RFC 7698
Framework and Requirements for GMPLS-Based Control of Flexi-Grid Dense Wavelength Division Multiplexing (DWDM) Networks
Pages: 42
Informational
Informational
Part 2 of 3 – Pages 14 to 31
4. GMPLS Applicability
The goal of this section is to provide an insight into the application of GMPLS as a control mechanism in flexi-grid networks. Specific control-plane requirements for the support of flexi-grid networks are covered in Section 5. This framework is aimed at controlling the media layer within the OTN hierarchy and controlling the required adaptations of the signal layer. This document also defines the term "Spectrum-Switched Optical Network" (SSON) to refer to a flexi-grid enabled DWDM network that is controlled by a GMPLS or PCE control plane. This section provides a mapping of the ITU-T G.872 architectural aspects to GMPLS and control-plane terms and also considers the relationship between the architectural concept or construct of a media channel and its control-plane representations (e.g., as a TE link, as defined in [RFC3945]).4.1. General Considerations
The GMPLS control of the media layer deals with the establishment of media channels that are switched in media channel matrices. GMPLS labels are used to locally represent the media channel and its associated frequency slot. Network media channels are considered a particular case of media channels when the endpoints are transceivers (that is, the source and destination of an OTSi).4.2. Consideration of TE Links
From a theoretical point of view, a fiber can be modeled as having a frequency slot that ranges from minus infinity to plus infinity. This representation helps us understand the relationship between frequency slots and ranges. The frequency slot is a local concept that applies within a component or element. When applied to a media channel, we are referring to its effective frequency slot as defined in [G.872]. The association sequence of the three components (i.e., a filter, a fiber, and a filter) is a media channel in its most basic form. From the control-plane perspective, this may be modeled as a (physical) TE link with a contiguous optical spectrum. This can be represented by saying that the portion of spectrum available at time t0 depends on which filters are placed at the ends of the fiber and how they have been configured. Once filters are placed, we have a one-hop media channel. In practical terms, associating a fiber with the terminating filters determines the usable optical spectrum.
---------------+ +----------------- | | +--------+ +--------+ | | | | +--------- ---o| =============================== o--| | | Fiber | | | --\ /-- ---o| | | o--| \/ | | | | | /\ ---o| =============================== o--| --/ \-- | Filter | | Filter | | | | | | +--------- +--------+ +--------+ | | |------- Basic Media Channel ---------| ---------------+ +----------------- --------+ +-------- |--------------------------------------| LSR | TE link | LSR |--------------------------------------| --------+ +-------- Figure 8: (Basic) Media Channel and TE Link Additionally, when a cross-connect for a specific frequency slot is considered, the resulting media support of joining basic media channels is still a media channel, i.e., a longer association sequence of media elements and its effective frequency slot. In other words, it is possible to "concatenate" several media channels (e.g., patch on intermediate nodes) to create a single media channel.
The architectural construct resulting from the association sequence of basic media channels and media-layer matrix cross-connects can be represented as (i.e., corresponds to) a Label Switched Path (LSP) from a control-plane perspective. ----------+ +------------------------------+ +--------- | | | | +------+ +------+ +------+ +------+ | | | | +----------+ | | | | --o| ========= o--| |--o ========= o-- | | Fiber | | | --\ /-- | | | Fiber | | --o| | | o--| \/ |--o | | o-- | | | | | /\ | | | | | --o| ========= o--***********|--o ========= o-- |Filter| |Filter| | | |Filter| |Filter| | | | | | | | | +------+ +------+ +------+ +------+ | | | | <- Basic Media -> <- Matrix -> <- Basic Media -> |Channel| Channel |Channel| ----------+ +------------------------------+ +--------- <-------------------- Media Channel ----------------> ------+ +---------------+ +------ |------------------| |------------------| LSR | TE link | LSR | TE link | LSR |------------------| |------------------| ------+ +---------------+ +------ Figure 9: Extended Media Channel
Furthermore, if appropriate, the media channel can also be represented as a TE link or Forwarding Adjacency (FA) [RFC4206], augmenting the control-plane network model. ----------+ +------------------------------+ +--------- | | | | +------+ +------+ +------+ +------+ | | | | +----------+ | | | | --o| ========= o--| |--o ========= o-- | | Fiber | | | --\ /-- | | | Fiber | | --o| | | o--| \/ |--o | | o-- | | | | | /\ | | | | | --o| ========= o--***********|--o ========= o-- |Filter| |Filter| | | |Filter| |Filter| | | | | | | | | +------+ +------+ +------+ +------+ | | | | ----------+ +------------------------------+ +--------- <------------------------ Media Channel -----------> ------+ +----- |------------------------------------------------------| LSR | TE link | LSR |------------------------------------------------------| ------+ +----- Figure 10: Extended Media Channel TE Link or FA4.3. Consideration of LSPs in Flexi-Grid
The flexi-grid LSP is a control-plane representation of a media channel. Since network media channels are media channels, an LSP may also be the control-plane representation of a network media channel (without considering the adaptation functions). From a control-plane perspective, the main difference (regardless of the actual effective frequency slot, which may be dimensioned arbitrarily) is that the LSP that represents a network media channel also includes the endpoints (transceivers), including the cross-connects at the ingress and egress nodes. The ports towards the client can still be represented as interfaces from the control-plane perspective.
