Overview
Generalized Multiprotocol Label
Switching(GMPLS)
„ Forms
of MPLS
MPLS?
„ Why MPλS ?
„ Why GMPLS?
„ Conclusion
„ Why
Jikai Li
Forms of MPLS
Why MPLS?
(From the IETF perspective)
„ MPLS -- MultiProtocol Label Switching
„ IP
•
The base technology (packet oriented)
MPλS -- MultiProtocol Lambda Switching
„
•
MPLS control of lightpaths / optical trails
GMPLS -- Generalized MPLS
„
•
MPLS control of
Packets, Circuits, Lambdas and Ports
Traffic Engineering
– Constraint-based Routing, explicit
routing
„ Virtual
Private Networks
– Controllable tunneling mechanism
„ Elimination
of redundant control
„ Ultra fast forwarding (once)
1
What is “Label Switching”?
One of the many ways of getting from A to B:
• BROADCAST: Go everywhere, stop when you get to B,
never ask for directions.
• HOP BY HOP ROUTING: Continually ask who’s closer to
B go there, repeat … stop when you get to B.
Label Switching
• Have a friend go to B ahead of you using one of the
previous two techniques. At every road they
reserve a lane just for you. At ever intersection they
post a big sign that says for a given lane which way
to turn and what new lane to take.
LANE#1 TURN RIGHT USE LANE#2
LANE#1
“Going to B? You’d better go to X, its on the way”.
• SOURCE ROUTING: Ask for a list (that you carry with
you) of places to go that eventually lead you to B.
LANE#2
“Going to B? Go straight 5 blocks, take the next left, 6 more
blocks and take a right at the lights”.
A label by any other name ...
SO WHAT IS MPLS ?
There are many examples of label substitution
protocols already in existence.
„
• ATM - label is called VPI/VCI and travels with cell.
•
Frame Relay - label is called a DLCI and travels with
frame.
•
TDM - label is called a timeslot its implied, like a
lane.
„
„
„
Separation of forwarding
information(label)from the content of the IP
header
Use of single forwarding paradigm(label
swapping) at the data plane to support
multiple routing paradigm at the control plane
Use of different technologies and link layer
mechanisms to realize label swapping
The concept of a forwarding hierarchy via
label stacking
2
MPLS: HOW DOES IT WORK
ROUTE AT EDGE, SWITCH IN CORE
TIME
UDP-Hello
UDP-Hello
IP
IP
#L1
IP
#L2
IP
#L3
TCP-open
IP
Initialization(s)
IP
IP Forwarding
LABEL SWITCHING
IP Forwarding
Label request
#L2
Label mapping
MPLS Terminology
BEST OF BOTH WORLDS
HYBRID
„ LDP: Label Distribution Protocol
„ LSP: Label Switched Path
IP
MPLS
+IP
ATM
•MPLS + IP form a middle ground that combines the best of
IP and the best of circuit switching technologies.
•ATM and Frame Relay cannot easily come to the middle
so IP has!!
„ FEC: Forwarding Equivalence Class
„ LSR: Label Switching Router
„ LER: Label Edge Router (Useful term not in
standards)
3
IP FORWARDING USED BY HOP-BYHOP CONTROL
D est
4 7 .1
4 7 .2
4 7 .3
D est
4 7 .1
4 7 .2
4 7 .3
3
O ut
1
2
3
D est
4 7 .1
4 7 .2
4 7 .3
O ut
1
2
3
MPLS Label Distribution
Out
1
2
3
1
IP 47.1.1.1
2
Intf
In
3
Intf Label Dest Intf Label
In In
Out Out
3
0.50 47.1 1
0.40
1 47.1
Label Dest Intf
In
Out
0.40 47.1 1
IP 47.1.1.1
2
Intf Dest Intf Label
In
Out Out
3
47.1 1
0.50
IP 47.1.1.1
1
47.2
47.3 3
ues
Req
1
47.3 3
2
2
IP 47.1.1.1
Request: 47.1
3
.1
t: 47
.50
g: 0
ppin
Ma
1
47.1
3
2
1
Mapping: 0.40
2
47.2
EXPLICITLY ROUTED OR ER-LSP
Route=
{A,B,C}
Label Switched Path (LSP)
#14
#216
Intf Label Dest Intf Label
In In
Out Out
3
0.50 47.1 1
0.40
Intf Dest Intf Label
In
Out Out
3
47.1 1
0.50
A
#14
C
#972
3
1
47.3 3
Label Dest Intf
In
Out
0.40 47.1 1
IP 47.1.1.1
1 47.1
3
1
Intf
In
3
#972
B
2
#462
2
47.2
2
IP 47.1.1.1
- ER-LSP follows route that source chooses. In
other words, the control message to establish
the LSP (label request) is source routed.
