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Internet Engineering Task Force (IETF) F. Zhang, Ed.
Request for Comments: 7062 D. Li
Category: Informational Huawei
ISSN: 2070-1721 H. Li
CMCC
S. Belotti
Alcatel-Lucent
D. Ceccarelli
Ericsson
November 2013
Framework for GMPLS and PCE Control of
G.709 Optical Transport Networks
Abstract
This document provides a framework to allow the development of
protocol extensions to support Generalized Multi-Protocol Label
Switching (GMPLS) and Path Computation Element (PCE) control of
Optical Transport Networks (OTNs) as specified in ITU-T
Recommendation G.709 as published in 2012.
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 a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7062.
Zhang, et al. Informational [Page 1]
RFC 7062 OTN Framework November 2013
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................3
2. Terminology .....................................................3
3. G.709 Optical Transport Network .................................4
3.1. OTN Layer Network ..........................................5
3.1.1. Client Signal Mapping ...............................6
3.1.2. Multiplexing ODUj onto Links ........................7
3.1.2.1. Structure of MSI Information ...............9
4. Connection Management in OTN ...................................10
4.1. Connection Management of the ODU ..........................11
5. GMPLS/PCE Implications .........................................13
5.1. Implications for Label Switched Path (LSP) Hierarchy ......13
5.2. Implications for GMPLS Signaling ..........................14
5.3. Implications for GMPLS Routing ............................16
5.4. Implications for Link Management Protocol .................18
5.5. Implications for Control-Plane Backward Compatibility .....19
5.6. Implications for Path Computation Elements ................20
5.7. Implications for Management of GMPLS Networks .............20
6. Data-Plane Backward Compatibility Considerations ...............21
7. Security Considerations ........................................21
8. Acknowledgments ................................................22
9. Contributors ...................................................22
10. References ....................................................23
10.1. Normative References .....................................23
10.2. Informative References ...................................24
Zhang, et al. Informational [Page 2]
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1. Introduction
Optical Transport Networks (OTNs) have become a mainstream layer 1
technology for the transport network. Operators want to introduce
control-plane capabilities based on GMPLS to OTN to realize the
benefits associated with a high-function control plane (e.g.,
improved network resiliency, resource usage efficiency, etc.).
GMPLS extends Multi-Protocol Label Switching (MPLS) to encompass Time
Division Multiplexing (TDM) networks (e.g., Synchronous Optical
NETwork (SONET) / Synchronous Digital Hierarchy (SDH), Plesiochronous
Digital Hierarchy (PDH), and G.709 sub-lambda), lambda switching
optical networks, and spatial switching (e.g., incoming port or fiber
to outgoing port or fiber). The GMPLS architecture is provided in
[RFC3945], signaling function and Resource Reservation Protocol -
Traffic Engineering (RSVP-TE) extensions are described in [RFC3471]
and [RFC3473], routing and Open Shortest Path First (OSPF) extensions
are described in [RFC4202] and [RFC4203], and the Link Management
Protocol (LMP) is described in [RFC4204].
The GMPLS signaling extensions defined in [RFC4328] provide the
mechanisms for basic GMPLS control of OTN based on the 2001 revision
of the G.709 specification. The 2012 revision of the G.709
specification, [G709-2012], includes new features, for example,
various multiplexing structures, two types of Tributary Slots (TSs)
(i.e., 1.25 Gbps and 2.5G bps), and extension of the Optical channel
Data Unit-j (ODUj) definition to include the ODUflex function.
This document reviews relevant aspects of OTN technology evolution
that affect the GMPLS control-plane protocols and examines why and
how to update the mechanisms described in [RFC4328]. This document
additionally provides a framework for GMPLS control of OTN and
includes a discussion of the implications for the use of the PCE
[RFC4655].
For the purposes of the control plane, the OTN can be considered to
be comprised of ODU and wavelength (Optical Channel (OCh)) layers.
This document focuses on the control of the ODU layer, with control
of the wavelength layer considered out of the scope. Please refer to
[RFC6163] for further information about the wavelength layer.
2. Terminology
OTN: Optical Transport Network
OPU: Optical Channel Payload Unit
ODU: Optical Channel Data Unit
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OTU: Optical Channel Transport Unit
OMS: Optical Multiplex Section
MSI: Multiplex Structure Identifier
TPN: Tributary Port Number
LO ODU: Lower Order ODU. The LO ODUj (j can be 0, 1, 2, 2e, 3, 4, or
flex) represents the container transporting a client of the OTN that
is either directly mapped into an OTUk (k = j) or multiplexed into a
server HO ODUk (k > j) container.
HO ODU: Higher Order ODU. The HO ODUk (k can be 1, 2, 2e, 3, or 4)
represents the entity transporting a multiplex of LO ODUj tributary
signals in its OPUk area.
ODUflex: Flexible ODU. A flexible ODUk can have any bit rate and a
bit rate tolerance of +/-100 ppm (parts per million).
In general, throughout this document, "ODUj" is used to refer to ODU
entities acting as an LO ODU, and "ODUk" is used to refer to ODU
entities being used as an HO ODU.
