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A Brief Introduction to Optical Networks

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Intro to Optical Hardware. Three generations of Optical. Various Switching Architectures ... Protection and Restoration. EECS - UC Berkeley. 17. Generation I ... – PowerPoint PPT presentation

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Title: A Brief Introduction to Optical Networks


1
A Brief Introduction to Optical Networks
  • Gaurav Agarwal
  • gaurav_at_eecs.berkeley.edu

2
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

3
Outline
  • Why Optical? (Any guesses???)
  • Intro to Optical Hardware
  • Three generations of Optical
  • Various Switching Architectures
  • Circuit, Packet and Burst
  • Protection and Restoration

4
Bandwidth Lots of it
  • Usable band in a fiber
  • 1.30?m - 1.65?m ? 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?

5
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

6
What a path will look like
Lasers generate the signal
Optical receivers
Optical Amplifier
All-optical Switch with wavelength converters
and optical buffers
7
Outline
  • Why Optical?
  • Intro to Optical Hardware
  • Three generations of Optical
  • Various Switching Architectures
  • Circuit, Packet and Burst
  • Protection and Restoration

8
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

9
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)

Now Optical Amps
Then Regenerators
10
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

11
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)

12
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.

13
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.

14
Wavelength Converters
  • Improve utilization of available wavelengths on
    links
  • All-optical WCs being developed
  • Greatly reduce blocking probabilities

3
2
3
2
WC
No ? converters
With ? converters
1
New request 1? 3
1
New request 1? 3
15
Optical Buffers
  • Fiber delay lines are used
  • To get a delay of 1msec
  • Speed of Light 3108 m/sec
  • Length of Fiber 3108 10-3 m
  • 300 km

16
Outline
  • Why Optical?
  • Intro to Optical Hardware
  • Three generations of Optical
  • Various Switching Architectures
  • Circuit, Packet and Burst
  • Protection and Restoration

17
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

Electronic data as the signal
Signal received as electronic
Regenerators
18
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

19
Gen II IP-over-Optical
20
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

21
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

22
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

23
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

24
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

25
Outline
  • Why Optical?
  • Intro to Optical Hardware
  • Three generations of Optical
  • Various Switching Architectures
  • Circuit, Packet and Burst
  • Protection and Restoration

26
State of the World Today
O/E/O
E/O
O/E/O
E/O
O/E/O
O/E/O
O/E/O
O/E/O
E/O
E/O
Optical Core
27
View of a E/O node
Input Port 1
Input Port 1
O P 1
Optical Link 1
Electrical
Optical
Input Port 2
Input Port 2
O P 2
Optical Link 2
Input Port 3
O P 3
Input Port 3
O P 4
Optical Link 3
Input Port 4
Input Port 4
O P N-1
O P N
Physical View
Logical View
28
Optical Circuit Switching
O/E/O
E/O
OS
O/E/O
E/O
OS
O/E/O
OS
O/E/O
OS
O/E/O
OS
O/E/O
OS
E/O
E/O
Optical Core
29
Optical Circuit Switching
O/E/O
E/O
OS
O/E/O
E/O
OS
O/E/O
OS
O/E/O
OS
O/E/O
OS
O/E/O
OS
WC
E/O
E/O
Optical Core
30
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

31
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 !
32
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?

33
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 _at_ 10 Gbps requires 1.2 ?s of
    delay gt 360 m of fiber)
  • Delay is quantized
  • How about QoS?

34
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 ?

35
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

36
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

37
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.

38
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

39
QoS using Offset-Times
Assume two classes of service Class 1 has higher
priority Class 2 has zero offset time
to1
i
Time
ta1
ts1
ts1 l1
i
Time
ta2( ts2)
ts2 l2
tai arrival time for class i request tsi
service time for class i request
toi offset time for class i request li burst
length for class i request
40
Comparison
41
Hierarchical Optical Network
E/O
E/O
E/O
E/O
E/O
All O
OS
All O
OS
E/O
E/O
E/O
OS
OS
OS
E/O
WC
E/O
E/O
E/O
All O
All O
Optical Core
E/O
E/O
E/O
E/O
42
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

43
Outline
  • Why Optical?
  • Intro to Optical Hardware
  • Three generations of Optical
  • Various Switching Architectures
  • Circuit, Packet and Burst
  • Protection and Restoration

44
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

45
Types of Protection
  • Path protection
  • Dedicated (11) send traffic on both paths
  • Dedicated (11) use backup only at failure
  • Shared (N1) 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)

46
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

47
Protection and Restoration
  • Time of action
  • Path calculation (before or after failure ?)
  • Channel Assignments (before or after failure ?)
  • OXC Reconfiguration
  • ATT proposal
  • Calculate Path before failure
  • Try channel assignment after failure
  • Simulations show 50 gain over channel allocation
    before failure

48
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)

49
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

50
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 MP?S
  • www.cs.buffalo.edu/pub/WWW/faculty/qiao/
  • www.lightreading.com
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