Network Working Group D. Papadimitriou
Document: draft-papadimitriou-optical-rings-00.txt Alcatel
Category: Internet Draft
Expires: August 2001 February 2001
Optical Rings and Hybrid Mesh-Ring Optical Networks
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 except that the right to
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Conventions used in this document:
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document are to be interpreted as described in RFC-2119 [1].
Abstract
The scope of this draft is to specify the IP-based signaled
protection mechanisms for optical rings and hybrid optical mesh-ring
topologies. With the dynamic ring configuration process, we determine
the information to be distributed to dynamically emulate optical
rings on top of a meshed optical network topology. This information
exchange further enables the specification of Optical Ring Traffic
Engineering. Within the IP Control-based signaling plane, we also
specify the mechanisms to provide dynamic and fast-protection
switching, and distributed LSP route computation on top of ring-based
and hybrid mesh-rings optical networks.
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1. Introduction
The concept of optical ring emulation is introduced. It applies when
considering the ring configuration on top of optical mesh topology
including Optical Cross-Connects (OXC) and not only Optical Add-Drop-
Multiplexers (O-ADM). Compared to the approach developed in [IPO-
RHMR], emulated optical rings add configuration flexibility when
considering optical network protection. The mechanisms developed here
are quite general and enable the deployment of hybrid mesh-rings
optical network topologies. It also provides a clear separation
between the dynamic ring configuration and the dynamic ring resource
allocation. This allows a greater ring resource management
flexibility that fits more suitably the bandwidth on demand
requirements for optical networks.
The complexity of ring emulation arises when defining several rings
on top of a mesh topology including Optical Cross-Connects (OXC)
connected through fiber trunks. This because by configuring several
optical rings on top of a meshed topology, a ring cover is defined.
Consequently, the shared protection of some parts of ring û
specifically the links and the nodes - with other contiguous rings
implies the definition of specific as described in [OPT-NET] and
[OPT-RINGS]. The corresponding fast link protection mechanism is
performed at the node level is completely distributed and autonomous.
Note that it still requires signalling message exchange in order to
recover unidirectional link failures.
The approach developed here combines distributed fast link protection
mechanism and signalling message exchange between nodes when a
failure is detected on a link connecting to adjacent nodes belonging
to the same ring. In order to specify these mechanisms, we first
describe the optical ring concept currently under development at the
ITU-T to determine the corresponding mechanism for all-optical rings.
2. Optical Rings - Concepts
2.1 ITU-T Optical Rings
The aim of this section is neither to describe the pro and cons of
optical rings with respect to optical mesh network nor to explain in
detail the well known ITU-T ring technology [ITUT-G841]. Many
references can be found comparing, the architecture, the protection
as well as the resource use of both kinds of topologies.
The objective is to determine the requirements and the functional
aspects of these ring technologies in order to define the
corresponding mechanisms for all-optical rings. For that purpose, we
first describe the ring technology and types of protected rings
currently defined (by using ITU-T terminology):
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- Optical Channel Dedicated Protection Ring (OCh-DPRing) or O-UPSR
(Optical Unidirectional Path Switched Ring). Dedicated protection can
also be provided through Single Optical Channel (1+1) Sub-network
Connection Protection (OCh-SNCP).
- Optical Channel Shared Protection Ring (OCh-SPRing) or O-BPSR
(Optical Bi-directional Path Switched Ring) existing in two flavors:
2 Fiber O-BPSR (O-BPSR/2) and 4-Fiber O-BPSR (O-BPSR/4) and 2
switching strategies: ring switch (2- and 4-Fiber) and span switch
(4-Fiber only).
- Optical Multiplex-Section Dedicated Protection Ring (OMS-DPRing) or
O-ULSR (Optical Unidirectional Line Switched Ring)
- Optical Multiplex-Section Shared Protection Ring (OMS-SPRing) or O-
BLSR (Optical Bi-directional Line Switched Ring) existing in 2
flavors: 2 Fiber O-BLSR (O-BLSR/2) and 4-Fiber O-BLSR (O-BLSR/4) and
2 switching strategies: ring switch and span switch.
Details about the corresponding SDH ring architectures can be found
in ITU-T G.841 (for SDH/Sonet networks). The ITU-T is currently
defining Optical Transport Network (OTN) Ring Architecture by
extending the G.841 specification.
These ring types can be treated separately if we differentiate the
unidirectional (OMS and OCh) Dedicated Protection Rings (DPRing) from
the bi-directional (OMS and OCh) Shared Protection Rings (SPRing).
This by taking into account that switched rings are also referred to
as self-healing rings (SHR) since they protect automatically against
failures. The main feature of self-healing rings is their ability to
recover any LSP in case of link (i.e. fiber) failure and part of the
LSP in case of node failure.
SHR applied on optical rings are referred to as WDM-SHR. The
corresponding protection mechanism are briefly described here:
1. OMS-DPRing (or O-ULSR):
- Unidirectional OMS protection is achieved by using 1+1 fast
protection switching at the OMS-layer.
- One fiber is dedicated as working fiber and the other is
dedicated as protection fiber. Working and protection fibers
operate in opposite directions: the working ring operates on
the clockwise direction on the protection ring on the counter
clockwise direction. The protection ring carries the same
signal than the working fiber but in the opposite direction.
The same mechanism applies if we replace the term fiber by
wavelength.
- Since single-ended protection (or unidirectional protection
switching) is used, OMS-DPRing does not require coordinated O-
APS signalling at the OMS-layer.
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2. OMS-SPRing (or O-BLSR):
- OMS switched rings are based on optical automatic protection
switching (O-APS) protocol through signalling channel by using
OMS overhead bytes (or equivalent). The O-APS mechanism enables
coordinated actions at the OMS-layer between nodes when a
failure occurs.
- OMS-SPRing performs bulk OCh-layer switching based on OMS-
level failure indications through OMS-layer O-APS signaling;
all optical-channels are protected (i.e. switched) as a group
within the OMS (so incapable of protecting optical channels
independently of one another based on OCh-layer failure
indications.
- Ring switching protection (2-fiber and 4-fiber) is based on
loopback protection switching and activated when both working
and protection link failure occurs simultaneously. By using O-
APS signalling, when a link failure occurs, the working lines
(wavelength) from the working fiber are looped back onto the
opposite direction on protection wavelength on the protection
fiber in the opposite direction. Note that combination of
working and protection link failure and node failure should
also be considered.
- Span switching protection (4-fiber only) is activated when
only working link failure occurs. When a link failure occurs,
the working lines (wavelengths) from the working fiber are
switched to the protection fiber in the same direction. Span
switching protection is also referred to as non-loopback
switched protection.
- In terms of SHR, OMS-SPRings are referred to as Shared Line
switched WDM-SHR (SLs-WDM-SHR) since they rely on shared line
switched protection.
3. OCh-DPRing (or O-UPSR)
- Unidirectional path switched-protection is achieved by using
1+1 fast protection switching at the OCh-layer.
- One fiber is dedicated as working fiber and the other is
dedicated as protection fiber. Working and protection fibers
operate in opposite directions: the working ring operates on
the clockwise direction on the protection ring on the counter
clockwise direction. The protection ring carries the same
signal than the working fiber but in the opposite direction so
that the protection ring fully protects the working ring.
The mechanism applies if we replace the term fiber by
wavelength.
- Since single-ended protection (or unidirectional protection
switching) is used, OCh-DPRing does not require coordinated O-
APS OCh-layer signalling. If a working OCh failure occurs, only
one direction is affected and for that direction OCh switching
is performed at the far-end. In the other direction, no OCh-
layer switching is performed.
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- OCh-layer protection is based on optical channel resilient
schemes by protecting individual path; so this protection
allows a selective recovery of the OMS between nodes
- In terms of SHR, OCh-DPRings are referred to as Dedicated
Path switched WDM-SHR (DPs-WDM-SHR) since they rely on
dedicated path switched protection.
4. OCh-SPRing (or O-BPSR)
- Bi-directional path switched protection requires the need for
a protection architecture performing OCh switching based on
independent OCh failure detection.
- This implies the specification of an O-APS signalling
protocol at the OCh-layer using the OCh overhead byte.
