Internet Engineering Task Force Q. Wang, Ed.
Internet-Draft ZTE
Intended status: Informational R. Valiveti, Ed.
Expires: January 3, 2018 Infinera Corp
H. Zheng, Ed.
Huawei
H. Helvoort
Hai Gaoming B.V
S. Belotti
Nokia
July 2, 2017
GMPLS Routing and Signaling Framework for B100G
draft-merge-ccamp-otn-b100g-fwk-01
Abstract
The 2016 revision of G.709 introduces support for OTU links with
rates larger than 100G. This document provides a framework to
address the GMPLS routing and signalling extensions that enable GMPLS
to setup paths through network that contain these newly introduced
OTUCn links.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2.2. OTN terminology used in this document . . . . . . . . . . 3
3. Overview of B100G in G.709 . . . . . . . . . . . . . . . . . 4
3.1. OTUCn . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. Carrying OTUCn between 3R points . . . . . . . . . . 5
3.2. ODUCn . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. OTUCn-M . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.4. OPUCn Time Slot Granularity . . . . . . . . . . . . . . . 9
3.5. Structure of OPUCn MSI with Payload type 0x22 . . . . . . 10
3.6. Client Signal Mappings . . . . . . . . . . . . . . . . . 10
4. Usecases . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. 100GE Client Service with a homogeneous chain of OTUC1
links . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2. 100GE Client Service with a mix of OTU4, and OTUC1 links 14
4.3. 400GE Client Service with a mix of OTUCn links . . . . . 14
4.4. FlexE aware transport over OTUCn links . . . . . . . . . 15
4.5. FlexE Client transport over OTUCn links . . . . . . . . . 16
4.6. Multihop ODUCn link . . . . . . . . . . . . . . . . . . . 17
4.7. Use of OTUCn-M links . . . . . . . . . . . . . . . . . . 18
4.8. Intermediate State of ODU mux . . . . . . . . . . . . . . 19
5. GMPLS Implications . . . . . . . . . . . . . . . . . . . . . 19
5.1. OTN ODUCn/OTUCn hierarchy . . . . . . . . . . . . . . . . 19
5.2. Implications for GMPLS Signaling . . . . . . . . . . . . 20
5.3. Implications for GMPLS Routing . . . . . . . . . . . . . 21
6. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 22
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22
8. Authors (Full List) . . . . . . . . . . . . . . . . . . . . . 22
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 23
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
11. Security Considerations . . . . . . . . . . . . . . . . . . . 24
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
12.1. Normative References . . . . . . . . . . . . . . . . . . 24
12.2. Informative References . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
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1. Introduction
The current GMPLS routing [RFC7138] and signaling extensions
[RFC7139] includes coverage for all the OTN capabilities that were
defined in the 2012 version of G.709 [ITU-T_G709_2012].
The 2016 version of G.709 [ITU-T_G709_2012] introduces support for
higher rate OTU signals, termed OTUCn (which have a nominal rate of n
x 100 Gbps). The newly introduced OTUCn represent a very powerful
extension to the OTN capabilities, and one which naturally scales to
transport any newer clients with bit rates in excess of 100G, as they
are introduced.
This document presents an overview of the changes introduced in
[ITU-T_G709_2016] and analyzes them to identify the extensions that
would be required in GMPLS routing and signaling to enable the new
OTN capabilities.
1.1. Scope
For the purposes of the B100G control plane discussion, the OTN
should be considered as a combination of ODU and OTSi layers. Note
that [ITU-T_G709_2016] is deprecating the use of the term "Och" for
B100G entities, and leaving it intact only for maintaining continuity
in the description of the signals with bandwidth upto 100G. This
document focuses on only the control of the ODU layer. The control
of the OTSi layer will be addressed in a separate document.
2. Terminology
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 RFC 2119 [RFC2119].
2.2. OTN terminology used in this document
a. OPUCn: Optical Payload Unit -Cn.
b. ODUCn: Optical Data Unit - Cn.
c. OTUCn: Fully standardized Optical Transport Unit - Cn.
d. 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
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payload area. Specifically the payload area consists of M 5G
tributary slots (where M is strictly less than 20*n).
e. PSI: OPU Payload structure Indicator. This is a multi-frame
message and describes the composition of the OPU signal. This
field is a concatenation of the Payload type (PT) and the
Multiplex Structrure Indicator (MSI) defined below.
f. MSI: Multiplex Structure Indicator. This structure indicates the
grouping of the tributary slots in an OPU payload area to realize
a client signal that is multiplexed into an OPU. The individual
clients multiplexed into the OPU payload area are distinguished
by the Tributary Port number (TPN).
g. GMP: Generic Mapping Procedure.
Detailed description of these terms can be found in
[ITU-T_G709_2016].
3. Overview of B100G in G.709
This section provides an overview of new features in
[ITU-T_G709_2016].