3. G.709 Optical Transport Network
This section provides an informative overview of the aspects of the
OTN impacting control-plane protocols. This overview is based on the
ITU-T Recommendations that contain the normative definition of the
OTN. Technical details regarding OTN architecture and interfaces are
provided in the relevant ITU-T Recommendations.
Specifically, [G872-2012] describes the functional architecture of
optical transport networks providing optical signal transmission,
multiplexing, routing, supervision, performance assessment, and
network survivability. The legacy OTN referenced by [RFC4328]
defines the interfaces of the optical transport network to be used
within and between subnetworks of the optical network. With the
evolution and deployment of OTN technology, many new features have
been specified in ITU-T recommendations, including, for example, new
ODU0, ODU2e, ODU4, and ODUflex containers as described in
[G709-2012].
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3.1. OTN Layer Network
The simplified signal hierarchy of OTN is shown in Figure 1, which
illustrates the layers that are of interest to the control plane.
Other layers below OCh (e.g., Optical Transmission Section (OTS)) are
not included in this figure. The full signal hierarchy is provided
in [G709-2012].
Client signal
|
ODUj
|
OTU/OCh
OMS
Figure 1: Basic OTN Signal Hierarchy
Client signals are mapped into ODUj containers. These ODUj
containers are multiplexed onto the OTU/OCh. The individual OTU/OCh
signals are combined in the OMS using Wavelength Division
Multiplexing (WDM), and this aggregated signal provides the link
between the nodes.
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3.1.1. Client Signal Mapping
The client signals are mapped into an LO ODUj. The current values of
j defined in [G709-2012] are: 0, 1, 2, 2e, 3, 4, and flex. The
approximate bit rates of these signals are defined in [G709-2012] and
are reproduced in Tables 1 and 2.
+-----------------------+-----------------------------------+
| ODU Type | ODU nominal bit rate |
+-----------------------+-----------------------------------+
| ODU0 | 1,244,160 Kbps |
| ODU1 | 239/238 x 2,488,320 Kbps |
| ODU2 | 239/237 x 9,953,280 Kbps |
| ODU3 | 239/236 x 39,813,120 Kbps |
| ODU4 | 239/227 x 99,532,800 Kbps |
| ODU2e | 239/237 x 10,312,500 Kbps |
| | |
| ODUflex for | |
|Constant Bit Rate (CBR)| 239/238 x client signal bit rate |
| Client signals | |
| | |
| ODUflex for Generic | |
| Framing Procedure | Configured bit rate |
| - Framed (GFP-F) | |
| Mapped client signal | |
+-----------------------+-----------------------------------+
Table 1: ODU Types and Bit Rates
NOTE: The nominal ODUk rates are approximately: 2,498,775.126 Kbps
(ODU1), 10,037,273.924 Kbps (ODU2), 40,319,218.983 Kbps (ODU3),
104,794,445.815 Kbps (ODU4), and 10,399,525.316 Kbps (ODU2e).
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RFC 7062 OTN Framework November 2013
+-----------------------+-----------------------------------+
| ODU Type | ODU bit rate tolerance |
+-----------------------+-----------------------------------+
| ODU0 | +/-20 ppm |
| ODU1 | +/-20 ppm |
| ODU2 | +/-20 ppm |
| ODU3 | +/-20 ppm |
| ODU4 | +/-20 ppm |
| ODU2e | +/-100 ppm |
| | |
| ODUflex for CBR | |
| Client signals | +/-100 ppm |
| | |
| ODUflex for GFP-F | |
| Mapped client signal | +/-100 ppm |
+-----------------------+-----------------------------------+
Table 2: ODU Types and Tolerance
One of two options is for mapping client signals into ODUflex
depending on the client signal type:
- Circuit clients are proportionally wrapped. Thus, the bit rate is
defined by the client signal, and the tolerance is fixed to +/-100
ppm.
- Packet clients are mapped using the Generic Framing Procedure
(GFP). [G709-2012] recommends that the ODUflex(GFP) will fill an
integral number of tributary slots of the smallest HO ODUk path
over which the ODUflex(GFP) may be carried, and the tolerance
should be +/-100 ppm.
Note that additional information on G.709 client mapping can be found
in [G7041].
3.1.2. Multiplexing ODUj onto Links
The links between the switching nodes are provided by one or more
wavelengths. Each wavelength carries one OCh, which carries one OTU,
which carries one ODU. Since all of these signals have a 1:1:1
relationship, we only refer to the OTU for clarity. The ODUjs are
mapped into the TSs (Tributary Slots) of the OPUk. Note that in the
case where j=k, the ODUj is mapped into the OTU/OCh without
multiplexing.
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The initial versions of G.709 referenced by [RFC4328] only provided a
single TS granularity, nominally 2.5 Gbps. [G709-2012] added an
additional TS granularity, nominally 1.25 Gbps. The number and type
of TS provided by each of the currently identified OTUk are provided
below:
Tributary Slot Granularity
2.5 Gbps 1.25 Gbps Nominal Bit Rate
OTU1 1 2 2.5 Gbps
OTU2 4 8 10 Gbps
OTU3 16 32 40 Gbps
OTU4 -- 80 100 Gbps
To maintain backward compatibility while providing the ability to
interconnect nodes that support a 1.25 Gbps TS at one end of a link
and a 2.5 Gbps TS at the other, [G709-2012] requires 'new' equipment
to fall back to the use of a 2.5 Gbps TS when connected to legacy
equipment. This information is carried in band by the payload type.
