a brief introduction to optical networks
DESCRIPTION
A Brief Introduction to Optical Networks. Gaurav Agarwal [email protected]. What I hope you will learn. Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching Architectures Circuit, Packet and Burst Protection and Restoration. Outline. - PowerPoint PPT PresentationTRANSCRIPT
A Brief Introduction to Optical Networks
Gaurav [email protected]
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What I hope you will learn Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching Architectures
Circuit, Packet and Burst Protection and Restoration
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Outline Why Optical? (Any guesses???) Intro to Optical Hardware Three generations of Optical Various Switching Architectures
Circuit, Packet and Burst Protection and Restoration
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Bandwidth: Lots of it Usable band in a fiber
1.30m - 1.65m 40 THz spaced at 100 GHz 400 s per fiber
Link Speeds upto 40 Gbps per OC-3 155Mbps OC-768 40Gbps becoming available
Total link capacity 400 * 40Gbps = 16 Tbps!
Do we need all this bandwidth?
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Other advantages Transparent to bit rates and
modulation schemes Low bit error rates
10-9 as compared to 10-5 for copper wires
High speed transmission To make this possible, we need:
All-Optical reconfigurable (within seconds) networks
Definitely a difficult task
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What a path will look like
* All-optical Switch with wavelength converters and optical buffers
All-OpticalSwitch*
All-OpticalSwitch*
All-OpticalSwitch*
Optical Amplifier
Lasers generate the signal Optical receivers
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Outline Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching Architectures
Circuit, Packet and Burst Protection and Restoration
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Fiber & Lasers Fiber
Larger transmission band Reduced dispersion, non linearity and
attenuation loss Lasers
Up to 40Gbps Tunability emerging Reduced noise (both phase and intensity) Made from semiconductor or fiber
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Optical Amplifiers As opposed to regenerators
Make possible long distance transmissions Transparent to bit rate and signal format Have large gain bandwidths (useful in WDM
systems) Expensive (~$50K)
Then:Regenerators
Now:Optical Amps
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Optical Add-Drop Multiplexers
Optical Add-Drop Multiplexer (OADM) Allows transit traffic to bypass node optically New traffic stream can enter without affecting
the existing streams
OADM
1
2
3
1
2
’3
’33
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Optical Switches Route a channel from any I/P port to any O/P
port Can be fixed, rearrangable, or with converters MEMS (Micro Electro Mechanical Systems)
Lucent, Optical Micro Machines, Calient, Xros etc. Thermo-Optic Switches
JDS Uniphase, Nanovation, Lucent Bubble Switches
Agilent (HP) LC (Liquid Crystal) Switches
Corning, Chorum Technologies Non-Linear Switches (still in the labs)
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MEMS Switches
2-D Optical Switches
Crossbar architecture Simple Digital Control of mirrors Complexity O(N²) for full non
blocking architecture Current port count limited to 32
x 32.
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3D MEMS Switch Architecture
3-D Optical Switches
Analog Control of Mirrors. Long beam paths (~1m) require
collimators. Complexity O(N) (Only 2N
mirrors required for a full non blocking NxN switch)
Lucent Lambda Router : Port 256 x 256; each channel
supports up to 320 Gbps.
