One document matched: draft-guo-optical-mesh-ring-00.txt
Network Working Group Dan Guo, James Fu,
Internet Draft Leah Zhang, Nasir Ghani
Expiration Date: June 2001 Sorrento Networks
Hybrid Mesh-Ring Optical Networks and Their Routing
Information Distribution Using Opaque LSA
draft-guo-optical-mesh-ring-00.txt
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026 [1].
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or made obsolete by other
documents at any time. It is inappropriate to use Internet- Drafts
as reference material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
2. Abstract
Optical rings provide a simplified and robust mechanism for failure
protection and are extensively used in current tranport networks.
Recently, efforts are under the way to build optical mesh networks
due to the latter's connection flexibility and better network capa-
city utilization. We advocate an optical network topology of mixing
rings together with meshes, either by embedding rings into meshes or
by connecting rings with meshes. A mesh-ring network provides both
connection flexibility and robust failure protection.
This draft first briefly discusses the unique architecture of mesh-
ring networks. We then focus on defining new attributes and methods
for mesh-ring's topology discovery and routing information distribu-
tion. We utilize the IS-IS/OSPF Opaque LSA mechanism, defined in RFC
2370. Finally, we discuss our work in the context of MPLS traffic
engineering and network service restoration (failure protection).
Guo et al. draft-guo-optical-mesh-ring-00.txt [Page 1]
3. Introduction
In the past several years, a large number of optical rings are deployed
by telecomm operators. One of advantages for using optical rings is
their simplified and robust mechanism for failure protection. We see
rings will be extensively used in the future due to their protection
support and "self-healing" property.
Ring topology has some drawbacks, which motivates the emergence of
optical mesh networks. Optical meshes provide better connection flexi-
bility and network resource utilization. The management complexities
for meshed networks however are higher.
We foresee that the networks consisting of hybrid rings and meshes,
called mesh-rings, are of particular importance. This is because the
migration from rings to meshes will be a gradual process. Furthermore,
the merit debates between rings and meshes are not expected to be
conclusive.
Mesh-ring networks can be formed by either embedding rings into meshes
or by connecting rings with meshes. A mesh-ring network provides both
connection flexibility and robust failure protection. In particular, we
can leverage the rings' protection schemes, which have been standardized
and widely deployed.
It is anticipated that the hybrid mesh-ring network topology becomes
popular among service providers for the following reasons:
- Traditional SONET ring network operators like to start with the same
ring topology with the new devices. They want the optical rings to
preserve the SONET ring's reliabilty, i.e., UPSR and BLSR protection
mechanism.
- As new services emerge, the ring operators want to add some meshed
connections to offer new services. One economic way to do that is
to add additional ports in the ring nodes to form meshed connections
among the ring nodes. The network ends up with a hybrid ring and
mesh topology.
A hybrid mesh-ring topology network has some unique issues for network
control, provisioning, resources discovery and protection.
This draft first briefly discusses the unique architecture of mesh-ring
networks. We then focus on defining new attributes and methods for mesh-
ring's topology discovery and routing information distribution. Of
particular importance is the identifer for rings (ring ID). Different
type of rings are also introduced. We utilize the IS-IS/OSPF Opaque LSA
mechanism, defined in RFC 2370. Those new attributes will be used by the
routing algorithms for mesh-ring networks.
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We also briefly discuss our work in the context of MPLS traffic
engineering and network service restoration (failure protection).
4. Mesh-Ring Networks Architecture
4.1 Network Architecture Descriptions
A mesh-ring network is loosely defined as a network mixing rings with
meshes. There are many ways to form a hybrid mesh-ring network:
a. Mesh links are added to an optical ring. For example, in Fig.
1.a, the network operator decides to add a mesh link between
node W and node Y;
b. Multiple optical rings are connected by a mesh (see Fig. 1.b).
For example, two mesh links are added to connect ring R1 and
ring R2;
c. In a network with a mesh topology, we embed one or more rings.
For example, in Fig 1.c, we define two rings (A-B-C-D-I-H-A)
and (I-D-E-F-I). These embedded rings can be considered "virtual
rings." The links on rings are also part of the mesh network.
__ +-+__ __+-+_______________+-+__ +-+ +-+ +-+
/ |X| \ / |X|___ ___|B| \ |A|--|B|--|C|
/ +-+ \ / +-+ \ / +-+ \ +-+ +-+ +-+
+-+ +-+ +-+ +-+ +-+ +-+ | |
|W|-------- |Y| |W| R1 |Y| |A| R2 |C| +-+ +-+ +-+
+-+ +-+ +-+ +-+ +-+ +-+ |H|--|I|--|D|
\ / \ / \ / +-+ +-+ +-+
\ +-+ / \ +-+___/ \___+-+ / | | |
-- |Z|--/ -- |Z|---------------|D|--/ +-+ +-+ +-+
+-+ +-+ +-+ |G|--|F|--|E|
+-+ +-+ +-+
Fig 1.a. Fig. 1. b. Fig. 1.c
Each of the optical rings in a mesh-ring network is considered as a
routing entity, with a unique ring identifier (Ring ID). For the
protection purpose, we need classify rings into different types -
bidirectional wavelength path switched ring (BWPSR), uni-directional
path-switched rings (UPSR) or bi-directional line-switched rings (BLSR).