- Ring switching protection can also be defined for 2- and 4-
Fiber OCh-SPRings. Span switching protection can be defined for
4-Fiber OCh-SPRings.
- In terms of SHR, OCh-SPRings are referred to as Shared Path
switched WDM-SHR (SPs-WDM-SHR) since they rely on shared path
switched protection
The distinction between Working and Protected path is defined as
follows:
- Working path: carrying optical channel defined between the source
and the destination node
- Protecting path: non-carrying optical channel defined between the
source and the destination node transported over the complement of
the ring
The distinction between Working and Protected line is defined as
follows:
- Working line: carrying OMS defined between the source and an
intermediate node or between intermediate nodes or between an
intermediate node and the destination node transported over the
complement of the ring
- Protection line: non-carrying OMS defined between the source and an
intermediate node or between intermediate nodes or between an
intermediate node and the destination node transported over the
complement of the ring
The following table gives the equivalence between the linear (mesh
networks) and ring protection.
--------------------------------------------------------------------
Linear Protection Ring Protection
--------------------------------------------------------------------
Dedicated Line Protection 1+1 û 1:1 OMS-DPRing (O-ULSR)
Shared Line Protection 1:N OMS-SPRing (O-BLSR)
Dedicated Path Protection 1+1 û 1:1 OCh-DPRing (O-UPSR)
Shared Path Protection 1:N OCh-SPRing (O-BPSR)
--------------------------------------------------------------------
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2.3 Transparent and All-Optical Rings
The previous section detailed the ring technologies and types for
Optical Transport Networks (i.e. ITU-T G.709 based OTN). The
objective here is to define the same kind of mechanisms for pure
optical rings.
A pure optical ring is defined as a ring including Optical Cross-
Connects (OXC) and Photonic Cross-Connects (PXC). The difference
between OXC and PXC is that O/E/O conversion is performed at each of
its interface while PXCs do not perform O/E/O conversion at all.
An all-optical ring is defined as ring including only PXC while a
transparent ring is defined as including at least one OXC. In order
to be independent of physical layer concerns like distance,
dispersion, jitter, PMD, BER, etc., only transparent optical rings
are considered in the remaining parts of this document. We refer to
these transparent optical rings as optical rings.
The fundamental problem of optical rings is to which extend the IP
control-based signaling plane need to be considered for defining ring
protection mechanism. In the model developed in this memo, we try to
extract the relevant information needed in order to provide the same
level of resiliency as the one currently available with SDH/Sonet
DXC-based rings [ITUT-G841] and the corresponding extension under
definition for Optical Transport Networks (OTN). This implies the
definition at IP control-plane level of the required O-APS signalling
protocol by keeping independence from the current protection
mechanisms defined for SDH/Sonet rings.
The information needed to dynamically configure an optical ring on
top of a mesh optical network topology and the corresponding link
(and wavelengths) resources management information depends on:
- the ring identification
- the ring protection type
- the ring directionality
- the ring architecture
Based on this information, the dynamic ring configuration is
performed (cf. Section 3). When the optical ring has been configured
(i.e. emulated on top of the mesh topology), the ring resources
allocation to the Lambda-switched LSPs (i.e. the optical channels)
segments or tunnels can be computed for this emulated ring.
The equivalence between ITU-T rings and the corresponding protection
mechanism in all-optical networks is summarized in the following
table:
--------------------------------------------------------
ITU-T Rings | Corresponding protection mechanism
--------------------------------------------------------
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OMS-DPRing | 1+1 dedicated fiber link (or wavelength)
--------------------------------------------------------
OMS-SPRing | M:N shared fiber link (or wavelength)
--------------------------------------------------------
OCh-DPRing | 1+1 dedicated LSP segment protection
--------------------------------------------------------
OCh-SPRing | M:N shared LSP segment protection
--------------------------------------------------------
The OMS-layer protection (dedicated or shared) concept corresponds to
the protection of a wavelength bundle transported on a fiber link
between two adjacent nodes. The OCh-layer protection (dedicated or
shared) concept corresponds to the protection of LSP segment(s)
transported on a wavelength switched path (i.e. partial LSP path)
between the ingress and the egress node of a given ring.
Knowing each of the SDH/Sonet and OTN ring functional aspects and the
mapping of the underlying concepts with their counterparts in all-
optical networks, the corresponding ring protection mechanism can be
defined.
2.3 Meshed Optical Network Topology
The basic assumptions concerning the optical network topology are:
- Mesh (and transparent) optical network including Optical Cross-
Connect (OXC) connected through fiber trunks as described in [IPO-
SRLG].
- OXC interfaces or ports are Lambda-Switch Capable (LSC) interfaces
as described in [GMPLS-SIG] meaning that any OXC interface includes
DWDM capabilities. OXC or eventually fiber switch capable (FSC)
interfaces (but they are considered as a particular outside the main
scope of this document).
- Each of these OXCs has its own IP controller that may be or not
included within the same device. Each controller is uniquely
identified by its IP Address. The inter-connection of the IP
controllers defines the IP based control-plane of the optical
network.
- Signaling channels between the IP-based controllers of OXCs is
realized through either dedicated Optical Supervisory Channels (OSC)
(out-of-band/in-fiber) or through a dedicated out-of-band/out-of-
fiber network.
- Signaling protocol is based on Generalized MPLS signaling as
described in [GMPLS-SIG] in combination with Generalized RSVP-TE
[GMPLS-RSVPTE] and Generalized CR-LDP [GMPLS-CRLDP] extensions.
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The basic meshed topology of the optical network can be represented
as a planar graph:
A ------ B ------ C
| | |
| | |
| | |
D ------ E ------ F
| | |
| | |
| | |
G ------ H ------ I
Each of the nodes (vertex) of this topology is an OXC. Nodes are
connected through fiber links. This topology (see above figure as
example) also defines a planar graph [OPT-NET], G(V,E) where V is the
vertex and E the edge of the planar graph. The considerations
developed here take into account this representation of the optical
network topology. The non-planar case is left for further study.
3. Optical Ring Emulation
Ring emulation concept refers to the configuration of optical rings
on top of a meshed optical topology including OXCs and not only O-
ADMs. This approach provides the advantage of ring configuration
flexibility without having to move or replace the devices already
included in the optical network.
The emulation concept provides also more flexibility during the
(dynamic) configuration of optical ring covers and the resource
allocation between the different rings included in the cover.
3.1 Optical Ring Covers
A ring cover is defined as a set of closed paths that covers all
links in the optical network at least once. So, a (complete) optical
meshed topology ring cover of the meshed optical topology will be
achieved when every node can be connected to at least one ring.
Two types of ring covers can be defined:
- non-overlapping ring cover: several rings covering (any node, in
case of complete ring-covers) the optical network are emulated on top
of a mesh topology; each of these nodes belongs to only one ring
except boundary nodes; non-overlapping ring covers can be complete
(covering the whole meshed topology) or incomplete (partially
covering the meshed topology)
- overlapping ring cover (or multi-ring cover): several rings
covering (any node in case of complete ring-covers) are configured on
top of an optical meshed topology; each of these nodes can be a
boundary node
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However, in the first release of this document, we only consider non-
overlapping incomplete or complete ring covers. This choice is
motivated by the complexity of the multi-ring covers as described in
[OPT-MWS] and [OPT-RINGS] where double covers of non-planar graphs
are studied.
In ring covers, fiber links shared between more than one ring are
referred to as shared links. However, wavelengths are dynamically
assigned to one (and defined as dedicated protection wavelengths) or
more than one ring (and defined as shared protection wavelengths).
Consequently, the emulation of an optical ring on top of meshed
optical network topology requires that:
- the configuration of the OXC optical switching matrix included
within a ring is designed to provide O-ADM functions (add, drop,
drop-and-continue, protection switching, etc.)
