Upload
freya
View
49
Download
1
Tags:
Embed Size (px)
DESCRIPTION
IP over Optical Networks. Debanjan Saha Bala Rajagopalan {dsaha, braja}@tellium.com. BOF Objectives. Determine areas of priority for operators in IP-centric control of optical networks IP over optical network service architectures New services & applications - PowerPoint PPT Presentation
Citation preview
IP over Optical Networks
Debanjan Saha
Bala Rajagopalan
{dsaha, braja}@tellium.com
NANOG, 10/2000 2
BOF Objectives
Determine areas of priority for operators in IP-centric control of optical networks IP over optical network service architectures New services & applications
– Traffic engineering & network re-configuration– Others
NANOG, 10/2000 3
Summary
Motivation
IP over optical network model
IP-centric control plane for optical networks MPLS signaling for optical networks IP routing protocol extensions for optical
networks Optical internetworking
IP over optical networks Service models Traffic engineering
Discussion
NANOG, 10/2000 4
Benefits of Optical Networking
Build Networks for 2/3’s less Optical Meshes are 50% more efficient than TDM Rings Eliminate SONET/DCS Equipment Layer
Dynamic Lambdas Fast provisioning Automatic restoration
NANOG, 10/2000 5
Applications for Dynamic Lambdas
Reconfigure Network to changing traffics Add lambdas on demand between IP Routers “Tune” IP layer topology with changing traffic patterns Just in time lambdas
Dynamic Optical Virtual Private Network (OVPNs) Shared s for bandwidth efficiency
Automatic lightpath restoration Restore at Layer 1 instead of Layer 3 Simplify restoration from large scale failures
– e.g. 100s of lambdas
NANOG, 10/2000 6
Routers experience congestion Step 1 - Router requests additional to relieve congestion Step 2 - Optical Switches dynamically add between congested
routers
Traffic Demand Changes Step 3 - Optical Switches reconfigure
Dynamic Lambdas: Routers request Dynamic
Router Network
Router Network
Step 1 - Request Step 3 - Release
Step 2 - OXC Provides
Optical SubnetOptical Subnet
NANOG, 10/2000 7
Tune IP layer topology to changing traffics
IP Layer Traffic Patterns Change Step 1- Add new from A to B Step 2 - Delete from A to C
OpticalNetwork
Subnet B
Subnet C
Subnet A
Subnet B
Subnet C
OpticalNetwork
NANOG, 10/2000 8
IP over Optical: Network Model
Opticalsubnet
Opticalsubnet
OpticalSubnet
Router NetworkOptical Network
End-to-end path (LSP)
Optical Path
NNI
MPS for signaling and routingwithin the optical network
NNI
NANOG, 10/2000 9
IP-Centric Control of Optical Networks
Ingredients IP addressing for optical network nodes (and termination
points) MPLS-based signaling for lightpath provisioning IP routing protocols adapted for resource discovery Route computation with resource optimization Restoration signaling???
NANOG, 10/2000 10
What is the MPS approach?
Each OXC is considered the equivalent of an MPLS Label-Switching Router (LSR)
MPLS control plane is implemented in each OXC
Lightpaths are considered similar to MPLS Label-Switched Paths (LSPs)
Selection of s and OXC ports are considered similar to selection of labels
MPLS signaling protocols (e.g., RSVP-TE, CR-LDP) adapted for lightpath establishment
IGPs (e.g., OSPF, ISIS) with “optical” extensions used for topology and resource discovery
NANOG, 10/2000 11
Optical Network Functions
Dynamic provisioning of lightpaths Just-in-time provisioning Path selection with constraints
Protection & restoration of lightpaths Protection paths with appropriate service levels
– Node & link disjoint primary & protection paths for resiliency
– Shared protection paths for cost savings Fast restoration of lightpaths after the failure
NANOG, 10/2000 12
Protocols for Realizing Optical Network Functions
Provisioning protocols Automatic neighbor discovery
– Neighbor Discovery Protocol– Link Management Protocol
Topology discovery – OSPF with optical extension– IS-IS with optical extensions
Signaling for path establishment– RSVP-TE, CR-LDP with optical extensions– Generalized MPLS
Restoration Protocols Proprietary techniques
