Packet-Optical Integration using
Virtual Topologies
Wes Doonan
TERENA
May 2012
Packet-Optical Integration
• WAN has converged to two layers: Packet, Optical
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Packet Service Layer
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Optical Transport Layer
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IP Routers, MPLS LSRs
Provides various IP/MPLS services directly to clients
Provides IP/MPLS infrastructure to Cloud/CDN applications
Packet technology, Packet focus, Packet operational practice
WDM transport elements, ROADMs, regenerators, amplifiers
Provides point-to-point wavelength services to Packet layer
Enables optical bypass at router sites where needed
Optical technology, Optical focus, Optical operational practice
How to Integrate/Virtualize?
ORD
LAX
ATL
DIA
PHX
2
DFW
© 2012 ADVA Optical Networking. All rights reserved.
O-PCE
P-PCE
Traditional Layering Concept
Client layer network
Server layer network
= link
= server
connections
3
= element
Connections in Server layer network
create Links in Client layer network
= client connection
© 2012 ADVA Optical Networking. All rights reserved.
Virtual Network Topologies
• Abstract representation of a real network
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Built from virtual components – virtual links, virtual nodes
• Purpose: Abstraction
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Represent multiple real components as a single virtual component
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Example: represent domain A as single virtual node in domain B
• Purpose: Adaptation
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Represent server layer network capabilities in client layer network
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Example: expose a lambda connection as a link in a packet topology
• Purpose: Activation
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Coordination activation of capabilities across layers, domains
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Example: server layer connection activated during client layer signaling
• Virtual Topologies are generally planned
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VNTs created during application planning process
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Represent "potentialities" of the real network
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Prior to service provisioning, ongoing over lifetime of network
E.g. what real connectivity "can" be, when requested
© 2012 ADVA Optical Networking. All rights reserved.
Virtual Topology Concept
Client layer network
Planning
Server layer network
= link
= server
connections
= element
Connections in Client network trigger
Connection setup Server network
= client connection
= virtual link
5
© 2012 ADVA Optical Networking. All rights reserved.
Virtual Links
• Represent "potential" connectivity in a topology
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Entered into standard Traffic Engineering databases (TEDB)
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Server network resources not committed to virtual link
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Standardized TE extensions to regular IGP routing
Advertised into client TE routing, standard LSA formats/TLVs
Annotated with standard TE attributes (metric, bandwidth, etc)
Essentially indistinguishable from normal "real" TE links
E.g. bandwidth/wavelength not committed until link is used
Made available to path computers in the client network
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PCE computes paths using links in TEDB, real or virtual
• When link is used …
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E.g. when signaling in client network traverses a virtual link
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Server network control plane is activated
Server network connections provisioned to commit resources
If successful, signaling in client network allowed to proceed
• Virtual links coordinate information, activation across networks
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© 2012 ADVA Optical Networking. All rights reserved.
GMPLS Overlay
• GMPLS UNI/ENNI
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Interoperable service activation across layers and domains
• Precursor: RFC4208
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Defines the overlay network model, concepts
Outlines multiple scenarios, options, mechanisms
Initially issued in 2005, considerable experience since then
• Update: draft-beeram-ccamp-gmpls-uni-bcp
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Presents "best current practice" for utilizing RFC4208
Derived from specific experiences, lessons learned
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Multi-layer activation, use of virtual topologies
Label signaling across technologies
Coordinating administrative status
Routing updates to support virtual nodes
Handling of generic constraints
• Codifies recent/ongoing experience with Packet/Optical interop
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© 2012 ADVA Optical Networking. All rights reserved.
User #1
ORD
Planning
ATL
LAX
PHX
DFW
Packet
Optical
O-PCE
= Packet
8
= Optical
© 2012 ADVA Optical Networking. All rights reserved.
User #2
ORD
Planning
ATL
LAX
PHX
DFW
Packet
Optical
O-PCE
= Packet
9
= Optical
© 2012 ADVA Optical Networking. All rights reserved.
User #3
ORD
Planning
ATL
LAX
PHX
DFW
Packet
Optical
O-PCE
= Packet
10
= Optical
© 2012 ADVA Optical Networking. All rights reserved.
Link Activation
ORD
P-PCE
LAX
ATL
User #2
User #3
PHX
DFW
User #1
Packet
Optical
O-PCE
= Packet
11
= Optical
© 2012 ADVA Optical Networking. All rights reserved.
Benefit: Diversity Control
• Virtual Links can reflect diversity of server network
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Server network connections may share fate
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Multiple wavelengths which share the same fiber
Path computations in client network may require diversity
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Virtual links must expose fate sharing of server network connections
• Shared Risk Link Groups (SRLGs)
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Integer annotations to TE links, identifying fate-sharing groups
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Path computation considers annotations as constraints
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Sharing
SRLGs are per-layer/domain, must be coordinated
If paths are SRLG-diverse, guaranteed to not share fate
Client Layer
Server Layer
SRLG = <nil>
SRLG = <X>
SRLG = <X>
12
© 2012 ADVA Optical Networking. All rights reserved.
