RFC 7698
Framework and Requirements for GMPLS-Based Control of Flexi-Grid Dense Wavelength Division Multiplexing (DWDM) Networks
1. Introduction 🎀
Okay bestie, let's get into it. This is RFC 7698 ✨, and it's titled "Framework and Requirements for GMPLS-Based Control of Flexi-Grid Dense Wavelength Division Multiplexing (DWDM) Networks." It's an Informational doc, so it's published for info purposes and is not an Internet Standards Track spec 💅. It came out in November 2015 from the IETF, with ISSN 2070-1721. The editors are O. Gonzalez de Dios (Telefonica I+D) and R. Casellas (CTTC), and the other authors are F. Zhang (Huawei), X. Fu (Stairnote), D. Ceccarelli (Ericsson), and I. Hussain (Infinera) 🫶. It doesn't obsolete or update any other RFCs 🧚.
Abstract
Okay so the ITU-T extended its Recommendations G.694.1 and G.872 to add a new DWDM grid 🌈. It defines a set of nominal central frequencies, channel spacings, and this concept called the "frequency slot" 🦋. In this setup, a data-plane connection gets switched based on allocated frequency ranges within the optical spectrum, and those ranges can be different sizes. That's what people call a flexible grid, or "flexi-grid" 🌸.
Given how flexi-grid optical networks work, this doc sets up a framework and the control-plane requirements for applying the existing GMPLS architecture and control-plane protocols to controlling flexi-grid DWDM networks 💜. The actual GMPLS protocol extensions will be defined in companion documents ✨.
Status of This Memo
This doc is not an Internet Standards Track spec 🙈. It's published for informational purposes.
It's a product of the IETF and represents the consensus of the IETF community 🫶. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG). Not every doc the IESG approves is a candidate for any level of Internet Standard, so check Section 2 of RFC 5741 if you're curious 🔥.
For the current status, any errata, and how to give feedback, go to http://www.rfc-editor.org/info/rfc7698 💖.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved 🔥.
This doc is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as they stood on the publication date 📜. Please read these carefully, because they spell out your rights and restrictions 🙏. Code Components pulled out of this doc must include the Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come without warranty, as described in the Simplified BSD License 💅.
Table of Contents
1. Introduction ....................................................4
2. Terminology .....................................................5
2.1. Requirements Language ......................................5
2.2. Abbreviations ..............................................5
3. Overview of Flexi-Grid Networks .................................6
3.1. Flexi-Grid in the Context of OTN ...........................6
3.2. Flexi-Grid Terminology .....................................6
3.2.1. Frequency Slots .....................................7
3.2.2. Media-Layer Elements ................................9
3.2.3. Media Channels .....................................10
3.2.4. Optical Tributary Signals ..........................10
3.2.5. Composite Media Channels ...........................11
3.3. Hierarchy in the Media Layer ..............................11
3.4. Flexi-Grid Layered Network Model ..........................12
3.4.1. DWDM Flexi-Grid Enabled Network Element Models .....13
4. GMPLS Applicability ............................................14
4.1. General Considerations ....................................14
4.2. Consideration of TE Links .................................14
4.3. Consideration of LSPs in Flexi-Grid .......................17
4.4. Control-Plane Modeling of Network Elements ................22
4.5. Media Layer Resource Allocation Considerations ............22
4.6. Neighbor Discovery and Link Property Correlation ..........26
4.7. Path Computation, Routing and Spectrum Assignment (RSA) ...27
4.7.1. Architectural Approaches to RSA ....................28
4.8. Routing and Topology Dissemination ........................29
4.8.1. Available Frequency Ranges (Frequency
Slots) of DWDM Links ...............................29
4.8.2. Available Slot Width Ranges of DWDM Links ..........29
4.8.3. Spectrum Management ................................29
4.8.4. Information Model ..................................30
5. Control-Plane Requirements .....................................31
5.1. Support for Media Channels ................................31
5.1.1. Signaling ..........................................32
5.1.2. Routing ............................................32
5.2. Support for Media Channel Resizing ........................33
5.3. Support for Logical Associations of Multiple Media
Channels ..................................................33
5.4. Support for Composite Media Channels ......................33
5.5. Support for Neighbor Discovery and Link Property
Correlation ...............................................34
6. Security Considerations ........................................34
7. Manageability Considerations ...................................35
8. References .....................................................36
8.1. Normative References ......................................36
8.2. Informative References ....................................37
Acknowledgments ...................................................39
Contributors ......................................................39
Authors' Addresses ................................................411. Introduction ✨
So "flexible grid" (or "flexi-grid" for short) is defined by ITU-T Study Group 15 in the latest version of [G.694.1] 🌸. It refers to the updated set of nominal central frequencies (the frequency grid), the channel spacing, and the optical spectrum management and allocation rules that were set up so optical spectral bandwidth can be allocated and configured efficiently and flexibly for high bit-rate systems 💖.
The key concept here is the "frequency slot" 🦋: a variable-sized optical frequency range that can be allocated to a data connection. We'll get into this more later, but a frequency slot is characterized by its nominal central frequency and its slot width. Per [G.694.1], that slot width has to be a multiple of a given slot width granularity 🧚.
Compare that to a traditional fixed-grid network, which uses fixed-size optical spectrum ranges (frequency slots) with typical channel separations of 50 GHz 🙈. A flexible-grid network can pick its media channels from a much wider range of slot widths, so it can allocate as much optical spectrum as it actually needs 💅.
From a networking point of view, a flexible-grid network is assumed to be a layered network [G.872] [G.800] 🔥. The media layer is the server layer, and the optical signal layer is the client layer. In the media layer, switching is based on a frequency slot, and the size of a media channel is set by the properties of its frequency slot 🌈. Inside this layered network, one media channel can carry more than one Optical Tributary Signal (OTSi), which we'll define later in the doc 🫶.