NANOG, 10/2000 13
Physical Topology
O3
O1
O5
O4
O2
Router Network
Router Network
Optical Network
Optical Network
NANOG, 10/2000 14
Topology Abstraction
O3
O1
O5
O4
O2
Router Network
Router Network
Optical Network
Optical Network
UNI
SRG #1
SRG #2 SRG #3
SRG #4 SRG #5
SRG #6
NDP
NDP
NDP NDP
NDP NDP
NDP
NDPUNI
NANOG, 10/2000 15
Neighbor Discovery
NDP allows adjacent OXCs to determine IP addresses of each other and port-level local connectivity information (i.e., port X in OXC O1 connected to port Y in OXC O2)
(IETF Status: Link Management Protocol (LMP) is being considered)
Port State Database of O1
TypeID RemotePort
Speed ResourceClass
RemoteNode
Status SROG
1
2
1024
1023
Drop
Network
Network
Network
Up
Up
SF
Up
OC-48
OC-48
OC-48
OC-192
F123, C231
F234, C251
F234, C231
F123, C231
9.2.1.3
8.4.1.3
11.3.1.3
129.2.1.3
10
123
345
15
Primary
Backup
Primary
Primary
NANOG, 10/2000 16
Topology Discovery with OSPF
O3
O1
O5
O4
O2
Router Network
Router Network
OSPFArea
0.0.0.3
UNI
UNIOSPFArea
0.0.0.2
OSPF Area 0.0.0.1
Summary LSA
Summary LSA
Router/Optical LSA
NANOG, 10/2000 17
OSPF Extensions
Recognition of optical link types
Link bundling Multiple, similar links between OXCs are abstracted
as a single link bundle Composition of link bundle described by parameters Single adjacency maintained between OXCs
regardless of the number of links Bundling considerations in preliminary stages in
IETF
NANOG, 10/2000 18
Example Scenario
SRLG S1
SRLG S2
O1 O2
5 OC-48, 2 OC-192,2 10G E/N
5 OC-48, 5 OC-192
NANOG, 10/2000 19
Desired Bundling Structure
5 OC-48, S1
2 OC-192, S1
2 10G E/N, S1
5 OC-48, S2
5 OC-192, S2
O1 O2
Sin
gle
bund
le b
etw
een
node
s
Resource sub-bundle# 1
Resource sub-bundle# 2
Resource sub-bundle# 3
Resource sub-bundle# 4
Resource sub-bundle# 5
NANOG, 10/2000 20
OSPF Extensions
New lightpath computation algorithms Path computation based on lightpath attributes and
constraints Proprietary algorithms for efficiency Algorithms not considered in IETF
Source-routing methodology Differs from traditional OSPF Considered in IETF as part of RSVP-TE/CR-LDP extensions
Reduction of link state propagation overhead Thresholds for reducing link state propagation overhead No framework yet in the IETF
NANOG, 10/2000 21
Link State Advertisements
LSA Type LSA IDAdvertising
NodeLSA content
Nodal LSA O1 AOS ID O1 All link bundles on O1Nodal LSA O2 AOS ID O2 All link bundles on O2Nodal LSA O3 AOS ID O3 All link bundles on O3Nodal LSA O4 AOS ID O4 All link bundles on O4Nodal LSA O5 AOS ID O5 All link bundles on O5Optical LSA O1-O2 O1 Link bundle composition between O1 and O2Optical LSA O2-O1 O2 Link bundle composition between O2 and O1Optical LSA O1-O5 O1 Link bundle composition between O1 and O5Optical LSA O5-O1 O5 Link bundle composition between O5 and O1Optical LSA O2-O5 O2 Link bundle composition between O2 and O5Optical LSA O5-O2 O5 Link bundle composition between O5 and O2Optical LSA O3-O4 O3 Link bundle composition between O3 and O4Optical LSA O4-O3 O4 Link bundle composition between O4 and O3Optical LSA O3-O5 O3 Link bundle composition between O3 and O5Optical LSA O5-O3 O5 Link bundle composition between O5 and O3Optical LSA O4-O5 O4 Link bundle composition between O4 and O5Optical LSA O5-O4 O5 Link bundle composition between O5 and O4Summary LSA Area 0002Summary LSA Area 0003
NANOG, 10/2000 22
Link State Database
O1 O2 O3 O4 O5Area
0.0.0.2Area
0.0.0.3Speed SRGs Class
O1
OC-48F123C245
Shared:2Open:5
OC-48 F234Shared:2Open:4
O2
OC-192F457C569
Open:2Shared:4
O3O4O5
Area 0.0.0.2Area 0.0.0.3
NANOG, 10/2000 23
Routing Across the NNI: BGPE-BGP is used between adjacent border OXCs in different sub-networks
I-BGP is used between border OXCs in the same sub-network
External addresses are passed between sub-networks, with indication of egress border OXC information
Routing policies may be applied, as per BGP features
Sub-network 1 Sub-network 2
E-BGP E-BGP
I-BGP
Sub-network 3
NANOG, 10/2000 24
Some Issues to Consider
What other information must be exchanged during neighbor discovery?
