Internet Engineering Task Force (IETF) Q. Wang, Ed.

Internet Engineering Task Force (IETF) Q. Wang, Ed.
Request for Comments: 9376 ZTE Corporation
Category: Informational R. Valiveti, Ed.
ISSN: 2070-1721 Infinera Corp
H. Zheng, Ed.
Huawei
H. van Helvoort
Hai Gaoming BV
S. Belotti
Nokia
March 2023

Applicability of GMPLS for beyond 100 Gbit/s Optical Transport Network

Abstract

This document examines the applicability of using existing GMPLS
routing and signaling mechanisms to set up Optical Data Unit-k (ODUk)
Label Switched Paths (LSPs) over Optical Data Unit-Cn (ODUCn) links
as defined in the 2020 version of ITU-T Recommendation G.709.

Status of This Memo

This document is not an Internet Standards Track specification; it is
published for informational purposes.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9376.

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Table of Contents

1. Introduction
2. OTN Terminology Used in This Document
3. Overview of OTUCn/ODUCn in G.709
3.1. OTUCn
3.1.1. OTUCn-M
3.2. ODUCn
3.3. Tributary Slot Granularity
3.4. Structure of OPUCn MSI with Payload Type 0x22
3.5. Client Signal Mappings
4. GMPLS Implications and Applicability
4.1. TE Link Representation
4.2. GMPLS Signaling
4.3. GMPLS Routing
5. IANA Considerations
6. Security Considerations
7. References
7.1. Normative References
7.2. Informative References
Appendix A. Possible Future Work
Contributors
Authors' Addresses

1. Introduction

The current GMPLS routing [RFC7138] and signaling [RFC7139]
extensions support the control of the Optical Transport Network (OTN)
signals and capabilities that were defined in the 2012 version of
ITU-T Recommendation G.709 [ITU-T_G709_2012].

In 2016, a new version of ITU-T Recommendation G.709 was published:
[ITU-T_G709_2016]. This version introduced higher-rate Optical
Transport Unit (OTU) and Optical Data Unit (ODU) signals, termed
"OTUCn" and "ODUCn", respectively, which have a nominal rate of n*100
Gbit/s. According to the definition in [ITU-T_G709_2016], OTUCn and
ODUCn perform only the digital section-layer role, and ODUCn supports
only ODUk clients. This document focuses on the use of existing
GMPLS mechanisms to set up ODUk (e.g., ODUflex) Label Switched Paths
(LSPs) over ODUCn links, independently from how these links have been
set up.

Because [ITU-T_G709_2020] does not introduce any new features to
OTUCn and ODUCn compared to [ITU-T_G709_2016], this document first
presents an overview of the OTUCn and ODUCn signals in
[ITU-T_G709_2020] and then analyzes how the current GMPLS routing and
signaling mechanisms can be utilized to set up ODUk (e.g., ODUflex)
LSPs over ODUCn links.

This document assumes that readers are familiar with OTN, GMPLS, and
how GMPLS is applied in OTN. As such, this document doesn't provide
any background pertaining to OTN that include links with capacities
of 100 Gbit/s or less; this background could be found in documents
such as [RFC7062] and [RFC7096]. This document provides an overview
of the data plane primitives that enable links with capacities
greater than 100 Gbit/s and analyzes the extensions that would be
required in the current GMPLS routing and signaling mechanisms to
support evolution in OTN.

2. OTN Terminology Used in This Document

FlexO: Flexible OTN information structure. This information
structure usually has a specific bitrate and frame format that
consists of overhead and payload, which are used as a group for
the transport of an OTUCn signal.

LSP: Label Switched Path

MSI: Multiplex Structure Indicator. This structure indicates the
grouping of the tributary slots in an OPU payload area that
realizes a client signal, which is multiplexed into an OPU. The
individual clients multiplexed into the OPU payload area are
distinguished by the Tributary Port Number (TPN).

ODU: Optical Data Unit. An ODU has the frame structure and
overhead, as defined in Figure 12-1 of [ITU-T_G709_2020]. ODUs
can be formed in two ways: a) by encapsulating a single non-OTN
client, such as SONET/SDH (Synchronous Optical Network /
Synchronous Digital Hierarchy) or Ethernet, or b) by multiplexing
lower-rate ODUs. In general, the ODU layer represents the path
layer in OTN. The only exception is the ODUCn signal (defined
below), which is defined to be a section-layer signal. In the
classification based on bitrates of the ODU signals, ODUs are of
two types: fixed rate and flexible rate. Flexible-rate ODUs,
called "ODUflex", have a rate that is 239/238 times the bitrate of
the client signal they encapsulate.

