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Transcript of Multi-Protocol Lambda Switching: The Role of IP Technologies in Controlling and Managing Future...
Multi-Protocol Multi-Protocol Switching: Switching: The Role of IP Technologies in The Role of IP Technologies in
Controlling and Managing Controlling and Managing Future Optical NetworksFuture Optical Networks††
Dr. Vishal SharmaDr. Vishal [email protected]@ieee.org
†A version of this seminar appeared in the First On-line Symposium for
Electronics Engineers (OSEE), 9 January 2001
Copyright 2001 2
Organization of the TalkOrganization 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
Copyright 2001 3
Motivation for agile optical networksMotivation for agile optical networks
Reduce expense and complexity of network provisioning
Growth in fibers and s 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 4
Basic requirements for agile optical networksBasic requirements for agile optical networks
Topology/resource discovery
Distributed routing
Dissemination of network state information
Path selection
Traffic engineering based on resource/policy constraints.
Signaling
Connection establishment and path management
Survivability mechanisms
OXCs
1. Resource Discovery
2. Routing
3. Path Selection
4. Signaling
Copyright 2001 5
Advantages of dynamic optical networksAdvantages of dynamic optical networks
Flexible connectivity via timely virtual topology reconfiguration
Simplifies higher-layer routing
Allows wider range of services
Enables interworking of: DCSs, OXCs, DWDM gear, routers
Eases management & control
Router Network
Optical Transport Network
R1
R2
R3
R4
Optical light-paths
Initial virtual links between routers
Final virtual topology
Copyright 2001 6
Required components for agile optical networksRequired components for agile optical networks
Addressing/naming scheme
Routing protocols
Path computation and selection algorithms
Signaling protocols
Protection and restoration schemes
Copyright 2001 7
Drawbacks of the traditional “control plane”: a.k.a. network managementDrawbacks 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
Copyright 2001 8
So what are likely options for the control plane?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
Copyright 2001 9
Issues in modifying a network management systemIssues 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
NMSNMSSetup
Request
EMS
1
3
2
5
4
6
7
8
9
10
11
12
Copyright 2001 10
Issues in modifying a network management systemIssues in modifying a network management system
Channel recovery & associated signaling can be complex
NMS network topology and resilience is itself an issue
NMS subject to vagaries of device architectures
Agreement on stds. complex
NMSNMSSetup
Request
EMS
NMS
Original path
Recovery path
2. Failure Indication
3. Recovery path configuration
1. Failure
4. Switchover
Copyright 2001 11
Issues in having a distributed control planeIssues in having a distributed control plane
Allows easier end-point initiated channel setup
Standardization of signaling and routing is not subject to debate
Control plane protocols are being worked on in standards bodies (IETF, OIF, ITU)
Control Plane
Element in service control plane is in use
Control message traffic is limited
1
2 4 6
5
7
8
9
Signaling messages between elements
Signal to program switching element
3
12
Basic Concept of MPLS
Routing fills routing table.
Signaling fills label forwarding table.
DA Next hoprouter
N/wInt.
129.89.10.x 198.168.7.6 1
179.69.x.x 198.168.7.6 1
128.89.10.x
1
179.69.x.x
21
128.89.10.12
179.69.42.3
198.168.7.6
Inlabel
Outlabel
Address Prefix N/wInt.
Advertises binding<5, 128.89.10.x>
Advertises binding<7, 179.69.x.x>
128.89.10.x 5 1
179.69.x.x 7 2
Advertises bindings<3, 128.89.10.x> <4, 179.69.x.x>
128.89.10.x 3 1
179.69.x.x 4 1
3
4
X
X
DA Next hoprouter
N/wInt.
129.89.10.x 129.89.10.1 1
179.69.x.x 179.69.42.3 2
Routing Table
Inlabel
Outlabel
Address Prefix N/wInt. Label
ForwardingTable
R1 R2
R3
R4
Step 1
Step 2
Step 3
Step 4
Step 5
13
Basic Concept of MPLS
At ingress, unlabeled packets are prepended with label
At egress, labels are removed and packets are routed
128.89.10.x
1
179.69.x.x
21
128.89.10.12
179.69.42.3
198.168.7.6
Inlabel
Outlabel
Address Prefix N/wInt.
Inlabel
Outlabel
Address Prefix N/wInt.
