Optical Internetworking: IPWDM

1
Optical Internetworking(IP/WDM)
Emerging Optical Network technologies such as IP
over Wave Division Multiplexing will enable a
paradigm shift in terms of the cost and
availability of bandwidth for Internetworks.
2
Agenda
What is Optical Internetworking (IP over
DWDM) Fundamentals and Concepts of Optical
Networking WDM vs DWDM Optical LANs, MANs,
WANs Framing, Restoration, etc. RD Optical
Internetworks
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What is an Optical Internet

• Consists of Routers interconnected via Fiber
  Optics.
• Individual wavelengths on fiber are the link
  layer and interconnect directly to routers.
• High Performance Routers acts as the main
  switching/ routing device.
• Uses SONET or Gigabit Ethernet framing (also
  10xGbE).
• Traffic engineering, network management and
  network restoration are done at the Network layer
  (IP layer).
• Network design optimized for unique
  characteristics of Internet traffic.

4
Advantages of Optical Internet
SONET Terminals and ATM Switches often not
needed Rings and protection fiber not needed Uses
existing fiber Coexists with current networks
Multiple wavelengths Higher interface speeds,
e.g., OC192, 10xGE More Bandwidth Less
Overhead Lower Cost

Reports indicate several orders of
magnitude advantage for high bandwidth scenarios
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Need for More Bandwidth
Source ATT Geopartners Research
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How to get More Bandwidth

• Network providers have 3 choices to get more
  bandwidth for Internetworks
• Install new fiber
• expensive
• Faster bit rates
• trade off between faster rates and link reach due
  to signal dispersion
• Wave Division Multiplexing
• now a viable alternative due to recent
  technology/product advances

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Towards an Optical Internet
Optical Internet
Connection Oriented Data
Data on Voice Network
Today's Internet
GigaBit Switch Router
Internet Protocol
Router
Modems, ISDN, Frame Relay
PSTN Switches
Switch
OC3 OC12
OC48 OC192 GB Ethernet
SONET or GE Framing
ATM Switches
ATM Circuit
TDM Circuit
Muxes, DACS, etc
Wave Division Multiplexer
SONET
SONET Terminals
Fiber Infrastructure
Fiber
Fiber
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Towards De-layering
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Optical Networking Layers
IP Layer
Router
Router
Router
ATM / SONET Layer
ATM
ATM
ATM
ATM
ATM
ATM
WDM
WDM
WDM
WDM Layer
WDM
WDM
WDM
10
Traditional Internet Architecture
Router
Router
VCs
VCs
ATM switch
ATM switch
OC3
OC3
OC12
OC12
SONET Mux
SONET Mux
OC3
OC3
OC48
OC48
SONET Transport
SONET Transport
SONET Ring
Working Fiber
Protection Fiber
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Optical Internet Architecture
OC48, OC192, POS
Traditional SONET Transport Node
Traditional SONET Transport Node
WDM
OC48, OC192, POS, GE, 10xGE
High Performance Router
High Performance Router
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Fundamentals Concepts

• Fiber
• Wavelengths
• Lasers
• Optical Amplifiers
• Optical Couplers
• Electrical Repeaters
• Transponders
• Multiplexers and Cross Connects
• Optical Switches

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Fundamentals Fiber

• Multimode Fiber
• Short distances (LANs, campus, between bays)
• Singlemode Fiber
• Long distances (large campus, MANs, WANs)
• 3 types 850 nm, 1310 nm, 1550 nm windows
• 3 types of 1550 nm fiber
• NDSF (No Dispersion Shifted Fiber)
• DSF (Dispersion Shifted Fiber)
• NZDSF (Non-Zero Dispersion Shifted Fiber)

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Fundamentals Wavelengths

• WDM (Wavelength Division Multiplexing)
• Wavelength in 1310 nm and 1550 nm windows
• DWDM (Dense WDM)
• Many wavelengths (4-40) in 1550 nm window
• ITU grid specifies minimum wavelength spacing and
  actual wavelengths
• EDFA optical amplifiers amplify all wavelengths
  in 1550 nm window
• Standards and interoperability not mature

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Fundamentals Lasers

• DWDM requires expensive high performance lasers
• Extremely stable
• Very narrow spectrum
• Highly temperature stable
• Precision external modulator
• Precision optical filter removes extraneous
  signal
• Maximum laser drive reach (approximately)
• 80 km at 2 Gbps (OC-48)
• 50 km at 10 Gbps (OC-192)

