TCOM 513 Optical Communications Networks

1
TCOM 513Optical Communications Networks

• Spring, 2006
• Thomas B. Fowler, Sc.D.
• Senior Principal Engineer
• Mitretek Systems

2
Topics for TCOM 513

• Week 1 Wave Division Multiplexing
• Week 2 Opto-electronic networks
• Week 3 Fiber optic system design
• Week 4 MPLS and Quality of Service
• Week 5 Heavy tails, Optical control planes
• Week 6 The business of optical networking
  economics and finance
• Week 7 Future directions in optical networking

3
Heavy-tailed Distributions

• For large x values, cumulative distribution
  function F(x) has property that its complementary
  distribution

and
where
Setting b2 and differentiating above equation,
4
Heavy-tailed Distributions (continued)

• Recall from calculus that
• only if p gt 1

5
Heavy-tailed Distributions (continued)

• Since
• is fixed, so then the variance is determined by
• If in addition b lt 1, then for the mean, since

6
Physical Significance of Infinite Variance

• Consider finite variance on expanding time
  scales

7
Physical Significance of Infinite Variance
(continued)

• Infinite variance case

-20
0
20
-5
5
0
-5
5
0
-50
50
0
8
Network session or connection size (length in
bytes)

• Empirical data from 220,000 connections at www
  site

Source Willinger Paxson, 1998
9
Network session or connection size (length in
bytes) (continued)

• Use points to calculate F(x), then plot 1- F(x)
  against corresponding session size
• Behavior agrees with Pareto distribution
• Yields
• Corresponds to infinite variance
• Aggregate property of traffic source

10
Heavy-tailed distributions (continued)

• Upper tail declines like power law with exponent
  lt 2
• Appears as lack of convergence of sample variance
  as function of sample size
• Pareto distribution is simplest heavy-tailed
  distribution
• Effect increases as a decreases

11
Heavy-tailed Distributions (continued)
Pareto distribution, a0.5, k1
Pareto distribution, a1, k1
12
Heavy-tailed Distributions (continued)

13
Heavy-tailed Distributions (continued)
14
Relationship of Key Traffic Concepts
Heavy tails
Files, transmission times

Order of discovery
Infinite variance
Transmission times
Self-similarity
Packets, sessions
Long-range dependence
Packets, sessions
Order of explanation
Burstiness on multiple scales
Packets
15
Analyzing networks in terms of planes

Management Deploys and manages services
Minimal in standard IP networks
Control Network-level coordination State
information management Decision-making Action
invocation
Best effort utilizing h/w and s/w in components
in standard IP networks
Data or bearer
Physical transmission of data through network
16
Traditional approaches to integration
17

18
Problems of traditional approach
19
Steps in the evolution of network architectures
(continued)

• Dynamic IP Optical Overlay Control Plane
• Ring replaced by mesh using DWDM
• Dynamic wavelength provisioning
• Easier, more scalable control
• Enhanced restoration capabilities
• Integrated IP Optical Peer Control Plane
• Integrate dynamic wavelength provisioning
  processes of Optical Transport Network (OTN) into
  IP network routing
• Make OTN visible to IP network

20
Old World networks

• Utilize SONET for delivering reliable WAN
  connectivity at layer 1
• Large, interconnecting rings
• Lots of expensive hardware, e.g., ADMs
• Utilize ATM for provisioning data services
• Connection oriented
• Can assure QoS, VPN
• High operational cost for high reliability
• High overhead (25)

21
New World networks

• Eliminate SONET, ATM
• Still need to provide layer 2 functionality

Source Tomsu Schmutzer
22
IP/Optical adaptation
Packet over SONET (POS) Ref. p. 91 PPP does L2
functions
Dynamic Packet Transport (DPT) SRPspatial reuse
protocol Intended for ring architecture Ref. p.
105
Gigabit Ethernet
ATM
Simple Data Link (SDL)
Source Tomsu Schmutzer
23
Two-layer architecture
IP edge routers aggregatetraffic and multiplex
it ontoBig Fat Pipes