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Wavelength Converters Improve utilization of available wavelengths on
links All-optical WCs being developed Greatly reduce blocking probabilities
No converters
1
2 3
New request 1 3
1
2 3
New request 1 3
With converters
WC
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Optical Buffers Fiber delay lines are used To get a delay of 1msec:
Speed of Light = 3*108 m/sec Length of Fiber = 3*108 *10-3 m
= 300 km
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Outline Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching Architectures
Circuit, Packet and Burst Protection and Restoration
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Generation I Point-to-point optical links used simply as a
transmission medium Fiber connected by Electronic routers/switches
with O-E-O conversion Regenerators used for long haul
E-OSwitch
O-E-OSwitch
O-ESwitch
Regenerators
Electronic data as the signal
Signal receivedas electronic
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Generation II Static paths in the core of the
network All-Optical Switches (may not be
intelligent) Circuit-switched Configurable (but in the order of
minutes/hours) Soft of here
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Gen II: IP-over-Optical
IP Router Network
IP Router Network
IP Router Network
Optical Subnet
Optical Subnet
Optical Subnet
UNI
NNI
Light Path
End-to-end path
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Peer Model
IP and optical networks are treated as a single integrated network
OXCs are treated as IP routers with assigned IP addresses
No distinction between UNI and NNI Single routing protocol instance runs
over both domains Topology and link state info maintained
by both IP and optical routers is identical
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Overlay Model
IP network routing and signaling protocols are independent of the corresponding optical networking protocols
IP Client & Optical network Server Static/Signaled overlay versions Similar to IP-over-ATM
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Integrated Model Leverages “best-of-both-worlds” by inter-
domain separation while still reusing MPLS framework
Separate routing instances in IP and ON domains
Information from one routing instance can be passed through the other routing instance
BGP may be adapted for this information exchange
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Generation III An All-Optical network Optical switches reconfigurable in milli-
seconds Intelligent and dynamic wavelength
assignment, path calculation, protection built into the network
Possibly packet-switched Dream of the Optical World
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Generation III (contd.) Optical “routers” perform L3 routing No differentiation between optical and
electrical IP domains Routing decision for each packet made
at each hop Statistical sharing of link bandwidth Complete utilization of link resources
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Outline Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching Architectures
Circuit, Packet and Burst Protection and Restoration
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State of the World Today
Electronic Network
Electronic Network
Electronic Network
Electronic Network
O/E/O
O/E/O
O/E/O
O/E/O
O/E/O
O/E/O
Optical Core
E/O
E/O E/O
E/O
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View of a E/O node
Electrical Optical
Input Port 1
Input Port 4
Input Port 3
Input Port 2
Optical Link 1
Optical Link 2
Optical Link 3
Input Port 1
Input Port 4
Input Port 3
Input Port 2
O P 1
O P 2
O P 3
O P 4
O P N-1
O P NPhysical View
Logical View
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Optical Circuit Switching
Electronic Network
Electronic Network
Electronic Network
Electronic Network
O/E/O
O/E/O
O/E/O
O/E/O
O/E/O
O/E/O
Optical Core
E/O
E/O E/O
E/OOS
OS
OS
OS
OS
OS
O/E/O
O/E/O
O/E/O
O/E/O
O/E/O
O/E/O
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Optical Circuit Switching
Electronic Network
Electronic Network
Electronic Network
Electronic Network
O/E/O
O/E/O
O/E/O
O/E/O
O/E/O
O/E/O
Optical Core
E/O
E/O E/O
E/OOS
OS
OS
OS
OS
OS
WC
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Optical Circuit Switching A circuit or ‘lightpath’ is set up through a
network of optical switches Path setup takes at least one RTT Need not do O/E/O conversion at every node No optical buffers since path is pre-set Need to choose path Need to assign wavelengths to paths Hope for easy and efficient reconfiguration
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Problems Need to set up lightpath from source to destination Data transmission initiated after reception of
acknowledgement (two way reservation) Poor utilization if subsequent transmission has small
duration relative to set-up time. (Not suited for bursty traffic)
Protection / fault recovery cannot be done efficiently
Example : Network with N switches, D setup time per switch, T interhop delay. Circuit Setup time = 2.(N-1).T + N.D If N = 10, T = 10ms, D = 5ms, setup time = 230 ms.
At 20 Gbps, equivalent to 575 MB (1 CD) worth of data !
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Optical Packet Switching Internet works with packets Data transmitted as packets
(fixed/variable length) Routing decision for each packet made
at each hop by the router/switch Statistical sharing of link bandwidth
leads to better link utilization Traffic grooming at the edges? Optical
header?
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Problems Requires intelligence in the optical layer Or O/E/O conversion of header at each hop Packets are small Fast switching (nsec) Need store-and-forward at nodes or Deflection
Routing. Also store packet during header processing
Buffers are extremely hard to implement Fiber delay lines
1 pkt = 12 kbits @ 10 Gbps requires 1.2 s of delay => 360 m of fiber)
Delay is quantized How about QoS?
