Network Working Group Fatai Zhang, Ed.
Internet Draft Dan Li
Category: Informational Huawei
Han Li
CMCC
S.Belotti
Alcatel-Lucent
D. Ceccarelli
Ericsson
Expires: December 18, 2013 June 18, 2013
Framework for GMPLS and PCE Control of
G.709 Optical Transport Networks
draft-ietf-ccamp-gmpls-g709-framework-13.txt
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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
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Optical Transport Networks (OTN) as specified in ITU-T Recommendation
G.709 as published in 2012.
Table of Contents
1. Introduction .................................................. 2
2. Terminology ................................................... 3
3. G.709 Optical Transport Network ............................... 4
3.1. OTN Layer Network ........................................ 4
3.1.1. Client signal mapping ............................... 5
3.1.2. Multiplexing ODUj onto Links ........................ 6
3.1.2.1. Structure of MSI information ................... 8
4. Connection management in OTN .................................. 9
4.1. Connection management of the ODU ........................ 10
5. GMPLS/PCE Implications ....................................... 12
5.1. Implications for Label Switch Path (LSP) Hierarchy ...... 12
5.2. Implications for GMPLS Signaling ........................ 13
5.3. Implications for GMPLS Routing .......................... 15
5.4. Implications for Link Management Protocol ............... 17
5.5. Implications for Control Plane Backward Compatibility ... 18
5.6. Implications for Path Computation Elements .............. 19
6. Data Plane Backward Compatibility Considerations ............. 19
7. Security Considerations ...................................... 20
8. IANA Considerations .......................................... 21
9. Acknowledgments .............................................. 21
10. References .................................................. 21
10.1. Normative References ................................... 21
10.2. Informative References ................................. 22
11. Authors' Addresses .......................................... 23
12. Contributors ................................................ 24
1. Introduction
OTN has become a mainstream layer 1 technology for the transport
network. Operators want to introduce control plane capabilities based
on GMPLS to OTN networks, 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
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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 networks 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., 1.25Gbps and 2.5Gbps), 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 the GMPLS control of OTN
networks and includes a discussion of the implication for the use of
the PCE [RFC4655].
For the purposes of the control plane the OTN can be considered as
being 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
OTU: Optical channel Transport Unit
OMS: Optical multiplex section
MSI: Multiplex Structure Identifier
TPN: Tributary Port Number
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LO ODU: Lower Order ODU. The LO ODUj (j can be 0, 1, 2, 2e, 3, 4,
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, 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).
3. G.709 Optical Transport Network
This section provides an informative overview of those 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].
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
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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.
3.1.1. Client signal mapping
The client signals are mapped into a LO ODUj. The current values of j
defined in [G709-2012] are: 0, 1, 2, 2e, 3, 4, Flex. The approximate
bit rates of these signals are defined in [G709-2012] and are
reproduced in Tables 1 and 2.
Table 1 - ODU types and bit rates
+-----------------------+-----------------------------------+
| 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 | |
+-----------------------+-----------------------------------+
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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Table 2 - ODU types and tolerance
+-----------------------+-----------------------------------+
| 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 |
+-----------------------+-----------------------------------+
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 2.5Gbps. [G709-2012] added an
additional TS granularity, nominally 1.25Gbps. The number and type of
TSs provided by each of the currently identified OTUk is provided
below:
Tributary Slot Granularity
2.5Gbps 1.25Gbps Nominal Bit rate
OTU1 1 2 2.5Gbps
OTU2 4 8 10Gbps
OTU3 16 32 40Gbps
OTU4 -- 80 100Gbps
To maintain backwards compatibility while providing the ability to
interconnect nodes that support 1.25Gbps TS at one end of a link and
2.5Gbps TS at the other, [G709-2012] requires 'new' equipment fall
back to the use of a 2.5Gbps 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 Table 7-9 of [G709-2012]):
- ODU0 into ODU1, ODU2, ODU3 or ODU4 multiplexing with 1,25Gbps 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 1,25Gbps TS
granularity
o ODU1 occupies 2 of the 8, 32 or 80 TSs for ODU2, ODU3 or ODU4
- ODU1 into ODU2, ODU3 multiplexing with 2.5Gbps TS granularity
o ODU1 occupies 1 of the 4 or 16 TSs for ODU2 or ODU3
- ODU2 into ODU3 or ODU4 multiplexing with 1.25Gbps TS granularity
o ODU2 occupies 8 of the 32 or 80 TSs for ODU3 or ODU4
- ODU2 into ODU3 multiplexing with 2.5Gbps TS granularity
o ODU2 occupies 4 of the 16 TSs for ODU3
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- ODU3 into ODU4 multiplexing with 1.25Gbps TS granularity
o ODU3 occupies 31 of the 80 TSs for ODU4
- ODUflex into ODU2, ODU3 or ODU4 multiplexing with 1.25Gbps 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 1.25Gbps 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, Network Management
System (NMS)) through Explicit Label Control [RFC3473].