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Fundamentals Optical Amplifiers

• WDM - Uses narrow pass Optical Amplifiers
• DWDM - Uses Erbium Doped Fiber Amplifiers (EDFA)
• Broadband optical amplification of all (or
  groups) of wavelengths in 1550 nm window
• Band pass is not flat and is accentuated by
  amplifier cascade
• Maximum number of cascaded amplifiers is
  approximately 5 before electrical regeneration is
  needed.
• Separate amplifiers for TX and Rx directions

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EDFA
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Fundamentals Optical Couplers

• Passive optical device for coupling or uncoupling
  individual wavelengths or groups of wavelengths
  onto or off of a fiber
• Pre or Post Optical Amplifier used to compensate
  for optical couplers loss
• Usually all Tx signals are coupled to one fiber
  and all Rx signals to another (due to Tx signals
  interference with Rx signals)

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Fundamentals Electrical Repeaters

• Not required for LAN or MAN systems
• Required for long haul systems (WAN)
• required due to signal attenuation, signal
  dispersion, spontaneous noise accumulation and
  unequal wavelength power distribution (due to
  EDFAs)
• 3 levels of regeneration
• R1 - Fully transparent electrical amplification
• R2 - Reshaping of the electrical pulses
• R3 - Adds signal retiming and jitter removal
• R1 and R2 are protocol and bit rate independent
  while R3 is dependent (e.g., SONET/SDH)

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Fundamentals Electrical Repeaters

• Electrical Repeaters continued...
• Electrical regeneration is a major cost component
• Most long haul WAN systems use SONET/SDH framing
  and R3 regeneration
• Most Optical LANs use GigaBit Ethernet framing
  with R2 regeneration
• Optical MANs may use either
• GigaBit Ethernet (and soon 10xGE) for the long
  haul case are under development

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Fundamentals Transponders

• Transponders
• Device that accepts the optical signal from a
  router or other device and converts it to the
  correct wavelength
• WDM Example - Convert 1310 nm signal to 1550 nm.
• DWDM example - Convert signal to correct ITU
  wavelength in 1550 nm window.
• May be data transparent using optical techniques
  only (optical gating or wave-mixing)
• May include electrical regeneration (to match the
  router signal to the transmission system timing,
  e.g., SONET/SDH)

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Fundamentals Muxes, X Connects

• Optical Add Drop Multiplexers (OADM)
• Selectively adds or drops selected wavelengths
  while optically passing the rest
• Optical Cross Connects (OXC)
• Essentially 2 OADMs back to back to allow cross
  connection of wavelengths
• OADMs and OXCs are configured and left (i.e., not
  switches)
• Suited for MAN case where optical and electrical
  amplifiers are not needed

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OADM
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Fundamentals Optical Switches

• Optical switches allow for dynamic
  reconfiguration of the wavelengths
• Too slow to be used for switching packets
• Better to do switching/routing at the electrical
  level with routers and switches

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Fundamentals Link Span

• Span limited by bit error rate performance (BER)
• BER is determined by the optical SNR at the
  receiver photodetector
• Typically an SNR of 20 dB required for BER of 10
  exp -15
• Transmit power constrained by present laser
  technology
• Signal is attenuated while noise accumulates
• Maximum repeater spacing depends on laser power,
  number of wavelengths, wavelength spacing,
  amplifier noise and gain tilt, fiber type, and
  signal bandwidth.
• Actual measurements may be needed to verify design

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WDM
Optical Demultiplexer
Optical Multiplexer
Transmission
SONET
OC3 OC12 OC48 (OC192)
Receiver
Transmitter
l1
l1
(Optional) Optical Amplifiers (or OADM)

ATM FR Gigabit E D1 Video FDDI
Receiver
ln
Transmitter
Optional OA
Optional OA
ln
A
D
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WDM Example
36170 ATM Switch
36170 ATM Switch
(1) One Fiber Pair for one OC-12/3
12.5 K
12.5 K
WDM 1550/1310
WDM 1550/1310
WAVE SHITER
1310
36170 ATM Switch
36170 ATM Switch
W/S
1550
1550
WAVE SHIFTER
WDM
WDM
W/S
1310
1550
1550
WDM
WDM
1310
1310
(2) One Fiber Pair for double network
capacity 2 x OC-12/3
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DWDM Optical Network
Optical Wavelengths (colors)
Single Fibers
Multiple Signals
1 2 3 4 5 6 7 8 etc.
SONET, GB Ethernet, Video
Optical Amplifier
Terminal
Repeater
Terminal
Optical Add/Drop Mux
Most systems use different fibers for transmit
and receive directions.
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DWDM Network Terminal
Multiple Fibers, Different Wavelengths
Single Fiber, Different Wavelengths
OC12 OC48, OC192, Gigabit Ethernet, Video, etc.
Transponders
Passive Optical Coupler
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Fiber Rings