The actual bit rate of the TS in an OTUk depends on the value of k.
Thus, the number of TSs occupied by an ODUj may vary depending on the
values of j and k. For example, an ODU2e uses 9 TSs in an OTU3 but
only 8 in an OTU4. Examples of the number of TSs used for various
cases are provided below (referring to Tables 7-9 of [G709-2012]):
- ODU0 into ODU1, ODU2, ODU3, or ODU4 multiplexing with 1.25 Gbps TS
granularity
o ODU0 occupies 1 of the 2, 8, 32, or 80 TSs for ODU1, ODU2,
ODU3, or ODU4
- ODU1 into ODU2, ODU3, or ODU4 multiplexing with 1.25 Gbps TS
granularity
o ODU1 occupies 2 of the 8, 32, or 80 TSs for ODU2, ODU3, or ODU4
- ODU1 into ODU2 or ODU3 multiplexing with 2.5 Gbps TS granularity
o ODU1 occupies 1 of the 4 or 16 TSs for ODU2 or ODU3
- ODU2 into ODU3 or ODU4 multiplexing with 1.25 Gbps TS granularity
o ODU2 occupies 8 of the 32 or 80 TSs for ODU3 or ODU4
- ODU2 into ODU3 multiplexing with 2.5 Gbps TS granularity
o ODU2 occupies 4 of the 16 TSs for ODU3
- ODU3 into ODU4 multiplexing with 1.25 Gbps TS granularity
o ODU3 occupies 31 of the 80 TSs for ODU4
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- ODUflex into ODU2, ODU3, or ODU4 multiplexing with 1.25 Gbps TS
granularity
o ODUflex occupies n of the 8, 32, or 80 TSs for ODU2, ODU3, or
ODU4 (n <= Total TS number of ODUk)
- ODU2e into ODU3 or ODU4 multiplexing with 1.25 Gbps TS granularity
o ODU2e occupies 9 of the 32 TSs for ODU3 or 8 of the 80 TSs for
ODU4
In general, the mapping of an ODUj (including ODUflex) into a
specific OTUk TS is determined locally, and it can also be explicitly
controlled by a specific entity (e.g., head end or Network Management
System (NMS)) through Explicit Label Control [RFC3473].
3.1.2.1. Structure of MSI Information
When multiplexing an ODUj into an HO ODUk (k>j), G.709 specifies the
information that has to be transported in-band in order to allow for
correct demultiplexing. This information, known as MSI, is
transported in the OPUk overhead and is local to each link. In case
of bidirectional paths, the association between the TPN and TS must
be the same in both directions.
The MSI information is organized as a set of entries, with one entry
for each HO ODUj TS. The information carried by each entry is:
- Payload Type: the type of the transported payload.
- TPN: the port number of the ODUj transported by the HO ODUk. The
TPN is the same for all the TSs assigned to the transport of the
same ODUj instance.
For example, an ODU2 carried by an HO ODU3 is described by 4 entries
in the OPU3 overhead when the TS granularity is 2.5 Gbps, and by 8
entries when the TS granularity is 1.25 Gbps.
On each node and on every link, two MSI values have to be provisioned
(referring to [G798]):
- The Transmitted MSI (TxMSI) information inserted in OPU (e.g.,
OPU3) overhead by the source of the HO ODUk trail.
- The Expected MSI (ExMSI) information that is used to check the
Accepted MSI (AcMSI) information. The AcMSI information is the
MSI valued received in-band, after a three-frame integration.
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As described in [G798], the sink of the HO ODU trail checks the
complete content of the AcMSI information against the ExMSI. If the
AcMSI is different from the ExMSI, then the traffic is dropped, and a
payload mismatch alarm is generated.
Provisioning of TPN can be performed by either a network management
system or control plane. In the last case, the control plane is also
responsible for negotiating the provisioned values on a link-by-link
basis.
4. Connection Management in OTN
OTN-based connection management is concerned with controlling the
connectivity of ODU paths and OCh. This document focuses on the
connection management of ODU paths. The management of OCh paths is
described in [RFC6163].
While [G872-2001] considered the ODU to be a set of layers in the
same way as SDH has been modeled, recent ITU-T OTN architecture
progress [G872-2012] includes an agreement to model the ODU as a
single-layer network with the bit rate as a parameter of links and
connections. This allows the links and nodes to be viewed in a
single topology as a common set of resources that are available to
provide ODUj connections independent of the value of j. Note that
when the bit rate of ODUj is less than the server bit rate, ODUj
connections are supported by HO ODU (which has a one-to-one
relationship with the OTU).
From an ITU-T perspective, the ODU connection topology is represented
by that of the OTU link layer, which has the same topology as that of
the OCh layer (independent of whether the OTU supports an HO ODU,
where multiplexing is utilized, or an LO ODU in the case of direct
mapping).