A Wavelength Switched Optical Network (WSON), covered in [RFC6163], is the commonly used name for a GMPLS-based control plane doing control work (like provisioning and recovery) on a fixed-grid Wavelength Division Multiplexing (WDM) network, where media (spectrum) and signal are considered together 👑.
This doc sets up the framework for GMPLS-based control of flexi-grid enabled Dense Wavelength Division Multiplexing (DWDM) networks, within the scope defined by ITU-T layered Optical Transport Networks [G.872] 🎀. It also lists a set of associated control-plane requirements. An important design idea is decoupling the management of the optical spectrum resource from the client signals being transported 💜.
2. Terminology 💅
More flexi-grid-specific terms live in Section 3.2 🦋.
2.1. Requirements Language ✨
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] 🙏.
Even though [RFC2119] explains these key words in terms of protocol specs and implementations, this doc uses them to describe design requirements for protocol extensions 🔥.
2.2. Abbreviations 🌸
FS: Frequency Slot
FSC: Fiber-Switch Capable
LSR: Label Switching Router
NCF: Nominal Central Frequency
OCC: Optical Channel Carrier
OCh: Optical Channel
OCh-P: Optical Channel Payload
OTN: Optical Transport Network
OTSi: Optical Tributary Signal
OTSiG: OTSi Group is a set of OTSi
PCE: Path Computation Element
ROADM: Reconfigurable Optical Add/Drop Multiplexer
SSON: Spectrum-Switched Optical Network
SWG: Slot Width Granularity3. Overview of Flexi-Grid Networks ✨
3.1. Flexi-Grid in the Context of OTN ✨
okay so [G.872] lays out the functional architecture of an OTN from a network level 🦋 It breaks the whole thing into independent-layer networks that have client/layer relationships with each other. Here's a simplified look at the OTN layers:
+----------------+
| Digital Layer |
+----------------+
| Signal Layer |
+----------------+
| Media Layer |
+----------------+
Figure 1: Generic OTN OverviewIn the OTN layering context, the media layer is the server layer of the optical signal layer 💅 The media layer guides the optical signal to its destination using a network media channel. And inside the media layer, switching is based on a frequency slot. So iconic 🌈
In this scope, this document uses the term "flexi-grid enabled DWDM network" to mean a network where switching is based on frequency slots defined with the flexible grid 🎀 This document mainly covers the media layer, plus the required adaptations coming from the signal layer. So the whole doc is focused on controlling and managing the media layer. Main character energy 👑
3.2. Flexi-Grid Terminology 📖
This section gives the definitions of the terms used in flexi-grid networks 🧚 If you want more details, check out the ITU-T Recommendations [G.694.1], [G.872], [G.870], [G.8080], and [G.959.1-2013].
Where it makes sense, this document also borrows terminology and lexicography from [RFC4397] 🫶
3.2.1. Frequency Slots 🍓
This subsection is all about the frequency slot and its related terms, bestie.
- Frequency Slot [G.694.1]: The frequency range allocated to a slot within the flexible grid, and unavailable to other slots. A frequency slot is defined by its nominal central frequency and its slot width.
- Nominal Central Frequency: Each of the allowed frequencies as per the definition of the flexible DWDM grid in [G.694.1]. The set of nominal central frequencies can be built with this expression:
f = 193.1 THz + n x 0.00625 THz
where 193.1 THz is the ITU-T "anchor frequency" for transmission over the C-band, and 'n' is a positive or negative integer, including 0 ✨
-5 -4 -3 -2 -1 0 1 2 3 4 5 <- values of n
...+--+--+--+--+--+--+--+--+--+--+-
^
193.1 THz <- anchor frequency
Figure 2: Anchor Frequency and Set of Nominal Central Frequencies- Nominal Central Frequency Granularity: The spacing between allowed nominal central frequencies. It's set to 6.25 GHz [G.694.1] 🔥
- Slot Width Granularity (SWG): 12.5 GHz, as defined in [G.694.1] 💜
- Slot Width: Determines the "amount" of optical spectrum, no matter where it actually sits on the frequency axis 🦋 A slot width is constrained to be m x SWG (that's m x 12.5 GHz), where 'm' is an integer greater than or equal to 1.
Frequency Slot 1 Frequency Slot 2
------------- -------------------
| | | |
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
...--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
------------- -------------------
^ ^
Slot NCF = 193.1 THz Slot NCF = 193.14375 THz
Slot width = 25 GHz Slot width = 37.5 GHz
n = 0, m = 2 n = 7, m = 3
Figure 3: Example Frequency Slots- The symbol '+' represents the allowed nominal central frequencies.
- The '--' represents the nominal central frequency granularity in units of 6.25 GHz.
- The '^' represents the slot nominal central frequency.
- The number on the top of the '+' symbol represents the 'n' in the frequency calculation formula.
- The nominal central frequency is 193.1 THz when n equals zero.
- Effective Frequency Slot [G.870]: That part of the frequency slots of the filters along the media channel that is common to all of the filters' frequency slots. Note that both the terms "frequency slot" and "effective frequency slot" are applied locally 🙈
- Figure 4 shows what happens when you combine two filters along a channel. Combining Frequency Slot 1 and Frequency Slot 2 applied to the media channel gives you the effective frequency slot shown 🌸
Frequency Slot 1
-------------
| |
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--...
Frequency Slot 2
-------------------
| |
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--...
===============================================
Effective Frequency Slot
-------------
| |
-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
..--+--+--+--+--X--+--+--+--+--+--+--+--+--+--+--+--...