3.1. OTUCn
In G.709 [ITU-T_G709_2012], the standard mechanism for transporting a
client signal is to first map it into an ODU signal (of the
appropriate rate), and then switch the resulting ODU signal through
the OTN network. In the course of its traversal through the OTN
network, the ODU signal generated by the mapper is either (a)
multiplexed into higher-order ODU, and then encapsulated to form an
OTU or (b) directly encapsulated into an OTU signal that defines the
section layer. The option (b), i.e. direct encapsulation into an OTU
was possible only for ODU1/ODU2/ODU3/ODU4; ODU signals with other
rates (e.g. ODUflex) would first have to be processed per option (a)
above. The term "client signal" is generic in the sense that it
encompasses both Constant Bit rate (CBR) clients (e.g. 10GBASE-R,
SONET OC-768), or packet traffic -- where the goal is to transfer the
payload from end-to-end (without regard for bit transparency at the
PCS layer). Given that OTU4 was the highest rate section layer
signal supported in [ITU-T_G709_2012], the client signal rates were
limited to be less than 100G (if ODU-VCAT was not used).
In order to carry client signals with rates greater than 100Gbps,
[ITU-T_G709_2016] takes a general and scalable approach that
decouples the rates of OTU signals from the client rate evolution.
The new OTU signal is called OTUCn; this signal is defined to have a
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rate of (approximately) n*100G. The following are the key
characteristics of the OTUCn signal:
a. The OTUCn signal contains one ODUCn, which in turn contains one
OPUCn signal. The OTUCn and ODUCn signals perform digital
section roles only (see [ITU-T_G709_2016]:Section 6.1.1). The
OTUCn and ODUCn can be seen as being analogous to the regenerator
section, and multiplex section in SDH respectively.
b. The OTUCn signals can be viewed as being formed by interleaving n
OTUC signals (where are labeled 1, 2, ..., n), each of which has
the format of a standard OTUk signal without the FEC columns (per
[ITU-T_G709_2016]:Figure 7-1). The ODUCn, and OPUCn have a
similar structure, i.e. they can be seen as being formed by
interleaving n instances of ODUC, OPUC signals (respectively) The
OTUC signal contains the ODUC, and OPUC signals, just as in the
case of fixed rate OTUs defined in G.709 [ITU-T_G709_2016].
c. Each of the OTUC "slices" have the same overhead (OH) as the
standard OTUk signal in G.709 [ITU-T_G709_2016]. The combined
signal OTUCn has n instances of OTUC OH, ODUC OH, and OPUC OH.
d. 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.
3.1.1. Carrying OTUCn between 3R points
As explained above, within G.709 [ITU-T_G709_2016], 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. Specifically, the definition of the OTUCn
signal does not cover aspects such as FEC, modulation formats, etc.
These details are defined as part of the adaptation of the OTUCn
layer to the optical layer(s). The specific interleaving of
OTUC/ODUC/OPUC signals onto the optical signals is interface specific
and specified for OTN interfaces with standardized application codes
in the interface specific recommendations (G.709.x).
The following scenarios of OTUCn transport need to be considered (see
Figure 1):
a. 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 networks. ITU-T has
standardized the Flexible OTN (FlexO) interfaces to support these
functions. Recommendation [ITU-T_G709.1] specifies a flexible
interoperable short-reach OTN interface over which an OTUCn (n
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>=1) is transferred, using bonded FlexO interfaces which belong
to a FlexO group. The FlexO group supports physical interface
bonding, management of the group members, overhead for
communication between FlexO peers etc. (these overheads are
separate from the GCC0 channel defined over OTUCn). In its
current form, Recommendation [ITU-T_G709.1] is limited to the
case of transporting OTUCn signals using n 100G Ethernet PHY(s).
The mechanisms for transporting the OTUCn signals over 100G
optical interfaces are specified in [ITU-T_G709.1] and are not
repeated here. When the PHY(s) for the emerging set of Ethernet
signals, e.g. 200GbE and 400GbE, become available, new
recommendations can define the required adaptations.
b. intra-domain interfaces: In these cases, the OTUCn is transported
using a proprietary (vendor specific) encapsulation, FEC etc. In
future, it may be possible to transport OTUCn for intra-domain
links using future variants of FlexO.
==================================================================
+--------------------------------------------------------+
| OTUCn signal |
+--------------------------------------------------------+
| Inter+Domain | Intra+Domain | Intra+Domain |
| Interface (IrDI)| Interface (IaDI)| Interface |
| FlexO (G.709.1) | FlexO (G.709.x) | Proprietary |
| | (Future) | Encap, FEC etc. |
+--------------------------------------------------------+
==================================================================
Figure 1: OTUCn transport possibilities
It is possible for an OTUCn signal to be transported via multiple
hops of lower-layer adaptation (see Figure 2). In this scenario, the
OTUCn spans multiple optical paths joined by a FlexO segment. An
end-to-end OTUCn LSP needs to be setup after the optical circuits are
established. The information about the FlexO interfaces (and group)
are configured at the FlexO endpoints, and there is no dynamic setup.
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==================================================================
Optical Segment Optical Segment
<--------------> <-------------->
+------+ +------+ +------+ +------+
| | | +-----------+ | | |
| A +---------+ B |-----------| C +--------+ D |
| | | +-----------+ | | |
+------+ +------+ ^ +------+ +------+
|
+
FlexO Group
<--------------------------------------------------> OTUCn
+-------+ +-------+ +-------+
| OTUCn | | OTUCn | | OTUCn |
+-------+ +-------+ +-------+
| OTSiG | | FlexO | | OTSiG |
+-------+ +-------+ +-------+
==================================================================
Figure 2: OTUCn transport - Multihop
This document views FlexO (even if there are some digital sub-layers
involved in the adaptation) and other OTUCn transport mechanisms as
"lower layers", and are therefore considered out-of-scope. The OTUCn
layer operates independent of the method used to transport the
signal.