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Multiprotocol Lambda Switching D. Awduche et. al., “Requirements for Traffic
Engineering Over MPLS,” RFC 2702 Problem decomposition by decoupling
the Control plane from the Data plane Exploit recent advances in MPLS traffic
engineering control plane All optical data plane Use as a “label” The on incoming port determines the
output port and outgoing
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OXCs and LSRs Electrical Network – Label Switched
Routers (LSR) Optical Network – Optical Cross
Connects Both electrical and optical nodes are IP
addressable Distinctions
No merging No push and pop No packet-level processing in data plane
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Optical Burst Switching Lies in-between Circuit and Packet Switching One-way notification of burst (not reservation) –
can have collisions and lost packets Header (control packet) is transmitted on a
wavelength different from that of the payload The control packet is processed at each node
electronically for resource allocation Variable length packets (bursts) do not undergo
O/E/O conversions The burst is not buffered within the ON
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Various OBSs The schemes differ in the way bandwidth
release is triggered. In-band-terminator (IBT) – header carries the
routing information, then the payload followed by silence (needs to be done optically).
Tell-and-go (TAG) – a control packet is sent out to reserve resources and then the burst is sent without waiting for acknowledgement. Refresh packets are sent to keep the path alive.
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Offset-time schemes Reserve-a-fixed-duration (RFD) Just Enough Time (JET) Bandwidth is reserved for a fixed duration
(specified by the control packet) at each switch
Control packet asks for a delayed reservation that is activated at the time of burst arrival
OBS can provide a convenient way for QoS by providing extra offset time
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QoS using Offset-TimesAssume two classes of serviceClass 1 has higher priorityClass 2 has zero offset time
i Time
tai = arrival time for class i
requestts
i = service time for class i request
toi = offset time for class i request
li = burst length for class i request
ta1 ts
1
to1
ts1+ l1ta
2(= ts2)ta
2(= ts2)
i Time
ta1
to1
ta2(= ts
2) ts1 ts
1+ l1ts2+ l2
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Comparison
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Hierarchical Optical Network
Optical MAN
Optical MANOptical MAN
Optical MAN
Optical Core
All O
All O All O
All O
E/O
E/O
E/O
E/O
E/O
E/OE/O
E/O
E/O
E/O
E/O
E/O
E/O
E/O
E/O E/O
OS
OS
OS
OS
OS
WC
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Hierarchical Optical Network Optical MAN may be
Packet Switched (feasible since lower speeds) Burst Switched Sub- circuit switching by wavelength merging
Interfaces boxes are All-Optical and merge multiple MAN streams into destination-specific core stream
Relatively static Optical Core Control distributed to intelligent edge boxes
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Outline Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching Architectures
Circuit, Packet and Burst Protection and Restoration
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Link vs Path Protection For failure times, need to keep available s on backup path Link: Need to engineer network to provide backup Path: need to do end-to-end choice of backup path
NormalPath
BackupPath
LinkProtection
NormalPath
BackupPath
PathProtection
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Types of Protection Path protection
Dedicated (1+1) – send traffic on both paths
Dedicated (1:1) – use backup only at failure
Shared (N:1) – many normal paths share common backup
Link Protection Dedicated (each
is also reserved on backup link)
Shared (a on backup link is shared between many)
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Restoration Do not calculate protection path ahead of time Upon failure, use signalling protocol to
generate new backup path Time of failover is more But much more efficient usage of s Need also to worry about steps to take when
the fault is restored
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Protection and Restoration
Time of action Path calculation (before or after failure ?) Channel Assignments (before or after
failure ?) OXC Reconfiguration
AT&T proposal Calculate Path before failure Try channel assignment after failure Simulations show 50% gain over channel
allocation before failure
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Protection Algorithms Various flavors
Shortest path type Flow type ILP (centralized) Genetic programming
In general, centralized algos are too inefficient
Need distributed algos, and quick signalling Have seen few algos that take into account
the different node types (LWC/FWC)
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Conclusion Optical is here to stay Enormous gains in going optical O/E/O will soon be the bottleneck Looking for ingenious solutions
Optical Packet Switching Flavors of Circuit Switching
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Collective References
“Optical Networks: A practical perspective” by Rajiv Ramaswami and Kumar Sivarajan, Morgan Kaufman.
IEEE JSAC September 1998 issue October 2000 issue
IEEE Communications Magazine
March 2000 issue September 2000 issue February 2001 issue March 2001 issue
INFOCOM 2001 ‘Optical Networking’
Session ‘WDM and Survivable
Routing’ Session INFOCOM 200
‘Optical Networks I’ Session
‘Optical Networks II’ Session
RFC 2702 for MPS www.cs.buffalo.edu/pub/
WWW/faculty/qiao/ www.lightreading.com