GMPLS DCSC: Generalized MPLS (GMPLS) Data Channel Switching Capable (DCSC) and Channel Set Label Extensions
Two additions to GMPLS: switching a whole channel, and carrying several labels in one path.
Berger, L. and D. Fedyk, "Generalized MPLS (GMPLS) Data Channel Switching Capable (DCSC) and Channel Set Label Extensions", RFC 6002, DOI 10.17487/RFC6002, October 2010, <https://www.rfc-editor.org/info/rfc6002>.
@misc{rfc6002,
series = {Request for Comments},
number = 6002,
howpublished = {RFC 6002},
publisher = {RFC Editor},
doi = {10.17487/RFC6002},
url = {https://www.rfc-editor.org/info/rfc6002},
author = {L. Berger and D. Fedyk},
title = {{Generalized MPLS (GMPLS) Data Channel Switching Capable (DCSC) and Channel Set Label Extensions}},
pagetotal = 10,
year = 2010,
month = oct,
} RFC text
Contents
Internet Engineering Task Force (IETF) L. Berger
Request for Comments: 6002 LabN
Updates: 3471, 3473, 3945, 4202, 4203, 5307 D. Fedyk
Category: Standards Track Alcatel-Lucent
ISSN: 2070-1721 October 2010
Generalized MPLS (GMPLS) Data Channel Switching Capable (DCSC)
and Channel Set Label Extensions
Abstract
This document describes two technology-independent extensions to
Generalized Multi-Protocol Label Switching (GMPLS). The first
extension defines the new switching type Data Channel Switching
Capable. Data Channel Switching Capable interfaces are able to
support switching of the whole digital channel presented on single
channel interfaces. The second extension defines a new type of
generalized label and updates related objects. The new label is
called the Generalized Channel_Set Label and allows more than one
data plane label to be controlled as part of a Label Switched Path
(LSP).
Status of This Memo
This is an Internet Standards Track document.
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). Further information on
Internet Standards is available in 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/rfc6002.
Copyright Notice
Copyright (c) 2010 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 ....................................................2
1.1. Conventions Used in This Document ..........................3
2. Data Channel Switching ..........................................3
2.1. Compatibility ..............................................4
3. Generalized Channel_Set Label Related Formats ...................4
3.1. Generalized Channel_Set LABEL_REQUEST Object ...............4
3.2. Generalized Channel_Set LABEL Object .......................4
3.3. Other Label-Related Objects ................................7
3.4. Compatibility ..............................................7
4. IANA Considerations .............................................8
4.1. Data Channel Switching Type ................................8
4.2. Generalized Channel_Set LABEL_REQUEST Object ...............8
4.3. Generalized Channel_Set LABEL Object .......................8
5. Security Considerations .........................................9
6. References ......................................................9
6.1. Normative References .......................................9
6.2. Informative References ....................................10
Acknowledgments ...................................................10
1. Introduction
This document describes two technology-independent extensions to
Generalized Multi-Protocol Label Switching (GMPLS). Both of these
extensions were initially defined in the context of Ethernet
services, see [RFC6004] and [RFC6005], but are generic in nature and
may be useful to any switching technology controlled via GMPLS.
The first extension defines a new switching type, which is called
Data Channel Switching Capable (DCSC). DCSC interfaces are able to
support switching of the whole digital channel presented on single
channel interfaces. The second extension defines a new type of
generalized label and updates related objects. The new label is
called the Generalized Channel_Set Label and allows more than one
data plane label to be controlled as part of a GMPLS Label Switched
Path (LSP).
1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Data Channel Switching
Current GMPLS switching types are defined in [RFC3945] and [RFC3471]
and support switching at the packet (PSC), frame (L2SC), time-slot
(TDM), frequency (LSC), and fiber (FSC) granularities. Parallel
definitions for these switching types are also made in [RFC4202],
[RFC4203], and [RFC5307].
One type of switching that is not well represented in this current
set is switching that occurs when all data received on an ingress
port is switched through a network to an egress port. While there
are similarities between this level of switching and the "opaque
single wavelength" case, described in Section 3.5 of [RFC4202], such
port-to-port switching is not limited to the optical switching
technology implied by the LSC type. FSC is also similar, but it is
restricted to fiber ports and also supports multiple data channels
within a fiber port.
