This is an early short tutorial from back in 2001 that focuses on the control of dynamic (or agile) optical networks. We begin by highlighting the motivation for such networks, their basic requirements, and the advantages of agility. We examine the functionality needed for routing and connection establishment in such dynamic networks, and compare possible candidates for the design of such a...

1. Multi-Protocol λ Switching:
The Role of IP Technologies in
Controlling and Managing
Future Optical Networks†
Dr. Vishal Sharma
†A version of this seminar appeared in the First On-line Symposium for
Electronics Engineers (OSEE), 9 January 2001 v.sharma@ieee.org

2. Organization of the Talk
 Agile (or dynamic) optical networks
 Motivation
 Analysis of basic requirements for agility
 Advantages of having dynamic optical networks
 Control Plane
 Possible candidates for the control plane
 Motivation for adopting/re-using an MPLS-based control plane
 What enhancements does this reuse/integration entail?
 Implementation choices for the control plane
 Architectural considerations in deployment
 Some open issues: path characterization, link management,
survivability
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3. Motivation for agile optical networks
 Reduce expense and complexity of network provisioning
 Growth in fibers and λs complicates path provisioning
 Shift from manual configuration to automatic signaled setup
 Increase responsiveness of optical transport network (OTN)
 Reduce provisioning time: weeks/months to hrs/minutes or less
 Facilitate deployment of new services that require quick setup
 Limit electronic termination and processing
 Today, higher aggregate link speeds (esp. with WDM), but limited
electronic processing
⇒ switch and route at optical channel level (not on a per-packet level)
Copyright 2001 3

4. Basic requirements for agile optical
networks
 Topology/resource discovery
 Distributed routing
 Dissemination of network state
3. Path Selection
information
 Path selection 1. Resource 2. Routing
Discovery
 Traffic engineering based on
resource/policy constraints.
 Signaling 4. Signaling
 Connection establishment and
path management
OXCs
 Survivability mechanisms
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5. Advantages of dynamic optical networks
 Flexible connectivity via timely Initial virtual
links between Router Network
R2
virtual topology reconfiguration routers
 Simplifies higher-layer routing
 Allows wider range of services Optical light-paths
R1
R4
Final virtual
topology
 Enables interworking of: DCSs,
Optical Transport R3
OXCs, DWDM gear, routers Network
 Eases management & control
Copyright 2001 5

6. Required components for agile optical
networks
 Addressing/naming scheme
 Routing protocols
 Path computation and selection algorithms
 Signaling protocols
 Protection and restoration schemes
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7. Drawbacks of the traditional “control
plane”: a.k.a. network management
 Slow convergence following failure
 Except for pre-provisioned, dedicated protection channels
 No instantaneous service provisioning
 Complicates interworking of equipment from different
manufacturers
 Incompatible EMSs cause integration problems
 Complicates inter-network provisioning
 Lack of EDI between operator NMSs causes significant
operator intervention
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8. So what are likely options for the control
plane?
 Devise new routing and signaling protocols for the
optical layer
⇒ Increased operation and maintenance cost
⇒ Significant interoperability concerns
⇒ Need careful coordination with higher layer restoration
mechanisms
 Modify network management to make it “dynamic”
 Adapt existing protocols from data networks. For
example, protocols from IP-based networks
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9. Issues in modifying a network
management system
 Lacks hop-by-hop signaling
 Multiple messages between NMS and network elements
 No common NMS for multi-vendor equipment
Setup 6
Request NMS NMS
1 4
7 11
2
9
EMS
3 5 8 10 12
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10. Issues in modifying a network
management system
 NMS network topology and resilience is itself an issue
 NMS subject to vagaries of device architectures
⇒ Agreement on stds. complex
 Channel recovery & associated signaling can be complex
2. Failure Indication
NMS
Setup 3. Recovery path
Request NMS
configuration NMS
1. Failure
Original path
EMS
4. Switchover
Recovery path
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11. Issues in having a distributed control
plane
 Allows easier end-point  Standardization of signaling
initiated channel setup and routing is not subject to
debate
 Element in service ⇒ control
⇒ Control plane protocols are
plane is in use
being worked on in
 Control message traffic is standards bodies (IETF, OIF,
limited ITU)
Signal to program
switching element
Control Plane
Signaling messages
between elements
2 3 4 6 7
1 9
5 8
Copyright 2001 11