Source Tomsu Schmutzer
24
Two-layer architecture (continued)

• Ingress traffic multiplexed onto big fat pipes
  (BFPs)
• Provided by optical layer
• Optical layer functions as cloud for
  interconnecting attached devices
• Key point is that configuration within optical
  layer controlled at same time that service layer
  is configured (common management)
• May use either DWDM or dark fiber
• Can be point-to-point, ring, or mesh
• Similar to ATM networks because any logical
  connectivity between IP nodes can be implemented

25
New World Overlay and Peer Models

• Main distinction in New World models is between
  overlay and peer models
• Overlay
• OTN (Optical Transport Network) or bearer plane
  is opaque to IP network
• OTN merely provides connections to IP network
  above
• Has its own control plane
• Peer
• Common control plane for both OTN and IP networks
• Optical connections derived from IP routing
  knowledge (paths)

26
Overlay and Peer Models (continued)
IP Network
IP Optical Network
Peer Model
Optical Transport Network
Overlay Model
Source Tomsu Schmutzer
27
MPlS overlay model

• Two separate control planes
• Interaction minimized
• IP network routing and signaling protocols
  independent of corresponding optical network
  protocols
• Edge devices see only lightpaths, not topology
• Similar to IP over ATM
• Client/Server model IP client, optical network
  server
• Two versions
• Static
• Signaled

28
MPlS overlay model
PXC
Core Optical Network
GigE OC12
PXC
PXC
Metro optical network (Access Ring) DWDM
Core optical network (Regional Ring) DWDM
Metro optical network (Access Ring) DWDM
PXC
OC12/ OC48
OC12/ OC48
Optical Network UNI
Source Cellstream
29
MPlS overlay modelanother view
30
Dynamic Optical Control Plane

• Central problem wavelength provisioning
• Optical cross-connects (OXCs) combined with IP
  routing intelligence to control wavelength
  allocation, setup, and teardown
• Done dynamically
• Allows same elements to be reconfigured rapidly
  to improve utilization
• Other benefits
• Expedited provisioning
• Enhanced restoration
• Any virtual topology can be provided

31
Implementing dynamic optical control plane
Wavelength routing

• IP routing protocols (e.g., OSPF) adapted to
  create routing protocol used by wavelength
  routers (WRs) in optical layer
• Connections can be dynamically provisioned to
  interconnect IP routers
• Wavelength routing protocol only protocol running
  on WRs
• IP network does not participate in wavelength
  routing process
• IP network interacts with OTN on client/server
  relationship
• Overlay model
• Typical use OTN owned by optical interexchange
  carrier, other service providers buy lightpaths
  to establish their own IP networks

32
Overlay model wavelength routing
IP Router A
IP Router B
IP Network
Wavelength RoutingNetwork
Lightpath (IP Connectivitybetween A and B)
WavelengthRouter
WavelengthRouter
Source Tomsu Schmutzer
33
Wavelength routing control plane

• Responsible for establishing end-end connection
  or lightpath
• Two methods of implementing IP-based control
  plane
• Attach external IP routers to each OXC
• Integrate IP routing functionality into OXC

Source Tomsu Schmutzer
34
Method 1 details

• Routers with control interface called wavelength
  routing controllers (WRCs)
• WRCs provide needed functions
• Resource management
• Configuration and capacity management
• Addressing
• Routing
• Traffic engineering
• Topology discovery
• Restoration

35
Method 1 details (continued)

• Control interface specifies primitives used by
  WRC
• Connect cross connect input, output channels
• Disconnect remove connection
• Switch change incoming channel/link combination
• OXC communicates with WRC
• Alarm failure condition

36
Cross-connect tables illustration
Source Tomsu Schmutzer
37
Digital communication network

• Control plane exchanges control traffic through
  Digital Communications Network (DCN)
• In band
• Default-routed lightpath used
• Out of band
• Routers and leased lines used to set up
  completely separate IP network interconnecting
  all WRs