ODUC: Optical Data Unit-C. This signal has a bandwidth of
approximately 100 Gbit/s and is of a slightly higher bitrate than
the fixed rate ODU4 signal. This signal has the format defined in
Figure 12-1 of [ITU-T_G709_2020]. This signal represents the
building block for constructing a higher-rate signal called
"ODUCn" (defined below).

ODUCn: Optical Data Unit-Cn, where Cn indicates the bitrate of
approximately n*100 Gbit/s. This frame structure consists of "n"
interleaved frame and multiframe synchronous instances of the ODUC
signal, each of which has the format defined in Figure 12-1 of
[ITU-T_G709_2020].

ODUflex: Optical Data Unit - flexible rate. An ODUflex has the same
frame structure as a "generic" ODU but with a rate that is a fixed
multiple of the bitrate of the client signal it encapsulates.
[ITU-T_G709_2020] defines specific ODUflex containers that are
required to transport specific clients such as 50GE, 200GE, 400GE,
etc.

ODUk: Optical Data Unit-k, where k is one of {0, 1, 2, 2e, 3, 4}.
The term "ODUk" refers to an ODU whose bitrate is fully specified
by the index k. The bitrates of the ODUk signal for k = {0, 1, 2,
2e, 3, 4} are approximately 1.25 Gbit/s, 2.5 Gbit/s, 10 Gbit/s,
10.3 Gbit/s, 40 Gbit/s, and 100 Gbit/s, respectively.

OPUC: Optical Payload Unit-C. This signal has a payload of
approximately 100 Gbit/s. This structure represents the payload
area of the ODUC signal.

OPUCn: Optical Payload Unit-Cn, where Cn indicates that the bitrate
is approximately n*100 Gbit/s. This structure represents the
payload area of the ODUCn signal.

OTN: Optical Transport Network

OTUC: Optical Transport Unit-C. This signal has a bandwidth of
approximately 100 Gbit/s. This signal forms the building block of
the OTUCn signal defined below, which has a bandwidth of
approximately n*100 Gbit/s.

OTUCn: Fully standardized Optical Transport Unit-Cn. This frame
structure is realized by extending the ODUCn signal with the OTU
layer overhead. The structure of this signal is illustrated in
Figure 11-4 of [ITU-T_G709_2020]. Note that the term "fully
standardized" is defined by ITU-T in Section 6.1.1 of
[ITU-T_G709_2020].

OTUCn-M: This signal is an extension of the OTUCn signal introduced
above. This signal contains the same amount of overhead as the
OTUCn signal but contains a reduced amount of payload area.
Specifically, the payload area consists of M tributary slots (each
5 Gbit/s), where M is less than 20*n, which is the number of
tributary slots in the OTUCn signal.

PSI: Payload Structure Indicator. This is a 256-byte signal that
describes the composition of the OPU signal. This field is a
concatenation of the payload type (PT) and the Multiplex Structure
Indicator (MSI) defined below.

TPN: Tributary Port Number. The tributary port number is used to
indicate the port number of the client signal that is being
transported in one specific tributary slot.

Detailed descriptions for some of these terms can be found in
[ITU-T_G709_2020].

3. Overview of OTUCn/ODUCn in G.709

This section provides an overview of the OTUCn/ODUCn signals defined
in [ITU-T_G709_2020]. The text in this section is purely descriptive
and is not normative. For a full description of OTUCn/ODUCn signals,
please refer to [ITU-T_G709_2020]. In the event of any discrepancy
between this text and [ITU-T_G709_2020], that other document is
definitive.

3.1. OTUCn

In order to carry client signals with rates greater than 100 Gbit/s,
[ITU-T_G709_2020] takes a general and scalable approach that
decouples the rates of OTU signals from the client rate. The new OTU
signal is called "OTUCn", and this signal is defined to have a rate
of (approximately) n*100 Gbit/s. The following are the key
characteristics of the OTUCn signal:

* The OTUCn signal contains one ODUCn. The OTUCn and ODUCn signals
perform digital section-layer roles only (see Section 6.1.1 of
[ITU-T_G709_2020])

* The OTUCn signals are formed by interleaving n synchronous OTUC
signals (which are labeled 1, 2, ..., n).