Figure 4: Effective Frequency Slot3.2.2. Media-Layer Elements 🌷
- Media Element: A media element directs an optical signal or affects the properties of an optical signal. It does not modify the properties of the information that has been modulated to produce the optical signal [G.870]. Examples of media elements include fibers, amplifiers, filters, and switching matrices 🧚
- Media Channel Matrix: The media channel matrix provides flexible connectivity for the media channels. In other words, it's a point of flexibility where relationships between the media ports at the edge of a media channel matrix can be created and broken 🦋 The relationship between these ports is called a "matrix channel". (Network) media channels are switched in a media channel matrix ✨
3.2.3. Media Channels 🎀
This section defines concepts like the (network) media channel. The mapping to GMPLS constructs (i.e., LSP) is detailed in Section 4 🫶
- Media Channel: A media association that represents both the topology (i.e., the path through the media) and the resource (frequency slot) that it occupies. As a topological construct, it represents a frequency slot (an effective frequency slot) supported by a concatenation of media elements (fibers, amplifiers, filters, switching matrices...). This term is used to identify the end-to-end physical-layer entity with its corresponding (one or more) frequency slots local at each link filter 💅
- Network Media Channel: Defined in [G.870] as a media channel that transports a single OTSi (defined in the next subsection) 💖
3.2.4. Optical Tributary Signals 🌈
- Optical Tributary Signal (OTSi): The optical signal that is placed within a network media channel for transport across the optical network. This may consist of a single modulated optical carrier or a group of modulated optical carriers or subcarriers. To provide a connection between the OTSi source and the OTSi sink, the optical signal must be assigned to a network media channel (see also [G.959.1-2013]) 🔥
- OTSi Group (OTSiG): The set of OTSi that are carried by a group of network media channels. Each OTSi is carried by one network media channel. From a management perspective, it SHOULD be possible to manage both the OTSiG and a group of network media channels as single entities 👑
3.2.5. Composite Media Channels 🍓
- It's possible to build an end-to-end media channel as a composite of more than one network media channel. A composite media channel carries a group of OTSi (i.e., OTSiG). Each OTSi is carried by one network media channel. This OTSiG is carried over a single fiber 🦋
- In this case, the effective frequency slots may be contiguous (i.e., there is no spectrum between them that can be used for other media channels) or non-contiguous 🌸
- It is not currently envisaged that such composite media channels may be constructed from slots carried on different fibers, whether those fibers traverse the same hop-by-hop path through the network or not 🙈
- It is also not considered likely that a media channel may be constructed from a different variation of slot composition on each hop. That is, the slot composition (i.e., the group of OTSi carried by the composite media channel) must be the same from one end of the media channel to the other, even if the specific slot for each OTSi and the spacing among slots may vary hop by hop 💀
- How the signal is carried across such groups of network media channels is out of scope for this document 🧚
3.3. Hierarchy in the Media Layer 🌈
In summary, the frequency slot is a logical abstraction that represents a frequency range, while the media layer represents the underlying media support 🫶 Media channels are media associations, characterized by their respective (effective) frequency slots, and they're switched in media channel matrices. From the control and management perspective, a media channel can be logically split into network media channels 💖
In Figure 5, a media channel has been configured and dimensioned to support two network media channels, and each of them carries one OTSi 🎀
Media Channel Frequency Slot
+-------------------------------X------------------------------+
| |
| Frequency Slot Frequency Slot |
| +-----------X-----------+ +----------X-----------+ |
| | OTSi | | OTSi | |
| | o | | o | |
| | | | | | | |
-4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12
--+---+---+---+---+---+---+---+---+---+---+---+--+---+---+---+---+--
<- Network Media Channel -> <- Network Media Channel ->
<------------------------ Media Channel ----------------------->
X - Frequency Slot Central Frequency
o - Signal Central Frequency
Figure 5: Example of Media Channel, Network Media Channels, and
Associated Frequency Slots3.4. Flexi-Grid Layered Network Model ✨
Okay so in the OTN layered network, the network media channel carries exactly one OTSi 🦋 (check Figure 6 bestie, it's giving clean diagram energy).
| OTSi |
O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O
| |
| Channel Port Network Media Channel Channel Port |
O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O
| |
+--------+ +-----------+ +--------+
| \ (1) | | (1) | | (1) / |
| \----|-----------------|-----------|-------------------|-----/ |
+--------+ Link Channel +-----------+ Link Channel +--------+
Media Channel Media Channel Media Channel
Matrix Matrix Matrix
The symbol (1) indicates a matrix channel
Figure 6: Simplified Layered Network ModelNote that a particular example of OTSi is the OCh-P 🌸. Figure 7 shows this specific example as defined in G.805 [G.805], and it's honestly so iconic.
OCh AP Trail (OCh) OCh AP
O- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O
| |
--- OCh-P OCh-P ---
\ / source sink \ /
+ +
| OCh-P OCh-P Network Connection OCh-P |
O TCP - - - - - - - - - - - - - - - - - - - - - - - - - - -TCP O
| |
|Channel Port Network Media Channel Channel Port |
O - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - O
| |
+--------+ +-----------+ +---------+
| \ (1) | OCh-P LC | (1) | OCh-P LC | (1) / |
| \----|-----------------|-----------|-----------------|------/ |
+--------+ Link Channel +-----------+ Link Channel +---------+
Media Channel Media Channel Media Channel
Matrix Matrix Matrix
The symbol (1) indicates a matrix channel
"LC" indicates a link connection
Figure 7: Layered Network Model According to G.8053.4.1. DWDM Flexi-Grid Enabled Network Element Models 💅
A flexible-grid network is built out of subsystems that include WDM links, tunable transmitters, and receivers (aka media elements, including media-layer switching elements that are media matrices), plus electro-optical network elements too 🫶. This is just the same as a fixed-grid network, except that each element has flexible-grid characteristics ✨.
As stated in Clause 7 of [G.694.1], the flexible DWDM grid has a nominal central frequency granularity of 6.25 GHz and a slot width granularity of 12.5 GHz 🎀. However, devices or applications that make use of the flexible grid might not be capable of supporting every possible slot width or position 😭. In other words, applications may be defined where only a subset of the possible slot widths and positions is required to be supported 💜. For example, an application could be defined where the nominal central frequency granularity is 12.5 GHz (by only requiring values of n that are even) and where slot widths are a multiple of 25 GHz (by only requiring values of m that are even) 🧚.