38
Operation of control plane

• WRs exchange info about network topology and
  status of OTN across DCN
• All elements have unique IP addresses
• Routers
• Amplifiers
• Interfaces
• MPlS used for lightpath routing and service
  provisioning in OTN
• Provisions LSPs in service layer

39
Route calculation for lightpaths

• Centralized
• Distributed

40
Centralized lightpath routing

• Uses traffic engineering control server
• Server maintains information database
• Topology
• Inventory of physical resources
• Current allocations
• WRs request lightpath to be set up
• Server checks resource availability and initiates
  resource allocation at each hop

41
Centralized lightpath routing (continued)
Source Tomsu Schmutzer
42
Distributed lightpath routing

• Each WR maintains information database and set of
  routing algorithms
• Perform neighbor discovery after bootup
• Builds topology map
• Creates resource hierarchies
• Constraint-based routing used to define
  appropriate path through network

43
Distributed lightpath routing (continued)
Source Tomsu Schmutzer
44
Distributed lightpath routing (continued)
Source Tomsu Schmutzer
45
Comparing WRs and LSRs

• Similar in architecture and functionality
• LSR (Label Switched Router) provides
  unidirectional point-to-point connections
  (LSPsLabel Switched Paths)
• Traffic aggregated in FECs (Forwarding
  Equivalence Classes)
• WR (Wavelength Router) provides unidirectional
  optical point-to-point connections (lightpaths)
• Used to transmit traffic aggregated by service
  layer
• Two key differences
• LSR must process packets (do label lookup)
• WR does not do any packet level processing
• Switching info for WR is lightpath ID, not any
  packet label

46
Comparing WRs and LSRs (continued)

• Lightpaths are very similar to LSP
• Unidirectional, point-to-point virtual paths
  between ingress and egress node
• LSPs define virtual topology over data network,
  as do lightpaths over OTN
• Allocating label ? allocating channel to a
  lightpath

Source Tomsu Schmutzer
47
Comparing WRs and LSRs (continued)

• MPLS label fixed length value in packet header
• MPlS label certain wavelength over fiber span
• Label space is significant
• In MPLS, may be thousands of FECs
• Wont work in MPlS, because only 40-128 labels
  (ls) available
• Must aggregate traffic into traffic trunks
  lightpath
• Suitable for core use

48
Integrated Optical Peer Control Plane

• Second of the methods of integrating IP and
  optical
• Differs from overlay model in that there is a
  single control plane rather than two separate
  control planes
• IP network sees optical network
• Uses MPLS Traffic Engineering (MPLS-TE) to
  implement control plane and provision lightpaths
  across OTN and service layer

49
MPlS peer model (continued)

• Single control plane spans entire network
• IP, Optical networks treated as single network
• OXCs treated as IP routers with assigned IP
  addresses
• Edge devices see entire network
• No distinction between NNI, UNI
• Single routing protocol over both domains
• Topology and link state information maintained by
  IP and optical routers is same
• Reuses existing MPLS framework

50
Control Plane Functions

• Control Channels
• May be on dedicated fiber(s)
• Could also be Ethernet connection or IP tunnel
• Bi-directional
• Manage links
• Restoration
• Establish LSPs

51
MPlS peer model
PXC
Core Optical Network
GigE OC12
PXC
PXC
Metro optical network (Access Ring) DWDM
Core optical network (Regional Ring) DWDM
Metro optical network (Access Ring) DWDM
PXC
OC12/ OC48
OC12/ OC48
Source Cellstream
52
MPlS peer modelanother view
53
Peer model connectivity
Source Tomsu Schmutzer
54
Peer model OTN (continued)

• Edge LSRs have two functions
• Aggregate traffic flows
• Request unidirectional lightpaths (LSPs) to be
  set up by WRs through OTN
• Dynamically switched through OTN
• Terminated at Edge LSRs
• Control plane requirements
• Establish optical channels
• Support traffic engineering functions
• Protection and restoration mechanisms

55
Building blocks for MPlS
Source Tomsu Schmutzer
56
MPlS control plane architecture
Source Tomsu Schmutzer
57
Multiprotocol lambda switching (MPlS)
58
Network-to-network issues
59