Thus, the OTU and OCh layers should be visible in a single
topological representation of the network, and from a logical
perspective, the OTU and OCh may be considered as the same logical,
switchable entity.
Note that the OTU link-layer topology may be provided via various
infrastructure alternatives, including point-to-point optical
connections, optical connections fully in the optical domain, and
optical connections involving hybrid sub-lambda/lambda nodes
involving 3R, etc. See [RFC6163] for additional information.
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4.1. Connection Management of the ODU
An LO ODUj can be either mapped into the OTUk signal (j = k) or
multiplexed with other LO ODUjs into an OTUk (j < k), and the OTUk is
mapped into an OCh.
From the perspective of the control plane, there are two kinds of
network topology to be considered.
(1) ODU layer
In this case, the ODU links are presented between adjacent OTN nodes,
as illustrated in Figure 2. In this layer, there are ODU links with
a variety of TSs available, and nodes that are Optical Digital Cross
Connects (ODXCs). LO ODU connections can be set up based on the
network topology.
Link #5 +--+---+--+ Link #4
+--------------------------| |--------------------------+
| | ODXC | |
| +---------+ |
| Node E |
| |
+-++---+--+ +--+---+--+ +--+---+--+ +--+---+-++
| |Link #1 | |Link #2 | |Link #3 | |
| |--------| |--------| |--------| |
| ODXC | | ODXC | | ODXC | | ODXC |
+---------+ +---------+ +---------+ +---------+
Node A Node B Node C Node D
Figure 2: Example Topology for LO ODU Connection Management
If an ODUj connection is requested between Node C and Node E,
routing/path computation must select a path that has the required
number of TSs available and that offers the lowest cost. Signaling
is then invoked to set up the path and to provide the information
(e.g., selected TSs) required by each transit node to allow the
configuration of the ODUj-to-OTUk mapping (j = k) or multiplexing (j
< k) and demapping (j = k) or demultiplexing (j < k).
(2) ODU layer with OCh switching capability
In this case, the OTN nodes interconnect with wavelength switched
nodes (e.g., Reconfiguration Optical Add/Drop Multiplexer (ROADM) or
Optical Cross-Connect (OXC)) that are capable of OCh switching; this
is illustrated in Figures 3 and 4. There are the ODU layer and the
OCh layer, so it is simply a Multi-Layer Network (MLN) (see
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RFC 7062 OTN Framework November 2013
[RFC6001]). OCh connections may be created on demand, which is
described in Section 5.1.
In this case, an operator may choose to allow the underlying OCh
layer to be visible to the ODU routing/path computation process, in
which case the topology would be as shown in Figure 4. In Figure 3,
however, a cloud representing OCh-capable switching nodes is
represented. In Figure 3, the operator choice is to hide the real
OCh-layer network topology.
Node E
Link #5 +--------+ Link #4
+------------------------| |------------------------+
| ------ |
| // \\ |
| || || |
| | OCh domain | |
+-+-----+ +------ || || ------+ +-----+-+
| | | \\ // | | |
| |Link #1 | -------- |Link #3 | |
| +--------+ | | +--------+ +
| ODXC | | ODXC +--------+ ODXC | | ODXC |
+-------+ +---------+Link #2 +---------+ +-------+
Node A Node B Node C Node D
Figure 3: OCh Hidden Topology for LO ODU Connection Management
Link #5 +---------+ Link #4
+------------------------| |-----------------------+
| +----| ODXC |----+ |
| +-++ +---------+ ++-+ |
| Node f | | Node E | | Node g |
| +-++ ++-+ |
| | +--+ | |
+-+-----+ +----+----+--| |--+-----+---+ +-----+-+
| |Link #1 | | +--+ | |Link #3 | |
| +--------+ | Node h | +--------+ |
| ODXC | | ODXC +--------+ ODXC | | ODXC |
+-------+ +---------+ Link #2+---------+ +-------+
Node A Node B Node C Node D
Figure 4: OCh Visible Topology for LO ODUj Connection Management
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In Figure 4, the cloud in the previous figure is substituted by the
real topology. The nodes f, g, and h are nodes with OCh switching
capability.
In the examples (i.e., Figures 3 and 4), we have considered the case
in which LO ODUj connections are supported by an OCh connection and
the case in which the supporting underlying connection can also be
made by a combination of HO ODU/OCh connections.
In this case, the ODU routing/path selection process will request an
HO ODU/OCh connection between node C and node E from the OCh domain.
The connection will appear at the ODU level as a Forwarding
Adjacency, which will be used to create the ODU connection.
5. GMPLS/PCE Implications
The purpose of this section is to provide a set of requirements to be
evaluated for extensions of the current GMPLS protocol suite and the
PCE applications and protocols to encompass OTN enhancements and
connection management.
5.1. Implications for Label Switched Path (LSP) Hierarchy
The path computation for an ODU connection request is based on the
topology of the ODU layer.