3.2. ODUCn
The ODUCn signal [ITU-T_G709_2016] 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 it has the same Overhead (OH) area, and the payload area
-- but has a higher rate since its payload area can embed an ODU4
signal. The ODUCn signal can be formed in one of the following ways:
By multiplexing lower-rate (i.e. both low-order and high-order)
ODUk signals.
Each of the n instances of ODUC can carry the NULL signal (as
specified in [ITU-T_G709_2016]: Section 17.5.1)
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Each of the n instances of ODUC can carry the PN-11 PRBS test
sequence (as specified in [ITU-T_G709_2016]: Section 17.5.2)
It is concievable that vendors might implement proprietary
mappings (Payload Type values of 0x80-x8F)of non-OTN client
signals. An interoperable control plane cannot make use of these
proprietary ODUCn signals, and hence this case isn't considered in
this document.
The ODUCn signals have a rate that is captured in Table 1.
+----------+--------------------------------------------------------+
| ODU Type | ODU Bit Rate |
+----------+--------------------------------------------------------+
| ODUCn | n x 239/226 x 99,532,800 kbit/s = n x 105,258,138.053 |
| | kbit/s |
+----------+--------------------------------------------------------+
Table 1: ODUCn rates
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 co-terminous, i.e.
they will have identical source/sink locations. [ITU-T_G709_2016]
and [ITU-T_G872] allow for the ODUCn signal to pass through a digital
regenerator node 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 (see
Figure 3). In this case, an ODUCn LSP needs to be set up to traverse
the 3 OTUCn segments.
Specifically, the OPUCn signal flows through these regenerators
unchanged. That is, the set of client signals, their TPNs, trib-slot
allocation remains unchanged. Note however that the ODUCn Overhead
(OH) might be modified if TCM sub-layers are instantiated in order to
monitor the performance of the repeater hops. In this sense, the
ODUCn should not be seen as a general ODU which can be switched via
an ODUk cross-connect.
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==================================================================
^ FlexO group ^ FlexO group
| |
+--------+ | +--------+ +--------+ | +--------+
| +-----------+ | | +----------+ |
| OTN |-----------| OTN | | OTN |----------| OTN |
| DXC +-----------+ WXC +----------------+ WXC +----------+ DXC |
| | | 3R | | 3R | | |
+--------+ +--------+ +--------+ +--------+
<------------------> <----------------------> <------------------>
OTUCn/FlexO OTUCn/OTSiG OTUCn/FlexO
<-----------------------------------------------------------------> ODUCn
==================================================================
Figure 3: Multi-hop ODUCn signal
3.3. OTUCn-M
The standard OTUCn signal has the same rate as that of the ODUCn
signal as captured in Table 1. This implies that the OTUCn signal
can only be transported over wavelength groups which have a total
capacity of multiples of (approximately) 100G. Modern DSPs support a
variety of bit rates per wavelength, depending on the reach
requirements for the optical link. With this in mind, ITU-T supports
the notion of a reduced rate OTUCn signal, termed the OTUCn-M. The
OTUCn-M signal is derived from the OTUCn signal by retaining all the
n instances of overhead (one per OTUC slice) and crunching the OPUC
tributary slots marked as "unavailable".
3.4. OPUCn Time Slot Granularity
[ITU-T_G709_2012] introduced the support for 1.25G granular tributary
slots in OPU2, OPU3, and OPU4 signals. With the introduction of
higher rate signals such as the OPUCn, it is no longer practical for
the optical networks (and the datapath hardware) to support a very
large number of flows at such a fine granularity. ITU-T has defined
the OPUC with a tributary slot granularity of 5G. This means that
the ODUCn signal has 20*n tributary slots (of 5Gbps capacity).
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3.5. Structure of OPUCn MSI with Payload type 0x22
As mentioned above, the OPUCn signal has 20*n 5G tributary slots.
The OPUCn contains n PSI structures, one per OPUC instance. The PSI
structure consists of the Payload Type (of 0x22), followed by a
Reserved Field (1 byte), followed by the MSI. The OPUCn MSI field
has a fixed length of 40*n bytes and indicates the ODTU content of
each TS of an OPUCn. Two bytes are used for each of the 20*n
tributary slots, and each such information structure has the
following format ([ITU-T_G709_2016] G.709:Section 20.4.1):
a. The TS availability bit 1 indicates if the tributary slot is
available or unavailable
b. The TS occupation bit 9 indicates if the tributary slot is
allocated or unallocated
c. The tributary port number in bits 2-8, 10-16 indicates the
identity of the OTN client signal (i.e. LO-ODU) that is being
transported in this TS; a flexible assignment of tributary port
to tributary slots is possible. Note that 1 <= TPN <= 10*n. The
value is set to all-0s when the occupation bit has the value 0
(tributary slot is unallocated). The same TPN value is used in
all the TS(s) assigned to a given OTN client client signal.