- in a shared link, each of the wavelengths belongs (for a given time
period) to one and only one ring precluding the usage of the
dynamically assigned wavelengths by the other ring
In the following mesh topology, a non-overlapping ring cover is
defined for instance by the following set of rings:
- Ring 1: A-B-E-D-A
- Ring 2: B-C-F-E-B
- Ring 3: E-F-I-H-E
- Ring 4: D-E-H-G-D
In this topology:
- Node C is an internal node since it belongs only to Ring 2
- Node D is a boundary node since it belongs to Ring 1 and Ring4
A ------ B ------ C
| | |
| Ring 1 | Ring 2 |
| | |
D ------ E ------ F
| | |
| Ring 4 | Ring 3 |
| | |
G ------ H ------ I
Node E has a particular situation in this topology since this
boundary node belongs to the four rings simultaneously. So, if we
consider each ring as an abstract node, the same topology can also
represented as follows
B,E
R1 --------------- R2
| \ / |
| \ / |
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| \ E / |
E,D| =====x===== |E,F
| / E \ |
| / \ |
| / \ |
R4 --------------- R3
E,H
As a result, if a node N1 connected to the ring R1 requests an LSP to
a node N2 connected to ring R3, the shortest ringed path is the one
going through Node E. This shows clearly that additional information
is required that takes into account the working (and protection) load
of the ring. This load information has to be shared between the rings
and between the rings and the external nodes to the rings.
In the same topology, an overlapping ring cover is defined by the
following set of rings:
- Ring 1: A-B-C-F-E-D-A
- Ring 2: D-E-F-I-H-G-D
- Ring 3: E-F-I-H-E
A ------ B ------ C
| | |
| Ring 1 |
| | |
D ------ E ------ F
| | |
| Ring 2 |
| | Ring 3 |
G ------ H ------ I
As mentioned previously, overlapping ring covers are not considered
in the first release of this document.
3.2 Dynamic Optical Ring Configuration
The emulation of a ring on top of optical meshed topology is
determined by the exchange of the following information between OXC:
- each ring is defined by a Ring ID (32-bit field)
- each ring shares a unique Virtual IPv4 Address (32-bit field)
- a Loopback IPv4 Address (32-bit field) is allocated per node
belonging to a given ring and per ring contiguous to a given node
such that neighboring nodes see a given ring as a single abstract
node identified by its loopback IPv4 address
- each ring is characterized by a Ring Protection Type (8-bit field)
which enables to select a given protection-type when establishing a
LSP over that ring
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- each ring knows the complete list of identifiers describing the
SRLGs to which a given link belongs.
- each ring owns an associated Ring Metric used to bootstrap the
initial ring resource allocation during the ring configuration
process
- each ring defines a internal Ring Policy (8-bit field) including
ring protection strategy, the ring protection scheme, and the
priority/preemption support
Consequently, the dynamic ring configuration includes the exchange of
basic identification information: the Ring Identifier, the Ring
Protection-Type, the Ring Virtual IP Address, the Ring Metric and the
Ring Policy.
3.2.1 Ring ID
Each of the node belonging to a given ring is identified by a node ID
defined as a Loopback IPv4 Address (in the future we will include
IPv6 node identification). So that a specific common identifier need
to exchanged between nodes belonging to the same ring.
For this purpose, a Ring ID defined as a 32-bit integer field that
uniquely identifies a given ring within a given optical domain (i.e.
administrative authority).
The ring ID is exchanged between neighboring nodes until reaching a
loop (on top of the meshed topology) constituted by nodes having the
same Ring ID. The Ring ID verification process at each node is
straightforward and does not require additional explanations.
3.2.2 Virtual IP Address
Each node included within a given ring shares a unique virtual IPv4
Address with other nodes belonging to the same ring. The IPv4 address
is uniquely defined per optical domain (i.e. administrative
authority).
By using a Virtual IPv4 Address to address a ring, a network
management system can reach any node of a given ring included within
a complex optical ringed topology without knowing the status of the
ring node or the corresponding ring topology.
Example:
If we refer to the previous optical network topology (see figure), we
have the following IP reachability between the multi-ring cover:
- Ring 1 is identified by the Ring ID 1 and Virtual IP Address 1
- Ring 2 à Ring ID 2 and Virtual IP Address 2
- Ring 3 à Ring ID 3 and Virtual IP Address 3
- Ring 4 à Ring ID 4 and Virtual IP Address 4
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3.2.3 Loopback IPv4 Address
In order to avoid the use of interface address and so potentially
experience disrupted communication between nodes belonging to the
same, a loopback IPv4 address is allocated per node.
For each ring contiguous to a given node, an additional loopback IPv4
address is allocated to this node. A ring can be considered as an
abstract single node for its neighboring OXC. Consequently, this IP
address identifies the abstract node constituted by a ring with
respect to the rings connected to this node.
From the neighboring rings point-of-view, this loopback IPv4 address
enables to reach a given node at any time independently of the status
of its incoming links.
The loopback IPv4 address is exchanged with the ring contiguous to
the node owner of this address but also between nodes belonging to
the same ring. These loopback IPv4 addresses are exchanged between
neighboring nodes in order to avoid the use of interface address for
intra-ring communication and duplicated loopback IPv4 address that
are subsequently distributed to neighboring rings.
Example:
From a nodal point of view, the neighbor relationship is determined
by local loopback IPv4 address to each of the neighboring ring from a
given node:
- Node B (belonging to ring 1 and ring 2) has 2 neighboring rings:
- Ring 1 identified by Loopback IP address B01
- Ring 2 identified by Loopback IP address B02
- Node 1 connected has 1 neighboring ring:
- Ring 1 identified by Loopback IP address A1
- Node 3 connected has 2 neighboring rings:
- Ring 1 identified by Loopback IP address D1
- Ring 2 identified by Loopback IP address D2
From a ring point of view, the neighbor relationship is determined by
the local loopback IPv4 address:
- Ring 1 has 3 neighboring rings:
- Ring 2 identified by Loopback IP address B21 and E21
- Ring 3 identified by Loopback IP address E31
- Ring 4 identified by Loopback IP address D41 and E41
Consequently, a boundary node belonging to two rings owns two virtual
IP addresses. In order to pass from one to ring to the other, the
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boundary node performs a shortcut. Imagine that Node 1 connected to
Ring 1 (through Node A) communicates with the Node 2 connected to
Ring 3 (through Node I). Then, the explicit route computed and
selected by Node 1 can be [A1 û E3 û Node 2]. However, the actual
route followed by the signalling message is [Node 1 - A1 (tunnel1) E3
(tunnel2) I3 û Node 2] where tunnel1 could.
Node 1 ------ A ------ B ------ C
| | |
| Ring 1 | Ring 2 |
| | |
Node 3 ------ D ------ E ------ F
| | |
| Ring 4 | Ring 3 |
| | |
G ------ H ------ I ------ Node 2
3.2.4 Optical Ring Protection Type
The Optical Ring Protection Type defines the protection technology
supported by nodes belonging to the same ring.
The Optical Ring Protection Type (which can be encoded as an 8-bit
field) is defined as the combination of the following parameters:
- Ring technology: Optical (= 0) or OTH-based (= 1)
- Ring protection type: Dedicated (= 0) or Shared (= 1)
- Ring protection level: Link-level (= 0) or Path-level (= 1)
- Ring protection fibers: 2-fiber (= 0) or 4-fiber (= 1)
- Ring switching: ring-switch (= 0) or span-switch (= 1)
- Other values (3 bits) are reserved for future use
So for a instance, a OCh-DPRing is defined by a 0xA0 protection type
and an 4-fiber shared path-level optical ring is defined by a 0x70
protection type. Since span-switch is only supported with 4-fiber
rings, one must avoid the 2-fiber and span-switch combination.
Note the ring technology could also be defined as Transparent (= 0)
and All-Optical (= 1) when the optical network topology includes only
OXC or PXC respectively.
3.2.5 Ring Link Diversity - SRLG
The shared link risk groups (SRLGs) are exchanged between nodes
belonging to the same ring. This in order to potentially avoid the
use of a shared resource that can affect all links belonging to this
group in case of failure of this shared resource. For instance, as
described in [IPO-SRLG], two LSPs flowing through the same fiber link
in the same fiber trunk.
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[IPO-BUNDLE] extends the SRLGs concept by demonstrating that a given
link could belong to more than one SRLG, and two links belonging to a
given SRLG may individually belong to two other SRLGs.
3.2.6 Ring Metric
The ring metric is used to bootstrap the initial ring resource
allocation during the ring configuration process. This metric is
exchanged during the initial ring configuration and only considered
by a node if its ring ID corresponds to the one advertised with the
ring metric.