The OTN path computation can be divided into two layers. One layer
is OCh/OTUk; the other is ODUj. [RFC4206] and [RFC6107] define the
mechanisms to accomplish creating the hierarchy of LSPs. The LSP
management of multiple layers in OTN can follow the procedures
defined in [RFC4206], [RFC6001], and [RFC6107].
As discussed in Section 4, the route path computation for OCh is in
the scope of the Wavelength Switched Optical Network (WSON)
[RFC6163]. Therefore, this document only considers the ODU layer for
an ODU connection request.
The LSP hierarchy can also be applied within the ODU layers. One of
the typical scenarios for ODU layer hierarchy is to maintain
compatibility with introducing new [G709-2012] services (e.g., ODU0
and ODUflex) into a legacy network configuration (i.e., the legacy
OTN referenced by [RFC4328]). In this scenario, it may be necessary
to consider introducing hierarchical multiplexing capability in
specific network transition scenarios. One method for enabling
multiplexing hierarchy is by introducing dedicated boards in a few
specific places in the network and tunneling these new services
through the legacy containers (ODU1, ODU2, ODU3), thus postponing the
need to upgrade every network element to [G709-2012] capabilities.
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In such cases, one ODUj connection can be nested into another ODUk
(j<k) connection, which forms the LSP hierarchy in the ODU layer.
The creation of the outer ODUk connection can be triggered via
network planning or by the signaling of the inner ODUj connection.
For the former case, the outer ODUk connection can be created in
advance based on network planning. For the latter case, the multi-
layer network signaling described in [RFC4206], [RFC6107], and
[RFC6001] (including related modifications, if needed) is relevant to
create the ODU connections with multiplexing hierarchy. In both
cases, the outer ODUk connection is advertised as a Forwarding
Adjacency (FA).
5.2. Implications for GMPLS Signaling
The signaling function and RSVP-TE extensions are described in
[RFC3471] and [RFC3473]. For OTN-specific control, [RFC4328] defines
signaling extensions to support control for the legacy G.709 Optical
Transport Networks.
As described in Section 3, [G709-2012] introduced some new features
that include the ODU0, ODU2e, ODU4, and ODUflex containers. The
mechanisms defined in [RFC4328] do not support such new OTN features,
and protocol extensions will be necessary to allow them to be
controlled by a GMPLS control plane.
[RFC4328] defines the LSP Encoding Type, the Switching Type, and the
Generalized Protocol Identifier (Generalized-PID) constituting the
common part of the Generalized Label Request. The G.709 traffic
parameters are also defined in [RFC4328]. In addition, the following
signaling aspects not included in [RFC4328] should be considered:
- Support for specifying new signal types and related traffic
information
The traffic parameters should be extended in a signaling message
to support the new ODUj, including:
- ODU0
- ODU2e
- ODU4
- ODUflex
For the ODUflex signal type, the bit rate must be carried
additionally in the traffic parameter to set up an ODUflex
connection.
For other ODU signal types, the bit rates and tolerances are fixed
and can be deduced from the signal types.
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- Support for LSP setup using different TS granularity
The signaling protocol should be able to identify the TS
granularity (i.e., the 2.5 Gbps TS granularity and the new 1.25
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.
- Support for LSP setup of new ODUk/ODUflex containers with related
mapping and multiplexing capabilities
A new label format must be defined to carry the exact TS's
allocation information related to the extended mapping and
multiplexing hierarchy (for example, ODU0 into ODU2 multiplexing
(with 1.25 Gbps TS granularity)), in order to set up the ODU
connection.
- Support for TPN allocation and negotiation
TPN needs to be configured as part of the MSI information (see
more information in Section 3.1.2.1). A signaling mechanism must
be identified to carry TPN information if the control plane is
used to configure MSI information.
- Support for ODU Virtual Concatenation (VCAT) and Link Capacity
Adjustment Scheme (LCAS)
GMPLS signaling should support the creation of Virtual
Concatenation of an ODUk signal with k=1, 2, 3. The signaling
should also support the control of dynamic capacity changing of a
VCAT container using LCAS ([G7042]). [RFC6344] has a clear
description of VCAT and LCAS control in SONET/SDH and OTN.
- Support for Control of Hitless Adjustment of ODUflex (GFP)
[G7044] has been created in ITU-T to specify hitless adjustment of
ODUflex (GFP) (HAO) that is used to increase or decrease the
bandwidth of an ODUflex (GFP) that is transported in an OTN.
The procedure of ODUflex (GFP) adjustment requires the
participation of every node along the path. Therefore, it is
recommended to use control-plane signaling to initiate the
adjustment procedure in order to avoid manual configuration at
each node along the path.
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From the perspective of the control plane, control of ODUflex
resizing is similar to control of bandwidth increasing and
decreasing as described in [RFC3209]. Therefore, the Shared
Explicit (SE) style can be used for control of HAO.
All the extensions above should consider the extensibility to match
future evolvement of OTN.
5.3. Implications for GMPLS Routing
The path computation process needs to select a suitable route for an
ODUj connection request. In order to perform the path computation,
it needs to evaluate the available bandwidth on each candidate link.
The routing protocol should be extended to convey sufficient
information to represent ODU Traffic Engineering (TE) topology.
