Transcript Generalized Multiprotocol Label Switching: An Overview of

Generalized Multiprotocol Label
Switching: An Overview of Signaling
Enhancements and Recovery Techniques
IEEE Communications Magazine
July 2001
Outline
Introduction
Enhancements to Signaling
GMPLS Protection & Restoration
Techniques
Conclusions
Introduction (1/3)
MPLS is based on
Separation of forwarding information (label) from the
content of the IP header
Use of a single forwarding paradigm at data plane to
support multiple routing paradigms at control plane
Use of different technologies and link layer mechanisms
to realize label swapping forwarding paradigm
Flexibility in the formation of forwarding equivalence
classes (FECs)
The concept of a forwarding hierarchy via label stacking
Introduction (2/3)
Recent work: extend MPLS control plane,
specifically MPLS constraint-based routing, from
routers/ATM switches to optical crossconnects
Using MPLS as the foundation for connection
establishment and a common control plane
Simplify network operations and management
Provide a wide range of deployment scenarios, ranging
from overlay to peer
Reuse and extend existing routing and signaling
protocols thus minimizing risks and reducing time to
market for advanced optical switching equipment
Introduction (3/3)
GMPLS: extensions to MPLS
Enhancements to RSVP-TE and CR-LDP signaling
protocols for optical transport networks
Enhancements to OSPF and IS-IS IGPs to advertise
availability of optical resources in the network
A new link management protocol for optical networks
Ability to establish bidirectional connections in a single
request
Ability of fault isolation, fault localization, fault
notification and fault mitigation
Enhancements to Signaling
Enhancements to the label distribution
protocols, RSVP-TE and CR-LDP
Hierarchical LSP Setup
The Suggested Label
Bidirectional LSP Setup
Notify Messages
Hierarchical LSP Setup (1/2)
Hierarchical LSP Setup (2/2)
The Suggested Label
GMPLS allows a label to be suggested by an
upstream node
Valuable when set up a bidirectional LSP using paired
Tx and Rx interfaces to the same physical port
Useful in optical subnetworks with limited wavelength
conversion capability
Permit an upstream node along a service path to start
hardware configuration before the downstream node
communicates a label to it
Downstream node may reject the suggested label and
pass a different label upstream, the upstream node must
accept the label
Bidirectional LSP Setup
LSPs in basic MPLS architecture are
unidirectional, a bidirectional LSP uses two
unidirectional LSP in opposite directions
Increased setup latency for LSP establishment
Twice the control overhead
Complicated route selection
Difficult to provide a clean interface for SONET
equipment which may rely on bidirectional hop-by-hop
paths for protection switching
Use of a single set of Path/Request and Resv/
Mapping messages to establish bidirectional LSPs
Notify Messages
A node passing transit connections should be able
to notify the node responsible for restoring the
connections when failures occur
The Notify message has been added to RSVP-TE
for GMPLS to provide a mechanism for informing
nonadjacent nodes of LSP-related failures
Application: to notify when the control plane of a
link fails but the data plane (LSP) is still functional,
such link is referred to as degraded link
GMPLS Protection and
Restoration Techniques
Features
Protection
Restoration
Require preallocated Rely on dynamic
resources, react to
resource establishment,
longer restore time
Technique failures rapidly
Path
Switching
Path Protection
Path Restoration
Line
Switching
Span Protection
Line Restoration
Protection Mechanisms (1/3)
Nomenclature
1+1 protection: payload data transmitted over two
disjoint path and a selector at receiving node
M:N protection: M preallocated backup paths shared
between N primary paths
1:N protection
1:1 pretection
Mechanisms
Span Protection
Path Protection
Protection Mechanisms (2/3)
Protection Mechanisms (3/3)
Restoration Mechanisms (1/2)
Line restoration
A new path is selected at an intermediate node
Beneficial for connections spanning multiple hops
and/or large distances
May break TE requirements
Path restoration
The new path is selected at the source node
Alternate routes may be precomputed by the head-end
of the connection and cached for future use
May reuse nodes in the original path
Restoration Mechanisms (2/2)
Conclusions
GMPLS will constitute an integral part of nextgeneration data and optical networks.
The functionality delivered by GMPLS allows
network operators to scale their network well
beyond current limitations.
The signaling capabilities of GMPLS will allow
service providers to quickly build out highcapacity agile infrastructures.
Flexible M:N protection and restoration
capabilities of GMPLS allow efficient addressing
of network survivability.