4. GMPLS Applicability 👑
The goal of this section is to give you an insight into how GMPLS applies 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 it 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 LinkAdditionally, 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 ChannelFurthermore, 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 ✨
okay so the flexi-grid LSP is the control-plane version of a media channel 🦋 And since network media channels are media channels too, an LSP can also be the control-plane version of a network media channel (ignoring the adaptation functions, bestie). The big difference from the control-plane point of view is that the LSP for a network media channel also covers the endpoints (the transceivers) and the cross-connects at the ingress and egress nodes. This is true no matter what the actual effective frequency slot is, since that can be sized pretty much however. The ports facing the client can still show up as interfaces from the control-plane side 💅
Figure 11 shows an LSP routed between three nodes. The LSP ends before the optical matrix of the ingress and egress nodes, so it can represent a media channel. It does not (and cannot) represent a network media channel, because it doesn't include (and can't 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. From the figures you can see that, from a GMPLS modeling perspective, there's no difference between these cases. They're shown as separate examples anyway, 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 🌈 Meanwhile, a signal-layer LSP (network media channel) is established mainly for managing and controlling 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 is great for spectral efficiency (reduced guard band between adjacent OChs in one FSC channel) and for LSP management. However, if 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 that situation, separating the signal layer from the media layer doesn't bring any benefit in spectral efficiency or in other aspects, and it makes the switching and control more complex 😭 If two OTSi must be switched to different ports, it's 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 can be achieved in two ways using LSPs. These mechanisms can be compared to the techniques GMPLS uses to support inverse multiplexing in Time Division Multiplexing (TDM) networks and in OTN [RFC4606] [RFC6344] [RFC7139].
- 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.
- 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. On top of that, 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:
- Slot widths: The minimum and maximum slot width.
- 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).
- 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".
- 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 ✨
okay so a media channel comes with an associated effective frequency slot 🎀 From the network control and management side, this effective slot is the "usable" end-to-end frequency slot, which is giving main character energy. Setting up an LSP is tied to setting up the media channel and configuring that effective slot, so they go together 🦋
A "service request" is characterized (at a minimum) by its required effective slot width 💅 It can add extra constraints too, like also asking for a particular 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. No matter how it's encoded, the LSP setup message says what minimum effective frequency slot width has to be met for the requested LSP to be successfully established 🫶
An effective frequency slot also has to be described by a central nominal frequency and its slot width, where the width is measured in terms of the usable spectrum of that effective slot 🌸 Basically, you must be able to work out the end-to-end values of the n and m parameters. We put it this way: the "effective frequency slot of the media channel or LSP must be valid" 💜
In GMPLS, the requested effective frequency slot goes into the TSpec in the RSVP-TE Path message, and the effective frequency slot gets mapped to the FlowSpec carried in the RSVP-TE Resv message 🧚
In GMPLS-controlled systems, the switched element is the 'label' 🍓 In flexi-grid, the switched element is a frequency slot, and the label represents a frequency slot. So the label in flexi-grid carries everything needed to get the frequency slot characteristics (the central frequency and slot width, aka the n and m parameters) ✨ The frequency slot is locally identified by the label 🌈
The local frequency slot can change at each hop, because hardware constraints and capabilities vary (for example, a given node might not support the finest granularity) 🙈 That means the values of n and m can change at each hop. As long as a downstream node allocates enough optical spectrum, m can be different along the path. This covers the situation where media matrices have different slot width granularities. These local changes to m show up in the allocated label that encodes the frequency slot, and in the FlowSpec that describes the flow 💖
There are different operational modes to think about. 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 what's described in Section 4.1.3 of [RFC6163] for Routing and Wavelength Assignment (RWA) and for Routing and Distributed Wavelength Assignment (R+DWA). The big difference is that the label set specifies the available nominal central frequencies that meet the LSP's slot width requirements 🔥
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 so it can assign the right frequency resource. Apart from identifying the resource (fixed wavelength for WSON, and frequency resource for flexible grids), the other signaling requirements (like unidirectional or bidirectional, and with or without converters) are the same as for WSON, as described in Section 6.1 of [RFC6163] 🦋
Now, about how a GMPLS control plane can assign n and m hop by hop along an LSP path, there are a few different cases 💅
- a.
nandmcan both change. What matters is the effective frequency slot, and it needs to stay valid along the path 🌸 - b.
mcan change, butnneeds to stay the same along the path. This keeps the nominal central frequency fixed while the slot width can vary along the path. Again, the key thing is that the effective frequency slot stays valid and satisfies the requested parameters along the whole LSP path 🫶 - c.
nandmneed to be unchanging along the path. This makes the frequency slot well known from end to end, and it's a simple way to keep the effective frequency slot valid for the whole LSP ✨ - d.
ncan change, butmneeds to stay the same along the path. This keeps the effective frequency slot valid while still letting the frequency slot move around within the spectrum from hop to hop 🦋
Path selection that keeps n and m continuous can be handed off to a dedicated entity like a Path Computation Element (PCE) 🧚 Any constraint (including frequency slot and width granularities) can be considered during path computation. Or, a PCE can compute the path and leave the actual frequency slot assignment to a distributed (signaling) procedure, for example:
- Each downstream node ensures that
mis>= requested_m. - A downstream node can't predict what an upstream node will allocate 🙈 One way to keep the effective frequency slot valid along the whole LSP is to allocate the same value of
nat each hop. By forcing the samen, we avoid cases where the effective frequency slot of the media channel is invalid (meaning the resulting frequency slot can't be described by itsnandmparameters) 💀 - This might be too restrictive, since a node (or even a centralized or combined RSA entity) may be able to make sure the resulting end-to-end effective frequency slot is valid, even if
nvaries locally 🌈 In that case, the end-to-end effective frequency slot that characterizes the media channel is still consistent and determined by itsnandmvalues. But those values are logical rather than mapping "direct" to the physically assigned spectrum. They're the result of the intersection of locally assigned frequency slots at local components (like filters), and each of those may have different frequency slots assigned to them 💖
As shown in Figure 15, the effective slot is made valid by making sure the minimum m is greater than the requested m. The effective slot (intersection) is the lowest m (the 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 nIn Figure 16, the effective slot is made valid by making sure it's valid at each hop in the upstream direction. The intersection has 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 nNote that when a media channel is bound to one OTSi (meaning it's 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 🦋
okay, real talk, there are potential interworking problems between fixed-grid DWDM nodes and flexi-grid DWDM nodes 😭 And even two flexi-grid nodes can have different grid properties, which leads to link property conflicts and limited interworking 💀
Devices or applications that use flexi-grid might not be able to support every possible slot width 🌸 So different applications may be defined, with each one supporting a different grid granularity. In that case, the link between two optical nodes with different grid granularities must be configured to line up with the larger of the two granularities 🫶 On top of that, different nodes may have different slot width tuning ranges 🧚
In summary, for a DWDM link between two nodes, at a minimum, these properties need to be negotiated 👑
- Grid capability (channel spacing), between fixed-grid and flexi-grid nodes.