3.6. Client Signal Mappings
Note that [ITU-T_G709_2016] introduces support for OTUCn signals with
rates of n*100G and also introduces support for client signals with
rates larger than 100G (e.g. the future 400GBASE-R client being
standardized by IEEE, higher packet streams from NPUs). The approach
taken by the ITU-T to map non-OTN client signals to the appropriate
ODU containers is as follows:
a. All client signals with rates less than 100G are mapped as
specified in [ITU-T_G709_2016]:Clause 17. These mappings are
identical to those specified in the earlier revision of G.709
[ITU-T_G709_2012]. Thus, for example, the 1000BASE-X/10GBASE-R
signals are mapped to ODU0/ODU2e respectively (see Table 2 --
based on Table 7-2 in [ITU-T_G709_2016])
b. Always map the new and emerging client signals to ODUflex signals
of the appropriate rates (see Table 2 -- based on Table 7-2 in
[ITU-T_G709_2016])
c. Drop support for ODU Virtual Concatenation. This simplifies the
network, and the supporting hardware since multiple different
mappings for the same client are no longer necessary. Note that
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legacy implementations that transported sub-100G clients using
ODU VCAT shall continue to be supported.
d. ODUflex signals are low-order signals only. If the ODUflex
entities have rates of 100G or less, they can be transported
using either an ODUk (k=1..4) or an ODUCn server layer. On the
other hand, ODUflex connections with rates greater than 100G will
require the server layer to be ODUCn. The ODUCn signals must be
adapted to an OTUCn signal. Figure 4 illstrates the hierarchy of
the digital signals defined in [ITU-T_G709_2016].
+----------------+--------------------------------------------------+
| ODU Type | ODU Bit Rate |
+----------------+--------------------------------------------------+
| ODU0 | 1,244,160 Kbps |
| ODU1 | 239/238 x 2,488,320 Kbps |
| ODU2 | 239/237 x 9,953,280 Kbps |
| ODU2e | 239/237 x 10,312,500 Kbps |
| ODU3 | 239/236 x 39,813,120 Kbps |
| ODU4 | 239/227 x 99,532,800 Kbps |
| ODUflex for | 239/238 x Client signal Bit rate |
| CBR client | |
| signals | |
| ODUflex for | Configured bit rate |
| GFP-F mapped | |
| packet traffic | |
| ODUflex for | s x 239/238 x 5 156 250 kbit/s: s=2,8,5*n, n >= |
| IMP mapped | 1 |
| packet traffic | |
| ODUflex for | 103 125 000 x 240/238 x n/20 kbit/s, where n is |
| FlexE aware | total number of available tributary slots among |
| transport | all PHYs which have been crunched and combined. |
+----------------+--------------------------------------------------+
Note that this table doesn't include ODUCn -- since it cannot be
generated by mapping a non-OTN signal. An ODUCn is always formed by
multiplexing multiple LO-ODUs.
Table 2: Types and rates of ODUs usable for client mappings
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==================================================================
Clients (e.g. SONET/SDH, Ethernet)
+ + +
| | |
+------------------+-------+------+------------------------+
| OPUk |
+----------------------------------------------------------+
| ODUk |
+-----------------------+---------------------------+------+
| OTUk, OTUk.V, OTUkV | OPUk | |
+----------+----------------------------------------+ |
| OTLk.n | | ODUk | |
+----------+ +---------------------+-----+ |
| OTUk, OTUk.V, OTUkV | OPUCn |
+----------+-----------------------+
| OTLk.n | | ODUCn |
+----------+ +------------+
| OTUCn |
+------------+
==================================================================
Figure 4: Digital Structure of OTN interfaces (from G.709:Figure 6-1)
4. Usecases
This section introduces various usecases that provide the rationale
for the requirements that any solution must satisfy. At a later
point in time, it is possible to consolidate these usecases so that
all the multiplexing (and demultiplexing) variants are encountered
along the path of an end-to-end ODU circuit.
Note-1: These usecases present scenarios in which OTUCn links are
depicted. These illustrations do not highlight how the OTUCn is
transported between the 3R points. That is, these usecases cover
cases in which a standard FlexO interface (e.g. as defined in
[ITU-T_G709.1]) is used, or whether a vendor specific mapping of
OTUCn to OTSiG (as defined in [ITU-T_G872]) is used. In other words,
multiple variants of these usecases based on FlexO usage (or not) are
not included in this document.
Note-2: This version of the document covers many usecases in detail.
Future versions of this document may combine multiple usecases (e.g.
all cases involving ODUflex into one broad category), and retain only
the minimal set of usecases.
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4.1. 100GE Client Service with a homogeneous chain of OTUC1 links
In the scenario illustrated in Figure 5 a 100GBASE-R client is mapped
into an ODU4 at NE1. The resulting ODU4 signal is multiplexed into
the ODUC1 server layer (using GMP) and further encapsulated to form
the OTUC1 signal. The links NE1-NE2, and NE2-NE3 are both OTUC1
links -- and they can carry one 100GE client mapped into an ODU4
server layer. Actions performed at NE2 are: (a) terminate OTUC1, and
ODUC1 towards NE1 (b) demultiplex the ODU4 signal from ODUC1 (c) map
the ODU4 signal onto a different ODUC1/OTUC1 towards NE3. NE3
performs the inverse sequence of steps performed at NE1, and recovers
the 100GBASE-R client from the ODU4 signal. Note that the ODU4 and
ODUC1 signals are not "interoperable" and that the ODUC1 is a server
layer to the ODU4 signal.