Figure 11 shows an LSP routed between three nodes. The LSP is terminated before the optical matrix of the ingress and egress nodes and can represent a media channel. This case does not (and cannot) represent a network media channel because it does not include (and cannot include) the transceivers. ---------+ +--------------------------------+ +-------- | | | | +------+ +------+ +------+ +------+ | | | | +----------+ | | | | -o| ========= o---| |---o ========= o- | | Fiber | | | --\ /-- | | | Fiber | | -o|>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>o- | | | | | /\ | | | | | -o| ========= o---***********|---o ========= o- |Filter| |Filter| | | |Filter| |Filter| | | | | | | | | +------+ +------+ +------+ +------+ | | | | ---------+ +--------------------------------+ +-------- >>>>>>>>>>>>>>>>>>>>>>>>>>>> LSP >>>>>>>>>>>>>>>>>>>>>>>> -----+ +---------------+ +----- |------------------| |----------------| LSR | TE link | LSR | TE link | LSR |------------------| |----------------| -----+ +---------------+ +----- Figure 11: Flexi-Grid LSP Representing a Media Channel That Starts at the Filter of the Outgoing Interface of the Ingress LSR and Ends at the Filter of the Incoming Interface of the Egress LSR
In Figure 12, a network media channel is represented as terminated at the network side of the transceivers. This is commonly named an OTSi-trail connection. |--------------------- Network Media Channel ----------------------| +----------------------+ +----------------------+ | | | +------+ +------+ +------+ +------+ | | +----+ | | | | +----+ | |OTSi OTSi| o-| |-o | +-----+ | o-| |-o |sink src | | | | | ===+-+ +-+==| | | | | O---|R T|***o******o******************************************************** | | |\ /| | | | | | | | |\ /| | | | o-| \/ |-o ===| | | |==| o-| \/ |-o | | | | /\ | | | +-+ +-+ | | | /\ | | | | o-|/ \|-o | | \/ | | o-|/ \|-o | |Filter| | | |Filter| | /\ | |Filter| | | |Filter| +------+ | | +------+ +-----+ +------+ | | +------+ | | | | | | | | +----------------------+ +----------------------+ LSP <-------------------------------------------------------------------> LSP <------------------------------------------------------------------> +-----+ +--------+ +-----+ o--- | |-------------------| |----------------| |---o | LSR | TE link | LSR | TE link | LSR | | |-------------------| |----------------| | +-----+ +--------+ +-----+ Figure 12: LSP Representing a Network Media Channel (OTSi Trail)
In a third case, a network media channel is terminated on the filter ports of the ingress and egress nodes. This is defined in G.872 as an OTSi Network Connection. As can be seen from the figures, from a GMPLS modeling perspective there is no difference between these cases, but they are shown as distinct examples to highlight the differences in the data plane. |--------------------- Network Media Channel --------------------| +------------------------+ +------------------------+ +------+ +------+ +------+ +------+ | | +----+ | | | | +----+ | | | o-| |-o | +------+ | o-| |-o | | | | | | =====+-+ +-+=====| | | | | | T-o******o********************************************************O-R | | |\ /| | | | | | | | |\ /| | | | o-| \/ |-o =====| | | |=====| o-| \/ |-o | | | | /\ | | | +-+ +-+ | | | /\ | | | | o-|/ \|-o | | \/ | | o-|/ \|-o | |Filter| | | |Filter| | /\ | |Filter| | | |Filter| +------+ | | +------+ +------+ +------+ | | +------+ | | | | | | | | +----------------------+ +----------------------+ <-----------------------------------------------------------------> LSP LSP <--------------------------------------------------------------> +-----+ +--------+ +-----+ o--| |--------------------| |-------------------| |--o | LSR | TE link | LSR | TE link | LSR | | |--------------------| |-------------------| | +-----+ +--------+ +-----+ Figure 13: LSP Representing a Network Media Channel (OTSi Network Connection)