- Grid granularity, between two flexi-grid nodes.
- Slot width tuning range, between two flexi-grid nodes.
bestie, the whole point of this part is that the effective slot has to stay valid end to end, so every node has to agree on n and m 💖
4.7. Path Computation, Routing and Spectrum Assignment (RSA) ✨
okay so in WSON, if there's no (available) wavelength converter in the optical network, an LSP gets hit with the "wavelength continuity constraint" 😤 (see Section 4 of [RFC6163]). Same vibe in flexi-grid: if the box can't shift or convert an allocated frequency slot, the LSP is stuck with the "spectrum continuity constraint" 💅
Converters are rare in a "sparse translucent optical network" 🥀 so the spectrum continuity constraint is basically always in play 🙈 If optical nodes do have spectrum conversion capabilities, RSA mechanisms can use that info 🫶
RSA is the process that picks a route and a frequency slot for an LSP 🦋 So once the route is computed, spectrum assignment decides the central frequency and slot width based on:
- the requested slot width
- the transmitter and receiver capabilities, including which central frequencies are available and how granular their slot widths are
- the available frequency slots (frequency ranges) and available slot widths on the links along the route
4.7.1. Architectural Approaches to RSA
4.7.1.1. Architectural Approaches
Like RWA for fixed grids [RFC6163], there are different ways to do RSA alongside the control plane 🌸 The approaches in this doc are just for reference, and other options could totally get deployed too ✨
Also, all of these models support a composite media channel, whether it's backed by one control-plane LSP or a set of associated LSPs 💜
4.7.1.2. Combined RSA (R&SA)
Here one computation entity does both routing and frequency slot assignment 👑 It needs the detailed network info, like the connectivity topology of nodes and links, the available frequency ranges on each link, and node capabilities 🧠
That entity could live on a dedicated PCE server, in the provisioning app that requests the service, or on the ingress node 🏠
4.7.1.3. Separated RSA (R+SA)
Now the routing and the frequency slot assignment are split between different entities 🎀 The first one computes the routes and hands them off to the second, which assigns the frequency slot 🧚
The first entity needs the connectivity topology to find proper routes. The second entity needs the available frequency ranges of the links and the node capabilities to assign spectrum 💖
4.7.1.4. Routing and Distributed SA (R+DSA)
In this one, an entity computes the route, but frequency slot assignment happens hop by hop, in a distributed way, along the route 🦋 The available central frequencies that meet the spectrum continuity constraint have to get collected hop by hop along the route 😭 This procedure can be implemented by the GMPLS signaling protocol ✨
4.8. Routing and Topology Dissemination
For the combined RSA architecture, the computation entity needs detailed network info: connectivity topology, node capabilities, and available frequency ranges of the links 🔥 Route computation runs on the connectivity topology and node capabilities, while spectrum assignment runs on the available frequency ranges of the links 💅 The computation entity may get this detailed info through 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]) 🌈 Apart from wavelength-specific availability info, flexi-grid info is the same as WSON's and can be distributed by the GMPLS routing protocol too 💜
This section looks at the link info changes that flexible grids need 🍓
4.8.1. Available Frequency Ranges (Frequency Slots) of DWDM Links
With flexible grids, channel central frequencies stretch from 193.1 THz toward both ends of the C-band spectrum, with a granularity of 6.25 GHz 🌸 Different LSPs can use different slot widths on the same link, so the available frequency ranges need to be advertised 🎀
4.8.2. Available Slot Width Ranges of DWDM Links
Available slot width ranges have to be advertised together with the available frequency ranges, so the computing entity can check whether an LSP with a given slot width can be set up 🔍 This is limited by the available slot width ranges of the media matrix 🥹 Depending on what slot width ranges are available, you might end up allocating more spectrum than the LSP strictly needs 🙃
4.8.3. Spectrum Management
The total available spectrum on a fiber can be treated as a resource that gets partitioned 🧁 For example, part of the spectrum could be handed to a third party to manage, or the operator could assign parts of it to different classes of traffic 🚦 This partitioning makes the spectrum look like a hierarchy to the management and control planes, since each partition could be partitioned again 🪆 But the hierarchy only exists inside the management system. It defines a hierarchy of access or management rights, and there's no matching resource hierarchy inside the fiber itself 🤯
The end of the fiber is a link end and shows up as a fiber port representing all the spectrum on the fiber 🔌 Each spectrum allocation shows up as a Link Channel Port (i.e., frequency slot port) inside the fiber 🧩 So there is a hierarchy of ownership (the Link Channel Port and corresponding LSP sit on a fiber, so they're tied to a fiber port), but there's no ongoing nesting of frequency slots inside larger frequency slots 🙅♀️ This kinda mirrors fixed-grid behavior, where a wavelength is tied to a fiber port and can't be subdivided, even though it's a slice of the total spectrum on the fiber 💫
4.8.4. Information Model
This section defines an information model that describes the data representing the capabilities and resources available in a flexi-grid network 📋 It's not a data model, and it isn't meant to limit any protocol solution, like an encoding for an IGP 🙅♀️ For example, the info needed for routing and path selection could be the set of available nominal central frequencies that a frequency slot of the required width can be allocated from 🎯 A convenient encoding for this info is left for further study in an IGP encoding document 📚
Fixed DWDM grids can also be described by choosing suitable slots in a flexible DWDM grid 🧠 But devices or apps that use the flexible grid might not support every possible slot width or central frequency position 🥺 So the information model needs to enable:
- the exchange of information to enable RSA in a flexi-grid network
- the representation of a fixed-grid device participating in a flexi-grid network
- full interworking of fixed-grid and flexible-grid devices within the same network
- 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
5. Control-Plane Requirements
Flexi-grid networks put extra requirements on the GMPLS protocols 🦾 This section sums up those requirements for signaling and routing 💻
5.1. Support for Media Channels
The control plane SHALL be able to support media channels, each characterized by a single frequency slot 🎧 In the GMPLS control plane, a media channel is represented as a so-called "flexi-grid LSP" 🌟 Since network media channels are media channels, an LSP can also be the control-plane representation of a network media channel 🔁 So the control plane will be able to support network media channels too 🙌
5.1.1. Signaling
The signaling procedure SHALL be able to configure the nominal central frequency (n) of a flexi-grid LSP 🎯
The signaling procedure SHALL allow a flexible range of values for the frequency slot width (m) parameter 📏 To be specific, the control plane SHALL allow setting up a media channel with a frequency slot width (m) from a minimum of m = 1 (12.5 GHz) up to the entire C-band (the wavelength range 1530 nm to 1565 nm, which matches the amplification range of erbium-doped fiber amplifiers), with a slot width granularity of 12.5 GHz 🌈
The signaling procedure SHALL be able to configure the minimum width (m) of a flexi-grid LSP ✨ On top of that, the signaling procedure SHALL be able to configure local frequency slots 🧩
The control-plane architecture SHOULD allow for support of the L-band (the wavelength range 1565 nm to 1625 nm) and the S-band (the wavelength range 1460 nm to 1530 nm) 🎶
The signaling process SHALL be able to collect the local frequency slot assigned at each link along the path 🛤️
The signaling procedures SHALL support all of the RSA architectural models (R&SA, R+SA, and R+DSA) within a single set of protocol objects, although some objects may only apply within one of the models 🫧
5.1.2. Routing
The routing protocol will support all functions described in [RFC4202] and extend them to a flexi-grid data plane 🗺️
The routing protocol SHALL distribute enough information to compute paths so the signaling procedure can establish LSPs as described in the previous sections 🧭 At a minimum, this includes the data described by the information model in Figure 17 📋
The routing protocol SHALL update its advertisements of available resources and capabilities as resource usage in the network changes with LSP establishment or teardown 🔄 These updates SHOULD be amenable to damping and thresholds, just like other traffic engineering routing advertisements 🫶
The routing protocol SHALL support all of the RSA architectural models (R&SA, R+SA, and R+DSA) without any configuration or change of behavior 💅 So the routing protocols SHALL be agnostic to the computation and signaling model in use 🦋
5.2. Support for Media Channel Resizing ✨
okay so the signaling procedures SHALL let you resize a media channel or network media channel, meaning grow it or shrink it 📏. the frequency slot width is the thing that changes here. the resize MAY also mean resizing the local frequency slots along the path of the flexi-grid LSP 🛤️
the routing protocol SHALL keep its advertisements of available resources and capabilities up to date as resource usage shifts with LSP resizing 📡. these updates SHOULD be friendly to damping and thresholds, just like the other traffic engineering routing advertisements 🫶
5.3. Support for Logical Associations of Multiple Media Channels 🔗
so a set of media channels can carry signals that are logically tied together 🧵. the control-plane architecture SHOULD allow multiple media channels to be logically associated 💜. the control plane SHOULD also allow a set of logically associated media channels to be co-routed 🛣️. bestie, that's the whole vibe.
5.4. Support for Composite Media Channels 🧩
as we covered in Sections 3.2.5 and 4.3, a media channel can be made up of multiple network media channels 🍰.
the signaling procedures SHOULD include support for signaling one single control-plane LSP that carries info about all the network media channels that together form that one compound media channel 📦.
the signaling procedures SHOULD include a mechanism to associate separately signaled control-plane LSPs, so the endpoints can correlate them into a single compound media channel 🔍.
the signaling procedures MAY include a mechanism to change the makeup of a composite media channel on the fly, adding network media channels to the whole or taking them away 🎢.
the routing protocols MUST provide enough info to compute paths and slots for composite media channels under any of the three RSA architectural models (R&SA, R+SA, and R+DSA). no skipping, no excuses ‼️
5.5. Support for Neighbor Discovery and Link Property Correlation 🤝
the control plane MAY include neighbor discovery so a flexi-grid network can be built in a "plug-and-play" way 🔌. heads up though: in normal operational practice, people use validation processes instead of automatic discovery, so don't get your hopes up too high 🙈.
the control plane SHOULD let the nodes at opposite ends of a link correlate the properties they'll each apply to that link 👯. that correlation SHOULD include at least the identities of the nodes and the identities they apply to the link 🪪. other properties, like the link characteristics described for the routing information model in Figure 17, SHOULD also be correlated ✨.
neighbor discovery and link property correlation, if they're provided, MUST be able to operate over both an out-of-band and an out-of-fiber control channel 🛰️.
6. Security Considerations 🔐
the control-plane and data-plane aspects of a flexi-grid system are basically the same as a fixed-grid system, so there's no real reason to expect the security considerations to be any different 🙌.
a good overview of security considerations for a GMPLS-based control plane can be found in [RFC5920] 📖.