MPlS and related technologies
60
Comparison of MPLS and MPlS Routers
61
Network architecture incorporating MPLS, MPlS
MPlS Inner core Highest degree of aggregation
Outer core MPLS
Edge aggregation (routing, lt OC48)
MAN aggregation (routing, lt OC12)
62
Future evolution
63
Lightpath networking architectures and topologies
Source Sycamore Networks/NGN1999
64
Architectures and topologies (continued)
Source Sycamore Networks/NGN1999
65
CISCO IP Optical network
66
The overall networking problem

• Metro access
• Need to handle much legacy (existing) access
  types
• First level of aggregation
• Likely will move more in the Ethernet direction
• Core switching
• Easier to implement newer technology
• MPLS, MPlS

67
Metro access methods
Source Tomsu Schmutzer
68
Possible IP and optical metro evolution
Source Tomsu Schmutzer
69
Optical core evolution migration to
intelligently controlled meshed core
Source Tomsu Schmutzer
70
Possible core evolution
Source Tomsu Schmutzer
71
MPLS Traffic Engineering (MPLS-TE)

• Standard routing protocols compute the optimum
  path from source to destination
• Use routing metric
• Hop count
• Cost
• Link bandwidth
• Single least cost (according to metric) path
  chosen
• Alternate paths ignored
• Possibly longer, but faster
• Do not understand nature of IP traffic
• Fractal
• Can lead to inefficiencies

72
MPLS-TE example of inefficiencies of standard
routing protocols
Source Tomsu Schmutzer
73
Solutions to traffic engineering problem

• Non-scaling
• Manipulate Interior Gateway Protocol (IGP)
  metrics
• Use of policy-based routing
• Define complex access lists and characterize
  traffic flows
• Static
• MPLS-TE
• Utilization of all network resources analyzed and
  taken into account in path calculation
• If multiple paths exist, best chosen based on
  current network situation

74
Traffic Engineering

• Objectives
• Maximize network resource efficiencies
• IP traffic has large variations, unpredictable
• Fractal distribution
• Continually tune network parameters
• Adjust resource partitions between
  working/protection segments
• Usually deals with longer timescales (hours,
  days)
• Shorter variations dealt with by higher layers
• On-line or off-line

75
Internet Time Scales
Multifractals Effects of network transport
protocols

Fractals Long-range dependency
Diurnal other effects
Measurement time
76
MPLS-TE functional components
Source Tomsu Schmutzer
77
Information flow for MPlS traffic engineering
78
Sample queue hysterisis control
79
MPlS Traffic Engineering (continued)

• Utilizes concepts from MPLS
• Overlay model centralized network controller
• Smaller networks, larger timescales
• Given traffic matrix, resolve (figure out)
  LSP/lightpath topologies
• Fewer resource synchronization and lockout
  problems due to central control
• Single point of failure
• Controller needs large amount of information
• Link states
• Router status
• Traffic patterns

80
MPlS Traffic Engineering (continued)

• Peer model distributed traffic engineering
• Localized decisions
• Better scalability
• Heuristic routing algorithms
• Robust
• Still active research area
• Multi-vendor operability may require standards

81
Network survivability principles

• Definition ability of a network to maintain an
  acceptable level of service during a network or
  equipment failure. (Lucent)
• Multilayer survivability possible nesting of
  survivability schemes among subtending network
  layers, and the way these schemes interact with
  each other. (Lucent)
• Survivability is important because of expected
  growth (scaling) of optical networks
• Failure of a single link can affect tens or
  hundreds of thousands of customers
• QoS is dependent on an effective restoration
  method

82
Survivability concepts

• Classification
• End-to-end single survivability mechanism used
  to deliver end-to-end survivability
• Example single backup line which takes over if
  any problem occurs with main line
• Cascaded multiple survivability mechanisms, each
  functioning in a limited area or domain
• Example Main line divided into segments with
  switches at each node backup lines between nodes
• Nested multiple survivability mechanisms for a
  single domain