12. Basic Concept of MPLS
Step 1
DA Next hop N/w DA Next hop N/w
router Int. router Int.
129.89.10.x 198.168.7.6 1 129.89.10.x 129.89.10.1 1 Routing Table
179.69.x.x 198.168.7.6 1 179.69.x.x 179.69.42.3 2
128.89.10.x
In Out Address Prefix N/w In Out Address Prefix N/w
label Step 3 label Label 128.89.10.1
label Int. label Int.
X 5 1 Forwarding 2
3 128.89.10.x 1 3 128.89.10.x
Table
X 4 179.69.x.x 1 4 7 179.69.x.x 2 R3
Step 5 Advertises binding
1 <5, 128.89.10.x>
R1 1 R2 Step 2
2
198.168.7.6
Step 4 Advertises bindings Advertises binding
<3, 128.89.10.x> <7, 179.69.x.x>
<4, 179.69.x.x>
179.69.x.x
 Routing fills routing table. R4
179.69.42.3
 Signaling fills label forwarding table.
12

13. Basic Concept of MPLS
Step 5
Step 4 Pop
label 5
In Out Address Prefix N/w In Out Address Prefix N/w Forward
label label Int. label label Int. packet
X 3 1 3 5
5 128.89.10.x 1 5
128.89.10.x 3 128.89.10.x
X 4 179.69.x.x 1 4 7 179.69.x.x 2 128.89.10.1
2
Step 3 R3
Swap
Label 5
3
1
R1 1 R2
Step 2 2
3 198.168.7.6
Push
Label
Packet arrives
DA=128.89.10.25 Step 1
179.69.x.x
At ingress, unlabeled packets are prepended with label R4
At egress, labels are removed and packets are routed 179.69.42.3
13

14. Elements of MPLS
 Label Forwarding:
 Use data link addressing. E.g. ATM VPI/VCI, FR DLCI
Data  Put “shim” header between data link and IP header
Variable 4 bytes 20 bytes
Plane
MPLS “shim” Higher Layers
L2 header L3 IP header
header
Label CoS S TTL
20 bits 3 bits 8 bits
 Label Creation and Binding.
Control
Plane  Label Assignment and Distribution:
 Ride piggyback on routing protocols, where possible
(BGP).
 Use separate label distrn. protocol:RSVP-TE, LDP/CR-LDP
14

15. Motivation for MPLS control plane:
Similarities between LSRs and OXCs
LSR OXC
Controller
Switching
Matrix
 De-couple control plane from data plane
 Path is setup using control plane
 Data is forwarded using data plane
 Analogous data plane processing
 LSR uses label swapping to transfer labeled pkt. from I/P to O/P
 OXC uses switching matrix to connect channel from I/P to O/P
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16. Motivation for MPLS control plane:
Similarities between LSRs and OXCs
Controller
1 1
2 2
Switching
Matrix
<1, label > → <2, label > <1, λ > → <2, λ >
 Data plane relationships
 LSR: <in_port, in_label> → <out_port, out_label>
 OXC: <in_port, in_channel> → <out_port, out_channel>
Copyright 2001 16

17. Motivation for MPLS control plane:
Similarities between LSPs and channels
LSPs Optical Channels
IP Routers OXCs
Induced virtual graph Induced virtual graph
 Point-to-point, virtual path connection abstractions
 Induce a virtual graph on the underlying topology
 Payload is transparent to intermediate nodes
 Constraint-based routing (CBR) used to select paths
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18. Similarities between the MPLS and optical
network control planes
 The two control planes have nearly identical functions:
 Addressing
 Resource discovery
 Routing
 Signaling/connection management
⇒ Constructs from MPLS-TE can be adapted for OXCs
 Local adaptation can be used to tailor the control plane to
specific OXC implementations with different hardware
capabilities
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19. What adaptations does this reuse entail?
Enhancements to signaling and routing
 Handle links with different capabilities
 Termination incapable  Termination capable
 Fiber switch capable  SONET capable
 Wavelength switch capable  Packet switch capable
OC-48
Router SONET frames λ2 Router
R1
R2
OC-48 λ1
OC-48
Wavelength λ 1
OC-192
OC-48 OC-192
SXC SXC OC-48
OXC
OC-192 SONET Fiber OC-192 SONET
frame frame
Copyright 2001 19