The ring metric is a composed metric including the following
components: the ring absolute weight, the ring capacity and the ring
maximum restoration time.
1. Ring absolute weight
The ring absolute weight translates the number of nodes that belongs
to the ring. This value is used during the initial configuration
process to determine the number of non-adjacent nodes belonging to
the same ring.
For instance, it the ring absolute weight metric of given ring is N
then by receiving this value (or simply by consulting this value), a
node belonging to a given ring knows that the number of non-adjacent
nodes belonging to the same ring equals N-3.
2. Ring Capacity
During the initial configuration process, the ring capacity defines
the number of incoming, outgoing and dropped channels (or
wavelengths) provisioned at a given node for a given ring ID. These
values are defined for the working as well as the protection
capacity. The number of potentially available but unused wavelengths
by this ring is also announced during the initial configuration
phase. These wavelengths are consequently left free for other rings
that can be defined using the same node.
The ring capacity (per node) is exchanged between adjacent nodes
until each node belonging to the same ring has received (N-1) copy of
the ring capacity.
The knowledge of these values will enable to determine the initial
working ring load, protection ring load and spare capacity (also
defined as non-allocated ring load) for the newly configured ring.
This in turn provides the required information for each node to
compute the number of potential LSPs that can pass through (i.e. bar-
state) or be dropped (i.e. cross-state).
3. Maximum Restoration Time
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Typically, this static value defines the maximum restoration time
(MRT) for a given ring type at the initial configuration time. The
MRT values are distributed between nodes in order to know the
performance of the other nodes belonging to the same ring.
With the current state of the usage of all-optical electro-mechanical
(i.e. MEMS) technology in OXC, typical MRT values are:
- Bi-directional rings: 1-50ms
- Unidirectional rings: 1-10ms
Note that these values are statically configured and only during the
initial ring configuration period. So, they are not considered during
the working period of the ring.
3.2.6 Ring Protection Policy
Ring protection policy refers to the different strategies applicable
to optical rings. The ring protection policy includes mainly the ring
protection strategy, the ring protection scheme and ring protection
priority.
1. Strategy
The ring protection strategy could be revertive (default for
dedicated 1:1 ring protection or shared protection 1:N and M:N ring
protection) or non-revertive (default for 1+1 rings).
Depending on the ring protection type, the ring protection strategy
is determined by the under-laying hardware (or low-layer) opto(-
electro-)-mechanical technology providing the automatic protection
switching function. However, these considerations are outside of the
scope of this document.
2. Scheme
The ring policy scheme can be configured as provisioned or non-
provisioned. The non-provisioned scheme refers to restoration (or re-
routing) so that this scheme is not generally used when considering
ring protection in optical networks.
The provisioned scheme is one used when the protection path or lines
are left unused and fully dedicated to protection purposes; switching
to these paths will only occur if a working path or line failure need
to be recovered.
3. Priority/Preemption
The prioritization capability refers to the support of initial setup
and recovery priority associated with the subsequent link working and
protection allocated to the LSP established on top of the emulated
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ring. Note that the priority support extends to the signalling
support of prioritized working and protection LSPs created on a given
ring.
The preemption capability refers to the support of link working and
protection resources pre-emptability in case of link or node failure
within a given ring.
3.2.7 Summary
Consequently, the exchange of information between nodes belonging to
the same ring enables the common knowledge of the identification and
properties that uniquely define a given optical ring.
- Ring Identifier
- Ring Virtual IP Address
- Ring Protection Type
- Ring SRLG per link
- Ring Metric including the absolute ring weight, the ring capacity
and the ring MRT
- Ring Policy including ring protection strategy, the ring protection
scheme, and the priority/preemption support
4. Dynamic Ring Resource Allocation
The dynamic ring resource allocation process is closely related to
intra-ring traffic engineering (intra-ring TE). The ring resource
allocation process is required to dynamically setup Lambda-switched
LSP segments on top of emulated rings.
4.1 Link TE Resource
Link TE resources are dynamically exchanged between nodes belonging
to the same ring to provide the necessary information for intra-ring
TE. Dynamic Ring Resource Allocation is based on the knowledge of the
following link TE resource-related information:
- Link identification (or link bundle identification)
- Maximum available bandwidth per link
- Minimum and maximum reservable bandwidth per link
- Link protection type including unprotected 0:1, dedicated 1:1,
shared M:N and dedicated 1+1 protection
- Link priority associated to the minimum/maximum reservable
bandwidth per link
- Link priority associated with the link protection type
- List of SRLGs per link (in order to compute disjoint working and
protection LSP, for instance)
- Resource Class/Color defined per link
The dynamic exchange of this information (IGP link-state
advertisements) during the working period of the ring enables the
real-time computation of the value(s) (i.e. the component values)
defined for the ring TE metric.
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4.2 Ring TE Metric
The ring traffic engineering metric (ring TE metric) can be
considered as a dynamic ring metric whose component value(s) are
periodically re-evaluated during the working period of the emulated
ring. This ring metric is a composed TE metric including the
following components:
- a ring weight
- a ring load
- a ring maximum restoration time
1. Ring weight
In the previous example, the Node A does not know the number of nodes
the (i.e. hop count) within a given neighboring ring. To make the
distinction between rings, we introduce the concept of ring weight.
Ring weight is inversely proportional to number of nodes belonging to
a ring multiply by 100. The ring weight is defined as:
Working ring weight = (1/[Number of nodes] x 100) x r1
where r1 is a weighted integer factor
r1 is a user customizable integer whose default value equal 1
For instance, in the above example each ring have a weight of 25
since 1/[Number of nodes = 4] x 100.
However, this definition does not allow discriminating between
working and protection path. So we define a working ring weight and a
protection ring weight (this applies only to bi-directional rings).
For bi-directional rings, the ring weight is defined in two flavors:
- Working ring weight = (1/[Number of nodes] x 100) x r1
- Protection ring weight = (100 û [Working ring weight]) x r2
where r1 and r2 are weighted integer factors defined by default as r1
= 1 and r2 = 1.
2. Ring Load
The ring load is only defined for bi-directional rings. The working
ring load quantity defines, for each direction of propagation, the
largest number of working LSPs (in any fiber link) flowing in
opposite direction of the protection LSPs. The working ring load is
defined at each time interval as:
Working ring load = [Number of working LSP]
However, this definition does not give the relative working load of
the ring compared to its total capacity. So, to normalize the working
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ring load, this value is divided by the total ring capacity (in terms
of total number of LSPs).
Working ring load = [Number of working LSP]/[Total number of LSPs]
Correspondingly, the protection ring load will be defined as the
number of protection LSPs divided by the total ring capacity (in
terms of total number of LSPs). The protection ring load is defined
at each time interval as:
Protection ring load = [Number of protection LSP]/[Total number of
LSPs]
Consequently, the working ring load, the protection ring load and the
non-allocated ring load are defined by the following formulas:
Working Ring Load = ([Number of working LSP]/[Ring capacity] x 100) x
r3
Protection Ring Load = ([Number of protection LSP]/[Ring capacity] x
100) x r4
Unallocated Ring Load = ((1 û ([Working Ring Load] + [Protection Ring
Load])/[Ring Capacity]) x 100) x mean(r3,r4)
Where the r3 and r4 parameters are weighted integer factors, defined
by default as r3 = 1 = r4.
3. Maximum Restoration Time
Typically, this value defines the maximum restoration time (MRT) for
a given ring type. Typical values are:
- Bi-directional rings (shared-path): 1-50ms
- Unidirectional rings (dedicated-path): 1-10ms
So, we define the associated metric value as:
MRT = (MRT[N] x 100) x r5
In this definition, the r5 parameter is a weighted integer factor
defined by default as equal to 1. Comparing to the MRT defined in the
ring metric, the values considered here are dynamic. The maximum
restoration time computation per ring depends on the failure history
of that ring. Each time a failure is experienced by a ring the MRT
value is adapted through the use of the following computation:
If MRT[N]>MRT[N-1]
then MaxMRT[N] = MRT[N-1] + (k/100 x MRT[N-1])
MRT[N] = Mean(MaxMRT[N]; MinMRT[N-1])
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If MRT[N]<MRT[N-1]
then MinMRT[N] = MRT[N-1] û (k/100 x MRT[N-1])
MRT[N] = Mean(MaxMRT[N-1]; MinMRT[N])
Where N is defined as the ring restoration process occurrence and k
is defined as the restoration time in ms experienced during the last
failure (at the last restoration process occurrence N-1).
