Network Working Group Qilei Wang Internet-Draft Xihua Fu Intended status: Standards Track ZTE Corporation Expires: April 25, 2013 Oct 22, 2012 RSVP-TE Extensions for GMPLS control of Spectrum Switched Optical Networks (SSONs) draft-wang-ccamp-gmpls-sson-rsvpte-02.txt Abstract A new architecture of optical transport networks which is addressed in the newest version of G.872 is being developed in ITU-T SG15. Compared with previous G.872 technology, this new technology allows the switch of large chunk of contiguous spectrum which may be wider than the spectrum occupied by a single optical channel signal. Since current control plane technology isn't able to control this kind of application, this document describes the signaling extension to support the control of this kind of new spectrum utilization and implementation way. This document also addresses the interworking between WSON optical channel and SSON (Spectrum Switched Optical Network) optical channel. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted 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." This Internet-Draft will expire on April 25, 2013. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Qilei Wang & Xihua Fu Expires April 25, 2013 [Page 1] Internet-Draft Spectrum Switched Optical Network Oct 2012 Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Requirements and Modeling of SSON . . . . . . . . . . . . . . 5 3.1. Hierarchy between Optical Channel and Media Channel . . . 5 3.2. Switching Type . . . . . . . . . . . . . . . . . . . . . . 6 3.3. Media Channel . . . . . . . . . . . . . . . . . . . . . . 6 3.3.1. Label Format . . . . . . . . . . . . . . . . . . . . . 6 3.3.2. Traffic Parameters . . . . . . . . . . . . . . . . . . 6 3.3.3. Grid Attributes of Forwarding Adjacency . . . . . . . 7 3.4. Optical Channel . . . . . . . . . . . . . . . . . . . . . 7 3.4.1. Overview of Flexible Grid and Fixed Grid . . . . . . . 7 3.4.2. Interwork between WSON OCh signal and SSON OCh signal . . . . . . . . . . . . . . . . . . . . . . . . 7 4. Signaling Protocol Extensions to Support Control of Media Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1. Switching Type . . . . . . . . . . . . . . . . . . . . . . 9 4.2. Label Format Extensions of Media Channel Layer . . . . . . 9 4.3. Traffic Parameters of Media Channel Layer . . . . . . . . 10 5. Signaling Procedures . . . . . . . . . . . . . . . . . . . . . 10 5.1. RSVP-TE Signaling Procedures to Support the Setup of Frequency Slot Channel . . . . . . . . . . . . . . . . . . 10 5.1.1. Centralized Spectrum Assignment . . . . . . . . . . . 10 5.1.2. Distributed Spectrum Assignment . . . . . . . . . . . 10 5.2. Interwork between WSON signal and SSON signal . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.1. Normative References . . . . . . . . . . . . . . . . . . . 13 7.2. Informative References . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 Qilei Wang & Xihua Fu Expires April 25, 2013 [Page 2] Internet-Draft Spectrum Switched Optical Network Oct 2012 1. Introduction In the newest version of G.872, a new kind of spectrum utilization and implementation way is introduced to current optical network. A new kind of entity called media channel which is similar to LSP is introduced. According to the description in [G.872v16], the media channel is a topological construct that represents both the path through the media and the resource (frequency slot) that it occupies. A media channel is bounded by ports on media elements. A media channel may be dimensioned to carry more than one OCh-P signal. That is to say, a chunk of contiguous spectrum which can be occupied by a group of optical channels can be forwarded via wide-band filters as a whole without filtering and switching everything down to the individual OCh (Optical Channel) level in long-haul systems. Compared with narrowband, wideband filters and switching has many advantages, for example, building OCh Signals for management convenience, maximizing the reach and traversing more nodes. Following is the description taken from [G.872v16], "below the OCh, the entities that provide for configuration of the media channels are described separately from the entities that provide management of the collections of the OCh-P signals that traverse the media". According to the description, we can conclude that the containment relationship exists between media channels and OCh signals, and the containment relationship should be announced to the source and end nodes of the media channels. Intermediate nodes are unnecessary to know the containment relationship because the media channel can be switched as a whole without filtering and switching everything down to individual OCh level. Two kinds of entities which are spectrum configuration entity and signal management entity should be provide by nodes creating media channels from the perspective of control plane. Note: Optical channels switched in a media channel may have different spectrum bandwidth. From the perspective of management plane and control plane, containment relationship indicates that hierarchy exists between the media channel and optical channel. GMPLS protocol are needed to extent to help manage this kind of spectrum utilization and implementation way. This document first describes the coexistence of media channel and optical channel, then the layer model base on the hierarchy between optical channels (OCh) and media channel from management plane or control plane perspective and defines signaling protocol extension to support the control of media channel. As the flexible grid framework document describes both the media channel and optical channel, this document also give a detail description about Qilei Wang & Xihua Fu Expires April 25, 2013 [Page 3] Internet-Draft Spectrum Switched Optical Network Oct 2012 the interworking between WSON optical channel and SSON (Spectrum Switched Optical Network) optical channel. 