• Fiber Rings are often used to increase
  survivability in the case of a fiber cut
• With SONET often a dual ring arrangement is used
  where the second ring is the protection ring
• The protection ring sits idle and is utilized
  only when there is a failure
• Connecting WDM wavelengths directly to a router
  allows both sides of the ring to be utilized
• In the case of a fiber cut all traffic continues
  impacted only by reduced ability to handle peaks
  without delay

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WDM Protected Ring
Large Node
A
B
D
2-Fiber Ring
Small Node
Small Node
C
Small Node
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Network Asymmetry

• Traditional SONET/TDM networks built for traffic
  symmetry, e.g., OC3
• Internet traffic is often not symmetrical
• There may be significantly more traffic in one
  direction compared to the other, e.g.,
  Canada/U.S. cross border traffic
• Bandwidth in one direction may sit idle
• WDM enables a different number of wavelengths in
  each direction therefore accommodating asymmetry

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Optical LAN vs MAN vs WAN

• Optical LANs (Local Area Network)
• Distances of up several hundred meters
• Extension of 10 Mbps Ethernet and 100Mbps
  Ethernet technology and product families
• Optical MANs (Metropolitan Area Network)
• Distances of up to a few tens of kilometers
• May require optical amplifiers
• Optical WANs (Wide Area Network)
• Distances of hundreds or thousands of kilometers
• Requires optical amplifiers and electrical
  repeaters

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Optical LAN
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Optical MAN
Location A
Packet over SONET
GigaBit Ethernet
OADM
Location C
Ethernet
Local WDM Fiber Ring
ATM
OADM
OADM
Reuse of same wavelength
Location B
Analog Video
OADM
Location D
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Optical WAN
WDM Coupler
WDM Coupler
50 km
Wideband Optical Repeater
SONET Regenerator or Gigabit Ethernet Regenerator
SONET Regenerator or Gigabit Ethernet Regenerator
250 km
Approximate Distances for OC-192 system
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Framing SONET

• SONET framing advantages
• Well established jitter specifications
• Out of band management systems
• Can be used in SONET networks for fast restoral
  and protection
• Very high efficiency - over 98
• SONET framing disadvantages
• SAR processing more complex as there can be
  multiple packets per frame, or packets can cross
  frame boundaries
• POS is packet over PPP over HDLC over SONET
• Tributary services require SONET mux services
• More expensive

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Framing GigaBit Ethernet

• Gigabit Ethernet Framing Advantages
• Frame size packet size therefore packet
  switching and SAR more efficient and easier to
  implement
• Data format consistent with LAN format with no
  translation
• Low cost tributary service - do not need to
  terminate link on a router or SONET DCS equipment
• New 10xGigabit Ethernet will equal OC-192
• Ideal for transparent networks
• Gigabit Ethernet Framing Disadvantages
• Lack features supporting long haul reliability
• Inefficient for small packets due to preamble
• No standard out of band management or monitoring

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Network Layer Restoration

• IP network is intrinsically self healing via
  routing protocols
• But it may take several seconds or minutes to
  restore
• By cranking down timers on interface cards and
  keep alive message time-out we can achieve 1/3
  second restoral
• Still too slow for real time traffic
• Network Layer (layer 3) Restoral allows for more
  intelligent restoral
• Enables consistent restoral over a hybrid mix of
  link layer technologies
• Can use QoS to prioritize customers and services
• Only UDP packets (e.g telephony) require fast
  restoral
• Allows simultaneous use of both working and
  protection circuits
• MPLS promises to simplify the problem
• Allows for label flows, explicit routing and
  explicit restoration
• Maintain a set of attributes for restoral and
  optimization

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Concluding Remarks

• IP/WDM is an enabler to
• Advanced Networking
• Advanced Multimedia
• Advanced Applications

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Dr. Muhammad A. Kalam
TARGET (Telecommunications Applied Research
in Gigabit and Emerging
Technologies) Lab Phone (972) 883 -
4623 Internet mkalam_at_utdallas.edu