4
EXPLICITLY ROUTED LSP ER-LSP
ER LSP - advantages
Intf Label Dest Intf Label
In In
Out Out
3
0.50 47.1 1
0.40
In tf
In
3
3
D est
In tf
O ut
2
1
4 7 . 1 .1
4 7 .1
Label
O ut
1 .3 3
0 .5 0
Intf
In
3
Label Dest Intf
In
Out
0.40 47.1 1
3
• Can use routes other than shortest path
3
1
1
• Operator has routing flexibility (policy-based, QoSbased)
IP 47.1.1.1
1 47.1
2
• Can compute routes based on constraints in exactly
the same manner as ATM based on
distributed topology database.
(traffic engineering)
2
47.3 3
47.2
2
IP 47.1.1.1
Label Encapsulation
ER LSP - discord!
L2
• Two signaling options proposed in the standards:
CR-LDP, RSVP extensions:
— CR-LDP = LDP + Explicit Route
— RSVP ext = Traditional RSVP + Explicit Route +
Scalability Extensions
• Not going to be resolved any time soon, market will
probably have to resolve it.
• Survival of the fittest not such a bad thing.
ATM
FR
Label VPI VCI
DLCI
Ethernet
PPP
“Shim Label”
“Shim Label” …….
IP | PAYLOAD
MPLS Encapsulation is specified over various media
types. Top labels may use existing format, lower
label(s) use a new “shim” label format.
5
Explicit Routing - MPLS vs. Traditional Routing
MPLS Link Layers
• MPLS is intended to run over multiple link layers
• Specifications for the following link layers currently exist:
•
ATM: label contained in VCI/VPI field of ATM header
•
Frame Relay: label contained in DLCI field in FR header
•
LAN: uses ‘shim’ header inserted between L2 and L3
headers
Translation between link layers types must be supported
Comparison - Hop-by-Hop vs. Explicit
Routing
ƒ Hop-by-Hop Routing
•
Distributes routing of control
traffic
•
Builds a set of trees either
fragment by fragment like a
random fill, or backwards, or
forwards in organized manner.
•
Explicit Routing
Source routing of control traffic
•
Builds a path from source to dest
•
Requires manual provisioning, or
automated creation mechanisms.
•
LSPs can be ranked so some
reroute very quickly and/or backup
paths may be pre-provisioned for
rapid restoration
„
•
Reroute on failure impacted by
convergence time of routing
protocol
•
Existing routing protocols are
destination prefix based
•
Operator has routing flexibility
(policy-based, QoS-based,
•
Difficult to perform traffic
engineering, QoS-based routing
•
Adapts well to traffic engineering
• Connectionless nature of IP implies that routing is based on
information in each packet header
• Source routing is possible, but path must be contained in each IP
header
• Lengthy paths increase size of IP header, make it variable size,
increase overhead
• Some gigabit routers require ‘slow path’ option-based routing of IP
packets
• Source routing has not been widely adopted in IP and is seen as
impractical
• Some network operators may filter source routed packets for
security reasons
• MPLS’s enables the use of source routing by its connectionoriented capabilities
- paths can be explicitly set up through the network
- the ‘label’ can now represent the explicitly routed path
• Loose and strict source routing can be supported
Various LDP(label distribution protocol)
„ CR-LDP(Constrain-based
Routing Label
Distribution Protocol)
„ RSVP-TE(Resource reSerVation
Protocol-Traffic Engineering )
6
CR-LDP
Extended RSVP
•Extension of the LDP approach
•Extension of the classical
connectionless RSVP
•Hard State Protocol
•Path and Resv messages used
•UDP used for peer discovery
•TCP used for session, advertisement, notification, and LDP
messages
with
•Label_Request Object
•Aggregation of flows to
reduce state information in
routers
•Soft State Control and
scalability concerns
•Explicit_Route Object
•Label Object
•Supports Diffserv and Operator configurable QOS classes
•Failure reported using the reliable TCP
MPλS
„
MPL(ambda)S combines:
– recent MPLS TE control plane developments
– optical cross-connect (OXC) technology
„
„
The result is an OXC control plane for realtime provisioning of optical channels
MPL(ambda)S extends MPLS TE base
functions and adds some new functionality
Why MPλS ?