This illustration is also applicable to the usecase in which members
of a FlexE group are transported in a flexe-unaware mode in the
transport network. Although this illustration included only OTUC1
signals, any higher rate OTUCn signal can be substituted for these
signals. In this particular scenario, there are two adjacent ODUC1
hops, and the NE2 demultiplexs (and multiplexes) the ODU4 onto the
ODUC1. It is possible to construct an alternative scenario in the
case when NE2 acts as a regenerator, and doesn't terminate the ODUC1
signals in the two hops, and instead repeats the ODUC1 signal; this
scenario is specifically discussed in Section 4.6.
==================================================================
+----------+ +----------+
| 100GE | | 100GE |
+----------+ +---------------+ +----------+
| ODU4 | | ODU4 | | ODU4 |
+----------+ +---------------+ +----------+
| ODUC1 | | ODUC1 | ODUC1 | | ODUC1 |
+----------+ +---------------+ +----------+
| OTUC1 +--------+ OTUC1 | OTUC1 +---------+ OTUC1 |
+----------+ +---------------+ +----------+
NE1 NE2 NE3
+-------------> +------------->
Scope of Scope of
OTUC1, ODUC1 OTUC1, ODUC1
==================================================================
Figure 5: 100GE Client service
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4.2. 100GE Client Service with a mix of OTU4, and OTUC1 links
In the scenario illustrated in Figure 6 a 100GBASE-R client is mapped
into an ODU4 at NE1. The resulting ODU4 signal is encapsulated with
an OTU layer to form the OTU4 signal. Actions performed at NE2 are:
(a) terminate OTU4 layer, and extract the ODU4 signal (b) map the
ODU4 signal onto a different ODUC1/OTUC1 towards NE3. NE3 performs
the same set of actions that were performed by NE3 in Figure 5. This
usecase illustrates a scenario in which an ODU4 signal can span
between network elements regardless of whether they support the OTUCn
interfaces or not.
==================================================================
+----------+ +----------+
| 100GE | | 100GE |
+----------+ +---------------+ +----------+
| ODU4 | | ODU4 | | ODU4 |
+----------+ +-------+-------+ +----------+
| OTU4 +--------+ OTU4 | ODUC1 | | ODUC1 |
+----------+ +---------------+ +----------+
| OTUC1 +---------+ OTUC1 |
--------+ +----------+
NE1 NE2 NE3
+--------------> +---------------->
Scope of Scope of
OTU4 layer OTUC1, ODUC1
==================================================================
Figure 6: 100GE Client Service with a mix of OTU4, and OTUC1 links
4.3. 400GE Client Service with a mix of OTUCn links
In the scenario illustrated in Figure 7 a 400GBASE-R client is mapped
into an ODUflex at NE1. The resulting ODUflex signal is multiplexed
into an ODUC4 (using GMP), and then transformed into an OTUC4 signal.
The links between NE1-NE2, and NE2-NE3 are OTUC4 and OTUC6
(respectively). Actions performed at NE2 are: (a) terminate OTUC4,
and ODUC4 towards NE1 (b) demultiplex the ODUflex signal from ODUC4
(c) map the ODUflex signal onto ODUC6/OTUC6 towards NE3. NE3
performs the inverse sequence of steps performed at NE1, and recovers
the 400GBASE-R client from the ODUflex signal.
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Although not specifically illustrated in this figure, the 200G of
spare capacity in the NE2-NE3 links can be used to carry other client
signals.. Although the scenario illustrated in Figure 7 is specific
to 400GE, the treatment for packet clients at other rates (e.g. 25G,
50G, 200G) follows a very similar processing sequence. In the case
of 25GBASE-R clients , the 25GE client signal will be mapped to an
ODUflex, and can be multiplexed into an ODU4 signal, or an ODUCn
signal as illustrated here.
==================================================================
+----------+ +----------+
| 400GE | | 400GE |
+----------+ +---------------+ +----------+
| ODUflex | | ODUflex | | ODUflex |
+----------+ +-------+-------+ +----------+
| ODUC4 | | ODUC4 | ODUC6 | | ODUC6 |
+----------+ +---------------+ +----------+
| OTUC4 +--------+ OTUC4 | OTUC6 +---------+ OTUC6 |
+----------+ +-------+-------+ +----------+
NE1 NE2 NE3
<-------------> <------------->
Scope of Scope of
OTUC4, ODUC4 OTUC6, ODUC6
==================================================================
Figure 7: 400GE transport over OTUCn links
4.4. FlexE aware transport over OTUCn links
In the scenario illustrated in Figure 8 NE1 interfaces to a client
equipment which includes the FlexE SHIM functions which originate/
terminate a FlexE group. The transport network edge node NE2 is
FlexE aware -- but doesn't terminate the FlexE group. NE1 may (as
defined in the FlexE draft [I-D.izh-ccamp-flexe-fwk]), crunch the
unavailable tributary slots in the FlexE PHY signals, and map the
resultant stream to one or more ODUflex signals. The links between
NE1-NE2, and NE2-NE3 are OTUC4 and OTUC6 (respectively). Actions
performed at NE2 are: (a) terminate OTUC4, and ODUC4 towards NE1 (b)
demultiplex the ODUflex signal from ODUC4 (c) map the ODUflex signal
onto ODUC6/OTUC6 towards NE3. NE3 recovers the Crunched and combined
PHY(s) from the ODUflex signal, re-adds the unavailable calendar
slots, and outputs the resulting stream towards the FlexE PHY(s).