Applying the notion of hierarchy at the media layer, by using the LSP as an FA (i.e., by using hierarchical LSPs), the media channel created can support multiple (sub-)media channels. +--------------+ +--------------+ | Media Channel| TE | Media Channel| Virtual TE | | link | | link | Matrix |o- - - - - - - - - - o| Matrix |o- - - - - - +--------------+ +--------------+ | +---------+ | | | Media | | |o----| Channel |-----o| | | | Matrix | +---------+ Figure 14: Topology View with TE Link or FA Note that there is only one media-layer switch matrix (one implementation is a flexi-grid ROADM) in SSON, while a signal-layer LSP (network media channel) is established mainly for the purpose of management and control of individual optical signals. Signal-layer LSPs with the same attributes (such as source and destination) can be grouped into one media-layer LSP (media channel); this has advantages in spectral efficiency (reduced guard band between adjacent OChs in one FSC channel) and LSP management. However, assuming that some network elements perform signal-layer switching in an SSON, there must be enough guard band between adjacent OTSi in any media channel to compensate for the filter concatenation effects and other effects caused by signal-layer switching elements. In such a situation, the separation of the signal layer from the media layer does not bring any benefit in spectral efficiency or in other aspects, and it makes the network switching and control more complex. If two OTSi must be switched to different ports, it is better to carry them via different FSC channels, and the media-layer switch is enough in this scenario. As discussed in Section 3.2.5, a media channel may be constructed from a composite of network media channels. This may be achieved in two ways using LSPs. These mechanisms may be compared to the techniques used in GMPLS to support inverse multiplexing in Time Division Multiplexing (TDM) networks and in OTN [RFC4606] [RFC6344] [RFC7139]. o In the first case, a single LSP may be established in the control plane. The signaling messages include information for all of the component network media channels that make up the composite media channel.
o In the second case, each component network media channel is
established using a separate control-plane LSP, and these LSPs are
associated within the control plane so that the endpoints may see
them as a single media channel.
4.4. Control-Plane Modeling of Network Elements
Optical transmitters and receivers may have different tunability
constraints, and media channel matrices may have switching
restrictions. Additionally, a key feature of their implementation is
their highly asymmetric switching capability, which is described in
detail in [RFC6163]. Media matrices include line-side ports that are
connected to DWDM links and tributary-side input/output ports that
can be connected to transmitters/receivers.
A set of common constraints can be defined:
o Slot widths: The minimum and maximum slot width.
o Granularity: The optical hardware may not be able to select
parameters with the lowest granularity (e.g., 6.25 GHz for nominal
central frequencies or 12.5 GHz for slot width granularity).
o Available frequency ranges: The set or union of frequency ranges
that have not been allocated (i.e., are available). The relative
grouping and distribution of available frequency ranges in a fiber
are usually referred to as "fragmentation".
o Available slot width ranges: The set or union of slot width ranges
supported by media matrices. It includes the following
information:
* Slot width threshold: The minimum and maximum slot width
supported by the media matrix. For example, the slot width
could be from 50 GHz to 200 GHz.
* Step granularity: The minimum step by which the optical filter
bandwidth of the media matrix can be increased or decreased.
This parameter is typically equal to slot width granularity
(i.e., 12.5 GHz) or integer multiples of 12.5 GHz.
4.5. Media Layer Resource Allocation Considerations
A media channel has an associated effective frequency slot. From the
perspective of network control and management, this effective slot is
seen as the "usable" end-to-end frequency slot. The establishment of
an LSP is related to the establishment of the media channel and the
configuration of the effective frequency slot.
