilayer FA-LSP, FA-LSP!_s
Explicit routes are specified via the Secondary Explicit Route
objects.
When the Higher-Layer node creates a service,it sends a route request
to PCE,in the response message of the route request from PCE, the
whole LSP!_s routes are specified.The Higher-Layer path's Explicit
routes are specified via the ERO.The FA-LSP!_s Explicit routes are
specified via the SEROs.
Consider the following topology:
PCE
H1---H2 H5---H6
\ /
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L3---L4
In this topology, H1,H2,H5,H6 are the network nodes of Higher-Layer,
while H2,L3,L4,H5 are the network nodes of low layer. And, H2 and H5
are the region boundaries.
The process of creating a LSP from H1 to H6 is as the following:
o H1 sends a route request to PCE,which responses a message with the
Higher-Layer path's explicit route specified via the ERO and the
FA-LSP's explicit routes specified via the subsequent
SEROs.Explicit routes are encoded as follows:ERO = {H1,H2, H5,
H6}, SERO = {H2,L3,L4,H5}.
o H1 Sends Path message to the downstream node H2 with ERO =
{H2,H5,H6} and SERO = {H2,L3,L4,H5}.
o After H2 receivs the Path message from H1,H2 confirm that it is
the initiator of FA-LSP via the SERO,and extracts the complete
route of the FA-LSP.
o Then H2 starts the creation of FA-LSP , the route is H2,L3,L4,H5.
o After the creation of the FA-LSPGBP[not]the Higher-Layer LSP!_s
creation is to be continued. And the SERO in the Path message is
deleted..
3.2. Process of multiple FA-LSPs in multiple layers
Consider the following topology:
PCE
H1---H2 H7---H8
\ /
M3 M6
\ /
L4---L5
In this topology, from top to down, the network is divided into three
layers.
Then H1,H2,H7,H8 belong to the first layer. H2,M3,M6,H7 are the
nodes of the second layer, while M3,L4,L5,M6 belong to the third
layer. And, H2 and H7 are regions boundaries between the first layer
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and the second layer. M3 and M6 are region boundaries between the
second layer and the third layer.
The process of creating a LSP from H1 to H8 is as the following :
o H1 sends a route request to PCE, in the response message of route
request from PCE, the first-layer path's Explicit routes are
specified via the ERO. The first FA-LSP!_s Explicit routes are
specified via the first SERO. The second FA-LSP!_s Explicit
routes are specified via the SERO. Encoded as follows:ERO =
{H1,H2,H7,H8},SERO = {H2,M3,M6,H7},SERO={M3,L4,L5,M6}.
o H1 sends Path message to the downstream node H2,with ERO = {H2,H7,
H8}, SERO = {H2,M3,M6,H7},SERO={M3,L4,L5,M6}.
o After H2 receives the Path message from H1,H2 confirms that it is
the initiator of the second layer!_s FA-LSP via the first SERO,and
extracts the route of the second layer!_s FA-LSP. Then H2 starts
the creation of the first FA-LSP, the route is H2,M3,M6,H7. H2
sends a new Path message to M3 with ERO =
{M3,M6,H7},SERO={M3,L4,L5,M6}.
o After M3 receives the Path message from H2,M3 confirms that it is
the initiator of the third layer!_s FA-LSP via the second SERO.and
extracts the complete route of the third layer!_s FA-LSP. Then M3
starts the creation of the second FA-LSP, the route is
M3,L4,L5,M6.M3 sends another new Path message to L4 with
ERO={L4,L5,M6}.
o After the creation of the third layer!_s FA-LSP,the second layer
FA-LSP!_s creation is to be continued.And the second SERO in the
second Path message is deleted.
o After the creation of the second layer!_s FA-LSP,the first layer
LSP!_s creation is to be continued.And the first SERO in the first
Path message is deleted.
3.3. Process of multiple FA-LSPs in the same layer
Consider the following topology:
Consider the following topology:
PCE
H1---H2 H5---H6 H9---H10
\ / \ /
L3---L4 L7---- L8
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In this topology, the network is divided into two
layers.H1,H2,H5,H6,H9,H10 are the nodes of the first
layer.H2,L3,L4,H5,H6,L7,L8,H9 belong to the second layer,and H2,H5,H6
and H9 are regions' boundaries.