More types will be introduced in the future (see [GHANI] for details).
Guo et al. draft-guo-optical-mesh-ring-00.txt [Page 3]
4.2 Routing Considerations in the hybrid mesh-ring networks
The hybrid mesh-ring topology has unique constraints and requirement
for resource discovery and maintenance as well as for lightpath
routing and signalling.
- We need differentiate links in a ring from links in a mesh. Certain
traffic such as voice traffic may desire to travel along the ring
topology due to its better protection capability;
- We need an automatic and efficient way to manage and provision
traffic across multiple rings.
5. Opaque LSA for Mesh-Ring Optical Networks
In this section, we describe the enhancements to IS-IS/OSPF in
support of hybrid mesh-ring networks. These are in addition to
the previous extensions:
- for supporting the MPLS traffic engineering ([OSPF-TE], [ISIS-TE]);
- for supporting MPL(ambda)S & optical routing ([KOMPELLA], [WANG]).
In particular, our LSA format follows closely the description in
[OSPF-TE], a de-facto standard.
5.1 LSA Type
This draft makes use of the Opaque LSA [OSPF-Opaque] (RFC2370).
Opaque LSAs are introduced as a means of distributing additional
OSPF routing information. Three types of Opaque LSA exist:
Type 9: link-local scope
Type 10: area-local scope
Type 11: Autonomous System (AS) scope
We use only Type 10 LSAs for area flooding scope.
5.2 LSA Header
In Opaque LSAs, the payload of the LSA could contain information that
has meaning only within a certain application and will be ignored
otherwise. The type of the application is identified by the Opaque
Type, contained in the LSA ID.
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The LSA ID of an Opaque LSA is defined as having eight bits of opaque
type and 24 bits of type-specific data. The new Opaque type number for
mesh-rings is TDB. The remaining 24 bits are broken up into eight bits
of reserved space (which must be zero) and sixteen bits of instance. A
maximum of 65536 LSAs may be sourced by a single node.
The new LSA for mesh-ring optical networks starts with the LSA header:
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 10 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBD | Reserved | Instance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Node ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.3 New Opaque LSA Payload
The LSA payload consists of one or more nested Type/Length/Value
(TLV) triplets for extensibility. They are used in path computation
algorithm to compute optical paths in the mesh-ring optical networks.
The format of each TLV is:
0 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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The new opaque LSA describe the nodes and links in a mesh-ring
networks. We define two top-level TLVs: Optical Node TLV and Link TLV.
5.3.1 Optical Node TLV
The optical node TLV specifies a stable IP address of the advertising
node that is always reachable if there is any connectivity to it. This
is typically implemented as a "loopback address." The optical node TLV
also indicates the wavelength conversion capability and regeneration
capability of node.
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The node TLV is type 1, and the length is variable.
The following sub-TLVs are defined:
1 - IP address (4 octets) (mandatory)
2 - Wavelength conversion capability (1 octet) (mandatory)
5.3.1.1 Wavelength Conversion Capability
The wavelength conversion capability sub-TLV indicates whether the node
is wavelength conversion capable: no wavelength conversion, full
wavelength conversion, or partial wavelength conversion (indicates
percentage).
The wavelength conversion capability sub-TLV is TLV type 2, and is one
octet long. It is mandatory.
00000000 no wavelength conversion
01100100 full wavelength conversion (100 percent)
00011001 partial wavelength conversion (25 percent)
5.3.2 Link TLV
Link TLV describes a single unidirectional link. The link TLV is type 2,
the length is variable. It is constructed as a set of sub-TLVs. There
are no ordering requirements for the sub-TLVs.
The following sub-TLVs are defined:
1 - Link type (1 octet)
2 - Link ID (4 octets)
3 - Local interface IP address (4 octets)
4 - Remote interface IP address (4 octets)
5 - Available link resource information
6 - Ring type and ID (4 octets)
7 - Shared Link Risk Group ID (4 octets)
In [OSPF-TE] and [WANG], many sub-TLVs are described. Here, we put our
emphasis on new sub-TLVs unique to the hybrid mesh-ring optical networks.
5.3.2.1 Link Type
Link type sub-TLV defines the type of the link (as describe in [WANG]):
3 - Service transparent (a point to point physical optical link)
4 - Service aware (a point to point logical optical link)
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By using this link type, we can represent both physical and logical
link and their connection type in optical domain.
5.3.2.2 Link ID
The Link ID sub-TLV identifies the optical link exactly as the
point to point case in [OSPF-TE].
5.3.2.3 Local and Remote Interface IP Addresses
The local interface IP address sub-TLV specifies the IP address of
the interface corresponding to this link. The remote interface IP
address sub-TLV specifies the IP address of the neighbor's interface
corresponding to this link. This and the local address are used to
discern multiple parallel links between two nodes.