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]. 2. Terminology o Frequency slot: As defined by Q6 in clause 3.1.2 of G.694.1, a frequency slot is a frequency range which is allocated to a slot and unavailable to other slots within a flexible grid. A frequency slot is defined by its nominal central frequency and its slot width. Detailed description can be found in the framework document. o Media channel: as defined in [G.872v16], media channel is used to indicate a media association that represents both the topology (i.e., the path through the media) and the resource (frequency slot) that it occupies. A media channel is bounded by ports on media elements and can span any combination of network elements and fibers. o Effective frequency slot: The effective frequency slot of a media channel is that part of the frequency slots of the filters along the media channel that is common to all of the filters' frequency slots. It is described by its nominal central frequency and its slot width. o Nominal central frequency (of a frequency slot) - as used by Q6/ SG15 in G.694.1. This parameter is associated with a grid position on the fixed grid and a slot in the flexible grid. o Network media channel: The end-to-end channel allocated to transport a single OCh payload signal is called a network media channel and supports a single OCh payload network connection. o SSON: Spectrum-Switched Optical Network. This concept and definition is introduced from the framework document. An optical network in which a data plane connection is switched based on an optical spectrum frequency slot of a variable slot width, rather than based on a fixed grid and fixed slot width. Qilei Wang & Xihua Fu Expires April 25, 2013 [Page 4] Internet-Draft Spectrum Switched Optical Network Oct 2012 3. Requirements and Modeling of SSON 3.1. Hierarchy between Optical Channel and Media Channel Spectrum may be allocated in larger and contiguous piece than spectrum occupied by a single optical channel which is called Frequency Slot. The frequency slot is described by its nominal central frequency and its slot width [ITU-T G.694.1]. The media Channel is a topological construct that represents both the path through the media and the resource (frequency slot) that it occupies. A media channel is bounded by ports on media elements and can span any combination of network elements and fibers, while the frequency slot is a local concept, while the media channel has an end-to-end meaning. A media channel may be dimensioned to carry more than one OCh P signal. Network media channel is a specific type of media channel which can only be used to transport a single OCh signal and support a single OCh connection. From the perspective of control plane or management plane, hierarchy exists between media channel and optical channel, as media channel can be used to transport optical channel signals. During the process of path setup, containment relationship between optical channel signal and media channel should be conveyed through signaling and announced to source node and end node in order to help group and detach optical channel signals from one another. Dependency relationship needs to be explicitly told. Notes: no hierarchy exists in either media channels or optical channels. Media channels can be switched in a media Matrix. The media channel matrix provides flexible connectivity for the media channels. Media ports at the edge of a media channel matrix may be created and broken to help route media channel path. Media channel connection will limit the connectivity of optical channel signals over the network element within the frequency slot. Media channel matrixes are not mandatory to have the function of optical channel matrix as signals in the media channel can be switched as a whole. In the case where the switching granularity of the media Matrix allows for independent switching of each OCh, it can be decided as a matter of policy that a request to establish an OCh connection will, internal to the NE, establish a network media channel Matrix Connection of the same spectrum slot width, and the network media Matrix Connection can be released when the OCh connection is released. As more than one optical channel signal can be carried in a media Qilei Wang & Xihua Fu Expires April 25, 2013 [Page 5] Internet-Draft Spectrum Switched Optical Network Oct 2012 channel, notion of hierarchy exists between them. current optical transport network can be modeled into two layers and managed independently from the perspective of management, one is optical channel layer and the other is media layer. Optical channel layer can be modeled as higher layer and media channel layer can be modeled as lower layer. Media layer LSP created in high layer appear as a data link in optical channel layer. One or more optical channel LSPs can be nested into media channel LSP. That is to say, media channel LSP appears as a H-LSP in the higher layer optical channel LSP. As a kind of resource, spectrum allows for the utilization by both optical channel layer and media layer. It's not necessary to setup media LSP first before the setup of OCh LSP. Coexistence of OCh and media channel in the same link is permitted. 