The Interface Switching Capability Descriptors defined in [RFC4202]
present a new constraint for LSP path computation. [RFC4203] defines
the Switching Capability, related Maximum LSP Bandwidth, and
Switching Capability specific information. When the Switching
Capability field is TDM, the Switching Capability specific
information field includes Minimum LSP Bandwidth, an indication
whether the interface supports Standard or Arbitrary SONET/SDH, and
padding. Hence, a new Switching Capability value needs to be defined
for [G709-2012] ODU switching in order to allow the definition of a
new Switching Capability specific information field. The following
requirements should be considered:
- Support for carrying the link multiplexing capability
As discussed in Section 3.1.2, many different types of ODUj can be
multiplexed into the same OTUk. For example, both ODU0 and ODU1
may be multiplexed into ODU2. An OTU link may support one or more
types of ODUj signals. The routing protocol should be capable of
carrying this multiplexing capability.
- Support any ODU and ODUflex
The bit rate (i.e., bandwidth) of each TS is dependent on the TS
granularity and the signal type of the link. For example, the
bandwidth of a 1.25 Gbps TS in an OTU2 is about 1.249409620 Gbps,
while the bandwidth of a 1.25 Gbps TS in an OTU3 is about
1.254703729 Gbps.
One LO ODU may need a different number of TSs when multiplexed
into different HO ODUs. For example, for ODU2e, 9 TSs are needed
when multiplexed into an ODU3, while only 8 TSs are needed when
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multiplexed into an ODU4. For ODUflex, the total number of TSs to
be reserved in an HO ODU equals the maximum of [bandwidth of
ODUflex / bandwidth of TS of the HO ODU].
Therefore, the routing protocol should be capable of carrying the
necessary link bandwidth information for performing accurate route
computation for any of the fixed rate ODUs as well as ODUflex.
- Support for differentiating between terminating and switching
capability
Due to internal constraints and/or limitations, the type of signal
being advertised by an interface could be restricted to switched
(i.e., forwarded to switching matrix without
multiplexing/demultiplexing actions), restricted to terminated
(demuxed), or both. The capability advertised by an interface
needs further distinction in order to separate termination and
switching capabilities.
Therefore, to allow the required flexibility, the routing protocol
should clearly distinguish the terminating and switching
capability.
- Support for Tributary Slot Granularity advertisement
[G709-2012] defines two types of TSs, but each link can only
support a single type at a given time. In order to perform a
correct path computation (i.e., the LSP endpoints have matching
Tributary Slot Granularity values) the Tributary Slot Granularity
needs to be advertised.
- Support different priorities for resource reservation
How many priority levels should be supported depends on the
operator's policy. Therefore, the routing protocol should be
capable of supporting up to 8 priority levels as defined in
[RFC4202].
- Support link bundling
As described in [RFC4201], link bundling can improve routing
scalability by reducing the number of TE links that have to be
handled by the routing protocol. The routing protocol should be
capable of supporting the bundling of multiple OTU links, at the
same line rate and muxing hierarchy, between a pair of nodes that
a TE link does. Note that link bundling is optional and is
implementation dependent.
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- Support for Control of Hitless Adjustment of ODUflex (GFP)
The control plane should support hitless adjustment of ODUflex, so
the routing protocol should be capable of differentiating whether
or not an ODU link can support hitless adjustment of ODUflex (GFP)
and how many resources can be used for resizing. This can be
achieved by introducing a new signal type "ODUflex(GFP-F),
resizable" that implies the support for hitless adjustment of
ODUflex (GFP) by that link.
As mentioned in Section 5.1, one method of enabling multiplexing
hierarchy is via usage of dedicated boards to allow tunneling of new
services through legacy ODU1, ODU2, and ODU3 containers. Such
dedicated boards may have some constraints with respect to switching
matrix access; detection and representation of such constraints is
for further study.
5.4. Implications for Link Management Protocol
As discussed in Section 5.3, path computation needs to know the
interface switching capability of links. The switching capability of
two ends of the link may be different, so the link capability of two
ends should be correlated.
LMP [RFC4204] provides a control-plane protocol for exchanging and
correlating link capabilities.
Note that LO ODU type information can be, in principle, discovered by
routing. Since in certain cases, routing is not present (e.g., in
the case of a User-Network Interface (UNI)), we need to extend link
management protocol capabilities to cover this aspect. If routing is
present, discovery via LMP could also be optional.
- Correlating the granularity of the TS
As discussed in Section 3.1.2, the two ends of a link may support
different TS granularity. In order to allow interconnection, the
node with 1.25 Gbps granularity should fall back to 2.5 Gbps
granularity.
Therefore, it is necessary for the two ends of a link to correlate
the granularity of the TS. This ensures the correct use of the TE
link.
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- Correlating the supported LO ODU signal types and multiplexing
hierarchy capability
Many new ODU signal types have been introduced in [G709-2012],
such as ODU0, ODU4, ODU2e, and ODUflex. It is possible that
equipment does not support all the LO ODU signal types introduced
by new standards or documents. Furthermore, since multiplexing
hierarchy may not be supported by the legacy OTNs, it is possible
that only one end of an ODU link can support multiplexing
hierarchy capability or that the two ends of the link support
different multiplexing hierarchy capabilities (e.g., one end of
the link supports ODU0 into ODU1 into ODU3 multiplexing while the
other end supports ODU0 into ODU2 into ODU3 multiplexing).