20. What adaptations does this reuse entail?
Enhancements to signaling and routing
 Bind the control and data (bearer) channels
 Activate/deactivate bearer channels
 Assign bearer channels to optical paths
 De-multiplex control traffic for different bearer channels
 Handle links with disparate bandwidth granularities
 Fiber, wavelength, and SONET channels
 Have routing protocol distribute info. on available b/w
resources
 Enhance routing to carry info. about physical fiber plant
diversity
Copyright 2001 20

21. What adaptations does this reuse entail?
Enhancements to optical elements
 Mechanism to exchange control information
Out-of-band In-band
 Via an optical supervisory  Via overhead in “digital wrapper”
channel (OSC) or SONET overhead bytes
 Via a separate IP network  Via sub-carrier modulation (SCM)
on the optical channel
Control Plane
Separate
network
OSC
Digital wrapper or SONET
overhead bytes
Copyright 2001 21

22. Implementation choices for the control
channel: Out-of-band signaling
 Use a separate λ as an OSC
 Possible when the wavelength count is large
MPLS
O-E E-O
Control signaling
wavelength
Wavelength
switching Outgoing
Incoming
fiber fiber
Data
wavelengths
 Use physically separate control network
Copyright 2001 22

23. Implementation choices for the control
channel: In-band signaling
Control MPLS
 Reserve part of bandwidth of a Packets signaling
O-E
λ for MPLS signaling Label
E-O
Control Processing
 Useful when λ count is small wavelength
 Assumes O-E-O at node Incoming Outgoing
fiber fiber
 Use sub-carrier modulation Subcarrier Subcarrier
Extraction MPLS Insertion
 Gives control channel with Mb/ signaling
s of bandwidth
 Use overhead in “digital
wrapper” or SONET frame
 Assumes all O-E-O devices
Copyright 2001 23

24. Architectural considerations in
deployment: Overlay model
IP Router Network
 Use different instances of the
control plane in the OTN and
IP domains
 IP domain a client of optical
domain
 OTN provides p2p optical
channels between IP network
elements
 Gives maximal control isolation
Optical Transport
Network
Overlay Model
Copyright 2001 24

25. Architectural considerations in
deployment: Peer model
 Use single instance of control plane in optical and IP domain
 Both domains run common signaling and routing protocol stacks
 IP reachability info. is passed around within optical domain
IP Router Network
Optical Transport
Network
Copyright 2001
Peer Model 25

26. Advantages of a uniform control
infrastructure
 Provides a framework for:
 Optical bandwidth management
 Real-time optical channel provisioning
 Allows uniform semantics for network management and
operational control in both transport and data networks
 Enables inter-working of network elements from different
vendors
 Simplifies inter-network provisioning
Copyright 2001 26

27. Some control plane issues currently under
development
 Setting up of symmetric, bi-directional channels (e.g.
SONET or GbE)
 Current signaling does not allow a bi-directional path to be setup
in a single reservation round.
 Optical path descriptor
 Describes the characteristics of the channel (a fiber,λ, or SONET
channel) to be established
 Useful to verify that all links along the the path can support the
descriptor (compatibility check)
 E.g. OC-48 channel reservation wishing to cross an OC-192 link will
be successful if the link supports OC-48 multiplexing
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28. Some control plane issues currently under
development
 Need protocols for link provisioning and fault isolation
 Discovery of OXC adjacency and port interconnections
 Negotiation of acceptable label ranges btwn. neighbors
 Setting up of port map tables (consulted during setting up
and tearing down channels)
Copyright 2001 28

29. Unresolved issues in control plane
development
 Need to extend protocols for high-reliability
 Require diverse routing, associated path computation algorithms
 Fault detection/isolation is an issue, esp. in pure OXCs
 Need characteristics and performance of paths for
dynamic bandwidth provisioning
 Digital overhead bits do not give channel performance data
∴ Identifying causes of degradation is difficult
 Setting appropriate threshold values for alarms is difficult
 Alarm correlation is imp. For e.g., a failed λ could trigger alarms
from all downstream OXCs.
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30. Summary
 Explored the need for agile optical networks.
 Examined components needed for agility.
 Analyzed drawbacks of existing network management
systems for providing dynamic control.
 Motivated choice of MPLS control plane as possible candidate
for adoption in optical networks.
 Examined optics-specific enhancements needed in MPLS
control plane, and control enhancements needed in optical
network elements.
 Discussed implementation choices and architectural
considerations
 Overviewed some open and unresolved issues.
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