Consequently, the Ring TE Metric is defined as:
Ring TE Metric = (Working Ring Weight x r1 | Protection Weight x r2)
+ (Working Ring Load x r3 | Protection Load x r4)
+ (Maximum Restoration Time x r5)
The corresponding advertisement will include both the working and the
protection part of the metric.
5. Ring Protection in Optical Networks
Within optical networks, the purpose of the ring protection
mechanisms is to incorporate optical layer survivability in network-
layered structures. Even if some of the higher layers have their own
protection mechanisms, by incorporating survivability mechanisms at
multiple layers leads to the following issues:
- the protection function allocation to each of the layers
- the coordination of the protection functions applied at each layer
during failure recovery process
Nevertheless, as described in [OPT-MRPS], providing optical layer
survivability through ring protection has been strongly suggested by
arguing a combination of optical ring protection with optical linear
protection as well as additional restoration mechanism provides the
best optical network survivability.
5.1 Escalation Strategy
The escalation strategy is defined by the set of detection functions
describing the originating failure, the protection functions applied
within recovery process to recover the failure and the interaction
between the upper and/or lower layers protection functions applied
during the recovery process. The escalation strategies are governed
either by arbitrarily setting failure detection and recovery
completion time (using hold-off timers) or by explicit message
exchange between the layers.
Two escalation strategies (also referred to as inter-working
strategy) have been proposed in [OPT-PRG] and summarized here:
- Bottom-up strategy starts at closest layer to the failure
(generally the bottom layer) and escalates toward the upper layer
upon expiration of the recovery timer (hold timer). This timer is
defined in such a way that is allocates ôenough timeö the lower
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layer(s) to detect the failure, execute the recovery process and
recovery completion time before triggering recovery process defined
at the higher layer(s).
- Top-down strategy starts at the upper(most) layer and escalates
downward to the lower layer(s); depending on the working level, the
top-down strategy is suitable when each of the layers define Class-
of-Services (CoS) so that the escalation strategy might take this CoS
into account when executing the recovery process.
5.2 Bottom-Up Strategy
We assume here a classical Bottom-up strategy since it has the
shortest recovery time (with respect to the Top-down escalation
strategy), and define the threshold at which the upper-layer
protection needs to be ôexecutedö.
In optical rings, the following escalation strategy can be defined
(here we do not assume FSC capable OXC interfaces, so that GMPLS
signalling is not considered at the lowest layer)
Packet Layer <==> PSC interface <==> GMPLS Signaling
^ ^
| |
| |
| |
LSP Layer <==> LSC interface <==> GMPLS Signaling
^
|
|
|
Fiber Layer <==> Physical Interface <==> Layer-1 Mechanisms
Compared to TDM SDH/Sonet Rings control through GMPLS signalling
[GMPLS-SIG] or Optical Rings (as defined in G.709 based OTN):
Packet Layer <==> PSC interface <==> GMPLS Signaling
^ ^
| |
| |
| |
Path (OCh) Layer <==> TDM (G.709) interface <==> GMPLS Signaling
^ ^
| |
| |
| |
MS (OMS) Layer <==> TDM (G.709) interface <==> GMPLS Signaling
^
|
|
|
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RS (OTS) Layer <==> Physical Interface <==> Layer-1 Mechanisms
This approach is based on the common coordination achieved by
resorting escalation strategies. At each level, the resiliency scheme
is activated sequentially starting from the lower to the upper layer.
This implies that at each level the detection of a failure condition
(and restoration time) triggers either a protection/restoration
mechanism and if the protection/restoration completion time is
reached then triggers an upper-layer protection/restoration
mechanism.
5.3 Ring Protection Mechanisms
In this section the two generic ring protection mechanisms are
discussed. The main difference between these mechanisms is that the
dedicated protection performs a physical-layer level protection
switching while the shared protection needs a dedicated O-APS
signalling protocol to synchronize the execution of the protection
switching mechanism.
5.3.1 Dedicated Protection
Dedicated LSP protection can be easily achieved by splitting the
incoming optical signal and send the one copy of the output signal
into working wavelength (or fiber) and the other copy into the
protection wavelength (or fiber).
This results in two copies of the signal propagating the ring in
opposite directions. The far-end (or receive-end) switches to the
protection wavelength (or fiber) if a degradation or failure occurs.
The proposed mechanism can restore a single link failure or a single
node failure.
Moreover, since the far-end (receiving end) needs to notify the near-
end (transmitting end) of the failure, an O-APS signalling mechanism
is not required. However, when a link failure is detected on the
working ring, the far-end switch to the protection ring (in the
opposite direction) but for any wavelength flowing through this link,
so that only a bulk LSP protection switching is achieved by using
this technique.
By using the optical signal splitting technique (as described in
[IPO-MULT]), fast protection is provided for 1+1 LSP protection.
However, this technique applies only for unidirectional LSP
protection rings. With this type of rings the optical signal is split
on both wavelengths (fibers) at the transmission end.
5.3.2 Shared Protection
Shared protection is mainly based on the use of an O-APS signalling
protocol (using the signalling IP-based control-plane). The
requirements as well as the specifications for the specification of
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such an IP-based protocol need to be seriously determined in order to
achieve a fast protection switching mechanism. The specifications of
the O-APS protocol are extensively detailed in [IPO-OAPS].
6. Routing in Optical Rings and Hybrid Mesh-Ring Networks
In optical networks, the following hierarchical routing model can be
considered:
- the intra-domain interfaces are included in an IGP (more precisely
link-state routing protocols) routing protocol instance included
within the same autonomous-system (AS)
- the inter-domain interfaces are defined between autonomous-systems
running over eBGP routing protocol.
The eBGP protocol is running between border LSRs (which from the
OSPF point-of-view are considered as an Autonomous System Boundary
Router - ASBR). The hierarchical optical network model provides the
capacity to connect several autonomous systems (i.e. optical domains)
together through eBGP protocol.
6.1 Intra-Domain Routing
The optical network architecture considered here is build such as the
corresponding control plane defines an hierarchical optical topology
as described in [IPO-FRAME]. Consequently, intra-domain routing can
be considered when the IP-based control plane defines an OSPF
Autonomous System (AS) on top of an hierarchical optical domain
(which defines the transport plane). The same considerations can be
applied when using IS-IS IGP protocol in hierarchical optical
networks.
With the intra-domain architecture, transparent optical network
devices (i.e. OXC including O/E/O conversion) are located at the
border of the corresponding areas. Consequently, OXC might be
considered as internal LSR as well as border LSR. All-optical network
devices (i.e. PXC without O/E/O conversion) are predominantly
configured as internal LSR but might in particular cases be
configured as border LSR.
++++++++++++++ ++++++++++++++
+ A ------ B + + H ------ I +
+ | | + + | | +
+ | Area10 | + + | Area20 | +
+ | | XXXXXXXXXX | | +
+ D ------ C ---------- E ------ J +
+++++++++X | | X+++++++++
X | | X
X | Area 0 | X
X | | X
+++++++++X | | X+++++++++
+ K ------ G ---------- F ------ N +
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+ | | XXXXXXXXXX | | +
+ | Area30 | + + | Area40 | +
+ | | + + | | +
+ M ------ L + + P ------ O +
++++++++++++++ ++++++++++++++
Taking into account this optical network topology:
- Ring CEFG defines backbone area 0
- Ring ABCD, HIJE, KGLM and FNOP define non-backbone area
In this hierarchical network topology, each of these nodes can be
considered as an abstract node so that each of them can also be
considered as defining an optical ring. Moreover, each of these areas
can include internal all-optical rings. However, in that case, the
only restriction is related to the Area Border Routers (ABR i.e.
border LSR) that can not be all-optical PXC. In order to avoid
optical signal regeneration related problems, one can consider here
that border LSRs are O/E/O transparent devices like OXCs.