3.2. Switching Type Switching type can be used to indicate the type of switching that should be performed on a particular link. According to the modeling in the previous section, a new switching type should be defined to indicate the switching capability of media channel layer. 3.3. Media Channel 3.3.1. Label Format Section 3.3 of [RFC3471] defines waveband switching: "A waveband represents a set of contiguous wavelengths which can be switched together to a new waveband". This is similar to the media channel switching, because they both switch multiple wavelengths or spectrum as a unit. But the wavelength label defined in [RFC3471] only has significance between neighbors, in order to control the setup and release of media channel with RSVP-TE signaling, a new media channel label which has definite information of nominal central frequency and slot width of the spectrum is needed. This chunk of spectrum can be used for subsequent setup of optical channel path. 3.3.2. Traffic Parameters In current network, like MPLS network, OTN network, signaling can be used to reserve bandwidth (i.e., bitrates) at each node along the path when set up LSPs. The bandwidth information describes the end- to-end traffic characteristic of a LSP, so the signaling SHOULD be able to carry bandwidth information that a LSP need to occupy. In the process of the setup of media channel, the most critical Qilei Wang & Xihua Fu Expires April 25, 2013 [Page 6] Internet-Draft Spectrum Switched Optical Network Oct 2012 traffic characteristic of a media channel LSP is spectrum, i.e., the spectrum width that a LSP can occupy. For example, if a third party wants to manage and operate a chunk of spectrum by itself, carrier could use the signaling to set up a media channel with a specific spectrum width to satisfy the requirement. Carrier doesn't care how this spectrum can be used by the party and how many data this chunk of spectrum can bear. So when we use signaling to set up a media channel, spectrum resource information (i.e.,spectrum width) should be carried in the signaling to reserve the spectrum resource along the path. 3.3.3. Grid Attributes of Forwarding Adjacency Media matrix connection may interconnect one or more media channels, which in turn may carry one or more OCh signals. In the case the media matrix just allow the switching of spectrum as a whole, internal flexible grid or fixed grid attributes are unnecessary to be known by the forwarding adjacency end points. 3.4. Optical Channel [Notes: This section mainly addresses the current status of optical channel interconnection, including interconnection between WSON optical channel signal and SSON optical channel signal.] 3.4.1. Overview of Flexible Grid and Fixed Grid Fixed grid signals have fixed slot width (e.g., 50GHz), while flexible grid signals allow different slot widths (e.g., 50GHz, 87.5GHz).GMPLS and PCE control of fixed grid network (i.e., WSON, Wavelength Switched Optical Network) is close to mature in IETF CCAMP, while flexible grid control plane technology is still being developed in IETF. This section mainly focuses on the interconnection between WSON optical channel signal and SSON optical channel signal. 3.4.2. Interwork between WSON OCh signal and SSON OCh signal Some open issues are listed in the recent flexible grid framework document and still need to be resolved if we want to push the framework document forward. Part of these issues which may have relation to the interwork between SSON and WSON are listed here: 1). If a new switching capability is needed to represent SSON optical channel layer? 2). Potential problems with having the same switching capability but the label format changes compared with WSON optical channel layer. Qilei Wang & Xihua Fu Expires April 25, 2013 [Page 7] Internet-Draft Spectrum Switched Optical Network Oct 2012 3). Role of LSP encoding type? I think the issue listed here intends to say if a new LSP encoding type is needed for flexible grid optical channel layer. 4). Notion of hierarchy? There is no notion of hierarchy between flexible grid OCh and fixed grid OCh. Just from my perspective, I think SSON optical channel layer should use the same switching capability as WSON optical channel layer. Some words are given here to describe my opinion. A LSP which has a bandwidth of 50GHz pass through both WSON network and SSON network. We assume that no OEOs exist in the LSP, so both the WSON optical channel path and SSON optical channel path occupy 50GHz. From the perspective of data plane, there is no change of the signal and no multiplexing when the WSON optical channel path interconnects with SSON optical channel path. From this scenario we can conclude that both WSON optical channel layer and SSON optical channel layer belong to the same layer. No notion of hierarchy exists between them. Base on these words, I think both WSON optical channel layer and SSON optical channel layer should use the same switching capability. The previous