This document defines a new switching type called Data Channel
Switching Capable (DCSC). Port switching seems a more intuitive
name, but this naming collides with PSC so is not used. DCSC
interfaces are able to support switching of the whole digital channel
presented on single channel interfaces. Interfaces that inherently
support multiple channels, e.g., Wavelength Division Multiplexing
(WDM) and channelized TDM interfaces, are specifically excluded from
this type. Any interface that can be represented as a single digital
channel are included. Examples include concatenated TDM and line-
encoded interfaces. Framed interfaces may also be included when they
support switching on an interface granularity, for example Ethernet
terminated at the physical (port) level and all traffic received on a
port is switched to a physical port at the LSP egress.
DCSC is represented in GMPLS, see [RFC3471] and [RFC4202], using the
value 125. The DCSC value is carried in routing protocols in the
Interface Switching Capability Descriptor defined in [RFC4202], and
used in OSPF [RFC4203] and IS-IS [RFC5307]. These documents are not
otherwise modified by this document.
The DCSC Switching Type may be used with the Generalized Label
Request object, [RFC3473], or the Generalized Channel_Set
LABEL_REQUEST object defined below. Port labels, as defined in
[RFC3471], SHOULD be used for LSPs signaled using the DCSC Switching
Type.
2.1. Compatibility
Transit and egress nodes that do not support the DCSC Switching Type
when receiving a Path message with a Label Request containing the
DCSC Switching Type will behave in the same way nodes generally
handle the case of an unsupported Switching Type. Specifically, per
[RFC3473], such nodes are required to generate a PathErr message,
with a "Routing problem/Unsupported Encoding" indication.
Ingress nodes initiating a Path message containing a Label Request
containing the DCSC Switching Type, receiving such a PathErr
messages, then notify the requesting application user as appropriate.
3. Generalized Channel_Set Label Related Formats
This section defines a new type of generalized label and updates
related objects. This section updates the label-related definitions
of [RFC3473]. The ability to communicate more than one label as part
of the same LSP was motivated by the support for the communication of
one or more VLAN IDs. Simple concatenation of labels as is done in
[RFC4606] was deemed impractical given the large number of VLAN IDs
(up to 4096) that may need to be communicated. The formats defined
in this section are not technology specific and may be useful for
other switching technologies. The LABEL_SET object defined in
[RFC3473] serves as the foundation for the defined formats.
3.1. Generalized Channel_Set LABEL_REQUEST Object
The Generalized Channel_Set LABEL_REQUEST object is used to indicate
that the Generalized Channel_Set LABEL object is to be used with the
associated LSP. The format of the Generalized Channel_Set
LABEL_REQUEST object is the same as the Generalized LABEL_REQUEST
object and uses a C-Type of 5.
3.2. Generalized Channel_Set LABEL Object
The Generalized Channel_Set LABEL Object communicates one or more
labels, all of which can be used equivalently in the data path
associated with a single LSP. The format of the Generalized
Channel_Set LABEL Object is based on the LABEL_SET object defined in
[RFC3473]. It differs from the LABEL_SET object in that the full set
may be represented in a single object rather than the multiple
objects required by the [RFC3473] LABEL_SET object. The object MUST
be used on LSPs that use the Generalized Channel_Set LABEL_REQUEST
object. The object MUST be processed per [RFC3473]. Make-before-
break procedures, see [RFC3209], SHOULD be used when modifying the
Channel_Set LABEL object.
The format of the Generalized Channel_Set LABEL object is:
o Generalized Channel_Set LABEL object: Class = 16, C-Type = 4
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Channel_Set Subobject 1 |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: : :
: : :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Channel_Set Subobject N |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Channel_Set Subobject size is measured in bytes and MUST always
be a multiple of 4, and at least 4, and has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Action | Num Subchannels | Label Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Subchannel 1 |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ :
: : :
: : :
: : :
: : :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Subchannel N |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Action: 8 bits
See [RFC3471] for definition of actions. Range actions SHOULD be
used when possible to minimize the size of the Channel_Set LABEL
Object.
Number of Subchannels: 10 bits
Indicates the number of subchannels carried in the subobject.