The practicality of obtaining SRG information
Resource metrics for OSPF
Distributed vs centralized path computation
Interdomain routing with resource constraints
NANOG, 10/2000 25
Multi-protocol Lambda Switching
Each OXC is considered the equivalent of an MPLS Label-Switching Router (LSR). An IP control channel must exist between neighboring OXCs
MPLS control plane is implemented in each OXC
The establishment of a lightpath from an ingress to an egress OXC requires the configuration of the cross-connect fabric in each OXC such that an input port is linked to an output port
MPS signaling allows an OXC to convey to the next OXC in the route the selected output port (“label”)
O3
O1
O5
O4
O2
Request (label)Response (P1)
Request (label)Response (P4)
NANOG, 10/2000 26
Generalized MPLSGMPLS is based on the premise that MPLS can be used as the control plane for different switching applications:
TDM where time slots are labels (e.g., SONET) FDM where frequencies (or s) are labels (e.g., WDM) Space-division multiplexing where ports are labels (e.g.,
OXCs) Generalized labels used in MPLS messaging:
Request Resv/Request Resv/Request
Allocate/Port=43Allocate/Port= 5Allocate/Port= 21
(OXC example)
Allocate/Fiber=43 = 9
Allocate/Fiber= 5 = 18
Allocate/Fiber= 21, = 8
(OXC with built-in WDM)
NANOG, 10/2000 27
Generalized Label
Used in place of traditional labels in MPLS signaling messages
May contain a Link ID in addition to the label value Link ID used when a single control channel is used
to control multiple data channels Label format depends on the link type. Presently
label formats have been defined for SONET/SDH, port, , waveband and generic
NANOG, 10/2000 28
GMPLS Actions
Generalized Label Request Indicates the type of label being requested
Generalized Label Response to label request. Format depends on the type of
label
Label Suggestion Sent along with label request, to aid in certain
optimizations
Label Set Sent along with label request. Constrains the allocation of
labels to those in the set to support OXCs without wavelength conversion capability
NANOG, 10/2000 29
Signaling Requirements: Bi-directional Lightpaths
Why not use two unidirectional paths?
Signaling twice is expensive SONET requires the forward and
backward paths to be on the same circuit pack
Who owns the label space? Avoid label assignment collision Resolve collision after in
happens
A B C D
E
F
L1
L2
NANOG, 10/2000 30
Signaling Requirements: Fault-Tolerance
Lightpaths must not be deleted due to failures in the control plane
Present RSVP/CR-LDP mechanisms associate the control path with data paths
– Failure in the control path is assumed to affect the data path
– Data path is therefore deleted or rerouted
In optical networks, the fabric cross-connects must remain if control path is affected
– Enhancements to RSVP/CR-LDP needed for this.
NANOG, 10/2000 31
Dynamic Provisioning Across the NNI
Lightpath request is routed inside source sub-network to border OXC (D) based on destination address and local routing scheme
D routes request to border OXC K in dest. sub-network (NNI signaling)
K routes request to destination, N based on destination address
Response routed along the reverse path
FE
A
B C
D
Req
Req
Req
Resp
Resp
Resp
K
L M
N
Req
Req
Req
Resp
Resp
Resp
NNI Path Request
NNI Path Resp
NANOG, 10/2000 32
Some Issues to Consider
Service definition and GMPLS semantics for different layer technologies
Optimization of optical layer signaling
NANOG, 10/2000 33
Restoration
Objectives Low restoration latency High restoration capacity efficiency by sharing capacity
among the backup paths High degree of robustness of the restoration protocols and
the related algorithms
Scope Fast and guaranteed restoration of lightpaths after “single
failure” events Best-effort restoration after multiple concurrent failures
NANOG, 10/2000 34
Supported Classes of Service
1+1 path protected Each primary path is protected by a dedicated
backup path No signaling is necessary during switching from the
primary path to the backup path
Mesh restorable Each primary path is protected by a shared backup
path Restoration signaling is necessary during switching
from the primary to the backup path
NANOG, 10/2000 35
Restoration Protocol Components
Primary and backup path setup Path computation from OSPF generated link state
database Path setup using RSVP-TE/CR-LDP signaling protocol May be done through the Wavelength Management
System (WMS)
Link-level restoration protocol Using SONET bit-oriented signaling at the link-level
Path-level restoration protocol Using SONET bit-oriented signaling at the end-to-end
path level
NANOG, 10/2000 36
Link-Level Restoration Overview
A lightpaths is locally restored by selecting an available pair of channels within the same link
If no channel is available then the end-to-end restoration is invoked
3 10 7 5 7
12
75 47
1 9
4
A
B C D
E
Drop port Drop port
14
Original Channel Pair
New Channel Pair
NANOG, 10/2000 37
End-to-End Restoration Overview
A shared backup path is “soft-setup” for each restorable primary path When local restoration fails, triggers are sent to the end-nodes End-to-end signaling over the backup path activates it and completes
end-to-end restoration
3 10 7 5 7
12
75 4
8 7 9 485
7
1 9
4
A
B C D
E
HGF
Drop port Drop port
14
Primary Path
Shared Backup
Path
Local Restoration
Failure
NANOG, 10/2000 38
Optical Control Plane: Restoration
Multi-domain restoration: Allow possibility of proprietary restoration in each sub-network Specify an overall end-to-end restoration scheme as backup. Signaling and routing for end-to-end restoration
NANOG, 10/2000 39
Issues to Consider
IP-based restoration protocol Protocol must satisfy time constraints Should a new “fast” protocol be developed?
