Request for Comments: 4394 O. Aboul-Magd
Category: Informational Nortel Networks
D. Brungard
AT&T
J. Lang
Sonos, Inc.
D. Papadimitriou
Alcatel
February 2006
A Transport Network View of the Link Management Protocol (LMP)
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
The Link Management Protocol (LMP) has been developed as part of the
Generalized MPLS (GMPLS) protocol suite to manage Traffic Engineering
(TE) resources and links. The GMPLS control plane (routing and
signaling) uses TE links for establishing Label Switched Paths
(LSPs). This memo describes the relationship of the LMP procedures
to ’discovery’ as defined in the International Telecommunication
Union (ITU-T), and ongoing ITU-T work. This document provides an
overview of LMP in the context of the ITU-T Automatically Switched
Optical Networks (ASON) and transport network terminology and relates
it to the ITU-T discovery work to promote a common understanding for
progressing the work of IETF and ITU-T.
Table of Contents
1. Introduction ....................................................2
2. ASON Terminology and Abbreviations Related to Discovery .........3
2.1. Terminology ................................................3
2.2. Abbreviations ..............................................4
3. Transport Network Architecture ..................................5
3.1. G.8080 Discovery Framework .................................7
4. Discovery Technologies ..........................................9
4.1. Generalized Automatic Discovery Techniques G.7714 ..........9
4.2. LMP and G.8080 Terminology Mapping .........................9
4.2.1. TE Link Definition and Scope .......................12
4.3. LMP and G.8080 Discovery Relationship .....................13
4.4. Comparing LMP and G.8080 ..................................14
5. Security Considerations ........................................15
6. Informative References .........................................15
7. Acknowledgements ...............................................16
1. Introduction
The GMPLS control plane consists of several building blocks as
described in [RFC3945]. The building blocks include signaling,
routing, and link management for establishing LSPs. For scalability
purposes, multiple physical resources can be combined to form a
single TE link for the purposes of path computation and GMPLS control
plane signaling.
As manual provisioning and management of these links are impractical
in large networks, LMP was specified to manage TE links. Two
mandatory management capabilities of LMP are control channel
management and TE link property correlation. Additional optional
capabilities include verifying physical connectivity and fault
management. [LMP] defines the messages and procedures for GMPLS TE
link management. [LMP-TEST] defines SONET/SDH-specific messages and
procedures for link verification.
ITU-T Recommendation G.8080 Amendment 1 [G.8080] defines control
plane discovery as two separate processes; one process occurs within
the transport plane space and the other process occurs within the
control plane space.
The ITU-T has developed Recommendation G.7714, "Generalized automatic
discovery techniques" [G.7714], defining the functional processes and
information exchange related to transport plane discovery aspects,
i.e., layer adjacency discovery and physical media adjacency
discovery. Specific methods and protocols are not defined in
Recommendation G.7714. ITU-T Recommendation G.7714.1, "Protocol for
automatic discovery in SDH and OTN networks" [G.7714.1], defines a
protocol and procedure for transport plane layer adjacency discovery
(e.g., discovering the transport plane layer endpoint relationships
and verifying their connectivity). The ITU-T is currently working to
extend discovery to control plane aspects providing detail on a
discovery framework architecture in G.8080 and a new Recommendation
on "Control plane initial establishment, reconfiguration".
2. ASON Terminology and Abbreviations Related to Discovery
ITU-T Recommendation G.8080 Amendment 1 [G.8080] and ITU-T
Recommendation G.7714 [G.7714] provide definitions and mechanisms
related to transport plane discovery.
Note that in the context of this work, "Transport" relates to the
data plane (sometimes called the transport plane or the user plane)
and does not refer to the transport layer (layer 4) of the OSI seven
layer model, nor to the concept of transport intended by protocols
such as the Transmission Control Protocol (TCP).
Special care must be taken with the acronym "TCP", which within the
context of the rest of this document means "Termination Connection
Point" and does not indicate the Transmission Control Protocol.
2.1. Terminology
The reader is assumed to be familiar with the terminology in [LMP]
and [LMP-TEST]. The following ITU-T terminology/abbreviations are
used in this document:
Connection Point (CP): A "reference point" that consists of a pair of
co-located "unidirectional connection points" and therefore
represents the binding of two paired bidirectional "connections".
Connection Termination Point (CTP): A connection termination point
represents the state of a CP [M.3100].
Characteristic Information: Signal with a specific format, which is
transferred on "network connections". The specific formats will be
defined in the technology-specific recommendations. For trails, the
Characteristic Information is the payload plus the overhead. The
information transferred is characteristic of the layer network.
Link: A subset of ports at the edge of a subnetwork or access group
that are associated with a corresponding subset of ports at the edge
of another subnetwork or access group.
Link Connection (LC): A transport entity that transfers information
between ports across a link.
Network Connection (NC): A concatenation of link and subnetwork
connections.
Subnetwork: A set of ports that are available for the purpose of
routing ’characteristic information’.
Subnetwork Connection (SNC): A flexible connection that is set up and
released using management or control plane procedures.