128.89.10.x 5 1
179.69.x.x 7 2128.89.10.x 3 1
179.69.x.x 4 1
3
4
X
X
3
5
Packet arrives DA=128.89.10.25
3Push Label
5Pop label
Forward packet
553
Swap Label
R1 R2
R3
R4
Step 1
Step 2
Step 3
Step 4
Step 5
14
Elements of MPLSElements of MPLS Label Forwarding:
Use data link addressing. E.g. ATM VPI/VCI, FR DLCI
Put “shim” header between data link and IP header
Label Creation and Binding.
Label Assignment and Distribution:
Ride piggyback on routing protocols, where possible (BGP).
Use separate label distrn. protocol:RSVP-TE, LDP/CR-LDP
Variable
L2 header L3 IP header MPLS “shim” header
Higher Layers
4 bytes 20 bytes
Label CoS TTL S
20 bits 3 bits 8 bits
Data Plane
Control Plane
Copyright 2001 15
Motivation for MPLS control plane: Similarities between LSRs and OXCsMotivation for MPLS control plane: Similarities between LSRs and OXCs
Analogous data plane processing
De-couple control plane from data plane
Path is setup using control plane
Data is forwarded using data plane
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
Controller
Switching Matrix
LSR OXC
Copyright 2001 16
Motivation for MPLS control plane: Similarities between LSRs and OXCsMotivation for MPLS control plane: Similarities between LSRs and OXCs
Data plane relationships
Controller
Switching Matrix
1
2
1
2
<1, label > <2, label >
OXC: <in_port, in_channel> <out_port, out_channel>
LSR: <in_port, in_label> <out_port, out_label>
<1, > <2, >
Copyright 2001 17
Motivation for MPLS control plane: Similarities between LSPs and channelsMotivation for MPLS control plane: Similarities between LSPs and channels
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
IP Routers OXCs
LSPs Optical Channels
Induced virtual graph Induced virtual graph
Copyright 2001 18
Similarities between the MPLS and optical network control planesSimilarities 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
Copyright 2001 19
What adaptations does this reuse entail?Enhancements to signaling and routingWhat adaptations does this reuse entail?Enhancements to signaling and routing
Termination incapable
Fiber switch capable
Termination capable
SONET capable
Handle links with different capabilities
OXC
Router
OC-48
OC-48
Router
OC-48
OC-48
Fiber
2
Wavelength 1
1
OC-48 SONET frames
Wavelength switch capable Packet switch capable
SXC
OC-192SXC
OC-192
OC-192 SONET frame
OC-192 SONET frame
R1
R2
Copyright 2001 20
What adaptations does this reuse entail?Enhancements to signaling and routingWhat 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 21
What adaptations does this reuse entail?Enhancements to optical elementsWhat adaptations does this reuse entail?Enhancements to optical elements
Mechanism to exchange control information
Out-of-band
Via an optical supervisory channel (OSC)
In-band
Via overhead in “digital wrapper” or SONET overhead bytes
Via a separate IP network Via sub-carrier modulation (SCM) on the optical channel
Control Plane
OSC
Separate network
Digital wrapper or SONET overhead bytes
Copyright 2001 22
Implementation choices for the control channel: Out-of-band signalingImplementation choices for the control channel: Out-of-band signaling
Use a separate as an OSC
Possible when the wavelength count is large
Use physically separate control network
O-EMPLS
signalingControl wavelength
Data wavelengths
Wavelength switchingIncoming
fiber
Outgoing fiber
E-O
Copyright 2001 23
Implementation choices for the control channel: In-band signalingImplementation choices for the control channel: In-band signaling
Use overhead in “digital wrapper” or SONET frame
Assumes all O-E-O devices
Use sub-carrier modulation
Gives control channel with Mb/s of bandwidth
Reserve part of bandwidth of a for MPLS signaling
Useful when count is small
Assumes O-E-O at node Outgoing fiber
Control wavelength
Incoming fiber
O-E E-O
MPLS signaling
Label Processing
Control Packets
MPLS signaling
SubcarrierExtraction
SubcarrierInsertion
Copyright 2001 24
Architectural considerations in deployment: Overlay modelArchitectural considerations in deployment: Overlay model
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
IP Router Network
Optical Transport Network
Overlay Model
Copyright 2001 25
Architectural considerations in deployment: Peer modelArchitectural 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 TransportNetwork
Peer Model
Copyright 2001 26
Advantages of a uniform control infrastructureAdvantages 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 27
Some control plane issues currently under developmentSome 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,, 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
Copyright 2001 28
Some control plane issues currently under developmentSome 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 29
Unresolved issues in control plane developmentUnresolved 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 could trigger alarms from all downstream OXCs.
Copyright 2001 30
SummarySummary
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.