* Each of the OTUC instances has the same overhead as the standard
OTUk signal in [ITU-T_G709_2020]. Note that the OTUC signal
doesn't include the Forward Error Correction (FEC) columns
illustrated in Figure 11-1 of [ITU-T_G709_2020]. The OTUC signal
includes an ODUC.

* The OTUC signal has a slightly higher rate compared to the OTU4
signal (without FEC); this is to ensure that the OPUC payload area
can carry an ODU4 signal.

* The combined signal OTUCn has n instances of OTUC overhead and n
instances of ODUC overhead.

The OTUCn, ODUCn, and OPUCn signal structures are presented in a
(physical) interface-independent manner, by means of n OTUC, ODUC,
and OPUC instances that are marked #1 to #n.

OTUCn interfaces can be categorized as follows, based on the type of
peer network element:

inter-domain interfaces: These types of interfaces are used for
connecting OTN edge nodes to (a) client equipment (e.g., routers)
or (b) hand-off points from other OTN. ITU-T Recommendation
G709.1 [ITU-T_G709.1] specifies a flexible interoperable short-
reach OTN interface over which an OTUCn (n >=1) is transferred,
using bonded Flexible OTN information structure (FlexO)
interfaces, which belong to a FlexO group.

intra-domain interfaces: In these cases, the OTUCn is transported
using a proprietary (vendor-specific) encapsulation, FEC, etc. It
is also possible to transport OTUCn for intra-domain links using
FlexO.

3.1.1. OTUCn-M

The standard OTUCn signal has the same rate as the ODUCn signal.
This implies that the OTUCn signal can only be transported over
wavelength groups that have a total capacity of multiples of
(approximately) 100 Gbit/s. Modern optical interfaces support a
variety of bitrates per wavelength, depending on the reach
requirements for the optical path. If the total rate of the ODUk
LSPs planned to be carried over an ODUCn link is smaller than n*100
Gbit/s, it is possible to "crunch" the OTUCn, and the unused
tributary slots are thus not transmitted. [ITU-T_G709_2020] supports
the notion of a reduced-rate OTUCn signal, termed "OTUCn-M". The
OTUCn-M signal is derived from the OTUCn signal by retaining all the
n instances of overhead (one per OTUC instance) but with only M (M is
less than 20*n) OPUCn tributary slots available to carry ODUk LSPs.

3.2. ODUCn

The ODUCn signal defined in [ITU-T_G709_2020] can be viewed as being
formed by the appropriate interleaving of content from n ODUC signal
instances. The ODUC frames have the same structure as a standard ODU
in the sense that the frames have the same overhead and payload areas
but have a higher rate since their payload area can embed an ODU4
signal.

The ODUCn is a multiplex section ODU signal and is mapped into an
OTUCn signal, which provides the regenerator section layer. In some
scenarios, the ODUCn and OTUCn signals will be coterminated, i.e.,
they will have identical source/sink locations (see Figure 1). In
Figure 1, the term "OTN Switch" has the same meaning as that used in
Section 3 of [RFC7138]. [ITU-T_G709_2020] allows for the ODUCn
signal to pass through one or more digital regenerator nodes (shown
as nodes B and C in Figure 2), which will terminate the OTUCn layer
but will pass the regenerated (but otherwise untouched) ODUCn towards
a different OTUCn interface where a fresh OTUCn layer will be
initiated. This process is termed as "ODUCn regeneration" in
Section 7.1 of [ITU-T_G872]. In this example, the ODUCn is carried
by three OTUCn segments.

Specifically, the OPUCn signal flows through these regenerators
unchanged. That is, the set of client signals, their TPNs, and
tributary-slot allocations remains unchanged.

