Network Working Group Y. Li Internet-Draft F. Zhang Intended status: Standards Track ZTE Expires: January 5, 2012 R. Casellas CTTC July 4, 2011 Flexible Grid Label Format in Wavelength Switched Optical Network draft-li-ccamp-flexible-grid-label-00 Abstract Flexible grid is regarded as an efficient way to improve the network capacity utilization. Mixed bit rate transmission systems can allocate their channel with different spectral bandwidths so that they can be optimized for the bandwidth requirements of the particular bit rate and modulation scheme of the individual channels. To support the flexible grid technique, this document extends the wavelength label to accommodate this new specification. It is demonstrated that the extended label format is compatible to the rigid one and can be used in the routing and signaling procedure in the Wavelength Switched Optical Network (WSON). 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 January 5, 2012. Copyright Notice Copyright (c) 2011 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 Provisions Relating to IETF Documents Li, et al. Expires January 5, 2012 [Page 1] Internet-Draft Flexible grid label July 2011 (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 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Label format . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Label values . . . . . . . . . . . . . . . . . . . . . . . 4 3.2. Flexible Label . . . . . . . . . . . . . . . . . . . . . . 5 4. Flexible label applications . . . . . . . . . . . . . . . . . 7 4.1. Application for Routing . . . . . . . . . . . . . . . . . 7 4.2. Applications for Signaling . . . . . . . . . . . . . . . . 8 4.3. Applications for PCE . . . . . . . . . . . . . . . . . . . 8 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 8.1. Normative references . . . . . . . . . . . . . . . . . . . 9 8.2. Informative References . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Li, et al. Expires January 5, 2012 [Page 2] Internet-Draft Flexible grid label July 2011 1. Introduction Dense Wavelength Division Multiplexing (DWDM) optical network is widely deployed by telecom operators to carry their data service. With the continuing exponential growth of internet traffic, more efficient utilization of optical network bandwidth for extremely high data rates is required. Although multi-level modulation formats and advanced photonics techniques have enabled 100 G/s transmission within a 50 GHz DWDM fixed gird (or channel spacing), much higher speed traffic, such as 400 Gbit/s and 1 Tbit/s signals are not expected to adapt such a narrow channel. So a wider fixed grid like 100 GHz spacing is required to enable these new transmission formats without inter-channel crosstalk. However, the total available spectrum resource of the specific band is limited (about 4.4 THz in C band). If a wider grid is chosen, the fewer wavelengths can be allocated to carry the data. Not to mention that some low bitrate signals will occupy too much spectral bandwidth so that the total utilization efficiency of the spectrum resource is relatively low. The recent revision of ITU-T Recommendation [G.694.1] has decided to introduce the flexible grid DWDM technique which provide a new tool that operators can implement to provide a higher degree of network optimization than fixed grid systems. Flexible grid network is composed of arbitrarily assigned spectral slices. That means in such networks the adjacent channel spacing and assigned spectral bandwidth per wavelength are variable. Mixed bitrate transmission systems can allocate their channel with different spectral bandwidths so that they can be optimized for the bandwidth requirements of the particular bit rate and modulation scheme of the individual channels. This technique is regarded to be a promising way to improve the network utilization efficiency and fundamentally reduce the cost of the IP core network. Based on the DWDM technique, Wavelength Switched Optical Network (WSON) uses the control plane to dynamically provide Label Switched Paths (LSPs) for the requested end to end connections. The label switching is performed selectively on wavelength label representing the center wavelength/frequency of the optical signal. To support the flexible grid technique, this document extends the wavelength label defined in [RFC6205] to accommodate the new specification. It is proved that the extended label format is compatible to the rigid one and can be used in the routing and signaling procedure in WSON and generic GMPLS network. 