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In the scenario illustrated in Figure 8 the lowest rate OTUCn link is
the OTUC4 link between NE1-NE2. This means that the size of the
FlexE group is at most 4. FlexE groups with greater sizes can be
handled by utilizing appropriate OTUCn links. Note that at most 400G
of the capacity of OTUC6 (or 600G) NE2-NE3 link is occupied by the
ODUflex signal; the remaining bandwidth can be allocated to other
client signals.
==================================================================
FlexE +----------+ +----------+ FlexE
group | Crunched | | Crunche | Group
+------> and | | and +-------->
| Combined | | Combined | Add
| PHY(s) | | PHY(s) | unavailable
+----------+ +---------------+ +----------+ Calendar
| ODUflex | | ODUflex | | ODUflex | slots
+----------+ +-------+-------+ +----------+
| ODUC4 | | ODUC4 | ODUC6 | | ODUC6 |
+----------+ +---------------+ +----------+
| OTUC4 +---+ OTUC4 | OTUC6 +---+ OTUC6 |
+----------+ +-------+-------+ +----------+
NE1 NE2 NE3
<---------> <----------->
Scope of Scope of
OTUC4, ODUC4 OTUC6, ODUC6
==================================================================
Figure 8: FlexE aware transport over OTUCn links
4.5. FlexE Client transport over OTUCn links
This use case (see Figure 9) concerns the scenario in which a FlexE
group is terminated at the transport network edge node (via the FlexE
SHIM function), and the FlexE clients are demultiplexed, and
independently transported through the OTN network. In the scenario
illustrated in Figure 9 the lowest rate OTUCn link is the OTUC4 link
between NE1-NE2. This means that the maximum bit rate of the FlexE
client is at most 400G. FlexE clients with greater sizes can be
handled by utilizing appropriate OTUCn links. This figure
illustrates the case in which one FlexE client is transported between
NE1 and NE3. Other FlexE clients recovered at NE1 can routed
independently to NE3, or to other network elements.
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==================================================================
+-----------------+ +---------------+
| FlexE | | FlexE |
| Client | | Client |
+-----------------+ +---------------+
| FlexE | | +---------------+ | | Flex |
| SHIM | ODUflex | | ODUflex | |ODUflex| SHIM |
+-----------------+ +---------------+ +---------------+
| FlexE | ODUC4 | | ODUC4 | ODUC6 | | ODUC6 | FlexE |
+----+ PHY(s +---------+ +---------------+ +-------+ PHY(s)+---->
FlexE | | OTUC4 +---+ OTUC4 | OTUC6 +---+ OTUC6 | | FlexE
Group +-----------------+ +---------------+ +---------------+ Group
NE1 NE2 NE3
<------------> <----------->
Scope of Scope of
OTUC4, ODUC4 OTUC6, ODUC6
==================================================================
Figure 9: FlexE client transport over OTUCn links
4.6. Multihop ODUCn link
As mentioned in the introductory section, the ODUCn is not a
switchable entity. The ODUCn layer is a server layer, which more-or-
less occupies the position of a section layer in OTN networks. As
such, the ODUCn signal must be terminated and the contained low-order
ODU flows can be switched independently to other OTN interfaces.
G.709 and G.872 however allow for digital regenerators to terminate
the OTUCn layer, and reinject the ODUCn layer towards another
interface (where a new OTUCn section layer is started). This
scenario is illustrated in Figure 10. In this figure, NE3 is the
regenerator. The ODUC2 signal is terminated at NE2, and NE4. At the
regeneration points, all the clients embedded inside the ODUCn signal
are not touched (i.e. no TS changes can occur). More specifically,
the OPUC2 signal is not modified in any way. However, the ODUC2 OH
may be modified if intrusive TCM monitoring points are applied to the
ODUC2 signal at NE3. It is for this reason that the ODUC2 entity
must be visible at NE3.
In scenarios involving multi-hop ODUCn links, GMPLS signalling will
be required to setup multiple ODUCn LSPs, each covering a regenerator
section (since an end-to-end ODUCn LSP is not possible except in very
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simple configurations). A LO-ODU can then be switched across
multiple ODUCn LSPs (possibly with different rates).
==================================================================
+----------+ +----------+
| 100GE | | 100GE |
+----------+ +---------------+ +----------+
| ODU4 | | ODU4 | | ODU4 |
+----------+ +-------+-------+ +---------+ +----------+
| ODUC1 | | ODUC1 | ODUC2 | | ODUC2 | | ODUC2 |
+----------+ +---------------+ +---------+ +----------+
| OTUC1 +-----+ OTUC1 | OTUC2 +-------+ OTUC2 +-------+ OTUC2 |
+----------+ +-------+-------+ +---------+ +----------+
NE1 NE2 NE3 NE4
<-------------> <-------------> <------------->
Scope of OTUC2 OTUC2
OTUC1, ODUC1
<--------------------------------->
ODUC2
==================================================================
Figure 10: Multihop ODUCn link
4.7. Use of OTUCn-M links
The scenario illustrated in Figure 11 is a variant of the basic
usecase presented in Figure 5. The only difference is that the
second hop of the ODU4 connection makes use of a OTUC2-30 link which
has a capacity of 150G.