„ To
cost effectively scale SP bandwidth
requirements for existing services
– need to be able to control optical
backbones as flexibly and dynamically as
we do IP backbones today
„ To
create new services
– e.g. lightpath
7
Why GMPLS?
„
Evolution of Networking
MPλS is a subset of GMPLS
– GMPLS is the name used in the IETF drafts
– GMPLS defined based on older MPλS drafts
„
Defines the extension of MPLS to cover:
– TDM switching
– Lambda switching
– Port switching
„
Reuses Tunnel LSP and Traffic Engineering
mechanisms
Modification and Additions required by
GMPLS
„
„
„
„
A new link management(LMP) for phontonic
switches
Enhancement to Open Shortest Path
First/Intermediate System to Intermediate
System (OSPF/IS-IS)
Enhancement to RSVP/CR-LDP for traffic
engineering purpose
Scalability enhancement such as hierarchical
LSP formation, link bundling, and
unnumbered links
„
„
„
„
IP: Carrying applications and services
ATM: Traffic Engineering
SONET/SDH: Transport
DWDM: Capacity
Link Management Protocol
„
Control channel management
– Establish and maintain connectivity between
adjacent nodes
„
Link connectivity verification
– Verify the physical connectivity of the component
links
„
Link property correlation
„
Fault isolation
– Links Ids, protection mechanisms and priorities
– Isolate link and channel failures in both opaque
and transparent networks, independent of the data
format
8
GMPLS: Signaling Extensions
IETF draft provides:
„ Generalized Label Request
– SONET/SDH specific version
„
Generalized Label
– For SONET, SDH, Ports, Wavelengths, Wavebands
„
and Generic Labels
Suggested Label
„
Label Set
– for optimization of certain switch types
„
„
„
FSC: fiber-switch-capable
LSC: lambada-switch-capable
PSC: packet-switchin-capable
GMPLS: Signaling Extensions (continued)
„
„
„
„
„
– to give upstream node(s) control over chosen labels
GMPLS: Routing Extensions
Adds New MPLS Functions:
„
– driven by lambda and generalized switching
„
requirements
Bi-directional LSP/Lightpath establishment
Generalized Notification mechanism
Explicit Label Control
(part of explicit route)
Defined for both IS-IS and OSPF
Provides:
–
–
–
–
–
Switching capabilities of links
Link encoding (SONET/SDH, Clear, GigE .)
Maximum reservable bandwidth per priority
Grouping of links that share same fate (SRLG)
Protection capabilities of link
9
„
„
Optical Network
Optical Network Objectives
A mesh of optical
transmission and
switching equipment
Providing dynamic
point-to-point
connections
„
– e.g. SDH/SONET,
Lambada
„
… to attached
internetworking devices
„
Real-time service provisioning
Easy / cheap operation and management
– uniform semantics for network management and operations
control in hybrid networks consisting of OXCs and label
switching routers (LSRs)
„
Better bandwidth utilization and survivability
„
Exploit lessons learnt from previous experiences
– from linear/ring towards meshed OXC topologies
– be pragmatic rather than re-inventing the wheel
– IP routers, SDH/SONET
add-drop muxes, and
ATM switches
Definitions
„
Optical channel:
„
Optical channel trail:
OXC Model
– an individual wavelength (lambda) on a fibre
– provides a point-to-point optical connection
between two access points
„
Optical cross-connect (OXC):
– device that connects optical channel trail from
input port to output port
10
Control Plane
„
„
Data Plane
Resource discovery
Topology state information dissemination
– Reliable broadcast/Flooding
„
„
Path Selection (constraint-based routing)
Optical channel connection management and
signaling
– Path placement
– Path maintenance
– Path revocation
Observation
„
LSRs and OXCs are isomorphic
–
–
–
–
„
conceptually similar input / output relations
labels are analogous to optical channels
similar LSR and OXC control plane requirements
LSPs and optical channel trails exhibit
commonality
Therefore, develop coherent control plane
technology that can be used for LSRs and
OXCs
– identify common elements and re-use where
appropriate
„
Switching matrix connects optical channel
trail from input port to output port
– <incoming interface, ingress Lambda> to
– <outgoing interface, egress Lambda>
LSP and Optical Trail Commonalities
„
„
Unidirectional point-to-point connections
Explicitly routed according to constraints