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", Li, et al. Expires January 5, 2012 [Page 3] Internet-Draft Flexible grid label July 2011 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 3. Label format 3.1. Label values The wavelength label format is defined in [RFC6205] and the corresponding wavelength or frequency value is referred to ITU-T Recommendations [G.694.1] and [G.694.2] for DWDM and CWDM grid respectively. The ITU-T fixed grid is based on nominal center frequency/wavelength. For DWDM system, the nominal center frequency is calculated as: Frequency (THz)=193.1 THz+n* channel spacing In the context of rigid grid, the channel spacing of DWDM can support 12.5 GHz, 25 GHz, 50 GHz, or 100 GHz. However, once chosen, the adjacent channel spacing of the wavelengths is fixed. As mentioned in the section 1, 50 GHz channel spacing is most commonly used. The recent revision of [G.694.1] has defined suggested values for the flexible DWDM grid. The concept of "frequency slot" is introduced to describe the frequency range allocated to a channel. A frequency slot is defined by its nominal central frequency and its required slot width values. For the flexible DWDM grid, the allowed frequency slots have a nominal central frequency (in THz) defined by: Frequency (THz)=193.1 THz + n * 0.00625 and a slot width (the same meaning as the spectral bandwidth) defined by: 12.5 GHz * m where m is a positive integer. The nominal center frequency representations of the fixed grid and flexible grid types are similar except that the latter has a more precise channel spacing granularity (6.25 GHz). Meanwhile the adjacent channel spacing (the spacing of the adjacent nominal center frequency) is implied to be (n1-n2) * 6.25 GHz, where n1 and n2 represent the n number defined above for the nominal center frequency of the adjacent frequency slots respectively (n is an integer Li, et al. Expires January 5, 2012 [Page 4] Internet-Draft Flexible grid label July 2011 including positive, negative integer and 0). The slot width assigned to a frequency slot is arbitrary times of the slot width granularity. It was agreed on flexible grids with a granularity of 6.25 GHz for the central frequency and slot width of a multiple of 12.5 GHz. The slot width granularity is twice the channel spacing granularity, so that by carefully choosing n and m, the spectral resources can be allocated without leaving any gaps between slots. Therefore, in contrast to the rigid label, the new flexible label should have a capability to indicating the slot width allocation. Note that in this document, the concepts "slot width" and "frequency slot" are similar to "spectral bandwidth" and "wavelength channel" respectively. 3.2. Flexible Label To accommodate the new feature mentioned above, the wavelength label supporting flexible grid is illustrated as follows : 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Additional slot width parameters | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Additional slot width parameters: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Grid: One new Grid type called "Flexible DWDM" is defined. +---------------+-------+ | Grid | Value | +---------------+-------+ | Reserved | 0 | +---------------+-------+ | ITU-T DWDM | 1 | +---------------+-------+ | ITU-T CWDM | 2 | +---------------+-------+ Li, et al. Expires January 5, 2012 [Page 5] Internet-Draft Flexible grid label July 2011 +---------------+-------+ | Flexible DWDM | 3 | +---------------+-------+ | Future use | 4-7 | +---------------+-------+ C.S.: For Grid=1 and 2, C.S. is referred to DWDM and CWDM channel spacing [RFC6205], which indicates that the adjacent channel spacing is constant. In this situation, the spectral bandwidth value allocated to every single channel is equal to value of the channel spacing. For Grid=3, C.S. is referred to channel spacing granularity, accordingly the slot width granularity is twice of the C.S.. Minimum channel spacing granularity of 6.25 GHz with a slot width granularity of 12.5 GHz is supported. +------------+-------+ | C.S. (GHz) | Value | +------------+-------+ | Reserved | 0 | +------------+-------+ | 100 | 1 | +------------+-------+ | 50 | 2 | +------------+-------+ | 25 | 3 | +------------+-------+ | 12.5 | 4 | +------------+-------+ | 6.25 | 5 | +------------+-------+ | Future use | 6-15 | +------------+-------+ Identifier: The identifier field in the flexible label format is left unmodified compared with [RFC6205]. It is defined to distinguish which transmitter is used to carry the lambda. This identifier only has a local significance that should be indicated in the signaling message for LSP establishment. For routing information flooding, this filed is meaningless and should be ignored on receipt. n: This field is used to compute the nominal center frequency/wavelength Li, et al. Expires January 5, 2012 [Page 6] Internet-Draft Flexible grid label July 2011 of the channel mentioned above. Together with the channel spacing granularity (C.S.), the spacing of the adjacent channel is (n1-n2) * 6.25 GHz in flexible grid network (see definition of n1 and n2 in section 3.1). Additional slot width parameters. The slot width parameters field is mandatory only when Grid is set to 3 for flexible grid condition. These 5 bits field are used to represent how many slot width granularity the label has occupied. As the granularity is defined to be twice of the channel spacing granularity, so the slot width is calculated to be m * 2 * C.S.. 4. Flexible label applications This section illustrated the routing, signaling, PCE application of the extended flexible grid label. 