+--------+ +--------+
| +-----------+ |
| OTN |-----------| OTN |
| Switch +-----------+ Switch |
| A | | B |
| +-----------+ |
+--------+ +--------+
<--------ODUCn------->
<-------OTUCn------>

Figure 1: ODUCn Signal

+---------+ +--------+ +--------+ +--------+
| +--------+ | | +----------+ |
| OTN |--------| OTN | | OTN |----------| OTN |
| Switch +--------+ Regen +--------+ Regen +----------+ Switch |
| A | | B | | C | | D |
| +--------+ | | +----------+ |
+---------+ +--------+ +--------+ +--------+

<-------------------------ODUCn-------------------------->
<---------------><-----------------><------------------>
OTUCn OTUCn OTUCn

Figure 2: ODUCn Signal - Multi-Hop

3.3. Tributary Slot Granularity

[ITU-T_G709_2012] introduced the support for 1.25 Gbit/s granular
tributary slots in OPU2, OPU3, and OPU4 signals. [ITU-T_G709_2020]
defined the OPUC with a 5 Gbit/s tributary slot granularity. This
means that the ODUCn signal has 20*n tributary slots (of 5 Gbit/s
capacity). The range of tributary port number (TPN) is 10*n instead
of 20*n, which restricts the maximum client signals that could be
carried over one single ODUC1.

3.4. Structure of OPUCn MSI with Payload Type 0x22

As mentioned above, the OPUCn signal has 20*n tributary slots (TSs)
(each 5 Gbit/s). The OPUCn MSI field has a fixed length of 40*n
bytes and indicates the availability and occupation of each TS. Two
bytes are used for each of the 20*n tributary slots, and each such
information structure has the following format (see Section 20.4.1 of
[ITU-T_G709_2020]):

* The TS availability bit indicates if the tributary slot is
available or unavailable.

* The TS occupation bit indicates if the tributary slot is allocated
or unallocated.

* The tributary port number (14 bits) indicates the port number of
the client signal that is being carried in this specific TS. A
flexible assignment of tributary port to tributary slots is
possible. Numbering of tributary ports is from 1 to 10*n.

The concatenation of the OPUCn payload type (PT) and the MSI field is
carried over the overhead byte designated as PSI in Figure 15-6 of
[ITU-T_G709_2020].

3.5. Client Signal Mappings

The approach taken by the ITU-T to map non-OTN client signals to the
appropriate ODU containers is as follows:

* All client signals are mapped into an ODUj or ODUk (e.g., ODUflex)
as specified in Section 17 of [ITU-T_G709_2020].

* The terms "ODUj" and "ODUk" are used in a multiplexing scenario,
with ODUj being a low-order ODU that is multiplexed into ODUk, a
high-order ODU. As Figure 3 illustrates, the ODUCn is also a
high-order ODU into which other ODUs can be multiplexed. The
ODUCn itself cannot be multiplexed into any higher-rate ODU
signal; it is defined to be a section-level signal.

* ODUflex signals are low-order signals only. If the ODUflex
entities have rates of 100 Gbit/s or less, they can be transported
over either an ODUk (k=1..4) or an ODUCn. For ODUflex connections
with rates greater than 100 Gbit/s, ODUCn is required.

* ODU Virtual Concatenation (VCAT) has been deprecated. This
simplifies the network and the supporting hardware since multiple
different mappings for the same client are no longer necessary.
Note that legacy implementations that transported sub-100 Gbit/s
clients using ODU VCAT shall continue to be supported.

Clients (e.g., SONET/SDH and Ethernet)

| | | | | |
| | | | | |
| | | | | |
+---+---+---+----+ | | |
| OPUj | | | |
+----------------+ | | |
| ODUj | | | |
+----------------+----------------------+---+---+----------+
| |
| OPUk |
+----------------------------------------------------------+
| |
| ODUk k in {0,1,2,2e,3,4,flex}|
+-------------------------+-----+--------------------------+
| | | |
| OTUk, OTUk-SC, OTUk-V | | OPUCn |
+-------------------------+ +--------------------------+
| |
| ODUCn |
+--------------------------+
| |
| OTUCn |
+--------------------------+

Figure 3: Digital Structure of OTN Interfaces (from Figure 6-1 of
[ITU-T_G709_2020])

4. GMPLS Implications and Applicability

4.1. TE Link Representation

Section 3 of [RFC7138] describes how to represent G.709 OTUk/ODUk
with TE links in GMPLS. In the same manner, OTUCn links can also be
represented as TE links. Figure 4 provides an illustration of a one-
hop OTUCn TE link.