SDN and OpenFlow
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Software Defined/Driven Networking
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OpenFlow defines protcols for flow/switch management
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Separation of control plane and data plane
Direct, programmatic access to payloads and forwarding tables
Centralized view of network topology and state
Applied to flows in Layer-2 (Ethernet) and Layer-3 (IP)
Flow table entries match MAC addresses, IP addresses, ports, etc
Virtual switch administration, physical switch slicing
OpenFlow provides an SDN mechanism for L2/L3 networks
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How could an optical network integrate with this?
SDN App
User
LAX
= Packet
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= Optical
= OF Controller
© 2012 ADVA Optical Networking. All rights reserved.
Opportunities, Challenges
• Opportunity: Optical Integration and Interworking
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Integrate optical networks with existing L2/L3 networks
Cross domain boundaries, leverage the SDN ecosystem
• Opportunity: Packet Networks are Digital
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Full payload visibility at every switch
Switch fabrics are fully orthogonal
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Any packet on any interface switchable to any other interface
Every network path is physically feasible
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All that matters is connectivity
• Challenge: Optical Networks are Analog
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No payload visibility at switches
Switch fabrics are highly non-orthogonal
Not all paths are feasible
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Paths may exist topologically which are not optically feasible
Equalization, power budgeting, impairments; physics are messy
• Need a practical approach to interworking across domains
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© 2012 ADVA Optical Networking. All rights reserved.
Analog Parameters
 Transponders / Muxponders
 Acceptable Rx Power, ONSR
 Actual Tx Power, ONSR
Source
Firmware / Table
Firmware / Table
 Filters / Multiplexers
P i,3
P i,2
 Attenuation
Firmware / Table
L A,1
nf 2
 ROADMs
g2
 Attenuation
 Set Point
Provisioned
Provisioned
 Constant Gain Amplifiers
 Per-channel Gain
 Noise Factor
nf 1
g1
P i,1
Firmware / Table
Firmware / Table
L Mux,1
 Constant Power Amplifiers
 Per-channel Output Power
 Noise Factor
Firmware / Table
Firmware / Table
Tx1
Tx2
 Fiber Span
 Span Loss
Measured
Connecting optical “flows” across optical networks requires deep/intimate
knowledge of analog component characteristics
15
© 2012 ADVA Optical Networking. All rights reserved.
Potential Approach
• How can optical networks integrate with Packet SDN?
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Most SDNs primarily interested in L2/L3 problems
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Optics seen as point-to-point "wires" between L2/L3 domains
Optics are complex, messy, configuration-intensive, constrained
Optical domain often run by different group than L2/L3
• Network Domains
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A "domain" represents a single region of administration and control
Control domains have various attributes …
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Attachment points  Ports
Adaptation functions at attachment points  Action Sets
Connectivity between attachment points  Flows
Sound familiar?
• Virtual Switch
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A single L2 switch / L3 router is a (highly localized) domain
OpenFlow commonly assumes a controller-to-device ratio of 1:1
Instead, how about a controller-to-domain ratio of 1:1?
© 2012 ADVA Optical Networking. All rights reserved.
User #1
SDN App
ORD
User #1
PHX
DFW
Packet
Optical
O-PCE
= Packet
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= Optical
= OF Controller
© 2012 ADVA Optical Networking. All rights reserved.
User #2
SDN App
ORD
User #2
PHX
DFW
Packet
Optical
O-PCE
= Packet
18
= Optical
= OF Controller
© 2012 ADVA Optical Networking. All rights reserved.
User #3
SDN App
ORD
User #3
PHX
DFW
Packet
Optical
O-PCE
= Packet
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= Optical
= OF Controller
© 2012 ADVA Optical Networking. All rights reserved.
Observations
• Virtual Links
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Topology exposed to client defines server-layer utilization
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"Just enough topology" exposed to client, to serve applications
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Transparent coordination between layers/domains
Operator concentrates on packet layer, automates optical layer
Hide transport details where possible, expose where needed
Packet layer can exercise more direct control over optical layer
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Helps with diversity discovery, needs more configuration
• Virtual Switches
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Simplest possible abstraction; "one big switch"
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Encapsulates optical complexity
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Whole companies have been named after this concept 
Again, operator concentrates on packet service delivery rather than span
losses and OSNR and Raman tilt and, and, and …
Limited topological control
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When L2/L3 is the primary SDN focus, simplicity is good
• Result: choose the right tool for the specific problem at hand
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© 2012 ADVA Optical Networking. All rights reserved.
Summary
• Multi-layer, multi-domain networks are a Reality
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Packet + Optical network technologies are intermixed
• Multi-layer control mechanisms are also real
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Architectures defined, standards in place
• Virtual Network Topologies enable inter-layer coordination
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Existing methods and abstractions, extended across layers
Overlay networks manage inter-layer/domain interactions
© 2012 ADVA Optical Networking. All rights reserved.
Thank you
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