words mention the issues 1) and 4). Another two issues are to be discussed in the following description in the process of path setup. Because there is no notion of hierarchy exists between WSON optical channel layer and SSON optical channel layer, hierarchy LSP which is addressed in [RFC4206] and [RFC6107] can't be applied. But stitching LSP which is described in [RFC5150] can be applied in one layer. LSP hierarchy allows more than one LSP to be mapped to an H-LSP, but in case of S-LSP, at most one LSP may be associated with an S-LSP. This is similar to the scenario of interconnection between WSON OCh LSP and SSON OCh LSP. Similar to an H-LSP, an S-LSP could be managed and advertised, although it is not required, as a TE link, either in the same TE domain as it was provisioned or a different one. Path setup procedure of stitching LSP can be applied in the scenario of interconnection between WSON optical channel path and SSON optical channel path. 4. Signaling Protocol Extensions to Support Control of Media Layer This section mainly addresses the signaling protocol extension in order to support the control of spectrum-switched optical network media layer and the facilitating of the setup of forwarding adjacency in G.872 optical transport network. Qilei Wang & Xihua Fu Expires April 25, 2013 [Page 8] Internet-Draft Spectrum Switched Optical Network Oct 2012 4.1. Switching Type A new switching type is defined here for media channel layer. Value Type ------- ------- XX(IANA) Media Channel Switched Capable (MCSC) Figure 1: Switching Capability 4.2. Label Format Extensions of Media Channel Layer According to the description in the section 3.2, label should be able to describe the frequency slot characteristic in order to facilitate the switch of this large piece of spectrum. Label format of flexible grid can be introduced here to depict the label of media channel. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Grid | C.S. | Identifier | n | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | m | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: label Grid Type: 3. A new grid value to support flexible grid. The meaning of C.S. and identifier is maintained from [RFC6205] and [draft-farrkingel-ccamp-flexigrid-lambda-label]. Similar to the definition in [draft-farrkingel-ccamp-flexigrid-lambda-label], n is used to identify the nominal central frequency, and m (16bits) is used to identify slot width of the media channel. [Notes: here we use 16 bits to represent the "m" value, because 8 bits maybe not enough for the setup of media channel with large chunk of spectrum. This document is different from current flexible grid document in CCAMP because of different model way.] Qilei Wang & Xihua Fu Expires April 25, 2013 [Page 9] Internet-Draft Spectrum Switched Optical Network Oct 2012 4.3. Traffic Parameters of Media Channel Layer Similar to the original signaling which carry the information of Bandwidth (i.e., bitrates) that a LSP may reserve at each node along the path, signaling that is used to set up media channel SHOULD be able to carry the information of spectrum width. The spectrum width traffic parameters can be organized as follow, and this information is carried in the Sender_Tspec object within a path message. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | m | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: traffic parameter m (16 bits): the spectrum width is specified by m*12.5 GHz. 5. Signaling Procedures 5.1. RSVP-TE Signaling Procedures to Support the Setup of Frequency Slot Channel 5.1.1. Centralized Spectrum Assignment In this case, both of the route and the frequency slot information (i.e., central frequency and spectrum width) are provided by the PCE or ingress node. When signaling a LSP, the assigned label information is carried in the ERO label sub-object which is addressed in [RFC3473]. When the nodes along the LSP receive the path message carrying the ERO and ERO label sub-object, the procedure of path setup is the same as the procedure which is described in [RFC3473] and [RFC4003]. RRO and RRO label sub-object are used to record the label information of the egress. 5.1.2. Distributed Spectrum Assignment In this case, only the route is provided by a PCE or ingress node before the signaling procedure. The available spectrum SHALL be collected hop by hop and the egress node SHOULD select a proper label for the LSP. After the route is computed, the ingress node SHOULD find out the available spectrum for the LSP on the next link of the route. Qilei Wang & Xihua Fu Expires April 25, 2013 [Page 10] Internet-Draft Spectrum Switched Optical Network Oct 2012 Then a path message is sent to the next node along the path according to the route information. The path message MUST contain a Sender_Tspec object to specify the spectrum width of the media channel. A Label_set object SHALL be added to the path message, which contains the candidate available spectrum for the LSP on the next link. When an intermediate node receives the path message, it can deserve the spectrum width information from the Sender_Tspec object. Then it SHOULD find the available spectrum for the LSP on the next link of the route similar to the ingress node. The common part of the two available spectrum sets. If the new set is null, the path message SHALL be rejected by a patherr message. Otherwise, the Label_set object in the path message SHALL be updated according to the new set and the path message is forwarded to the next node according to the route. When an egress node receives a path message, it SHOULD select an available spectrum from the Label_set object based on local policy and determine the media channel base on the spectrum width and the available spectrum. Then a Resv message is responded so that the nodes along the LSP can establish the optical cross-connect based on the Label object which is determined by the spectrum width in the traffic parameters and the available spectrum in the Label_set object. 