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==================================================================
+----------+ +-----------+
| 100GE | | 100GE |
+----------+ +------------------+ +-----------+
| ODU4 | | ODU4 | | ODU4 |
+----------+ +-------+----------+ +-----------+
| ODUC1 | | ODUC1 | ODUC2 | | ODUC2 |
+----------+ +------------------+ +-----------+
| OTUC1 +--------+ OTUC1 | OTUC2-30 +------+ OTUC2-30 |
+----------+ +-------+----------+ +-----------+
NE1 NE2 NE3
+-------------> +------------->
Scope of Scope of
OTUC1, ODUC1 OTUC2-30
ODUC2
==================================================================
Figure 11: 100GE Client service over OTUCn-M links
4.8. Intermediate State of ODU mux
The ODUCn links have a tributary slot granularity of 5G -- and this
makes it a bit inefficient if a small number of ODU0 flows have to be
switched across an ODUCn links. In these cases, it is conceivable
that the intermediate nodes may offer the convenience of a
intermediate-stage multiplexing, whereby multiple ODU0 flows are
first multiplexed into a higher rate container (e.g. ODU2), and then
multiplexed into an ODUCn signal. This however assumes that all
these ODU0 flows are co-routed in the network. If this assumption
cannot be made, the only solution is to multiplex these ODU0 flows
into higher rate flows, from the source of the traffic. This usecase
isn't elaborated in this document. We can add details if required.
5. GMPLS Implications
5.1. OTN ODUCn/OTUCn hierarchy
As described in [ITU-T_G872], the digital layers of the OTN are
divided into the OTU layer and a hierarchy of one or more ODU layers.
As an ODUCn cannot be used to support non-OTN client signals, the OTN
client signals (e.g. ODU0, ODU1, ODU2, ODU2e, ODU3, ODU4, ODUflex)
are first multiplexed into an ODUCn container, then the ODUCn
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container is then mapped into OTUCn (see Figure 1). The signal
hierarchy supported by the ODUCn and OTUCn needs to be taken into
consideration in control plane Routing and Signaling.
ODUCn based connection management is concerned with controlling the
connectivity of ODUCn paths. According to [ITU-T_G872], the
intermediate nodes with ODUCn do not support the switching of ODUCn
tributary slot. Intermediate ODUCn points are only considered as a
forwarding node. Once an ODUCn path is used to transport client
signal, the TS occupied will not change across the ODUCn network.
5.2. Implications for GMPLS Signaling
[RFC7139] extends the base RSVP-TE signaling specification [RFC4328]
to define RSVP-TE signaling extensions that can used to control OTN
networks built in accordance with [ITU-T_G709_2012].
[ITU-T_G709_2016] introduced some new containers, such as OPUCn,
ODUCn, and OTUCn. The mechanisms defined in [RFC7139] do not support
these new OTN features. Therefore, GMPLS signaling protocols MUST be
extended to support this new functionality. The following summarizes
key aspects that should be considered for GMPLS signaling extensions:
a. Per the description in clause 7 of [ITU-T_G872], "the digital
layers of the OTN are divided into the OTU layer and a hierarchy
of one or more ODU layers". In B100G links, the ODUCn layer is
the bottom of the ODU hierarchy, and an ODUCn (induced) LSP needs
to be established before the LO-ODUs can flow across this link.
The traffic parameters in a signaling message should be extended
to support the new signal type(s) for the ODUCn signals. This
approach keeps the treatment for ODUCn signals consistent with
that of other ODU(s).
b. Support the new TS granularity: the signaling protocol should be
able to identify the TS granularity (i.e., the new 5 Gbps TS
granularity) to be used for establishing a Hierarchical LSP that
will be used to carry service LSP(s) requiring a specific TS
granularity.
c. Support for LSP setup of new ODUCn containers with related
mapping and multiplexing capabilities.
d. A new label format MUST carry the information about the set of
ODUCn tributary slots allocated to a specific LO-ODU. It MUST be
possible for a single LO-ODU to occupy an arbitrary set of
tributary slots, selected from one or more OTUC/ODUC instances.
e. Support for TPN allocation and negotiation: TPN needs to be
configured as part of the MSI information. A signaling mechanism
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must be identified to carry TPN information if the control plane
is used to configure MSI information. The range of TPN is
[1..10*n] and the range of TPN is smaller than the number of
tributary slots (20*n); e.g. it is not possible to carry 15 5G
ODUflex signals in an ODUC1. This constraint MUST be taken into
account in the control plane supported).
f. Support for LSP setup of OTUCn sub rates (OTUCn-M) path: based on
previous extensions, there should be new signal mechanism to
declare the OTUCn-m information. The GMPLS signalling protocol
SHALL support the setup of OTUCn sub rates (OTUCn-M) LSP, which
includes the negotiation of unavaliable slots number, slots
postion and allocation of slot resources.
g. The GMPLS signalling protocol should be able to specify the new
ODUCn/OTUCn signal types and related traffic information. The
traffic parameters should be extended in a signalling message to
support the new ODUCn/OTUCn signal types
5.3. Implications for GMPLS Routing
The path computation process needs to select a suitable route for an
ODUCn/OTUCn/OTUCn-M connection request. In order to perform the path
computation, it needs to evaluate the available bandwidth/slots
available on one or more candidate links. The routing protocol
SHOULD be extended to carry sufficient information to represent ODU
Traffic Engineering (TE) topology.