When the number of subchannels required exceeds the limit of the
field, i.e., 1024, multiple Channel_Set Subobjects MUST be used.
Note that the size of the subobject may result in a Path message
being larger than a single unfragmented IP packet. See Section
4.4 of [RFC6004] for an example of how this case may be handled.
A value of zero (0) has special meaning and MAY be used in either
the LABEL or UPSTREAM_LABEL object. A value of zero (0) is used
in a LABEL or UPSTREAM_LABEL object to indicate that the
subchannel(s) used in the corresponding (downstream or upstream)
direction MUST match the subchannel(s) carried in the reverse
directions label object. When value of zero (0) is used, no
subchannels are included in the Channel_Set Subobject and only one
Channel_Set Subobject may be present. The zero (0) value MUST NOT
be used in both the LABEL and UPSTREAM_LABEL objects of the same
LSP. Note that unacceptable label values continue to be handled
according to [RFC3209] and [RFC3473], i.e., they result in PathErr
or ResvErr messages with a "Routing problem/Unacceptable label
value" indication. For example, in the case where a Resv message
containing a zero (0) in both the LABEL and UPSTREAM_LABEL objects
is received, the node would generate a ResvErr message.
Label Type: 14 bits
See [RFC3473] for a description of this field.
Subchannel: Variable
See [RFC3471] for a description of this field. Note that this
field might not be 32-bit aligned.
Padding: Variable
Padding is used to ensure that the length of a Channel_Set
Subobject meets the multiple of 4 byte size requirement stated
above. The field is only required when the Subchannel field is
not 32-bit aligned and the number of included Subchannel fields
result in the Subobject not being 32-bit aligned.
The Padding field MUST be included when the number of bits
represented in all the Subchannel fields included in a Generalized
Channel_Set Subobject result in the Subobject not being 32-bit
aligned. When present, the Padding field MUST have a length that
results in the Subobject being 32-bit aligned. When present, the
Padding field MUST be set to a zero (0) value on transmission and
MUST be ignored on receipt. These bits SHOULD be passed through
unmodified by transit nodes.
Note that the overall length of a Channel_Set Subobject is
determined based on the value of the Num Subchannels field
together with the size of each Subchannel field as well as any
required padding. The size of the Subchannel field is uniquely
identified by the Label Type field.
3.3. Other Label-Related Objects
The previous section introduced a new LABEL object. As such the
formats of the other label-related objects and subobjects are also
impacted. Processing of these objects and subobjects is not modified
and remains per their respective specifications. The other label
related objects and subobjects are defined in [RFC3473] and include:
- SUGGESTED_LABEL object
- LABEL_SET object
- ACCEPTABLE_LABEL_SET object
- UPSTREAM_LABEL object
- RECOVERY_LABEL object
- Label ERO subobject
- Label RRO subobject
The label-related objects and subobjects each contain a Label field,
all of which may carry any label type. As any label type may be
carried, the introduction of a new label type means that the new
label type may be carried in the Label field of each of the label-
related objects and subobjects. No new definition needs to specified
as their original specification is label-type agnostic.
3.4. Compatibility
Transit and egress nodes that do not support the Generalized
Channel_Set Label related formats will first receive a Path message
containing Generalized Channel_Set LABEL_REQUEST object. When such a
node receives the Path message, per [RFC3209], it will send a PathErr
with the error code "Unknown object C_Type".
Ingress nodes initiating a Path message containing a Generalized
Channel_Set LABEL_REQUEST object on receiving such a PathErr
messages, then notify the requesting application user as appropriate.
4. IANA Considerations
IANA has assigned new values for namespaces defined in this document
and summarized in this section. The registries are available from
http://www.iana.org.
4.1. Data Channel Switching Type
IANA has made the following assignment in the "Switching Types"
section of the "GMPLS Signaling Parameters" registry.
Value Type Reference
----- ------------------------------------ ---------
125 Data Channel Switching Capable (DCSC) [RFC6002]
The assigned value is reflected in IANAGmplsSwitchingTypeTC of the
IANA-GMPLS-TC-MIB available from http://www.iana.org.
4.2. Generalized Channel_Set LABEL_REQUEST Object
IANA has made the following assignment in the "Class Names, Class
Numbers, and Class Types" section of the "RSVP PARAMETERS" registry.