A "service request" is characterized (at a minimum) by its required effective slot width. This does not preclude the request from adding additional constraints, such as also imposing the nominal central frequency. A given effective frequency slot may be requested for the media channel in the control-plane LSP setup messages, and a specific frequency slot can be requested on any specific hop of the LSP setup. Regardless of the actual encoding, the LSP setup message specifies a minimum effective frequency slot width that needs to be fulfilled in order to successfully establish the requested LSP. An effective frequency slot must equally be described in terms of a central nominal frequency and its slot width (in terms of usable spectrum of the effective frequency slot). That is, it must be possible to determine the end-to-end values of the n and m parameters. We refer to this by saying that the "effective frequency slot of the media channel or LSP must be valid". In GMPLS, the requested effective frequency slot is represented to the TSpec present in the RSVP-TE Path message, and the effective frequency slot is mapped to the FlowSpec carried in the RSVP-TE Resv message. In GMPLS-controlled systems, the switched element corresponds to the 'label'. In flexi-grid, the switched element is a frequency slot, and the label represents a frequency slot. Consequently, the label in flexi-grid conveys the necessary information to obtain the frequency slot characteristics (i.e., central frequency and slot width: the n and m parameters). The frequency slot is locally identified by the label. The local frequency slot may change at each hop, given hardware constraints and capabilities (e.g., a given node might not support the finest granularity). This means that the values of n and m may change at each hop. As long as a given downstream node allocates enough optical spectrum, m can be different along the path. This covers the issue where media matrices can have different slot width granularities. Such variations in the local value of m will appear in the allocated label that encodes the frequency slot as well as in the FlowSpec that describes the flow. Different operational modes can be considered. For Routing and Spectrum Assignment (RSA) with explicit label control, and for Routing and Distributed Spectrum Assignment (R+DSA), the GMPLS signaling procedures are similar to those described in Section 4.1.3 of [RFC6163] for Routing and Wavelength Assignment (RWA) and for Routing and Distributed Wavelength Assignment (R+DWA). The main difference is that the label set specifies the available nominal central frequencies that meet the slot width requirements of the LSP.
The intermediate nodes use the control plane to collect the acceptable central frequencies that meet the slot width requirement hop by hop. The tail-end node also needs to know the slot width of an LSP to assign the proper frequency resource. Except for identifying the resource (i.e., fixed wavelength for WSON, and frequency resource for flexible grids), the other signaling requirements (e.g., unidirectional or bidirectional, with or without converters) are the same as for WSON as described in Section 6.1 of [RFC6163]. Regarding how a GMPLS control plane can assign n and m hop by hop along the path of an LSP, different cases can apply: a. n and m can both change. It is the effective frequency slot that matters; it needs to remain valid along the path. b. m can change, but n needs to remain the same along the path. This ensures that the nominal central frequency stays the same, but the width of the slot can vary along the path. Again, the important thing is that the effective frequency slot remains valid and satisfies the requested parameters along the whole path of the LSP. c. n and m need to be unchanging along the path. This ensures that the frequency slot is well known from end to end and is a simple way to ensure that the effective frequency slot remains valid for the whole LSP. d. n can change, but m needs to remain the same along the path. This ensures that the effective frequency slot remains valid but also allows the frequency slot to be moved within the spectrum from hop to hop. The selection of a path that ensures n and m continuity can be delegated to a dedicated entity such as a Path Computation Element (PCE). Any constraint (including frequency slot and width granularities) can be taken into account during path computation. Alternatively, A PCE can compute a path, leaving the actual frequency slot assignment to be done, for example, with a distributed (signaling) procedure: o Each downstream node ensures that m is >= requested_m. o A downstream node cannot foresee what an upstream node will allocate. A way to ensure that the effective frequency slot is valid along the length of the LSP is to ensure that the same value of n is allocated at each hop. By forcing the same value of n, we
avoid cases where the effective frequency slot of the media
channel is invalid (that is, the resulting frequency slot cannot
be described by its n and m parameters).
o This may be too restrictive, since a node (or even a centralized/
combined RSA entity) may be able to ensure that the resulting
end-to-end effective frequency slot is valid, even if n varies
locally. That means that the effective frequency slot that
characterizes the media channel from end to end is consistent and
is determined by its n and m values but that the effective
frequency slot and those values are logical (i.e., do not map
"direct" to the physically assigned spectrum) in the sense that
they are the result of the intersection of locally assigned
frequency slots applicable at local components (such as filters),
each of which may have different frequency slots assigned to them.
As shown in Figure 15, the effective slot is made valid by ensuring
that the minimum m is greater than the requested m. The effective
slot (intersection) is the lowest m (bottleneck).
