Internet Draft 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. Guo et al. draft-guo-optical-mesh-ring-00.txt [Page 2] 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. Guo et al. draft-guo-optical-mesh-ring-00.txt [Page 4] 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. Guo et al. draft-guo-optical-mesh-ring-00.txt [Page 5] 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) Guo et al. draft-guo-optical-mesh-ring-00.txt [Page 6] 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 Guo et al. draft-guo-optical-mesh-ring-00.txt [Page 9]