+----------+ +---------+
| OTN | | OTN |
| Switch +-------------------+ Switch |
| A | | B |
+----------+ +---------+

|<---------OTUCn Link---------->|

|<---------TE Link------------->|

Figure 4: One-Hop OTUCn TE Link

It is possible to create TE links that span more than one hop by
creating forward adjacencies (FAs) between non-adjacent nodes (see
Figure 5). In Figure 5, nodes B and C are performing the ODUCn
regeneration function described in Section 7.1 of [ITU-T_G872] and
are not electrically switching the ODUCn signal from one interface to
another. As in the one-hop case, multi-hop TE links advertise the
ODU switching capability.

+--------+ +--------+ +--------+ +---------+
| OTN | | OTN | | OTN | | OTN |
| Switch |<------->| Regen |<-------->| Regen |<------->| Switch |
| A | OTUCn | B | OTUCn | C | OTUCn | D |
+--------+ Link +--------+ Link +--------+ Link +---------+

|<-------------------- ODUCn Link -------------------->|

|<---------------------- TE Link --------------------->|

Figure 5: Multi-Hop ODUCn TE Link

The two endpoints of a TE link are configured with the supported
resource information (which may include whether the TE link is
supported by an ODUCn, ODUk, or OTUk), as well as the link attribute
information (e.g., slot granularity and list of available tributary
slot).

4.2. GMPLS Signaling

Once the ODUCn TE link is configured, the GMPLS mechanisms defined in
[RFC7139] can be reused to set up ODUk/ODUflex LSPs with no changes.
As the resource on the ODUCn link that can be seen by the ODUk/
ODUflex client signal is a set of 5 Gbit/s slots, the label defined
in [RFC7139] is able to accommodate the requirement of the setup of
an ODUk/ODUflex client signal over an ODUCn link. In [RFC7139], the
OTN-TDM GENERALIZED_LABEL object is used to indicate how the lower-
order (LO) ODUj signal is multiplexed into the higher-order (HO) ODUk
link. In a similar manner, the OTN-TDM GENERALIZED_LABEL object is
used to indicate how the ODUk signal is multiplexed into the ODUCn
link. The ODUk signal type is indicated by Traffic Parameters. The
IF_ID RSVP_HOP object provides a pointer to the interface associated
with TE link; therefore, the two nodes terminating the TE link know
(by internal/local configuration) the attributes of the ODUCn TE
Link.

The TPN defined in [ITU-T_G709_2020] (where it is referred to as
"tributary port #") for an ODUCn link has 14 bits while this field in
[RFC7139] only has 12 bits, so some extension work will eventually be
needed. Given that a 12-bit TPN field can support ODUCn links with
up to n=400 (i.e., 40 Tbit/s links), this need is not urgent.

The example in Figure 6 illustrates the label format defined in
[RFC7139] for multiplexing ODU4 onto ODUC10. One ODUC10 has 200
slots (each 5 Gbit/s), and twenty of them are allocated to the ODU4.
With this label encoding, only 20 out of the 200 bits mask are non-
zero, which is very inefficient. The inefficiency grows for larger
values of "n", and an optimized label format may be desirable.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TPN = 3 | Reserved | Length = 200 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0| Padding Bits(0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 6: Label Format

4.3. GMPLS Routing

For routing, it is deemed that no extension to the current mechanisms
defined in [RFC7138] is needed.

The ODUCn link, which is the lowest layer of the ODU multiplexing
hierarchy involving multiple ODU layers, is assumed to have been
already configured when GMPLS is used to set up ODUk over ODUCn;
therefore, the resources that need to be advertised are the resources
that are exposed by this ODUCn link and the ODUk multiplexing
hierarchy on it. The 5 Gbit/s OPUCn time slots do not need to be
advertised, while the 1.25 Gbit/s and 2.5 Gbit/s OPUk time slots need
to be advertised using the mechanisms already defined in [RFC7138].

Since there is a 1:1 correspondence between the ODUCn and the OTUCn
signal, there is no need to explicitly define a new value to
represent the ODUCn signal type in the OSPF-TE routing protocol.

5. IANA Considerations

This document has no IANA actions.

6. Security Considerations

This document analyzes the applicability of protocol extensions in
[RFC7138] and [RFC7139] for use in the 2020 version of ITU-T
Recommendation G.709 [ITU-T_G709_2020] and finds that no new
extensions are needed. Therefore, this document introduces no new
security considerations to the existing signaling and routing
protocols beyond those already described in [RFC7138] and [RFC7139].
Please refer to [RFC7138] and [RFC7139] for further details of the
specific security measures. Additionally, [RFC5920] addresses the
security aspects that are relevant in the context of GMPLS.