For control and management consideration, it is necessary for the
two ends of an HO ODU link to correlate the types of LO ODU that
can be supported and the multiplexing hierarchy capabilities that
can be provided by the other end.
5.5. Implications for Control-Plane Backward Compatibility
With the introduction of [G709-2012], there may be OTN composed of a
mixture of nodes, some of which support the legacy OTN and run the
control-plane protocols defined in [RFC4328], while others support
[G709-2012] and the new OTN control plane characterized in this
document. Note that a third case, for the sake of completeness,
consists of nodes supporting the legacy OTN referenced by [RFC4328]
with a new OTN control plane, but such nodes can be considered new
nodes with limited capabilities.
This section discusses the compatibility of nodes implementing the
control-plane procedures defined in [RFC4328] in support of the
legacy OTN and the control-plane procedures defined to support
[G709-2012] as outlined by this document.
Compatibility needs to be considered only when controlling an ODU1,
ODU2, or ODU3 connection because the legacy OTN only supports these
three ODU signal types. In such cases, there are several possible
options, including:
- A node supporting [G709-2012] could support only the control-plane
procedures related to [G709-2012], in which case both types of
nodes would be unable to jointly control an LSP for an ODU type
that both nodes support in the data plane.
- A node supporting [G709-2012] could support both the control plane
related to [G709-2012] and the control plane defined in [RFC4328].
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o Such a node could identify which set of procedures to follow
when initiating an LSP based on the Switching Capability value
advertised in routing.
o Such a node could follow the set of procedures based on the
Switching Type received in signaling messages from an upstream
node.
o Such a node, when processing a transit LSP, could select which
signaling procedures to follow based on the Switching
Capability value advertised in routing by the next-hop node.
5.6. Implications for Path Computation Elements
[RFC7025] describes the requirements for GMPLS applications of PCE in
order to establish GMPLS LSP. PCE needs to consider the GMPLS TE
attributes appropriately once a Path Computation Client (PCC) or
another PCE requests a path computation. The TE attributes that can
be contained in the path calculation request message from the PCC or
the PCE defined in [RFC5440] include switching capability, encoding
type, signal type, etc.
As described in Section 5.2, new signal types and new signals with
variable bandwidth information need to be carried in the extended
signaling message of path setup. For the same consideration, the PCE
Communication Protocol (PCECP) also has a desire to be extended to
carry the new signal type and related variable bandwidth information
when a PCC requests a path computation.
5.7. Implications for Management of GMPLS Networks
From the management perspective, the management function should be
capable of managing not only the legacy OTN referenced by [RFC4328],
but also new management functions introduced by the new features as
specified in [G709-2012] (for more information, see Sections 3 and
4). OTN Operations, Administration, and Maintenance (OAM)
configuration could be done through either Network Management Systems
(NMS) or the GMPLS control plane as defined in [TDM-OAM]. For
further details on management aspects for GMPLS networks, refer to
[RFC3945].
In case PCE is used to perform path computation in OTN, the PCE
manageability should be considered (for more information, see
Section 8 of [RFC5440]).
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6. Data-Plane Backward Compatibility Considerations
If MI AUTOpayloadtype is activated (see [G798]), a node supporting
1.25 Gbps TS can interwork with the other nodes that support 2.5 Gbps
TS by combining specific TSs together in the data plane. The control
plane must support this TS combination.
Path
+----------+ ------------> +----------+
| TS1==|===========\--------+--TS1 |
| TS2==|=========\--\-------+--TS2 |
| TS3==|=======\--\--\------+--TS3 |
| TS4==|=====\--\--\--\-----+--TS4 |
| | \ \ \ \----+--TS5 |
| | \ \ \------+--TS6 |
| | \ \--------+--TS7 |
| | \----------+--TS8 |
+----------+ <------------ +----------+
node A Resv node B
Figure 5: Interworking between 1.25 Gbps TS and 2.5 Gbps TS
Take Figure 5 as an example. Assume that there is an ODU2 link
between node A and B, where node A only supports the 2.5 Gbps TS
while node B supports the 1.25 Gbps TS. In this case, the TS#i and
TS#i+4 (where i<=4) of node B are combined together. When creating
an ODU1 service in this ODU2 link, node B reserves the TS#i and
TS#i+4 with the granularity of 1.25 Gbps. But in the label sent from
B to A, it is indicated that the TS#i with the granularity of 2.5
Gbps is reserved.
In the opposite direction, when receiving a label from node A
indicating that the TS#i with the granularity of 2.5 Gbps is
reserved, node B will reserve the TS#i and TS#i+4 with the
granularity of 1.25 Gbps in its data plane.
7. Security Considerations
The use of control-plane protocols for signaling, routing, and path
computation opens an OTN to security threats through attacks on those
protocols. However, this is not greater than the risks presented by
the existing OTN control plane as defined by [RFC4203] and [RFC4328].