A new class type for the existing LABEL_REQUEST Object class number
(19) with the following definition:
Class Types or C-Types:
5 Generalized Channel_Set [RFC6002]
4.3. Generalized Channel_Set LABEL Object
IANA has made the following assignment in the "Class Names, Class
Numbers, and Class Types" section of the "RSVP PARAMETERS" registry.
A new class type for the existing RSVP_LABEL Object class number (16)
with the following definition:
Class Types or C-Types:
4 Generalized Channel_Set [RFC6002]
5. Security Considerations
This document introduces new message object formats for use in GMPLS
signaling [RFC3473]. It does not introduce any new signaling
messages, nor change the relationship between LSRs that are adjacent
in the control plane. As such, this document introduces no
additional security considerations. See [RFC3473] for relevant
security considerations. Additionally, the existing framework for
MPLS and GMPLS security is documented in [RFC5920].
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004.
[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.
[RFC5307] Kompella, K., Ed., and Y. Rekhter, Ed., "IS-IS Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 5307, October 2008.
6.2. Informative References
[RFC4606] Mannie, E. and D. Papadimitriou, "Generalized Multi-
Protocol Label Switching (GMPLS) Extensions for
Synchronous Optical Network (SONET) and Synchronous
Digital Hierarchy (SDH) Control", RFC 4606, August 2006.
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
[RFC6004] Berger, L. and D. Fedyk, "Generalized MPLS (GMPLS) Support
for Metro Ethernet Forum and G.8011 Ethernet Service
Switching", RFC 6004, October 2010.
[RFC6005] Berger, L. and D. Fedyk, "Generalized MPLS (GMPLS) Support
for Metro Ethernet Forum and G.8011 User Network Interface
(UNI)", RFC 6005, October 2010.
Acknowledgments
Dimitri Papadimitriou provided substantial textual contributions to
this document and coauthored earlier versions of this document.
The authors would like to thank Evelyne Roch, Stephen Shew, and
Adrian Farrel for their valuable comments.
Authors' Addresses
Lou Berger
LabN Consulting, L.L.C.
Phone: +1-301-468-9228
EMail: lberger@labn.net
Don Fedyk
Alcatel-Lucent
Groton, MA, 01450
Phone: +1-978-467-5645
EMail: donald.fedyk@alcatel-lucent.com
ISO Plain Language
On this page
§1The Two Extensions
The document describes two technology-independent extensions to Generalized Multi-Protocol Label Switching. Both were initially defined in the context of Ethernet services, in RFC 6004 and RFC 6005, but they are generic in nature and may be useful to any switching technology controlled through GMPLS.
The first extension defines a new switching type called Data Channel Switching Capable, or DCSC. DCSC interfaces are able to support switching of the whole digital channel presented on single-channel interfaces. The second extension defines a new type of generalized label and updates the related objects. The new label is called the Generalized Channel_Set Label and allows more than one data plane label to be controlled as part of one GMPLS label switched path.
The first addition names a kind of interface that carries one channel and switches it whole. The second addition lets one path hold several labels at once, instead of one label per path.
§2Where DCSC Fits Among the Switching Types
The current GMPLS switching types are defined in RFC 3945 and RFC 3471, and support switching at the packet, frame, time-slot, frequency and fiber granularities. Parallel definitions are also made in RFC 4202, RFC 4203 and RFC 5307.
One type of switching is not well represented in that set: switching where all the data received on an ingress port is switched through the network to an egress port. There are similarities with the opaque single wavelength case of Section 3.5 of RFC 4202, but this port-to-port switching is not limited to the optical technology implied by the frequency switching type. Fiber switching is similar too, but it is restricted to fiber ports and also supports multiple data channels within a fiber port.
The new switching type is called Data Channel Switching Capable. Port switching would be a more intuitive name, but it collides with packet switching, so it is not used. DCSC interfaces support switching of the whole digital channel presented on single-channel interfaces. Interfaces that inherently support multiple channels, such as wavelength division multiplexing and channelised TDM interfaces, are specifically excluded from this type. Any interface that can be represented as a single digital channel is included. The examples given are concatenated TDM and line-encoded interfaces. Framed interfaces may also be included when they support switching at interface granularity, for example Ethernet terminated at the physical port level, where all the traffic received on a port is switched to a physical port at the path egress.