6.2 Inter-domain Routing
Inter-domain Optical Routing is considered when defining inter-
optical domain routing between several carriers. In the most basic
network topology, optical domains (i.e. BGP AS) are inter-connected
through direct links (or redundant links) combined with linear
protection mechanisms as represented in the following figure:
++++++++++++++ ++++++++++++++
+ A ------ B + + H ------ I +
+ | | + + | | +
+ | AS 10 | + + | AS 20 | +
+ | | + + | | +
+ D ------ C ========= E ------ J +
+++++++++++|++ ++|+++++++++++
| |
direct --> | |
| |
+++++++++++|++ ++|+++++++++++
+ K ------ G ========= F ------ N +
+ | | + + | | +
+ | AS 30 | + + | AS 40 | +
+ | | + + | | +
+ M ------ L + + P ------ O +
++++++++++++++ ++++++++++++++
In this topology, the Nodes CEFG can define an inter-domain ring.
This enhancement provides higher resiliency to the classical inter-
domain connections since in that case ring protection mechanism can
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be used. However, the most reliable topology will be achieved when
the optical domains are inter-connected through a BGP Transit AS.
When considering a Transit AS, the Client AS can be inter-connected
by using optical rings or direct links to the Transit AS.
As mentioned above the use of a meshed inter-connectivity between
nodes does not preclude the use linear protection (and restoration)
mechanisms such as dedicated 1+1 or shared (1:1, 1:N, M:N) LSP
protection.
The following figure compares optical ring from direct link inter-
connection approach:
+ + + +
—|—+————————+—|— | + + |
---—C-+--------+-E—--- ---C-+--------+-E---
+++—+++ +++—+++ +++++++ +++++++
—| |— | |
+—++++++++++++++—+ ++++++++++++++++++
+—Q------------R—+ + Q------------R +
+—|————————————|—+ + | | +
+ | Transit AS | + + | Transit AS | +
+—|————————————|—+ + | | +
+—T------------S—+ + T------------S +
+—++++++++++++++—+ ++++++++++++++++++
—| |— | |
+++—+++ +++—+++ +++++++ +++++++
---—G-+--------+-F—--- ---G-+--------+-F---
—|—+————————+—|— | + + |
+ + + +
Optical Rings Direct Links
As mentioned before, a trade-off between link (or wavelength)
redundancy and lost capacity need to be defined. However, these
considerations are out of the scope of this document.
6.3 Inter-Ring Traffic-Engineering
As described in the previous section, the network hierarchical model
considered is divided into Autonomous Systems (ASs), where each AS is
divided into IGP areas to allow the hiding, aggregation and
summarization of routing information. The hierarchical routing model
currently can be extended for traffic engineering as it hides the
route taken by a LSP to the destinations in the other routing areas.
Hence, from the TE perspective, requirements such as path selection
and crank-back mechanism need different architectural additions to
the existing link-state routing and signaling protocols for inter-
area LSP setup. The protection requirements as well as crank-back
mechanisms can be implemented by using the optical ring techniques
described in this document.
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Note that in a fully distributed approach, since LSRs in different
ASÆs have different views of the network at any given time, re-
routing and crank-back mechanisms are needed. This approach requires
also to clearly defining when the steady state of the optical network
is reached in order to execute the protection/restoration mechanisms
specified in the escalation strategy to apply when failure(s) occurs.
The problems related to LSP protection/restoration are also described
in [IPO-REST].
Traffic engineering (TE) practice currently involves the setup and
use of Label Switched Paths (LSPs) as dedicated bandwidth pipes
between two end points (i.e. between an ingress and an egress LSR).
LSPs can be setup across several LSRs through the use of dynamically
computed path. Since this memo focuses on fully distributed CSPF path
computation, we consider here that the routes can be computed
dynamically through the use of online constraint-based routing
algorithms such as incremental Linear or Heap Dijkstra Algorithm (or
Dijkstra-like algorithms for non-additive metrics) as described for
instance in [SPT-DYN]).
The online constraint-based routing model requires:
(1) a set of flooding mechanism to maintain the state of TE-related
information within the optical network topology
(2) a constraint-based routing process implemented on certain LSRs
that serve as ingress LSRs for the LSPs,
(3) a topology change(s) within the optical domain does not result in
a complete re-computation of the routes
Most of the traffic engineering extensions for intra-area TE routing
are described in [OSPF-TE] and [GMPLS-OSPF] the latter in particular
when considering intra-area GMPLS TE routing. Note that new traffic
engineering attributes can be defined in future versions of this
document. We describe here the TE extensions for inter-ring TE
routing in optical ring topologies when considering summarization of
the TE values at boundaries (see also [OSPF-IRTE] concerning
summarization of TE attributes).
As described in [OSPF-IRTE], traffic engineering (TE) summary LSA can
be originated at Area Border Router (ABR) into an area. This TE
summary LSA is a type-10 opaque LSA flooded within the area. The
functionality of the TE summary LSA is similar to the one of summary
LSA of standard OSPF [RFC2328], but in addition it carries the
traffic engineering metrics to the remote destination (IP network or
ASBR). The inter-ring TE summary LSA described here has exactly the
same functionality except that the corresponding LSA is generated at
ring boundary nodes.
6.3.1 Ring Count
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The ring count is the cost in rings to reach the destination network
(or the destination ring) from the source node (or the source ring).
This parameter is equivalent to the hop count defined in [OSPF-IRTE]
since a ring appears as an abstract node for the neighboring rings or
OXCs (not belonging to the same ring). The ring count (as the hop
count) is an additive metric. Note that the ring count can be
generalized to an additive weighted metric.
6.3.2 Maximum Reservable Bandwidth
The maximum reservable bandwidth is defined as the smallest maximum
reservable bandwidth among all the rings included into the path from
the source to the destination.
Note the maximum reservable bandwidth should be the same for the
working and the protected path.
6.3.3 Minimum Reservable Bandwidth
The minimum reservable bandwidth is defined as the largest minimum
reservable bandwidth among all the rings included into the path from
the source to the destination.
Note the minimum reservable bandwidth should be the same for the
working and the protected path.
6.3.4 Delay
The delay attribute is defined as the delay cost to reach the
destination ring in microseconds. The delay is defined an average
delay taking into account the delay introduced by the worst case
protection path and best case working path since this value can not
up to now be updated dynamically. The delay is an additive metric
that could be generalized to an additive weighted metric.
Note that the delay of the working path could be different from the
delay of the protected path.
6.3.5 Resource Class/Coloring
The resource class or color of the destination network is a
combination of the colors for the various ringed paths to the
destination network. Path coloring technique can be found in [IPO-
PATH].
Path coloring can be used to prune resources as a first step of the
LSP route computation and as a tie when two distinct routes having
the same Inter-Ring TE Metric (see section 6.3.6) to the same
destination network may be used but only differ from their color. In
that case, the choice of one route or another is a local policy
matter.
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6.3.6 Inter-ring TE Metric
The inter-ring TE metric is defined as the TE metric representing the
TE cost of reaching the destination network (or the destination ring)
from the advertising ring.
This metric is composition of ring TE metrics (described in section
4.2) defined by the following formula:
Inter-Ring TE Metric =
(Working Ring Weight x r1 | Protected Weight x r2)
+ (Working Ring Load x r3 | Protected Load x r4)
+ (Maximum Restoration Time x r5)
So that the inter-ring TE metric is defined as the weighted sum of
the ring metrics and representing the traffic-engineering cost of
reaching the destination ring (i.e. Ring N) from the advertising ring
(i.e. Ring 1).
Ring TE Metric = k[1] x Ring Metric 1 + k[2] x Ring Metric 2
k[n-1] Ring Metric N-1 à k[n] x Ring Metric N
6.4 Routing Protocol Extensions for Dynamic Ring Configuration
We describe here the IGP routing protocol extensions needed in order
to enable dynamic ring configuration within an area (intra-area
routing) between areas (inter-area routing).
6.4.1 Opaque LSA
Opaque LSA are application specific link-state advertisements defined
in [OSPF-OPA] used mainly for IGP traffic engineering (TE) extension
purposes, see for instance [OSPF-TE] concerning intra-area TE routing
and [OSPF-IRTE] concerning inter-area TE routing.