3.1.2.1. Structure of MSI information
When multiplexing an ODUj into a 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 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 a HO ODU3 is described by 4 entries
in the OPU3 overhead when the TS granularity is 2.5Gbps, and by 8
entries when the TS granularity is 1.25Gbps.
On each node and on every link, two MSI values have to be provisioned
(Referring to [G798-V4]):
- The Transmitted MSI (TxMSI) information inserted in OPU (e.g.,
OPU3) overhead by the source of the HO ODUk trail.
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- 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.
As described in [G798-V4], 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 either by network management
system or control plane. In the last case, control plane is also
responsible for negotiating the provisioned values on a link by link
base.
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 as 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 HO ODU, where
multiplexing is utilized, or 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
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 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 setup 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 TS 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
node (e.g., Reconfiguration Optical Add/Drop Multiplexer (ROADM),
Optical Cross-Connect (OXC)) that are capable of OCh switching, which
is illustrated in Figure 3 and Figure 4. There are ODU layer and OCh
layer, so it is simply a Multi-Layer Networks (MLN) (see [RFC6001]).
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OCh connections may be created on demand, which is described in
section 5.1.
In this case, an operator may choose to allow the underlined 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
below, instead, 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 of previous figure is substitute by the real
topology. The nodes f, g, h are nodes with OCh switching capability.
In the examples (i.e., Figure 3 and Figure 4), we have considered the
case in which LO ODUj connections are supported by OCh connection,
and the case in which the supporting underlying connection can be
also 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 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 Switch Path (LSP) Hierarchy
The path computation for ODU connection request is based on the
topology of 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], etc.
As discussed in section 4, the route path computation for OCh is in
the scope of Wavelength Switched Optical Network (WSON) [RFC6163].
Therefore, this document only considers ODU layer for ODU connection
request.
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,
ODUflex) into a legacy network configuration (i.e., the legacy OTN
referenced by [RFC4328]). In this scenario, it may be needed 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
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containers (ODU1, ODU2, ODU3), thus postponing the need to upgrade
every network element to [G709-2012] capabilities.
In such case, one ODUj connection can be nested into another ODUk
(j<k) connection, which forms the LSP hierarchy in 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) are 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]. The following signaling
aspects should be considered additionally since [RFC4328] was
published:
- Support for specifying the new signal types and the related
traffic information
The traffic parameters should be extended in signaling message to
support the new ODUj including:
- ODU0
- ODU2e
- ODU4
- ODUflex
For ODUflex signal type, its bit rate must be carried additionally
in the Traffic Parameter to setup an ODUflex connection.
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For other ODU signal types, their bit rates and tolerances are
fixed and can be deduced from the signal types.
- Support for LSP setup using different TS granularity
The signaling protocol should be able to identify the TS
granularity (i.e., the 2.5Gbps TS granularity and the new 1.25Gbps
TS granularity) to be used for establishing an Hierarchical LSP
which will be used to carry service LSP(s) requiring 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 TSs
allocation information related to the extended mapping and
multiplexing hierarchy (For example, ODU0 into ODU2 multiplexing
(with 1.25Gbps 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 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 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 networks.
- 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
network.
The procedure of ODUflex (GFP) adjustment requires the
participation of every node along the path. Therefore, it is
recommended to use the control plane signaling to initiate the
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adjustment procedure in order to avoid the manual configuration at
each node along the path.