Creat a LSP from H1 to H10,the process is as the following:
o H1 sends a route request to PCE,in the response message of route
request from PCE, the first layer path Explicit routes are
specified via the ERO. The first FA-LSP!_s Explicit routes are
specified via the first SERO. The second FA-LSP!_s Explicit
routes are specified via the SERO. Encoded as follows: ERO =
{H1,H2,H5,H6,H9,H10}, SERO ={H2,L3,L4,H5},SERO={H6,L7,L8,H9}.
o H1 Sends Path message to the downstream node H2,with ERO = {H2,
H5, H6,H9,H10}, SERO = {H2,L3,L4,H5},SERO={H6,L7,L8,H9}
o After H2 receives the Path message from H1,H2 confirms that it is
the initiator of the second layer!_s first FA-LSP via the first
SERO,and extracts the route of the second layer!_s first FA-LSP.
Then H2 starts the creation of the first FA-LSP, the route is
H2,L3,L4,H5. H2 sends a new Path message to L3 with ERO =
{L3,L4,H5}.
o After the creation of the second layer!_s first FA-LSP,the first-
layer LSP!_s creation is to be continued.And the first SERO in the
Path message is deleted.
o After H6 receive the Path Message from H5,H6 confirm it is the
initiator of the second layer!_s second FA-LSP via the second SERO
and extracts the complete route of the second layer!_s second FA-
LSP. Then H6 starts the creation of the second FA-LSP, the route
is H6,L7,L8,H9.
o After the creation of the second FA-LSP,the first-layer LSP!_s
creation is to be continued.And the second SERO in the Path
message is deleted.
4. Updated Message Formats
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4.1. Updated PCEP Message Formats
The format of a PCRep message is as follows:
<PCRep Message> ::= <Common Header>
<response-list>
The format of the response-list is:
<response-list>::=<response>[<response-list>]
<response>::=<RP>
[<NO-PATH>]
[<attribute-list>]
[<path-list>]
<path-list>::=<path>[<path-list>]
<path>::= <ERO>[<sero-list>]<attribute-list>
The format of the sero-list is:
<sero-list> ::= <SERO>[<sero-list>]
<attribute-list>::= [<of-list>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>]
[<INTER-LAYER>]
[<SWITCH-LAYER>]
[<REQ-ADAP-CAP>]
<of-list>::=<OF>[<of-list>]
<metric-list>::=<METRIC>[<metric-list>]
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4.2. Updated RSVP Message Formats
The format of a Path message is as follows:
<Path Message> ::= <Common Header> [ <INTEGRITY> ]
[ [<MESSAGE_ID_ACK> | <MESSAGE_ID_NACK>] ... ]
[ <MESSAGE_ID> ]
<SESSION> <RSVP_HOP>
<TIME_VALUES>
[ <EXPLICIT_ROUTE> ]
<LABEL_REQUEST>
[ <PROTECTION> ]
[ <LABEL_SET> ... ]
[ <SESSION_ATTRIBUTE> ]
[ <NOTIFY_REQUEST> ]
[ <ADMIN_STATUS> ]
[<sero-list>]
[ <POLICY_DATA> ... ]
<sender descriptor>
<sero-list> ::= <SERO>[<sero-list>]
5. Security Considerations
This document has no requirement for a change to the security models
within PCEP and associated protocols.
6. IANA Considerations
6.1. SERO Object-Class in PCEP
SERO Object-Class is 25 (suggested value)
SERO Object-Type is 2 (suggested value).
6.2. SERO Object-Type in RSVP
SERO Object-Type is 3 (suggested value).
7. Acknowledgments
The RFC text was produced using Marshall Rose's xml2rfc tool.
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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.
[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
Xuefeng Lin
ZTE Corporation
12F,ZTE Plaza,No.19,Huayuan East Road,Haidian District
Beijing 100191
P.R.China
Phone: +8615901011821
Email: lin.xuefeng@zte.com.cn
URI: http://www.zte.com.cn/
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Gang Xie
ZTE Corporation
12F,ZTE Plaza,No.19,Huayuan East Road,Haidian District
Beijing 100191
P.R.China
Phone: +8613691280432
Email: xie.gang@zte.com.cn
Xiaoshan Xiang
ZTE Corporation
12F,ZTE Plaza,No.19,Huayuan East Road,Haidian District
Beijing 100191
P.R.China
Phone: +8613718525451
Email: xiang.xiaoshan@zte.com.cn
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/
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