– bandwidth, priority, pre-emption, policy colour, reoptimisation
„
„
„
Payload is transparent to intermediate nodes
on path / trail
Survivability properties on a per LSP / optical
trail basis
Same label / lambda cannot be allocated
twice on an interface
11
LSR & OXC Commonalities
„
„
„
Data and Control planes
– both LSRs and OXCs de-couple data and control
planes
Data planes driven by a similar switching matrices:
– LSR:
– (iif, ingress label) to (oif, egress label)
– OXC:
– (iif, ingress λ) to (oif, egress λ)
Switching independent of switching unit payload
– LSR / OXC only switch based on incoming label /
lambda
Control Plane Paradigm
GMPLS
Instead:
„
adapt existing IGP extensions for MPLS traffic
engineering
„
adapt existing MPLS constraint-based routing
algorithms
adapt existing MPLS signaling protocol
– Add new TLVs (Link-type TLV, SRLG TLV, …
„
– e.g. RSVP-TE to instantiate optical channels
„
identify additional (optical) domain specific
requirements
Domain specific requirements
„ New
functionality has been added to
support (optical) domain specific
requirements:
– Control channel
– Link Management Protocol (LMP)
– Link bundling
– LSP nesting
12
Control Channel
Link Management Protocol
„ Used
„
to exchange MPLS control-plane
information between adjacent nodes
– i.e. signalling, routing, management
„ Need
not be same physical media as
data channel
– could be in-band (possibly separate
wavelength or fibre) or out-of-band
„ Still
„
„
„
under design …
Link Bundling
„
„
Adjacent nodes may be connected by several
hundreds of parallel physical links (i.e.
wavelengths)
Link bundling allows multiple parallel links
between nodes to be advertised as a single
link into the IGP
Improves routing scalability by reducing
amount of information handled by IGP ISIS/OSPF only see the bundle, not the
component links
With de-coupling of control plane and data
plane, control plane neighbours need not be
data plane neighbours
Link Management Protocol (LMP) runs
between adjacent nodes to verify connectivity
of bearer channels
Also establishes and maintains control
channel connectivity
LSP Nesting
„
Optical channel trails have discrete
bandwidth granularity in units of individual
wavelength capacity:
„
Nested LSPs enhance scalability and avoid
wasting bandwidth:
– e.g. OC-48, OC-192, OC-768
– allow many “low-bandwidth” LSPs to be mapped
to a single higher capacity optical channel trail
– lambda of container optical channel trail is
analogous to the outermost label
13
GMPLS
„
“Generalised” MPLS builds on the concepts of
MPL(ambda) to create a consistent control plane to
support multiple switching layers
– packet switching: forwarding based upon packet/cell headers
– time-division switching: forward data based upon the data’s
time-slot in a repeating cycle (e.g. SDH/SONET, PDH)
– wavelength (lambda) switching: forward data based upon the
wavelength on which it was received
– spatial switching: forward data based upon a position of the
data in real-world physical spaces (e.g. incoming port or
fibre)
Models
„
Overlay Model
– different instances of the control plane in the
optical transport network (OXC) and IP (LSR)
domains
– allows maximal isolation between optical and IP
domains
„
Peer Model
– single instance of control plane that spans LSRs
and OXCs
„
„
allows for bandwidth-on-demand networking
GMPLS supports both models giving SPs the
freedom to choose
GMPLS
„
„
Real-time provisioning of optical channels
Pragmatic
– exploit advances in MPLS TE control technology
– leverage operational experience with IP routing
Conclude
„
„
„
„
Simplify LSR / OXC network operation and
management
Trivialize control coordination problems
Support overlay AND peer model
Framework for the “Optical Internet”
14
Reference
„
„
„
„
„
„
MPL(ambda)S & Generalised MPLS: An Overview , John Evans
Generalized Multiprotocol Label Switching: An Overview of
Routing and Management Enhancements, Ayan Banerjee, et.al
Generalized Multiprotocol Label Switching: An Overview of
Signaling Enhancements and Recovery Techniques, Ayan Banerjee,
et.al
“Multiprotocol Label Switching, The future of IP Backbone
Technology”,Ravikumar Pragada&Girish Srinivasan
MPLS Tutorial, Peter Ashwood-Smith
and Bilel N. Jamoussi
MPLS and Traffic Engineering, Sunit Chauhan and Sunil Bakhru
15