5.2. Interwork between WSON signal and SSON signal The path setup procedure of WSON OCh signal's interworking with SSON OCh signal is described as follows: Let's take the following network into consideration. e2e LSP +++++++++++++++++++++++++++++++++++> (LSP1-2) LSP segment (flexi-LSP) ====================> (LSP-AB) C --- E --- G /|\ | / |\ / | \ | / | \ R1 ---- A \ | \ | / | / B --- R2 \| \ |/ |/ D --- F --- H fixed grid --A-- flexi-grid --B-- fixed grid Qilei Wang & Xihua Fu Expires April 25, 2013 [Page 11] Internet-Draft Spectrum Switched Optical Network Oct 2012 Figure 4: Interworking between WSON OCh and SSON OCh In this scenario, R1 and R2 are traditional WSON signal capable nodes, A and B are both WSON optical channel signal and SSON optical channel signal capable nodes, the other nodes are SSON optical channel capable nodes. We assume that a 40Gbit/s LSP from R1 to R2 needs to be set up. Node R1 prepares signaling path message for the end-to-end path setup from R1 to the destination node R2. Before R1 sends path message, R1 should fist send a path computation request to the path computation element in order to compute an end-to-end path from R1 to R2. After path computation, PCRep message which contains ERO and label information is send back to R1 from PCE. R1 encapsulates the path message which contains ERO to explicitly indicate the path and label used and RRO to record the path traversed and label used by node traversed. Then R1 sends the path message to the next hop node A. Here we assume path computation element is capable of fixed grid and flexible grid path computation, and the ERO contain the path information (R1, A, B, R2). When the path message arrives at node A, node A verifies the path message and finds incomplete ERO information, then send another path computation request message to the PCE in order to obtain the whole path information. PCE sends path computation response message which contain ERO (A, D, F, H, B) and label information. Here the label is flexible label information which is addressed in [draft-farrkingel]. To facilitate the control of stitching LSP boundaries, we may use a different encoding type for flexible grid to help control. Encoding type can be used to help stitching LSP boundaries control. Stitching LSP boundaries control looks like FA-LSP boundaries control, but has many differences. After matching the switching type and encoding type of the interface, Node A blocks the signaling process and decides to set up a stitching LSP according to the flexible grid LSP setup procedure using another signaling process. Procedure for set up stitching LSP can be found in RFC5150. The stitching LSP can be seen as a TE link in the fixed grid network. After the setup of stitching LSP between A and B, A then continues the blocking signaling procedure and sends the path message to the next hop B directly and finishes the end-to-end LSP. In this scenario of interconnection between WSON OCh and SSON OCh, dynamic stitching LSP setup is frequent, static stitching LSP configuration may not be needed here. Qilei Wang & Xihua Fu Expires April 25, 2013 [Page 12] Internet-Draft Spectrum Switched Optical Network Oct 2012 6. Security Considerations TBD 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching (GMPLS) Architecture", RFC 3945, October 2004. 7.2. Informative References [G.694.1 v6] International Telecommunications Union, "Draft revised G.694.1 version 1.6". [G.872 v16] International Telecommunications Union, "Draft revised Recommendation ITU-T G.872". [flexible-grid-ospf-ext] Fatai Zhang, Xiaobing Zi, Ramon Casellas, O. Gonzalez de Dios, and D. Ceccarelli, "GMPLS OSPF-TE Extensions in support of Flexible-Grid in DWDM Networks", draft-zhang-ccamp-flexible-grid-ospf-ext-00.txt . [flexible-grid-requirements] Fatai Zhang, Xiaobing Zi, O. Gonzalez de Dios, and Ramon Casellas, "Requirements for GMPLS Control of Flexible Grids", draft-zhang-ccamp-flexible-grid-requirements-01.txt . [flexigrid-lambda-label] D. King, A. Farrel, Y. Li, F. Zhang, and R. Casellas, "Generalized Labels for the Flexi-Grid in Lambda-Switch- Capable (LSC) Label Switching Routers", draft-farrkingel-ccamp-flexigrid-lambda-label-01.txt . [ospf-ext-constraint-flexi-grid] L Wang, Y Li, "OSPF Extensions for Routing Constraint Encoding in Flexible-Grid Networks", draft-wangl-ccamp-ospf-ext-constraint-flexi-grid-00.txt . Qilei Wang & Xihua Fu Expires April 25, 2013 [Page 13] Internet-Draft Spectrum Switched Optical Network Oct 2012 Authors' Addresses Qilei Wang ZTE Corporation Email: wang.qilei@zte.com.cn Xihua Fu ZTE Corporation ZTE Plaza, No.10, Tangyan South Road, Gaoxin District Xi'an P.R.China Email: fu.xihua@zte.com.cn Qilei Wang & Xihua Fu Expires April 25, 2013 [Page 14]