C B A
|Path(m_req) | ^ |
|---------> | # |
| | # ^
-^--------------^----------------#----------------#--
Effective # # # #
FS n, m # . . . . . . .#. . . . . . . . # . . . . . . . .# <-fixed
# # # # n
-v--------------v----------------#----------------#---
| | # v
| | # Resv |
| | v <------ |
| | |FlowSpec(n, m_a)|
| | <--------| |
| | FlowSpec(n, |
<--------| min(m_a, m_b))
FlowSpec(n, |
min(m_a, m_b, m_c))
m_a, m_b, m_c: Selected frequency slot widths
Figure 15: Distributed Allocation with Different m and Same n
In Figure 16, the effective slot is made valid by ensuring that it is valid at each hop in the upstream direction. The intersection needs to be computed; otherwise, invalid slots could result. C B A |Path(m_req) ^ | | |---------> # | | | # ^ ^ -^-------------#----------------#-----------------#-------- Effective # # # # FS n, m # # # # # # # # -v-------------v----------------#-----------------#-------- | | # v | | # Resv | | | v <------ | | | |FlowSpec(n_a, m_a) | | <--------| | | | FlowSpec(FSb [intersect] FSa) <--------| FlowSpec([intersect] FSa,FSb,FSc) n_a: Selected nominal central frequency by node A m_a: Selected frequency slot widths by node A FSa, FSb, FSc: Frequency slot at each hop A, B, C Figure 16: Distributed Allocation with Different m and Different n Note that when a media channel is bound to one OTSi (i.e., is a network media channel), the effective FS must be the frequency slot of the OTSi. The media channel set up by the LSP may contain the effective FS of the network media channel effective FS. This is an endpoint property; the egress and ingress have to constrain the effective FS to be the OTSi effective FS.4.6. Neighbor Discovery and Link Property Correlation
There are potential interworking problems between fixed-grid DWDM nodes and flexi-grid DWDM nodes. Additionally, even two flexi-grid nodes may have different grid properties, leading to link property conflict and resulting in limited interworking. Devices or applications that make use of flexi-grid might not be able to support every possible slot width. In other words, different applications may be defined where each supports a different grid granularity. In this case, the link between two optical nodes with
different grid granularities must be configured to align with the
larger of both granularities. Furthermore, different nodes may have
different slot width tuning ranges.
In summary, in a DWDM link between two nodes, at a minimum, the
following properties need to be negotiated:
o Grid capability (channel spacing) - Between fixed-grid and
flexi-grid nodes.
o Grid granularity - Between two flexi-grid nodes.
o Slot width tuning range - Between two flexi-grid nodes.
4.7. Path Computation, Routing and Spectrum Assignment (RSA)
In WSON, if there is no (available) wavelength converter in an
optical network, an LSP is subject to the "wavelength continuity
constraint" (see Section 4 of [RFC6163]). Similarly, in flexi-grid,
if the capability to shift or convert an allocated frequency slot is
absent, the LSP is subject to the "spectrum continuity constraint".
Because of the limited availability of spectrum converters (in what
is called a "sparse translucent optical network"), the spectrum
continuity constraint always has to be considered. When available,
information regarding spectrum conversion capabilities at the optical
nodes may be used by RSA mechanisms.
The RSA process determines a route and frequency slot for an LSP.
Hence, when a route is computed, the spectrum assignment process
determines the central frequency and slot width based on the
following:
o the requested slot width
o the information regarding the transmitter and receiver
capabilities, including the availability of central frequencies
and their slot width granularity
o the information regarding available frequency slots (frequency
ranges) and available slot widths of the links traversed along
the route
4.7.1. Architectural Approaches to RSA
Similar to RWA for fixed grids [RFC6163], different ways of performing RSA in conjunction with the control plane can be considered. The approaches included in this document are provided for reference purposes only; other possible options could also be deployed. Note that all of these models allow the concept of a composite media channel supported by a single control-plane LSP or by a set of associated LSPs.4.7.1.1. Combined RSA (R&SA)
In this case, a computation entity performs both routing and frequency slot assignment. The computation entity needs access to detailed network information, e.g., the connectivity topology of the nodes and links, available frequency ranges on each link, and node capabilities. The computation entity could reside on a dedicated PCE server, in the provisioning application that requests the service, or on the ingress node.4.7.1.2. Separated RSA (R+SA)
In this case, routing computation and frequency slot assignment are performed by different entities. The first entity computes the routes and provides them to the second entity. The second entity assigns the frequency slot. The first entity needs the connectivity topology to compute the proper routes. The second entity needs information about the available frequency ranges of the links and the capabilities of the nodes in order to assign the spectrum.4.7.1.3. Routing and Distributed SA (R+DSA)
In this case, an entity computes the route, but the frequency slot assignment is performed hop by hop in a distributed way along the route. The available central frequencies that meet the spectrum continuity constraint need to be collected hop by hop along the route. This procedure can be implemented by the GMPLS signaling protocol.