DCSC is represented in GMPLS using the value 125. That value is carried in the routing protocols in the Interface Switching Capability Descriptor of RFC 4202, and used in OSPF and IS-IS. Those documents are not otherwise modified.
GMPLS already has switching types for packets, frames, time slots, wavelengths and whole fibres. The new type covers the case of an interface that carries one channel: everything that arrives on it is switched to another port. Interfaces that carry several channels are excluded, because they are a different case.
§2.1Using the New Switching Type
The DCSC switching type may be used with the Generalized Label Request object of RFC 3473, or with the Generalized Channel_Set LABEL_REQUEST object defined in the document. Port labels, as defined in RFC 3471, should be used for paths signalled with the DCSC switching type.
Nodes that do not support the DCSC switching type and receive a Path message with a label request containing it behave in the way nodes generally handle an unsupported switching type: per RFC 3473, they generate a PathErr message with a Routing problem, Unsupported Encoding indication. An ingress node that initiated such a Path message, on receiving that error, notifies the requesting application user as appropriate.
A router that does not know the new switching type rejects the request with the usual error for an unknown encoding, and the node that asked tells the application which asked for the path.
§3Why a Label Can Hold Several Labels
The document defines a new type of generalized label and updates the related objects, updating the label-related definitions of RFC 3473. The ability to communicate more than one label as part of the same path was motivated by the support for communicating one or more VLAN identifiers. Simply concatenating labels, as done in RFC 4606, was deemed impractical given the large number of VLAN identifiers, up to 4096, that may need to be communicated. The formats defined here are not technology specific and may be useful for other switching technologies, and the LABEL_SET object of RFC 3473 serves as the foundation for them.
The Generalized Channel_Set LABEL_REQUEST object indicates that the Generalized Channel_Set LABEL object is to be used with the associated path. Its format is the same as the Generalized LABEL_REQUEST object and uses a C-Type of 5.
The Generalized Channel_Set LABEL object communicates one or more labels, all of which can be used equivalently in the data path associated with a single path. Its format is based on the LABEL_SET object of RFC 3473, and differs from it in that the full set may be represented in a single object rather than the multiple objects that the LABEL_SET object requires. The object must be used on paths that use the Generalized Channel_Set LABEL_REQUEST object, and it must be processed per RFC 3473. Make-before-break procedures should be used when modifying the Channel_Set LABEL object.
One path can carry several labels, and each of them works the same way in the data path. The reason is that a service may need a list of VLAN identifiers, and there can be thousands of them, so sending one label per identifier as separate objects does not scale.
| Object | Class and type | What it does |
|---|---|---|
| DCSC switching type | Value 125 | Describes an interface that carries and switches one whole digital channel |
| Generalized Channel_Set LABEL_REQUEST | LABEL_REQUEST, C-Type 5 | Asks for the Generalized Channel_Set LABEL object on the path |
| Generalized Channel_Set LABEL | Class 16, C-Type 4 | Carries the list of subchannels, each with its own label |
§3.2The Format of the Channel Set Label
The Generalized Channel_Set LABEL object has Class 16 and C-Type 4, and its body is a list of Channel_Set Subobjects, one after another.
The size of a Channel_Set Subobject is measured in bytes and must always be a multiple of 4, and at least 4. Its first three fields are the Action, 8 bits, which is defined in RFC 3471, with range actions recommended where possible to keep the object small; the Number of Subchannels, 10 bits, which says how many subchannels the subobject carries; and the Label Type, 14 bits, described in RFC 3473. The subchannels follow, each of variable length and described in RFC 3471, and the subchannel field might not be 32-bit aligned. Padding is used to make the length of the subobject a multiple of 4 bytes, and it is only required when the subchannels do not come out aligned.