Inter-domain restoration Is there a need for end-to-end restoration
across domains? Can this need be satisfied by domain-local
restoration plus re-provisioning as a fall-back?
Restoration time requirements
IP-Optical Internetworking
NANOG, 10/2000 41
IP over Optical Service Models: Domain Services Model
Optical network provides well-defined services (e.g., lightpath set-up)
IP-optical interface is defined by actions for service invocation
IP and optical domains operate independently; need not have any routing information exchange across the interface
Lightpaths may be treated as point-to-point links at the IP layer after set-up
Optical Cloud
Router Network Router Network
Service Invocation Interface Physical connectivity
NANOG, 10/2000 42
Optical Network Services
Discrete capacity, high-bandwidth connectivity (lightpaths)
Lightpath Creation, Deletion, Modification, Status Enquiry
Directory Services Determine client devices of interest
Supporting Mechanisms Neighbor discovery Service discovery
NANOG, 10/2000 43
UNI Abstract Messages
Lightpath Create Request - UNI-C UNI-N
Lightpath Create Response - UNI-N UNI-C
Lightpath Delete Request - UNI-C UNI-N
Lightpath Delete Response - UNI-N UNI-C
Lightpath Modify Request - UNI-C UNI-N
Lightpath Modify Response - UNI-N UNI-C
Lightpath Status Enquiry - UNI-C UNI-N
Lightpath Status Response - UNI-N UNI-C
Notification - UNI-N UNI-C
Concrete realization based on MPλS signaling constructs
NANOG, 10/2000 44
Signaling Example
Optical Network
Lightpath Create Request
UNI-C(Terminating)
Lightpath Create Response
UNI-C(Initiating)
UNI-C(Initiating)
UNI-C(Terminating)
1 2
34
Lightpath Create Request
Lightpath Create Response
NANOG, 10/2000 45
UNI Parameters
Identification-related
Service-related
Routing-related
Security-related
Administrative
Miscellaneous
NANOG, 10/2000 46
Service Models: Unified Service ModelNo distinction between UNI, NNI and router-router (MPLS) control plane
Services are not specifically defined at IP-optical interface, but folded into end-to-end MPLS services.
Routers may control end-to-end path using TE-extended routing protocols deployed in IP and optical networks.
Decision about lightpath set-up, end-point selection, etc similar in both models.
Optical Network
Router Network Router Network
NANOG, 10/2000 47
IP over Optical Services Evolution Scenario
First phase: Domain services model realized using appropriate MPλS signaling constructs
Optical Cloud(with or w/o internal
MPλS capability)
MPλS-based signaling forservice invocation, No routing exchange
Router Network Router Network
NANOG, 10/2000 48
Evolution Scenario
Second phase: Enhanced MPλS signaling constructs for greater path control outside of the optical network.
Abstracted routing information exchange between optical and IP domains.
MPλS-based signaling forservice invocation (enhanced). Abstracted
routing information exchange
Router Network Router Network
Optical Cloud(with internal MPλS
capability)
NANOG, 10/2000 49
Evolution Scenario
Third Phase: Peer organization with the full set of MPλS mechanisms.
MPλS-based signaling for end-to-end path set-up.MPλS-based signaling within IP and optical networks.
Full routing information exchange.
Router Network Router Network
Optical Cloud(with internal MPλS capability)
NANOG, 10/2000 50
Routing for Interworking: BGPClient network sites belong to a VPN. Client border devices and border OXCs run E-BGP. Routing in optical and client networks can be different
Address prefixes in each site (along with VPN id) are advertised by border devices to optical network.