4.8. Routing and Topology Dissemination
In the case of the combined RSA architecture, the computation entity needs the detailed network information, i.e., connectivity topology, node capabilities, and available frequency ranges of the links. Route computation is performed based on the connectivity topology and node capabilities, while spectrum assignment is performed based on the available frequency ranges of the links. The computation entity may get the detailed network information via the GMPLS routing protocol. For WSON, the connectivity topology and node capabilities can be advertised by the GMPLS routing protocol (refer to Section 6.2 of [RFC6163]). Except for wavelength-specific availability information, the information for flexi-grid is the same as for WSON and can equally be distributed by the GMPLS routing protocol. This section analyzes the necessary changes to link information required by flexible grids.4.8.1. Available Frequency Ranges (Frequency Slots) of DWDM Links
In the case of flexible grids, channel central frequencies span from 193.1 THz towards both ends of the C-band spectrum with a granularity of 6.25 GHz. Different LSPs could make use of different slot widths on the same link. Hence, the available frequency ranges need to be advertised.4.8.2. Available Slot Width Ranges of DWDM Links
The available slot width ranges need to be advertised in combination with the available frequency ranges, so that the computing entity can verify whether an LSP with a given slot width can be set up or not. This is constrained by the available slot width ranges of the media matrix. Depending on the availability of the slot width ranges, it is possible to allocate more spectrum than what is strictly needed by the LSP.4.8.3. Spectrum Management
The total available spectrum on a fiber can be described as a resource that can be partitioned. For example, a part of the spectrum could be assigned to a third party to manage, or parts of the spectrum could be assigned by the operator for different classes of traffic. This partitioning creates the impression that the spectrum is a hierarchy in view of the management plane and the control plane: each partition could itself be partitioned. However,
the hierarchy is created purely within a management system; it defines a hierarchy of access or management rights, but there is no corresponding resource hierarchy within the fiber. The end of the fiber is a link end and presents a fiber port that represents all of the spectrum available on the fiber. Each spectrum allocation appears as a Link Channel Port (i.e., frequency slot port) within the fiber. Thus, while there is a hierarchy of ownership (the Link Channel Port and corresponding LSP are located on a fiber and therefore are associated with a fiber port), there is no continued nesting hierarchy of frequency slots within larger frequency slots. In its way, this mirrors the fixed-grid behavior where a wavelength is associated with a fiber port but cannot be subdivided even though it is a partition of the total spectrum available on the fiber.4.8.4. Information Model
This section defines an information model to describe the data that represents the capabilities and resources available in a flexi-grid network. It is not a data model and is not intended to limit any protocol solution such as an encoding for an IGP. For example, information required for routing and path selection may be the set of available nominal central frequencies from which a frequency slot of the required width can be allocated. A convenient encoding for this information is left for further study in an IGP encoding document. Fixed DWDM grids can also be described via suitable choices of slots in a flexible DWDM grid. However, devices or applications that make use of the flexible grid may not be capable of supporting every possible slot width or central frequency position. Thus, the information model needs to enable: o the exchange of information to enable RSA in a flexi-grid network o the representation of a fixed-grid device participating in a flexi-grid network o full interworking of fixed-grid and flexible-grid devices within the same network o interworking of flexible-grid devices with different capabilities
The information model is represented using the Routing Backus-Naur Format (RBNF) as defined in [RFC5511]. <Available Spectrum> ::= <Available Frequency Range-List> <Available NCFs> <Available Slot Widths> where <Available Frequency Range-List> ::= <Available Frequency Range> [<Available Frequency Range-List>] <Available Frequency Range> ::= ( <Start NCF> <End NCF> ) | <FS defined by (n, m) containing contiguous available NCFs> and <Available NCFs> ::= <Available NCF Granularity> [<Offset>] -- Subset of supported n values given by p x n + q -- where p is a positive integer -- and q (offset) belongs to 0,..,p-1. and <Available Slot Widths> ::= <Available Slot Width Granularity> <Min Slot Width> -- given by j x 12.5 GHz, with j a positive integer <Max Slot Width> -- given by k x 12.5 GHz, with k a positive integer (k >= j) Figure 17: Routing Information Model
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