When the number of subchannels needed exceeds the limit of the field, which is 1024, several Channel_Set Subobjects must be used. The size of the subobject may result in a Path message being larger than a single unfragmented IP packet. The document notes that a value of zero in the number of subchannels has a special meaning and may be used in either the LABEL or the UPSTREAM_LABEL object: it indicates that the subchannels used in the corresponding direction must match the subchannels carried in the reverse direction's label object. When zero is used, no subchannels are included in the subobject and only one Channel_Set Subobject may be present, and the zero value must not be used in both the LABEL and the UPSTREAM_LABEL objects of the same path. Label values that are unacceptable continue to be handled as RFC 3209 and RFC 3473 require, with a PathErr or ResvErr message carrying a Routing problem, Unacceptable label value indication. So a Resv message with a zero in both the LABEL and the UPSTREAM_LABEL objects makes the node generate a ResvErr.
The padding field must be included when the bits represented by all the subchannel fields do not leave the subobject 32-bit aligned, and when present its length must make the subobject aligned. It must be set to zero on transmission and ignored on receipt, and those bits should be passed through unmodified by transit nodes. The overall length of a subobject is determined by the number of subchannels, the size of each subchannel field, and any required padding, and the size of the subchannel field is uniquely identified by the Label Type field.
The object is a list of subobjects, each holding a count, a label type and the labels themselves. The list is padded so that it fits the alignment rules. A count of zero is a special case meaning that the two directions of the path use the same subchannels.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
ACTION | Action | 1 byte | The action defined in RFC 3471. Range actions keep the object small. | |
SUBCHANNELS | Num Subchannels | 10 bits | How many subchannels this subobject carries. A value of zero has a special meaning. | |
RESERVED | Reserved | 6 bits | Unassigned bits. | |
TYPE | Label Type | 14 bits | The type of the labels that follow, which also fixes their size. |
- SizeA multiple of 4 bytes, and at least 4 bytes.
- Subchannel limitAt most 1024 subchannels in one subobject; more needs several subobjects.
- A count of zeroMeans the two directions use the same subchannels. Only one subobject may then be present.
- PaddingFills the subobject to a 32-bit boundary, set to zero on transmission and ignored on receipt.
§3.3The Other Label Objects and Older Nodes
Because the document introduces a new LABEL object, the formats of the other label-related objects and subobjects are also affected, although their processing is not modified and remains as their respective specifications state. The other label-related objects and subobjects are defined in RFC 3473 and are the SUGGESTED_LABEL object, the LABEL_SET object, the ACCEPTABLE_LABEL_SET object, the UPSTREAM_LABEL object, the RECOVERY_LABEL object, the Label ERO subobject and the Label RRO subobject.
Each of them contains a Label field, and all of those may carry any label type. Since any label type may be carried, the introduction of a new label type means that it may be carried in the Label field of each of these objects and subobjects, and no new definition needs to be given, because their original specification is label-type agnostic.
Nodes that do not support the Generalized Channel_Set Label formats first receive a Path message containing the Generalized Channel_Set LABEL_REQUEST object. Such a node, per RFC 3209, answers with a PathErr carrying the error code Unknown object C_Type. An ingress node that initiated such a Path message, on receiving that error, notifies the requesting application user as appropriate.
The other places where a label can appear, such as the recorded route and the upstream label, can all carry the new label type without any change to their own definitions. A node that does not know the new request object refuses it with an unknown-object error.
§4IANA Assignments
IANA has made three assignments. In the Switching Types section of the GMPLS Signaling Parameters registry, the value 125 has been assigned to Data Channel Switching Capable, and the assignment is reflected in the IANAGmplsSwitchingTypeTC object of the IANA-GMPLS-TC-MIB. In the Class Names, Class Numbers and Class Types section of the RSVP PARAMETERS registry, a new class type has been added for the existing LABEL_REQUEST object class number 19, with the value 5 for Generalized Channel_Set. A new class type has also been added for the existing RSVP_LABEL object class number 16, with the value 4 for Generalized Channel_Set.
The document asks IANA for three numbers: one for the new switching type, one for the new request object and one for the new label object.
§5Security Considerations
The document introduces new message object formats for use in GMPLS signalling. It does not introduce any new signalling messages, nor change the relationship between label switching routers that are adjacent in the control plane, and so it introduces no additional security considerations. The security considerations of RFC 3473 apply, and the existing framework for MPLS and GMPLS security is documented in RFC 5920.
Nothing here changes how routers talk to each other or what is protected between them, so the existing security rules for GMPLS signalling apply unchanged.