83
Survivability concepts (continued)
Source Tomsu Schmutzer
84
Protection and restoration

• Two closely related concepts
• Difference is in scope and layer
• Protection lower layers, narrower scope
• Restoration higher layers, broader scope
• Both commonly used to provide maximum degree of
  survivability

Restoration Node failures Multiple failures
Protection Link failures
Protection Link failures
Protection Link failures
85
Protection

• Lower layer (physical layer) mechanism
• First line of defense against faults such as
  fiber cuts
• Topology and technology specific
• Fast
• Limited usefulness
• Does not correct node faults
• Cannot handle multiple faults, e.g., two cable
  cuts
• Types
• Dedicated 50 of entire network capacity set
  aside
• Example Unidirectional Path Switched Rings
  (UPSR) used in SONET
• Shared certain amount of total capacity set
  aside and shared across all network resources
• Example Multiple LSP tunnels sharing single
  backup LSP tunnel

86
Protection types

• 11
• All traffic sent over 2 paths simultaneously
• Destination receives both, selects one
• In case of failure, destination switches to other
  path
• 11
• Two parallel paths, only one used in normal
  operation
• In unidirectional systems, source will not know
  if one path is cut
• Requires additional signaling
• In normal operation, low priority traffic can use
  backup path
• 1N
• Similar to 11, except that n working paths share
  one protection path

87
Protection switching characteristics

• Methods of handling traffic when failed path
  comes back on line
• Nonreverting
• Backup remains as primary path
• Restored path becomes backup
• Reverting (common in 1n protection)
• Restored path resumes normal role
• Backup path reverts to backup role
• Switching methods
• Path
• Source, destination control
• Entirely new, disjoint path used
• Line
• Adjacent nodes handle
• Only local link affected

88
Path and line switching
Source Tomsu Schmutzer
89
Restoration

• Overlaid mechanism
• Can handle more types of failures
• Links
• Nodes
• Multiple failures
• Typically used in mesh topologies
• Basic idea is to utilize alternate paths to route
  traffic around failure location
• Two approaches
• Centralized
• Distributed
• Precomputed alternate paths
• No single point of failure for restoration method
  itself

90
Restoration (continued)

• Typically done at layer 2 or layer 3
• ATM
• PNNI routing protocol reroutes virtual circuits
• IP
• Dynamic routing protocol (OSPF, IS-IS, RIP, BGP)
  find new path through network
• MPLS
• Reroute onto backup paths (labels)
• Backup paths may be preselected

91
ITU restoration time components
Source Tomsu Schmutzer
92
Higher-layer survivability mechanisms
Source Tomsu Schmutzer
93
Optical network (layer 1) survivability
Optical channel sublayer
Optical channel protection (OCH)
Optical multiplex sublayer
Optical multiplex section protection (OMS)
OTN
Optical transmission section sublayer
Line protection
94
Optical line 11 protection
Source Tomsu Schmutzer
95
Optical line 11 protection
Source Tomsu Schmutzer
96
Optical channel protection (11)
Source Tomsu Schmutzer
97
Survivability mechanisms for OTN
Source Tomsu Schmutzer
98
Multilayer survivability

• Typically layer 1 protection is fastest
• 100 ms
• If this is adequate, higher layer restoration
  unnecessary
• Higher layer restoration slower
• Kicks in if layer 1 protection cannot solve
  problem
• 1 s or more
• Coordination of mechanisms may be necessary if
  time constants too close
• To prevent network from becoming unstable

99
Survivability design trends for optical networks

• Eliminating SONET and ATM
• Eases problem of interaction between layers
• But decreases available survivability mechanisms
• DWDM system may not automatically provide optical
  protection
• Forces higher layers (IP or ATM) to handle
• Not designed to do this
• Necessary to modify routing protocols to converge
  faster
• 1 s about the best at present

100
Survivability in MPlS networks

• Typically 11 or 1n protection used
• Optical LSPs (OLSP) for protection predefined
• If failure occurs, adjacent nodes switch all
  aggregated LSPs onto backup OLSP
• No end-end signaling required
• Path protection can also be used
• Requires signaling between endpoints of OLSP