5.3.2.4 Available Link Resource Information
Refer to [WANG] for descriptions.
5.3.2.5 Ring type and ID:
When a link belongs to a ring, a Ring sub-TLV is added. The Ring sub-TLV
is TLV type 6, and has four octets in length.
The first 8 bits represents the ring type (eg. BWPSR, BLSR, UPSR, etc).
The other 24 bits identifies a ring. This field is called Ring ID that
is unique within an IGP domain.
0 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 | Ring ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Ring sub-TLV is optional. For a link not belonging to a ring, it is
omitted. A link may belong to multiple rings, in which cases multiple
ring sub-TLVs are included.
5.3.2.6 Shared Link Risk Group
The shared link risk group sub-TLV specifies group membership for
"shared risk link group" (SRLG). A set of links may constitute a "shared
risk link group" if they share a resource whose failure may affect all
links in the set. An example would be two fibers in the same conduit.
Also, a link may be part of more than one SRLG. Refer to [KOMPELLA] for
more descriptions.
Guo et al. draft-guo-optical-mesh-ring-00.txt [Page 7]
6. Routing and Signaling Requirement for Mesh-Ring Networks
New opaque LSAs are subsequently used by the constrainted shortest path
first (CSPF) algorithm. It may be desireable for network operators to
specify the type of light path from a source to a destination:
- Path P passes a BWPSR ring, or
- Path P passes a BLSR ring, or
- Path P passes a UPSR ring;
Exactly how the CSPF algorithm incorporates the information contained in
new opaque LSAs is proprietary in nature and beyond this document.
After obtaining an explicit lightpath from a source to a destination, we
use GMPLS [GMPLS] to provision this lightpath. When setting up a light
path in RSVP-TE or CR-LDP, we may treat a ring as an abstract node. More
treatments will follow in this area.
7. Failure Protection for Mesh-Ring Networks
There are clearly advantages in supporting failure protection by
identifying the rings in a hybrid mesh-ring network. A ring can provide
fast re-route with little signalling overheads. Existing SONET protection
schemes can be extended for this purpose [SONET-APS] and more details
can be found in [GHANI]. This topic deserves more detailed treatment, due
to its primary importance.
8. Security Considerations
There is no known security problem caused by this draft.
9. Acknowledgements
We would like to thank Yangguang Xu of Lucent Technology for the
insightful discussion and John Moy of Sycamore Networks for his
comments and encouragement. We are also grateful to Frank Barnes
for the careful review.
10. References
[OSPF] J. Moy, OSPF Version 2. (RFC 2328)
[OSPF-Opaque] R. Coltun, The OSPF Opaque LSA Option. (RFC 2370)
[GMPLS] Ashwood-Smith, P. et al, "Generalized MPLS -
Signaling Functional Description", Internet Draft,
draft-ietf-mpls-generalized-signaling-01.txt,
November 2000.
Guo et al. draft-guo-optical-mesh-ring-00.txt [Page 8]
[GHANI] N. Ghani, J. Fu, Z. Zhang, X. Liu, D. Guo, "Optical Rings,"
work in progress (draft to be submitted), December 2000.
[TE-REQ] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
McManus, "Requirements for Traffic Engineering Over MPLS", RFC
2702, September 1999.
[ISIS-TE] Smit, H., Li, T., "IS-IS extensions for Traffic
Engineering", draft-ietf-isis-traffic-01.txt (work in progress)
[OSPF-TE] Katz, D., Yeung, D., "Traffic Engineering Extensions to
OSPF", draft-katz-yeung-ospf-traffic-01.txt (work in progress)
[SONET-APS] Gorshe, S., Revised Draft T105.01 SONET Automatic
Protection Switching Standard, April 1999.
[KOMPELLA] Kompella, K., et al, Extensions to IS-IS/OSPF and RSVP in
support of MPL(ambda)S, draft-kompella-mpls-optical-00.txt, August
2000.
[MCADAMS] McAdams, L. and Yates, J., Lightpath attributes and related
service definitionsdraft-mcadams-lightpath-attributes-00.txt,
September, 2000.
[WANG] Wang, G., et al., "Extensions to OSPF/IS-IS for Optical Routing",
Internet Draft, draft-wang-ospf-isis-lambda-te-routing-00.txt,
Work in Progress, March 2000.
11. Authors' Addresses
Dan Guo James Fu
Sorrento Networks, Inc. Sorrento Networks, Inc.
9990 Mesa Rim 9990 Mesa Rim
San Diego, CA 92121 San Diego, CA 92121
Email: dguo@sorrentonet.com Email: jfu@sorrentonet.com
Leah Zhang Nasir Ghani
Sorrento Networks, Inc. Sorrento Networks, Inc.
9990 Mesa Rim 9990 Mesa Rim
San Diego, CA 92121 San Diego, CA 92121
Email: leahz@sorrentonet.com Email: nghani@sorrentonet.com
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