The [RFC2370] describing the Opaque LSAs concepts for application
specific information distributed additionally to the IGP routing
information. In [OSPF-OPA], three types of Opaque LSA were defined:
- Type-9 Opaque LSA: link-local scope
- Type-10 Opaque LSA: area-local scope (or intra-area scope)
- Type-11 Opaque LSA: Autonomous System (AS) scope (or inter-area
scope)
The flooding scope associated with each Opaque link-state type is
defined as follows.
- Type-9 Opaque LSAs are not flooded beyond the local sub-network.
- Type-10 Opaque LSAs are not flooded beyond the borders of their
associated area.
- Type-11 Opaque LSAs are flooded throughout the Autonomous System
(AS) and is equivalent to the flooding scope of AS-external (type-5)
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LSAs.
As a generic rule, see [RFC2370], when flooding Opaque-LSAs to
adjacent neighbors, an opaque-capable router looks at the neighbor's
opaque capability. Opaque LSAs are only flooded to opaque-capable
neighbors. When a non-opaque-capable router inadvertently receive
Opaque LSAs, it simply discard the Opaque LSA.
Consequently, to achieve intra-area dynamic ring configuration we use
Opaque LSAs of Type 10 area-local flooding scope.
6.4.2 Opaque LSA Header
Opaque LSAs are types 9, 10 and 11 link-state advertisements. The
Link-State ID [RFC2328] of the Opaque LSA is divided into an Opaque
Type field (8-bit sub-field) and a Opaque Type-specific ID (24-bit
sub-field). The range of topological distribution (i.e., the flooding
scope) of an Opaque LSA is identified by its link-state type.
In Opaque LSAs are application specific LSAs meaning that their
payload has meaning only within a certain application; otherwise,
they will be ignored. The Opaque Type that is contained in the Opaque
Type field identifies the type of the application.
The Opaque Type-specific ID (i.e. Opaque ID) is a 24-bit sub-field
sub-divided in a reserved sub-field (8 MSB) and a Source specific
sub-field (16 LSB).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | LS Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque Type | Opaque ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Node ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where LS Type value = 9, 10 or 11
For the purpose of dynamic ring configuration, only Opaque LSA Type-
10 will be considered. Moreover the dynamic ring configuration Opaque
Type still remains to be determined.
6.4.3 Opaque LSA Payload
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As described in [OSPF-OPA], the Opaque LSA payload consists of one or
more nested Type/Length/Value (TLV) structures. The format of the
Opaque LSA TLV structure is defined as:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length (in bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following additional TLV need to be defined in order to enable
dynamic ring configuration through the use of application-specific
Opaque LSAs.
1. Ring ID TLV
The Ring ID is defined as a 32-bit integer field that uniquely
identifies a given ring within a given optical domain (i.e.
administrative authority).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD) | 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ring ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A additional field might be defined in the future to identify the
Autonomous System number (16-bit) into which the ring is included.
2. Ring Virtual Address TLV
Each node included within a given ring shares a unique virtual IPv4
Address with other nodes belonging to the same ring. The IPv4 address
is uniquely defined per administrative authority. This information is
exchanged between nodes by using the following TLV:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD) | 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Virtual IPv4 Ring Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3. Loopback IP Address TLV
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One loopback IPv4 address is allocated per node in order to avoid
communication disruption between nodes belonging to the same ring
when a given node interface becomes unreachable. The local loopback
IPv4 address must be the first one included in the loopback IPv4
address list.
For each ring contiguous to a given node, an additional loopback IPv4
address is allocated. Since a ring is viewed as an abstract single
node for its neighboring OXC, these loopback IP addresses identify
the abstract node constituted by a ring for the neighboring nodes
(external to this ring) and neighboring rings.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD) | n x 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Loopback IPv4 Address 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ ... /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Loopback IPv4 Address n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4. Ring Protection Type TLV
The Optical Ring Protection Type (encoded as an 8-bit flagged field)
is defined as:
- Ring technology: Optical (Bit0=0) or OTH-based (Bit0=1)
- Ring Protection: Dedicated (Bit1=0) or Shared (Bit1=1)
- Ring Protection level: Link-level (Bit2=0) or Path-level (Bit2=1)
- Ring Protection fibers: 2-fiber (Bit3=0) or 4-fiber (Bit3=1)
- Ring switching: ring-switch (Bit4=0) or span-switch (Bit4=1)
- Other values (3 bits) are reserved for future use
The corresponding TLV is defined as:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD) | 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protection | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5. Link TLV
To encode the list of SRLG(s) to which a given link belongs, we
propose to use the Link TLV by including the following sub-TLVs:
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- Link ID (32-bit)
- Link Local Interface ID (32-bit)
- Link Remote Interface ID (32-bit)
- Link Encoding Type (8-bit)
- Link Protection Type (8-bit)
- List of SRLG(s) (n x 32-bit)
The corresponding TLV are already defined in [GMPLS-OSPF] and [OSPF-
TE]. Note that for optical rings, the relevant Link Protection Type
are dedicated 1+1, dedicated 1:1, shared M:N and unprotected 0:1.
Additional sub-TLVs can also be included within the Link TLV for
intra-ring traffic engineering purposes. So, we can refer to these
sub-TLVs as Link TE sub-TLVs:
- Maximum Available Bandwidth per link
- Minimum and Maximum Reservable Bandwidth per link
- Link Priority associated to Minimum/Maximum Reservable Bandwidth
- Link Priority associated with the Link Protection Type
- Resource Class/Color defined per link
The link resource allocation is performed dynamically here;
consequently the Link TLV does not need to include the Ring ID to
which this link might be allocated (or de-allocated) during the
working period of the ring. A given link can include several
wavelengths belonging to more than one ring if this is a shared link.
This means that the per-ring resource allocation
Note also that even if a fiber link can belong to more than one ring
(if the link is defined as a boundary link) the wavelengths available
on that link when allocated to one ring, they can not be shared by
the other ring.
6. Ring Metric TLV
As described in section 3.6, the ring metric is a component metric
including the ring absolute weight, the ring capacity and the ring
initial MRT.
The corresponding TLV is defined as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD) | 20 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Weight | Initial MRT |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| R | Incoming | Outgoing |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| R | Dropped | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| R | Incoming | Outgoing |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| R | Unused |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Ring Metric TLV includes:
- Ring absolute weight (8-bit): number of nodes belonging to the same
ring ID
- Ring initial MRT (24-bit): in microsecond units
- Ring capacity:
. number of working wavelengths: incoming (14-bit), outgoing
(14-bit) and dropped (14-bit)
. number of protection wavelengths: incoming (14-bit) and
outgoing (14-bit)
. number of unused wavelengths (28-bit) for this ring
7. Ring Protection Policy TLV
Ring protection policy refers to the different strategies applicable
to optical rings. The ring protection policy includes mainly the ring
protection strategy, the ring protection scheme and ring resource
priority and preemptability support. The Ring Protection Policy TLV
format is defined as:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD) | 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|1|2 3| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The values are defined as follows:
The ring protection strategy:
- Bit 0 set to 0 defines a non-revertive strategy
- Bit 0 set to 1 defines a revertive strategy
The ring protection scheme:
- Bit 1 set to 0 defines a provisioned scheme
- Bit 1 set to 1 defines a non-provisioned scheme
The ring resource Priority-Preemption:
- Bit 2 set to 0 enables setup pre-emptability of working and
protection link resources during LSP setup process (meaning implicit
priority support for link resources)
- Bit 2 set to 1 disables setup pre-emptability of working and
protection link resources during LSP setup process
- Bit 3 set to 0 enables recovery pre-emptability of working and
protection link resources during LSP recovery process (meaning
implicit priority support for link resources)
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- Bit 3 set to 1 disables recovery pre-emptability of working and
protection link resources during LSP recovery process
Other bits (bit 4 to 31) are reserved for future use.
6.5 Routing Protocol Extensions for Dynamic Ring Resource Allocation
The only additional TLVs to define as additional Opaque LSA payload
is the Ring TE Metric TLV. Other traffic engineering extensions such
as Link TE TLVs have already been defined in [OSPF-TE] and [GMPLS-
OSPF].