7. References

7.1. Normative References

[ITU-T_G709_2020]
ITU-T, "Interfaces for the optical transport network",
ITU-T Recommendation G.709, June 2020.

[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
<https://www.rfc-editor.org/info/rfc5920>.

[RFC7138] Ceccarelli, D., Ed., Zhang, F., Belotti, S., Rao, R., and
J. Drake, "Traffic Engineering Extensions to OSPF for
GMPLS Control of Evolving G.709 Optical Transport
Networks", RFC 7138, DOI 10.17487/RFC7138, March 2014,
<https://www.rfc-editor.org/info/rfc7138>.

[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,
<https://www.rfc-editor.org/info/rfc7139>.

7.2. Informative References

[ITU-T_G709.1]
ITU-T, "Flexible OTN short-reach interfaces", ITU-T
Recommendation G.709.1, June 2018.

[ITU-T_G709_2012]
ITU-T, "Interfaces for the optical transport network",
ITU-T Recommendation G.709, February 2012.

[ITU-T_G709_2016]
ITU-T, "Interfaces for the optical transport network",
ITU-T Recommendation G.709, June 2016.

[ITU-T_G872]
ITU-T, "Architecture of optical transport networks", ITU-T
Recommendation G.872, December 2019.

[RFC7062] Zhang, F., Ed., Li, D., Li, H., Belotti, S., and D.
Ceccarelli, "Framework for GMPLS and PCE Control of G.709
Optical Transport Networks", RFC 7062,
DOI 10.17487/RFC7062, November 2013,
<https://www.rfc-editor.org/info/rfc7062>.

[RFC7096] Belotti, S., Ed., Grandi, P., Ceccarelli, D., Ed.,
Caviglia, D., Zhang, F., and D. Li, "Evaluation of
Existing GMPLS Encoding against G.709v3 Optical Transport
Networks (OTNs)", RFC 7096, DOI 10.17487/RFC7096, January
2014, <https://www.rfc-editor.org/info/rfc7096>.

Appendix A. Possible Future Work

As noted in Section 4.2, the GMPLS TPN field defined in Section 6.1
of [RFC7139] is only 12 bits, whereas an ODUCn link could require up
to 14 bits. Although the need is not urgent, future work could
extend the TPN field in GMPLS to use the Reserved bits immediately
adjacent. This would need to be done in a backward-compatible way.

Section 4.2 further notes that the current encoding of GMPLS labels
can be inefficient for larger values of n in ODUCn. Future work
might examine a more compact, yet generalized, label encoding to
address this issue should it be felt, after analysis of the
operational aspects, that the current encoding is causing problems.
Introduction of a new label encoding would need to be done using a
new pairing of LSP encoding type and Generalized Payload Identifier
(G-PID) to ensure correct interoperability.

Contributors

Iftekhar Hussain
Infinera Corp
Sunnyvale, CA
United States of America
Email: [email protected]

Daniele Ceccarelli
Ericsson
Email: [email protected]

Rajan Rao
Infinera Corp
Sunnyvale,
United States of America
Email: [email protected]

Fatai Zhang
Huawei
Email: [email protected]

Italo Busi
Huawei
Email: [email protected]

Dieter Beller
Nokia
Email: [email protected]

Yuanbin Zhang
ZTE
Beijing
Email: [email protected]

Zafar Ali
Cisco Systems
Email: [email protected]

Daniel King
Email: [email protected]

Manoj Kumar
Cisco Systems
Email: [email protected]

Antonello Bonfanti
Cisco Systems
Email: [email protected]

Yuji Tochio
Fujitsu
Email: [email protected]

Authors' Addresses

Qilei Wang (editor)
ZTE Corporation
Nanjing
China
Email: [email protected]

Radha Valiveti (editor)
Infinera Corp
Sunnyvale, CA
United States of America
Email: [email protected]

Haomian Zheng (editor)
Huawei
China
Email: [email protected]

Huub van Helvoort
Hai Gaoming BV
Almere
Netherlands
Email: [email protected]

Sergio Belotti
Nokia
Email: [email protected]