The Interface Switching Capability Descriptors defined in [RFC4203]
present a new constraint for LSP path computation. [RFC4203] defines
the Switching Capability, related Maximum LSP Bandwidth, and
Switching Capability specific information. [RFC7138] updates the
ISCD to support ODU4, ODU2e and ODUflex. The new Switching
Capability specific information provided in [RFC7138] have to be
adapted to support new features contained in [G709-2016]. The
following requirements should be considered:
a. Support for carrying the link multiplexing capability: As
discussed in Section 3.1.2, many different types of low-order
ODU(s) (e.g. ODUflex, ODU4) can be multiplexed into the ODUCn.
An ODUCn path may support one or more types of ODUk signals. The
routing protocol should be capable of carrying this multiplexing
capability.
b. Support for advertising 5G Tributary Slot Granularity introduced
[ITU-T_G709_2016].
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c. Support for advertisement of available bandwidth in an ODUCn
path.
6. Open Issues
1. [Note (RSV)]: This document elaborates on several FlexE and 400GE
usecases. Since all these cases map the non-OTN client signals
into ODUflex signals of various rates, it might be better to
combine all these usecases into one category that handles ODUflex
LSPs. From a control plane point of view, the differences in the
data plane processing are not relevant. This change will be made
in a future revision of this document (if there is agreement).
7. Acknowledgements
8. Authors (Full List)
Qilei Wang (editor)
ZTE
Nanjing, China
Email: wang.qilei@zte.com.cn
Radha Valiveti (editor)
Infinera Corp
Sunnyvale, CA, USA
Email: rvaliveti@infinera.com
Haomian Zheng (editor)
Huawei
CN
EMail: zhenghaomian@huawei.com
Wang, et al. Expires January 3, 2018 [Page 22]
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Huub van Helvoort
Hai Gaoming B.V
EMail: huubatwork@gmail.com
Sergio Belotti
Nokia
EMail: sergio.belotti@nokia.com
Iftekhar Hussain
Infinera Corp
Sunnyvale, CA, USA
Email: IHussain@infinera.com
Daniele Ceccarelli
Ericsson
Email: daniele.ceccarelli@ericsson.com
9. Contributors
Rajan Rao, Infinera Corp, Sunnyvale, USA, rrao@infinera.com
Fatai Zhang, Huawei,zhangfatai@huawei.com
Italo Busi, Huawei,italo.busi@huawei.com
Zheyu Fan, Huawei, fanzheyu2@huawei.com
Yuanbin Zhang, ZTE, Beiing, zhang.yuanbin@zte.com.cn
Zafar Ali, Cisco Systems, zali@cisco.com
Daniel King, d.king@lancaster.ac.uk
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Manoj Kumar, Cisco Systems, manojk2@cisco.com
Antonello Bonfanti, Cisco Systems, abonfant@cisco.com
Akshaya Nadahalli, Cisco Systems, anadahal@cisco.com
10. IANA Considerations
This memo includes no request to IANA.
11. Security Considerations
None.
12. References
12.1. Normative References
[ITU-T_G709.1]
ITU-T, "ITU-T G.709.1: Flexible OTN short-reach interface;
2016", , 2016.
[ITU-T_G709_2012]
ITU-T, "ITU-T G.709: Optical Transport Network Interfaces;
02/2012",
http://www.itu.int/rec/T-REC-G..709-201202-S/en, February
2012.
[ITU-T_G709_2016]
ITU-T, "ITU-T G.709: Optical Transport Network Interfaces;
07/2016",
http://www.itu.int/rec/T-REC-G..709-201606-P/en, July
2016.
[ITU-T_G872]
ITU-T, "ITU-T G.872: The Architecture of Optical Transport
Networks; 2017", http://www.itu.int/rec/T-REC-G.872/en,
January 2017.
[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>.
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[RFC4328] Papadimitriou, D., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Extensions for G.709 Optical
Transport Networks Control", RFC 4328,
DOI 10.17487/RFC4328, January 2006,
<http://www.rfc-editor.org/info/rfc4328>.
[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,
<http://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,
<http://www.rfc-editor.org/info/rfc7139>.
12.2. Informative References
[I-D.izh-ccamp-flexe-fwk]
Hussain, I., Valiveti, R., Pithewan, K., Wang, Q.,
Andersson, L., Zhang, F., Chen, M., Dong, J., Du, Z.,
zhenghaomian@huawei.com, z., Zhang, X., Huang, J., and Q.
Zhong, "GMPLS Routing and Signaling Framework for Flexible
Ethernet (FlexE)", draft-izh-ccamp-flexe-fwk-00 (work in
progress), October 2016.
Authors' Addresses
Qilei Wang (editor)
ZTE
Nanjing
CN
Email: wang.qilei@zte.com.cn
Radha Valiveti (editor)
Infinera Corp
Sunnyvale
USA
Email: rvaliveti@infinera.com
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Haomian Zheng (editor)
Huawei
CN
Email: zhenghaomian@huawei.com
Huub van Helvoort
Hai Gaoming B.V
Email: huubatwork@gmail.com
Sergio Belotti
Nokia
Email: sergio.belotti@nokia.com
Wang, et al. Expires January 3, 2018 [Page 26]