Subnetwork Point (SNP): SNP is an abstraction that represents an
actual or potential underlying connection point (CP) or termination
connection point (TCP) for the purpose of control plane
representation.
Subnetwork Point Pool (SNPP): A set of SNPs that are grouped together
for the purpose of routing.
Termination Connection Point (TCP): A reference point that represents
the output of a Trail Termination source function or the input to a
Trail Termination sink function. A network connection represents a
transport entity between TCPs.
Trail Termination source/sink function: A "transport processing
function" that accepts the characteristic information of the layer
network at its input, removes the information related to "trail"
monitoring, and presents the remaining information at its output.
Unidirectional Connection: A "transport entity" that transfers
information transparently from input to output.
Unidirectional Connection Point: A "reference point" that represents
the binding of the output of a "unidirectional connection" to the
input of another "unidirectional connection".
2.2. Abbreviations
LMP: Link Management Protocol
OTN: Optical Transport Network
PDH: Plesiosynchronous Digital Hierarchy
SDH: Synchronous Digital Hierarchy
SONET: Synchronous Optical Network
3. Transport Network Architecture
A generic functional architecture for transport networks is defined
in International Telecommunication Union (ITU-T) Recommendation
[G.805]. This recommendation describes the functional architecture
of transport networks in a technology-independent way. This
architecture forms the basis for a set of technology-specific
architectural recommendations for transport networks (e.g., SDH, PDH,
OTN, etc.).
The architecture defined in G.805 is designed using a layered model
with a client-server relationship between layers. The architecture
is recursive in nature; a network layer is both a server to the
client layer above it and a client to the server layer below it.
There are two basic building blocks defined in G.805: "subnetworks"
and "links". A subnetwork is defined as a set of ports that are
available for the purpose of routing "characteristic information". A
link consists of a subset of ports at the edge of one subnetwork (or
"access group") and is associated with a corresponding subset of
ports at the edge of another subnetwork or access group.
Two types of connections are defined in G.805: link connection (LC)
and subnetwork connection (SNC). A link connection is a fixed and
inflexible connection, while a subnetwork connection is flexible and
is set up and released using management or control plane procedures.
A network connection is defined as a concatenation of subnetwork and
link connections. Figure 1 illustrates link and subnetwork
connections.
(++++++++) (++++++++)
( SNC ) LC ( SNC )
(o)--------(o)----------(o)--------(o)
( ) CP CP ( )
(++++++++) (++++++++)
subnetwork subnetwork
Figure 1: Subnetwork and Link Connections
G.805 defines a set of reference points for the purpose of
identification in both the management and the control planes. These
identifiers are NOT required to be the same. A link connection or a
subnetwork connection is delimited by connection points (CPs). A
network connection is delimited by a termination connection point
(TCP). A link connection in the client layer is represented by a
pair of adaptation functions and a trail in the server layer network.
A trail represents the transfer of monitored adapted characteristics
information of the client layer network between access points (APs).
A trail is delimited by two access points, one at each end of the
trail. Figure 2 shows a network connection and its relationship with
link and subnetwork connections. Figure 2 also shows the CP and TCP
reference points.
|<-------Network Connection---------->|
| |
| (++++++++) (++++++++) |
|( SNC ) LC ( SNC ) |
(o)--------(o)----------(o)--------(o)|
TCP( )| CP CP |( )TCP
(++++++++) | | (++++++++)
| |
| Trail |
|<-------->|
| |
--- ---
\ / \ /
- -
AP 0 0 AP
| |
(oo)------(oo)
Figure 2: Network Connection with Link and Subnetwork Connections
For management plane purposes, the G.805 reference points are
represented by a set of management objects described in ITU-T
Recommendation M.3100 [M.3100]. Connection termination points (CTPs)
and trail termination points (TTPs) are the management plane objects
for CP and TCP, respectively.
In the same way as in M.3100, the transport resources in G.805 are
identified for the purposes of the control plane by entities suitable
for connection control. G.8080 introduces the reference architecture
for the control plane of the Automatically Switched Optical Networks
(ASONs). G.8080 introduces a set of reference points relevant to the
ASON control plane and their relationship to the corresponding points
in the transport plane. A subnetwork point (SNP) is an abstraction
that represents an actual or potential underlying CP or an actual or
potential TCP. A set of SNPs that are grouped together for the
purpose of routing is called SNP pool (SNPP). Similar to LC and SNC,
the SNP-SNP relationship may be static and inflexible (this is
referred to as an SNP link connection), or it can be dynamic and
flexible (this is referred to as an SNP subnetwork connection).
3.1. G.8080 Discovery Framework
G.8080 provides a reference control plane architecture based on the
descriptive use of functional components representing abstract
entities and abstract component interfaces. The description is
generic, and no particular physical partitioning of functions is
implied. The input/output information flows associated with the
functional components serve for defining the functions of the
components and are considered to be conceptual, not physical.
Components can be combined in different ways, and the description is
not intended to limit implementations. Control plane discovery is
described in G.8080 by using three components: Discovery Agent (DA),
Termination and Adaptation Performer (TAP), and Link Resource Manager
(LRM).