Meanwhile, the Data Communication Network (DCN) for OTN GMPLS
control-plane protocols is likely to be in the in-fiber overhead,
which, together with access lists at the network edges, provides a
significant security feature. For further details of specific
security measures, refer to the documents that define the protocols
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([RFC3473], [RFC4203], [RFC5307], [RFC4204], and [RFC5440]).
[RFC5920] provides an overview of security vulnerabilities and
protection mechanisms for the GMPLS control plane.
8. Acknowledgments
We would like to thank Maarten Vissers and Lou Berger for their
reviews and useful comments.
9. Contributors
Jianrui Han
Huawei Technologies Co., Ltd.
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129
P.R. China
Phone: +86-755-28972913
EMail: hanjianrui@huawei.com
Malcolm Betts
EMail: malcolm.betts@rogers.com
Pietro Grandi
Alcatel-Lucent
Optics CTO
Via Trento 30
20059 Vimercate (Milano)
Italy
Phone: +39 039 6864930
EMail: pietro_vittorio.grandi@alcatel-lucent.it
Eve Varma
Alcatel-Lucent
1A-261, 600-700 Mountain Av
PO Box 636
Murray Hill, NJ 07974-0636
USA
EMail: eve.varma@alcatel-lucent.com
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10. References
10.1. Normative References
[G709-2012] ITU-T, "Interface for the Optical Transport Network
(OTN)", G.709/Y.1331 Recommendation, February 2012.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description", RFC
3471, January 2003.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC
3473, January 2003.
[RFC4201] Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling
in MPLS Traffic Engineering (TE)", RFC 4201, October
2005.
[RFC4202] Kompella, K., Ed., and Y. Rekhter, Ed., "Routing
Extensions in Support of Generalized Multi-Protocol Label
Switching (GMPLS)", RFC 4202, October 2005.
[RFC4203] Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, October 2005.
[RFC4204] Lang, J., Ed., "Link Management Protocol (LMP)", RFC
4204, October 2005.
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October
2005.
[RFC4328] Papadimitriou, D., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Extensions for G.709 Optical
Transport Networks Control", RFC 4328, January 2006.
[RFC5307] Kompella, K., Ed., and Y. Rekhter, Ed., "IS-IS Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 5307, October 2008.
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RFC 7062 OTN Framework November 2013
[RFC5440] Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path
Computation Element (PCE) Communication Protocol (PCEP)",
RFC 5440, March 2009.
[RFC6001] Papadimitriou, D., Vigoureux, M., Shiomoto, K., Brungard,
D., and JL. Le Roux, "Generalized MPLS (GMPLS) Protocol
Extensions for Multi-Layer and Multi-Region Networks
(MLN/MRN)", RFC 6001, October 2010.
[RFC6107] Shiomoto, K., Ed., and A. Farrel, Ed., "Procedures for
Dynamically Signaled Hierarchical Label Switched Paths",
RFC 6107, February 2011.
[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, August
2011.
10.2. Informative References
[G798] ITU-T, "Characteristics of optical transport network
hierarchy equipment functional blocks", G.798
Recommendation, December 2012.
[G872-2001] ITU-T, "Architecture of optical transport networks",
G.872 Recommendation, November 2001.
[G872-2012] ITU-T, "Architecture of optical transport networks",
G.872 Recommendation, October 2012.
[G7041] ITU-T, "Generic framing procedure", G.7041/Y.1303, April
2011.
[G7042] ITU-T, "Link capacity adjustment scheme (LCAS) for
virtual concatenated signals", G.7042/Y.1305, March 2006.
[G7044] ITU-T, "Hitless adjustment of ODUflex (HAO)",
G.7044/Y.1347, October 2011.
[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006.
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RFC 7062 OTN Framework November 2013
[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, April 2011.
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
[RFC7025] Otani, T., Ogaki, K., Caviglia, D., Zhang, F., and C.
Margaria, "Requirements for GMPLS Applications of PCE",
RFC 7025, September 2013.
[TDM-OAM] Kern, A., and A. Takacs, "GMPLS RSVP-TE Extensions for
SONET/SDH and OTN OAM Configuration", Work in Progress,
November 2013.
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Authors' Addresses
Fatai Zhang (editor)
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129
P.R. China
Phone: +86-755-28972912
EMail: zhangfatai@huawei.com
Dan Li
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129
P.R. China
Phone: +86-755-28973237
EMail: huawei.danli@huawei.com
Han Li
China Mobile Communications Corporation
53 A Xibianmennei Ave. Xuanwu District
Beijing 100053
P.R. China
Phone: +86-10-66006688
EMail: lihan@chinamobile.com
Sergio Belotti
Alcatel-Lucent
Optics CTO
Via Trento 30
20059 Vimercate (Milano)
Italy
Phone: +39 039 6863033
EMail: sergio.belotti@alcatel-lucent.it
Daniele Ceccarelli
Ericsson
Via A. Negrone 1/A
Genova - Sestri Ponente
Italy
EMail: daniele.ceccarelli@ericsson.com
Zhang, et al. Informational [Page 26]