[RFC6163] has a section on security considerations for WSON, and it's fair to infer that those considerations apply to flexi-grid SSON systems too, and may be even worse there 😭. the detailed, granular information describing a flexi-grid network and the capabilities of its nodes could put stress on the routing protocol or on the out-of-band control channel the protocol uses. an attacker might be able to cause small variations in how the network is used or in the resources available (maybe by messing with the environment of a fiber 👀), and that could trigger the routing protocol to send new flooding announcements. this is explicitly handled in the routing protocol extension requirements, which say the protocol must include damping and configurable thresholds, just like the core GMPLS routing protocols already do 🛡️.
7. Manageability Considerations 🛠️
GMPLS systems already come with a bunch of management tools 🧰:
- MIB modules already exist to model the control-plane protocols and the network elements [RFC4802] [RFC4803], and there's early work to offer similar access through YANG 📚. these models are currently designed for fixed-label technologies like optical networks using the fixed grid, so extensions may be needed to represent bandwidth, frequency slots, and effective frequency slots in flexi-grid networks 🌈.
- GMPLS signaling already has protocol extensions that let control-plane systems report faults affecting LSPs [RFC4783] 🚨. but be careful here: these mechanisms are NOT an alarm mechanism that could rapidly spread fault info so the data plane could do protection switching 🙅♀️. these mechanisms could easily be enhanced with technology-specific reason codes if any are needed 💅.
- the GMPLS protocols already include their own fault detection and recovery mechanisms, like the PathErr and Notify messages in RSVP-TE signaling as used by GMPLS [RFC3473] 🔁. it's not expected that these will need enhancing to support flexi-grid, though additional reason codes may be needed to describe technology-specific error cases 🍓.
- [RFC7260] describes a framework for the control and configuration of data-plane Operations, Administration, and Maintenance (OAM) 🧭. it would not be appropriate for the IETF to define or describe data-plane OAM for optical systems. still, the framework described in RFC 7260 could be used, with minor protocol extensions, to enable data-plane OAM defined by the originators of the flexi-grid data-plane technology (the ITU-T) 🦋.
- the Link Management Protocol (LMP) [RFC4204] is designed to let the two ends of a network link coordinate and confirm the configuration and capabilities they'll apply to the link 🤙. LMP is especially useful for optical links, where device characteristics can seriously affect how the link is used, and where misconfiguration or mis-fibering could make physical interoperability impossible 💀. LMP could easily be extended to collect and report info between the endpoints of links in a flexi-grid network 🌸.
8. References 📚
8.1. Normative References
- [G.694.1] International Telecommunication Union, "Spectral grids for WDM applications: DWDM frequency grid", ITU-T Recommendation G.694.1, February 2012,
https://www.itu.int/rec/T-REC-G.694.1/en. - [G.800] International Telecommunication Union, "Unified functional architecture of transport networks", ITU-T Recommendation G.800, February 2012,
http://www.itu.int/rec/T-REC-G.800/. - [G.805] International Telecommunication Union, "Generic functional architecture of transport networks", ITU-T Recommendation G.805, March 2000,
https://www.itu.int/rec/T-REC-G.805-200003-I/en. - [G.8080] International Telecommunication Union, "Architecture for the automatically switched optical network", ITU-T Recommendation G.8080/Y.1304, February 2012,
https://www.itu.int/rec/T-REC-G.8080-201202-I/en. - [G.870] International Telecommunication Union, "Terms and definitions for optical transport networks", ITU-T Recommendation G.870/Y.1352, October 2012,
https://www.itu.int/rec/T-REC-G.870/en. - [G.872] International Telecommunication Union, "Architecture of optical transport networks", ITU-T Recommendation G.872, October 2012,
http://www.itu.int/rec/T-REC-G.872-201210-I. - [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997,
http://www.rfc-editor.org/info/rfc2119. - [RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Architecture", RFC 3945, DOI 10.17487/RFC3945, October 2004,
http://www.rfc-editor.org/info/rfc3945. - [RFC4202] Kompella, K., Ed., and Y. Rekhter, Ed., "Routing Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4202, DOI 10.17487/RFC4202, October 2005,
http://www.rfc-editor.org/info/rfc4202. - [RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP) Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS) Traffic Engineering (TE)", RFC 4206, DOI 10.17487/RFC4206, October 2005,
http://www.rfc-editor.org/info/rfc4206. - [RFC5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax Used to Form Encoding Rules in Various Routing Protocol Specifications", RFC 5511, DOI 10.17487/RFC5511, April 2009,
http://www.rfc-editor.org/info/rfc5511.
8.2. Informative References
okay so this is the bibliography bit, but make it cute 🎀 these are the background reads that helped build the whole vibe, and I'm keeping every single entry exactly as it was because bestie, citations are sacred 🫶
[G.959.1-2013]
International Telecommunication Union, "Optical transport
network physical layer interfaces", Update to ITU-T
Recommendation G.959.1, 2013.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
DOI 10.17487/RFC3473, January 2003,
<http://www.rfc-editor.org/info/rfc3473>.
[RFC4204] Lang, J., Ed., "Link Management Protocol (LMP)", RFC 4204,
DOI 10.17487/RFC4204, October 2005,
<http://www.rfc-editor.org/info/rfc4204>.
[RFC4397] Bryskin, I. and A. Farrel, "A Lexicography for the
Interpretation of Generalized Multiprotocol Label
Switching (GMPLS) Terminology within the Context of the
ITU-T's Automatically Switched Optical Network (ASON)
Architecture", RFC 4397, DOI 10.17487/RFC4397,
February 2006, <http://www.rfc-editor.org/info/rfc4397>.
[RFC4606] Mannie, E. and D. Papadimitriou, "Generalized
Multi-Protocol Label Switching (GMPLS) Extensions for
Synchronous Optical Network (SONET) and Synchronous
Digital Hierarchy (SDH) Control", RFC 4606,
DOI 10.17487/RFC4606, August 2006,
<http://www.rfc-editor.org/info/rfc4606>.