From the perspective of control plane, the control of ODUflex
resizing is similar to control of bandwidth increasing and
decreasing 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.
Interface Switching Capability Descriptors defined in [RFC4202]
present a new constraint for LSP path computation. [RFC4203] defines
the switching capability and related Maximum LSP Bandwidth and the
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 definition. 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 1.25G TS in an OTU2 is about 1.249409620Gbps,
while the bandwidth of a 1.25G TS in an OTU3 is about
1.254703729Gbps.
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One LO ODU may need 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
multiplexed into an ODU4. For ODUflex, the total number of TSs to
be reserved in a 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 of them. 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 TS 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 end points have matching
Tributary Slot Granularity values) the Tributary Slot Granularity
needs to be advertised.
- Support different priorities for resource reservation
How many priorities 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 amount of TE links that has to be
handled by routing protocol. The routing protocol should be
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capable of supporting bundling multiple OTU links, at the same
line rate and muxing hierarchy, between a pair of nodes as a TE
link. Note that link bundling is optional and is implementation
dependent.
- 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 an ODU link can support hitless adjustment of ODUflex
(GFP) or not, and how much resource 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, 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. User-
Network Interface (UNI) case) we need to extend link management
protocol capabilities to cover this aspect. In case of routing
presence, the 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 1.25Gbps granularity should fall back to 2.5Gbps
granularity.
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Therefore, it is necessary for the two ends of a link to
correlate the granularity of the TS. This ensures the correct use
and of the TE link.
- 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 those new standards or drafts. Furthermore, since multiplexing
hierarchy was not allowed by the legacy OTN referenced by
[RFC4328], it is possible that only one end of an ODU link can
support multiplexing hierarchy capability, or 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 the control and management consideration, it is necessary for
the two ends of an HO ODU link to correlate which types of LO ODU
can be supported and what multiplexing hierarchy capabilities 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 networks
composed of a mixture of nodes, some of which support the legacy OTN
and run control plane protocols defined in [RFC4328], while others
support [G709-2012] and new OTN control plane characterized in this
document. Note that a third case, for the sake of completeness,
consists on nodes supporting the legacy OTN referenced by [RFC4328]
with a new OTN control plane, but such nodes can be considered as new
nodes with limited capabilities.
This section discusses the compatibility of nodes implementing the
control plane procedures defined [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 ODU1 or
ODU2 or ODU3 connection, because the legacy OTN only support these
three ODU signal types. In such cases, there are several possible
options including:
- A node supporting [G709-2012] could support only the [G709-2012]
related control plane procedures, in which case both types of
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nodes would be unable to jointly control an LSP for an ODU type
that both nodes support in the data plane. Note that this case is
supported by the procedures defined in [RFC3473] as a different
Switching Capability/Type value is used for the different control
plane versions.
- A node supporting [G709-2012] could support both the [G709-2012]
related control plane and the control plane defined in [RFC4328].
o Such a node could identify which set of procedure 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
[PCE-APS] 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 which can
be contained in the path calculation request message from the PCC or
the PCE defined in [RFC5440] includes switching capability, encoding
type, signal type, etc.
As described in section 5.2.1, 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, 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.
6. Data Plane Backward Compatibility Considerations
If MI AUTOpayloadtype is activated (see [G798-V4]), a node supporting
1.25Gbps TS can interwork with the other nodes that supporting
2.5Gbps TS by combining Specific TSs together in data plane. The
control plane must support this TS combination.
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Path
+----------+ ------------> +----------+
| TS1==|===========\--------+--TS1 |
| TS2==|=========\--\-------+--TS2 |
| TS3==|=======\--\--\------+--TS3 |
| TS4==|=====\--\--\--\-----+--TS4 |
| | \ \ \ \----+--TS5 |
| | \ \ \------+--TS6 |
| | \ \--------+--TS7 |
| | \----------+--TS8 |
+----------+ <------------ +----------+
node A Resv node B
Figure 5 - Interworking between 1.25Gbps TS and 2.5Gbps 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 2.5Gbps TS while
node B supports the 1.25Gbps 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 1.25Gbps. But in the label sent from B to A, it is
indicated that the TS#i with the granularity of 2.5Gbps is reserved.