4.1. Application for Routing Flexible grid is regarded as an enabler for another kind of networks, requiring network elements, or nodes, that go past beyond the functional requirements of OXCs or ROADMs, in the sense that they do switching based on a frequency range. This means that a new swithing type called e.g. "Spectrum Selective Switching" in Interface Switching Capability Descriptor (ISCD) SHOULD be defined. However this is beyond the scope of this document and will be studied in the routing draft. In addition to the topology information, wavelength constraints information like Port Label Restrictions, Shared Backup Labels, Resource Pool Wavelength Constrains, Resource Block Available Wavelengths detailed in [I-D.ietf-ccamp-rwa-info] should be flooded in the network through routing protocol like OSPF-TE. All the information is described by the label set object. The general label set is described in [RFC3471] and specific wavelength label set in [I-D.ietf-ccamp-general-constraint-encode] . There are 5 ways to represent the wavelength label set 1. Inclusive list 2. Exclusive list 3. Inclusive range 4. Exclusive range 5. Bitmap set For flexible grid optical network, the label set should be more actually to represent the spectral resources constraints. For type 1 Li, et al. Expires January 5, 2012 [Page 7] Internet-Draft Flexible grid label July 2011 and 2, flexible label with different slot width is acceptable to put into the list. For type 3 and 4, start label and end label with minimal slot width (while it is not mandatory) is RECOMMENDED. For type 5, the base label/frequency slot is REQUIRED to have a minimum slot width (m=1). As there MAY exist some situations that the unused bandwidth between two occupied bandwidth is odd times of the channel spacing granularity (not integral times of the slot with granularity), two bits are needed to represent a single slot. It can be seen that these 5 types of representations can be easily inherited by incorporating the new flexible label into the object. Note that in the procedure of wavelength constraints flooding, any combination of the 5 types of label sets is feasible. 4.2. Applications for Signaling In flexibel grid network, flexible label representing frequency "slots" or "ranges" rather than individual wavelengths is requested to establish the LSP. The extensions to the Genralized Label Request object and TSPEC object are needed, this will be studied in the future. To establish a label switched path, an available wavelength label satisfying the wavelength continuity constraints is reserved with signaling protocol like RSVP-TE. For the flexible grid DWDM network, this procedure should be modified to assign available spectral resources. In other words, the label is not only assigning the nominal center frequency of wavelength but also the slot width for the LSP. The slot width is definitely clarified through the field m in the label. Nevertheless in the procedure, wavelength continuity constraint is unchanged. 4.3. Applications for PCE [RFC6163] describes a Path Computation Element (PCE) can be used to performing routing and wavelength assignment in WSON. [RFC5440] details the path computation element communication protocol messages for this purpose. According to the modulation format, FEC type, client bitrates[I-D.ietf-ccamp-rwa-info][I-D.ietf-ccamp-rwa-wson-encode], and physical impairment, the required frequency slot indicated by flexible label should be calculated out by the PCE to carry the client signal. Li, et al. Expires January 5, 2012 [Page 8] Internet-Draft Flexible grid label July 2011 5. Acknowledgements 6. IANA Considerations A future revision of this document will present requests to IANA for codepoint allocation. 7. Security Considerations 8. References 8.1. Normative references [G.694.1] International Telecommunications Union, "Spectral grids for WDM applications: DWDM frequency grid", Recommendation G.694.1, June 2002 . [G.694.2] International Telecommunications Union, "Spectral grids for WDM applications: CWDM wavelength grid", Recommendation G.694.2, December 2003 . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description", RFC 3471, January 2003. [RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, March 2009. [RFC6163] Lee, Y., Bernstein, G., and W. Imajuku, "Framework for GMPLS and Path Computation Element (PCE) Control of Wavelength Switched Optical Networks (WSONs)", RFC 6163, April 2011. [RFC6205] Otani, T. and D. Li, "Generalized Labels for Lambda- Switch-Capable (LSC) Label Switching Routers", RFC 6205, March 2011. 8.2. Informative References [I-D.ietf-ccamp-general-constraint-encode] Bernstein, G., Lee, Y., Li, D., and W. Imajuku, "General Li, et al. Expires January 5, 2012 [Page 9] Internet-Draft Flexible grid label July 2011 Network Element Constraint Encoding for GMPLS Controlled Networks", draft-ietf-ccamp-general-constraint-encode-05 (work in progress), May 2011. [I-D.ietf-ccamp-rwa-info] Bernstein, G., Lee, Y., Li, D., and W. Imajuku, "Routing and Wavelength Assignment Information Model for Wavelength Switched Optical Networks", draft-ietf-ccamp-rwa-info-11 (work in progress), March 2011. [I-D.ietf-ccamp-rwa-wson-encode] Bernstein, G., Lee, Y., Li, D., Imajuku, W., and J. Han, "Routing and Wavelength Assignment Information Encoding for Wavelength Switched Optical Networks", draft-ietf-ccamp-rwa-wson-encode-11 (work in progress), March 2011. Authors' Addresses Yao Li ZTE P.R.China Phone: +86 025 52871109 Email: li.yao3@zte.com.cn Zhang Fei ZTE P.R.China Phone: +86 025 52871109 Email: zhang.fei3@zte.com.cn Ramon Casellas CTTC Spain Phone: +34 936452916 Email: ramon.casellas@cttc.es Li, et al. Expires January 5, 2012 [Page 10]