The objective of the discovery framework in G.8080 is to establish
the relationship between CP-CP link connections (transport plane) and
SNP-SNP link connections (control plane). The fundamental
characteristics of G.8080 discovery framework is the functional
separation between the control and the transport plane discovery
processes and name spaces. From G.8080: "This separation allows
control plane names to be completely separate from transport plane
names, and completely independent of the method used to populate the
DAs with those transport names. In order to assign an SNP-SNP link
connection to an SNPP link, it is only necessary for the transport
name for the link connection to exist". Thus, it is possible to
assign link connections to the control plane without the link
connection being physically connected.
Discovery encompasses two separate processes: (1) transport plane
discovery, i.e., CP-to-CP and TCP-to-TCP connectivity; and (2)
control plane discovery, i.e., SNP-to-SNP and SNPP links.
G.8080 Amendment 1 defines the Discovery Agent (DA) as the entity
responsible for discovery in the transport plane. The DA operates in
the transport name space only and in cooperation with the Termination
and Adaptation Performer (TAP), provides the separation between that
space and the control plane names. A local DA is only aware of the
CPs and TCPs that are assigned to it. The DA holds the CP-CP link
connection in the transport plane to enable SNP-SNP link connections
to be bound to them at a later time by the TAP. The CP-CP
relationship may be discovered (e.g., per G.7714.1) or provided by a
management system.
Control plane discovery takes place entirely within the control plane
name space (SNPs). The Link Resource Manager (LRM) holds the SNP-SNP
binding information necessary for the control plane name of the link
connection, while the termination adaptation performer (TAP) holds
the relation between the control plane name (SNP) and the transport
plane name (CP) of the resource. Figure 3 shows the relationship and
the different entities for transport and control discoveries.
LRM LRM
+-----+ holds SNP-SNP Relation +-----+
| |-------------------------| |
+-----+ +-----+
| |
v v
+-----+ +-----+
| o | SNPs in SNPP | o |
| | | |
| o | | o |
| | | |
| o | | o |
+-----+ +-----+
| |
v v Control Plane
+-----+ +-----+ Discovery
| | Termination and | |
---|-----|-------------------------|-----|---------
| | Adaptation Performer | |
+-----+ (TAP) +-----+ Transport Plane
| \ / | Discovery
| \ / |
| +-----+ +-----+ |
| | DA | | DA | |
| | | | | |
| +-----+ +-----+ |
| / \ |
V/ \V
O CP (Transport Name) O CP (Transport Name)
Figure 3: Discovery in the Control and the Transport Planes
4. Discovery Technologies
4.1. Generalized Automatic Discovery Techniques G.7714
Generalized automatic discovery techniques are described in G.7714 to
aid resource management and routing for G.8080. The term routing
here is described in the transport context of routing connections in
an optical network as opposed to the routing context typically
associated in packet networks.
G.7714 is concerned with two types of discovery:
- Layer adjacency discovery
- Physical media adjacency discovery
Layer adjacency discovery can be used to correlate physical
connections with management configured attributes. Among other
features this capability allows reduction in configuration and the
detection of mis-wired equipment.
Physical media adjacency discovery is a process that allows the
physical testing of the media for the purpose of inventory capacity
and verifying the port characteristics of physical media adjacent
networks.
G.7714 does not specify specific protocols but rather the type of
techniques that can be used. G.7714.1 specifies a protocol for layer
adjacency with respect to SDH and OTN networks for layer adjacency
discovery. A GMPLS method for layer discovery using elements of LMP
is included in this set of procedures.
An important point about the G.7714 specification is that it
specifies a discovery mechanism for optical networks but not
necessarily how the information will be used. It is intended that
the transport management plane or a transport control plane may
subsequently make use of the discovered information.
4.2. LMP and G.8080 Terminology Mapping
GMPLS is a set of IP-based protocols, including LMP, providing a
control plane for multiple data plane technologies, including
optical/transport networks and their resources (i.e., wavelengths,
timeslots, etc.) and without assuming any restriction on the control
plane architecture (see [RFC3945]). On the other hand, G.8080
defines a control plane reference architecture for optical/transport
networks without any restriction on the control plane implementation.
Being developed in separate standards forums, and with different
scopes, they use different terms and definitions.
Terminology mapping between LMP and ASON (G.805/G.8080) is an
important step towards the understanding of the two architectures and
allows for potential cooperation in areas where cooperation is
possible. To facilitate this mapping, we differentiate between the
two types of data links in LMP. According to LMP, a data link may be
considered by each node that it terminates on as either a ’port’ or a
’component link’. The LMP notions of port and component link are
supported by the G.805/G.8080 architecture. G.8080’s variable
adaptation function is broadly equivalent to LMP’s component link,
i.e., a single server-layer trail dynamically supporting different
multiplexing structures. Note that when the data plane delivers its
own addressing space, LMP Interface_IDs and Data Links IDs are used
as handles by the control plane to the actual CP Name and CP-to-CP
Name, respectively.
The terminology mapping is summarized in the following table: Note