Optical network passes these addresses to border devices in other sites of the same VPN (along with egress OXC address)
Network N1 Network N3
Network N2
R1 R2
R3
R6 R5
R4
x.y.a.*, x.y.b.*
x.y.c.*a.b.c.*
O1O2
O3
O4O5
NANOG, 10/2000 51
Issues to Consider
Which service model? Determines complexity of signaling at
the IP-optical interface
What are the service requirements on routing and signaling?
Traffic Engineering
NANOG, 10/2000 53
IP-over-Optical TE Example : Peer Model
Optical network links are OC-48 (2.5 Gbps) Sequence:
1. 100 Mbps LSP from R3 to R82. 300 Mbps LSP from R1 to R63. 200 Mbps LSP from R2 to R12
Optical Network
Router Network
Router Network
R5R4
R6
R9
R8R7
Router Network
R1R2
R3
O12O15
O14
O13Router Network
R10R11
R12
O10
O11
NANOG, 10/2000 54
TE Example Cont. To set up LSP1:
1. R3 computes path R3-R2-O12-R7-R82. R2 establishes an OC-48 FA to R73. LSP occupies 100 Mbps on the FA4. Links R2-O12, R7-O12 must be removed from database when FA R2-R7 is advertised.
FA, 2.5G
Optical Network
Router Network
Router Network
R5R4
R6
R9
R8R7
Router Network
R1R2
R3
O12O15
O14
O13Router Network
R10R11
R12
O10
O11
NANOG, 10/2000 55
TE Example Cont.
To set up LSP2 (R1-R6):1. Path: R1-R2-O11-O13-O14-R4-R62. R2 establishes an OC-48 FA to R43. LSP occupies 300 Mbps on the FA4. Link R2-OC11 removed from database
FA, 2.5G
Optical Network
R9
R8R7R1
R2
R3
O12O15
O14
O13R10R11
R12
R4R5
R6
O10
O11
NANOG, 10/2000 56
TE Example Cont.
R9
R8
R7R1 R2
R3
To set up LSP3 (R2-R12):1. Path: R2-R7-R9-O15-O14-O13-O10-R10-R122. R9 establishes an OC-48 FA to R103. LSP occupies 200 Mbps on the FA4. Link R9-O15 & R10-O10 removedfrom database.
The next LSP set-up utilizes an overlaytopology of FAs only!
It may make sense to change this topologybased on observed traffic pattern betweenrouters
Thus, the design of this overlay is an importantTE issue.
R10R11
R12R5
R4
R6
NANOG, 10/2000 57
Topology Design
General objective Design topology of least cost that accommodates traffic demand
When LSPs are routed over an FA topology Routers may have to optimize overlay topology to utilize
available resources (ports, etc) efficiently and minimize cost Co-ordination among routers may be required for this
Internally, some optimizations are possible in the optical network to minimize capacity usage, based on overall view of lightpaths routed. It is difficult to push this functionality outside of the optical network
NANOG, 10/2000 58
IP-over-Optical TE Example : Domain Model
1. Each border router gets reachability of others2. Each border router keeps track of availability of edge links3. Lightpaths are set up internally in optical network4. Overlay virtual link (VL) topology is formed based on LSP demand between router networks.
Optical Network
Router Network
Router Network
R5R4
R6
R9
R8R7
Router Network
R1R2
R3
O12O15
O14
O13Router Network
R10R11
R12
O10
O11
NANOG, 10/2000 59
TE Example - Domain Model To set up LSP1:
1. R3 computes path R3-R2-<unspecified>-R82. R2 sends a request to optical net to set-up a path to R73. Lightpath is established from R2 to R74. LSP occupies 100 Mbps on the virtual link5. The VL is also a new routing adjacency
FA, 2.5G
Optical Network
Router Network
Router Network
R5R4
R6
R9
R8
R7
Router Network
R1R2
R3
O12O15
O14
O13Router Network
R10R11
R12
O10
O11
NANOG, 10/2000 60
IP-over-Optical TE Issues
TE rules should be incorporated in all routers to decide when to select new optical paths, as opposed to using existing FAs or VLs
Should resource optimization in optical network be an objective of LSP routing? (This requirement may be handled best internally in the optical network)
TE work must investigate to what degree internal optical network information (topology, etc) aid in IP over optical TE decisions.
Specifically, with regard to protection, requiring physical topology characteristics (e.g. SRLG) of optical network at the IP layer for computing alternate paths may be impractical.
NANOG, 10/2000 61
Finally….
What applications may be built based on dynamic bandwidth provisioning?