[RFC4783] Berger, L., Ed., "GMPLS - Communication of Alarm
Information", RFC 4783, DOI 10.17487/RFC4783,
December 2006, <http://www.rfc-editor.org/info/rfc4783>.
[RFC4802] Nadeau, T., Ed., Farrel, A., and , "Generalized
Multiprotocol Label Switching (GMPLS) Traffic Engineering
Management Information Base", RFC 4802,
DOI 10.17487/RFC4802, February 2007,
<http://www.rfc-editor.org/info/rfc4802>.
[RFC4803] Nadeau, T., Ed., and A. Farrel, Ed., "Generalized
Multiprotocol Label Switching (GMPLS) Label Switching
Router (LSR) Management Information Base", RFC 4803,
DOI 10.17487/RFC4803, February 2007,
<http://www.rfc-editor.org/info/rfc4803>.
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
<http://www.rfc-editor.org/info/rfc5920>.
[RFC6163] Lee, Y., Ed., Bernstein, G., Ed., and W. Imajuku,
"Framework for GMPLS and Path Computation Element (PCE)
Control of Wavelength Switched Optical Networks (WSONs)",
RFC 6163, DOI 10.17487/RFC6163, April 2011,
<http://www.rfc-editor.org/info/rfc6163>.
[RFC6344] Bernstein, G., Ed., Caviglia, D., Rabbat, R., and H. van
Helvoort, "Operating Virtual Concatenation (VCAT) and the
Link Capacity Adjustment Scheme (LCAS) with Generalized
Multi-Protocol Label Switching (GMPLS)", RFC 6344,
DOI 10.17487/RFC6344, August 2011,
<http://www.rfc-editor.org/info/rfc6344>.
[RFC7139] Zhang, F., Ed., Zhang, G., Belotti, S., Ceccarelli, D.,
and K. Pithewan, "GMPLS Signaling Extensions for Control
of Evolving G.709 Optical Transport Networks", RFC 7139,
DOI 10.17487/RFC7139, March 2014,
<http://www.rfc-editor.org/info/rfc7139>.
[RFC7260] Takacs, A., Fedyk, D., and J. He, "GMPLS RSVP-TE
Extensions for Operations, Administration, and Maintenance
(OAM) Configuration", RFC 7260, DOI 10.17487/RFC7260,
June 2014, <http://www.rfc-editor.org/info/rfc7260>.Acknowledgments
big thank yous to the squad 🙏💖 the authors want to shout out Pete Anslow for his insights and clarifications, and Matt Hartley and Jonas Maertensson for their reviews. 🫶
also this work was supported in part by the FP-7 IDEALIST project under grant agreement number 317999. ✨ literally funded by a real grant, so iconic 🌈
Contributors
the people who helped shape this one, all listed exactly as they appear in the original 🦋
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
Daniel King
Old Dog Consulting
Email: daniel@olddog.co.uk
Xian Zhang
Huawei
Email: zhang.xian@huawei.com
Cyril Margaria
Juniper Networks
Email: cmargaria@juniper.net
Qilei Wang
ZTE
Ruanjian Avenue, Nanjing, China
Email: wang.qilei@zte.com.cn
Malcolm Betts
ZTE
Email: malcolm.betts@zte.com.cn
Sergio Belotti
Alcatel-Lucent
Optics CTO
Via Trento 30 20059 Vimercate (Milano) Italy
Phone: +39 039 686 3033
Email: sergio.belotti@alcatel-lucent.com
Yao Li
Nanjing University
Email: wsliguotou@hotmail.com
Fei Zhang
Huawei
Email: zhangfei7@huawei.com
Lei Wang
Email: wang.lei@bupt.edu.cn
Guoying Zhang
China Academy of Telecom Research
No.52 Huayuan Bei Road, Beijing, China
Email: zhangguoying@ritt.cn
Takehiro Tsuritani
KDDI R&D Laboratories Inc.
2-1-15 Ohara, Fujimino, Saitama, Japan
Email: tsuri@kddilabs.jp
Lei Liu
UC Davis, United States
Email: leiliu@ucdavis.edu
Eve Varma
Alcatel-Lucent
Phone: +1 732 239 7656
Email: eve.varma@alcatel-lucent.com
Young Lee
Huawei
Jianrui Han
Huawei
Sharfuddin Syed
Infinera
Rajan Rao
Infinera
Marco Sosa
Infinera
Biao Lu
Infinera
Abinder Dhillon
Infinera
Felipe Jimenez Arribas
Telefonica I+D
Andrew G. Malis
Huawei
Email: agmalis@gmail.com
Huub van Helvoort
Hai Gaoming BV
The Netherlands
Email: huubatwork@gmail.comAuthors' Addresses
and last but not least, where to find the editors and authors 💌🌸
Oscar Gonzalez de Dios (editor)
Telefonica I+D
Ronda de la Comunicacion s/n
Madrid 28050
Spain
Phone: +34 91 312 96 47
Email: oscar.gonzalezdedios@telefonica.com
Ramon Casellas (editor)
CTTC
Av. Carl Friedrich Gauss n.7
Castelldefels Barcelona
Spain
Phone: +34 93 645 29 00
Email: ramon.casellas@cttc.es
Fatai Zhang
Huawei
Huawei Base, Bantian, Longgang District
Shenzhen 518129
China
Phone: +86 755 28972912
Email: zhangfatai@huawei.com
Xihua Fu
Stairnote
No.118, Taibai Road, Yanta District
Xi'An
China
Email: fu.xihua@stairnote.com
Daniele Ceccarelli
Ericsson
Via Calda 5
Genova
Italy
Phone: +39 010 600 2512
Email: daniele.ceccarelli@ericsson.com
Iftekhar Hussain
Infinera
140 Caspian Ct.
Sunnyvale, CA 94089
United States
Phone: 408 572 5233
Email: ihussain@infinera.comthat's the whole thing, bestie! 🎉💅 every spec, every email, every reference is right where it belongs ✨
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