In the opposite direction, when receiving a label from node A
indicating that the TS#i with the granularity of 2.5Gbps is reserved,
node B will reserved the TS#i and TS#i+4 with the granularity of
1.25Gbps 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. Although, this is not greater than the risks presented by
the existing OTN control plane as defined by [RFC4203] and [RFC4328].
For further details of the specific security measures refer to the
documents that define the protocols ([RFC3473], [RFC4203], [RFC5307],
[RFC4204], and [RFC5440]). [RFC5920] provides an overview of security
vulnerabilities and protection mechanisms for the GMPLS control
plane.
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8. IANA Considerations
This document makes not requests for IANA action.
9. Acknowledgments
We would like to thank Maarten Vissers and Lou Berger for their
review and useful comments.
10. References
10.1. Normative References
[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., Editor, "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description", RFC
3471, January 2003.
[RFC3473] L. Berger, Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC
3473, January 2003.
[RFC4201] K. Kompella, Y. Rekhter, Ed., "Link Bundling in MPLS
Traffic Engineering (TE)", RFC 4201, October 2005.
[RFC4202] K. Kompella, Y. Rekhter, Ed., "Routing Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4202, October 2005.
[RFC4203] K. Kompella, 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.
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[RFC4206] K. Kompella, Y. Rekhter, Ed., "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October
2005.
[RFC4328] D. Papadimitriou, Ed. "Generalized Multi-Protocol
LabelSwitching (GMPLS) Signaling Extensions for G.709
Optical Transport Networks Control", RFC 4328, Jan 2006.
[RFC5307] K. Kompella, Y. Rekhter, Ed., "IS-IS Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 5307, October 2008.
[RFC5440] JP. Vasseur, JL. Le Roux, Ed.," Path Computation Element
(PCE) Communication Protocol (PCEP)", RFC 5440, March
2009.
[RFC6001] Dimitri Papadimitriou et al, "Generalized Multi-Protocol
Label Switching (GMPLS) Protocol Extensions for Multi-
Layer and Multi-Region Networks (MLN/MRN)", RFC6001,
February 21, 2010.
[RFC6107] K. Shiomoto, A. Farrel, "Procedures for Dynamically
Signaled Hierarchical Label Switched Paths", RFC6107,
February 2011.
[RFC6344] G. Bernstein et al, "Operating Virtual Concatenation
(VCAT) and the Link Capacity Adjustment Scheme (LCAS)
with Generalized Multi-Protocol Label Switching (GMPLS)",
RFC6344, August, 2011.
[G709-2012] ITU-T, "Interface for the Optical Transport Network
(OTN)", G.709/Y.1331 Recommendation, February 2012.
10.2. Informative References
[G798-V4] ITU-T, "Characteristics of optical transport network
hierarchy equipment functional blocks", G.798
Recommendation, October 2010.
[G7042] ITU-T, "Link capacity adjustment scheme (LCAS) for
virtual concatenated signals", G.7042/Y.1305, March 2006.
[G872-2001] ITU-T, "Architecture of optical transport networks",
G.872 Recommendation, November 2001.
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[G872-2012] ITU-T, "Architecture of optical transport networks",
G.872 Recommendation, October 2012.
[G7044] ITU-T, "Hitless adjustment of ODUflex", G.7044/Y.1347,
October 2011.
[G7041] ITU-T, "Generic framing procedure", G.7041/Y.1303, April
2011.
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, October 2004.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture",
RFC 4655, August 2006.
[RFC6163] Y. Lee, G. Bernstein, W. Imajuku, "Framework for GMPLS
and PCE Control of Wavelength Switched Optical Networks
(WSON)", RFC6163, April 2011.
[PCE-APS] Tomohiro Otani, Kenichi Ogaki, Diego Caviglia, and Fatai
Zhang, "Requirements for GMPLS applications of PCE",
draft-ietf-pce-gmpls-aps-req, Work in Progress.
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC5920, July 2010.
11. 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 Co., Ltd.
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
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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
+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
12. 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
Huawei Technologies Co., Ltd.
Email: malcolm.betts@huawei.com
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Pietro Grandi
Alcatel-Lucent
Optics CTO
Via Trento 30 20059 Vimercate (Milano) Italy
+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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