1. Ring TE Metric TLV
The Ring TE Metric is a component metric including the ring weight,
the ring load and the ring MRT.
The Working TE Metric (16-bit) part of the Ring TE Metric includes
the following components
- the working ring weight
- the working ring load
- the computed MRT
The Protection TE Metric (16-bit) part of the Ring TE Metric includes
the following components:
- the protection ring weight
- the protection ring load
- the computed MRT
The Ring TE Metric TLV is encoded as:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD) | 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Working TE Metric | Protection TE Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7. Signaling Extensions in Ring Protected optical networks
The signaling extensions are related to the following functions:
- signalling of the working and the protected path from source ring
node to the destination ring node
- specific signaling extension in order to support drop-and-continue
functionality; this is equivalent to define signalling extension for
point-to-multipoint LSP
Drop-and-continue function can be required when considering protected
ring interconnection:
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- For dedicated-protection ring inter-connection: drop-and-continue
function is used together with path selector function
- For shared-protection ring inter-connection: drop-and-continue
function is used together with service selector function
- For both type of ring are inter-connected: drop-and-continued is
used together with path selector function (dedicated-protection ring)
and service selector function (shared-protection ring)
7.1 Intra-ring signalling extension
When entering the ring, the signaling of the working and the
protected channel need to be executed simultaneously.
The principle defined for this purpose is to æsplitÆ the signaling
message (corresponding to the LSP create message) for the working and
protected path through the corresponding signalling channel. For this
purpose, the same technique as the one defined in [IPO-REST] can be
applied. The proposed mechanism applied to emulated rings provides
the suitable signalling extensions for the creation of backup LSP
segments from the ingress to egress ring node when LSP protection is
required.
[IPO-MULT] proposes a more efficient mechanism to achieve this by
considering the split of the physical optical signal. In that case,
fast protection is provided for the 1+1 protected LSP. However, this
technique applies only for unidirectional LSP protection rings. With
this type of rings the optical signal is split on both wavelengths
(fibers) at the transmission end. This results in two copies of the
signal propagating the ring in opposite directions. The far-end (or
receive-end) switches to the protection wavelength (or fiber) if a
failure occurs. The proposed mechanism can restore a single link
failure or a single node failure.
When using 1+1 LSP protection, since the far-end (receiving end) does
need to notify the near-end (transmitting end) of the failure, an O-
APS signalling mechanism is not required. The decision is made at the
far-end on an LSP-by-LSP basis.
7.2 Inter-ring signalling extension
Inter-ring signalling extensions are considered for drop-and-continue
ring inter-connection. In this case, the signalling message (i.e. the
LSP create message) need to be continued meaning duplicated when
reaching the primary destination node (far end) for that LSP. However
only one LSP must be defined (in particular only one LSP segment
needs to be defined from the ingress to egress ring nodes). Details
concerning inter-ring signalling extensions are left for further
study.
8. Security Considerations
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Security considerations are left for further study.
9. References
1. [GMPLS-CRLDP] P. Ashwood-Smith et al., æGeneralized MPLS Signaling
- CR-LDP Extensions,Æ Internet Draft, draft-ietf-mpls-generalized-cr-
ldp-00.txt, November 2000.
2. [GMPLS-ISIS] K. Kompella et al., æIS-IS Extensions in Support of
MPL(ambda)S,Æ Internet Draft, draft-kompella-isis-gmpls-extensions-
00.txt, November 2000.
3. [GMPLS-OSPF] K. Kompella et al., æOSPF Extensions in Support of
MPL(ambda)S,Æ Internet Draft, draft-kompella-ospf-gmpls-extensions-
00.txt, November 2000.
4. [GMPLS-SIG] P. Ashwood-Smith et al., æGeneralized MPLS Signaling û
Signaling Functional Requirements,Æ Internet Draft, draft-ietf-mpls-
generalized-signaling-01.txt, November 2000.
5. [GMPLS-BUNDLE] K. Kompella et al., æLink Bundling in MPLS Traffic
Engineering,Æ Internet Draft, draft-kompella-mpls-bundle-04.txt,
November 2000.
6. [IPO-OAPS] D. Papadimitriou et al., æOptical Automatic Protection
Switching û An IP-based ProtocolÆ, Work in Progress, draft-
papadimitriou-ipo-ip-based-oaps-00.txt, February 2001.
7. [IPO-BUNDLE] Bala Rajagopalan et al., æLink Bundling in Optical
Networks,Æ Internet Draft, draft-rs-optical-bundling-01.txt, November
2000.
8. [IPO-FRAME] B. Rajagopalan et al., æIP over Optical Networks: A
Framework,Æ Internet Draft, draft-many-ip-optical-framework-02.txt,
November 2000.
9. [IPO-LMP] A. Fredette et al., æLink Management Protocol (LMP) for
WDM Transmission Systems,Æ Internet Draft, draft-fredette-lmp-wdm-
00.txt, December 2000.
10. [IPO-MPLS] D. Awduche et al., æMulti-Protocol Lambda Switching:
Combining MPLS Traffic Engineering Control With Optical
Crossconnects,Æ Internet Draft, draft-awduche-mpls-te-optical-02.txt,
July 2000.
11. [IPO-MULT] D. Papadimitriou et al., æAll-Optical Multicast û A
Framework,Æ Internet Draft, draft-poj-all-optical-multicast-00.txt,
February 2001.
Internet Draft û Expires August 2001 35
Draft-papadimitriou-optical-rings-00.txt February 2001
12. [IPO-REST] J. Hahm et al., æRestoration Mechanisms and Signaling
in Optical Networks,Æ Internet Draft, draft-many-optical-restoration-
02.txt, February 2001.
13. [IPO-RHMR] D. Guo et al, æOptical Hybrid-Meshed Rings,Æ Internet
Draft, draft-guo-optical-mesh-rings, January 2000.
14. [IPO-SRLG] D. Papadimitriou et al., æInference of Shared Risk
Link Groups,Æ Internet Draft, draft-many-inference-srlg-00.txt,
February 2001.
15. [MPLS-CRLDP] B. Jamoussi et al., æConstraint-Based LDP Setup
using LDP,Æ Internet Draft, draft-ietf-mpls-cr-ldp-04.txt, July 2000.
16. [OPT-MWS] T. Stern and K. Bala, æMultiwavelength Optical Network
û A Layered Approach,Æ Addison Wesley Longman, Inc, May 1999.
17. [OPT-RINGS] G. Ellinas et al, æProtection Cycles in Mesh WDM
Networks,Æ IEEE Journal on Selected Areas in Communications, Volume
18, Number 10, October 2000.
18. [OSPF-TE] D. Katz and D. Yeung, "Traffic Engineering Extensions
to OSPF,Æ Internet Draft, draft-katz-yeung-ospf-traffic-03.txt,
October 2000.
19. [OSPF-IRTE] S. Venkatachalam et al, æOSPF Extensions to
Support Inter-Area Traffic Engineering,Æ draft-venkatachalam-ospf-
traffic-00.txt, November 2000.
20. [RFC2328] J. Moy, æOSPF Version 2,Æ Internet RFC û Standard
Track, April 1998.
21. [RFC2370] R. Coltun, æThe OSPF Opaque LSA Option,Æ Internet RFC
2370 û Standard Track, July 1998.
22. [SPT-DYN] P. Narvaez et al., æNew Dynamic Algorithms for Shortest
Path Tree Computation,Æ IEEE/ACM Transactions on Networking, Volume
8, Number 6, December 2000.
10. Acknowledgments
The authors would like to be thank Bernard Sales, Emmanuel Desmet,
Hans De Neve, Fabrice Poppe, Stefan Ansorge, Katrien Skerra, Mathieu
Garnot, Jim Jones and Gert Grammel for their constructive comments,
suggestions and inputs.
11. Author's Addresses
Papadimitriou Dimitri
Alcatel - IPO NSG
Francis Wellesplein, 1
Internet Draft û Expires August 2001 36
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B-2018 Antwerpen, Belgium
Phone: +323 240-8491
Email: dimitri.papadimitriou@alcatel.be
Internet Draft û Expires August 2001 37
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Full Copyright Statement
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translate it into
Internet Draft û Expires August 2001 38