Introduction to Multiwavelength Optical Networks

Introduction to Multiwavelength Optical Networks
Introduction to Multiwavelength
Optical Networks
Switching Technology S38.165
http://www.netlab.hut.fi/opetus/s38165
Source: Stern-Bala (1999), Multiwavelength Optical Networks
P. Raatikainen
Switching Technology / 2004
L11 - 1
Contents
• The Big Picture
• Network Resources
• Network Connections
P. Raatikainen
Switching Technology / 2004
L11 - 2
Optical network
• Why ?
–
–
–
–
technology push, but no significant demand pull yet
evolving bandwidth hungry applications
optical transport already in the trunk network
“The information superhighway is still a dirt road; more accurately, it is a
set of isolated multilane highways with cow paths for entrance.”
• Why not yet ?
– optical last mile (also known as the first mile) solutions still relatively
primitive
– still too expensive
– administrative, political, etc. reasons
=> “The information superhighway is still a dirt road; more accurately,
it is a set of isolated multilane highways with cow paths for entrance.”
• However, development getting pace
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Optical network (cont.)
• An optical network is defined to be a telecommunications network
– with transmission links that are optical fibers, and
– with an architecture designed to exploit the unique features of fibers
• The term optical network (as used here)
– does not necessarily imply a purely optical network,
– but it does imply something more than a set of fibers terminated by
electronic devices
• The “glue” that holds the purely optical network together consists of
– optical network nodes (ONN) connecting the fibers within the network
– network access stations (NAS) interfacing user terminals and other nonoptical end-systems to the network
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Optical network (cont.)
ONN (Optical Network Node)
• provides switching and routing functions to control optical signal paths,
configuring them to create required connections
NAS (Network Access Station)
• provides termination point for optical paths within the optical network layer
Basic types of optical networks
• transparent (purely optical) networks
– Static network = broadcast-and-select network
– Wavelength Routed Network (WRN)
– Linear Lightwave Network (LLN) = waveband routed network
• hybrid optical network = layered optical network
– Logically Routed Network (LRN)
P. Raatikainen
Switching Technology / 2004
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Physical picture of the network
ATM
LAN
Workstation
Supercomputer
NAS
NAS
NAS
NAS
ATM
NAS
ONN
ATM
NAS
Multimedia
terminal
ATM
Multimedia
terminal
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LAN
LAN
Switching Technology / 2004
ONN - Optical Network Node
NAS - Network Access Station
LAN - Local Area Network
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A wish list of optical networks
• Connectivity
– support of a very large number of stations and end systems
– support of a very large number of concurrent connections including
multiple connections per station
– efficient support of multi-cast connections
• Performance
–
–
–
–
–
–
–
high aggregate network throughput (hundreds of Tbps)
high user bit rates (few Gbps)
small end-to-end delay
low error rate (digital) / high SNR (analog)
low processing load in nodes and stations
adaptability to changing and unbalanced loads
efficient and rapid means of fault identification and recovery
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Switching Technology / 2004
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A wish list of optical networks (cont.)
• Structural features
– scalability
– modularity
– survivability (fault tolerance)
• Technology/cost issues
– access stations: small number of optical transceivers per station and
limited complexity of optical transceivers
– network: limited complexity of the optical network nodes, limited
number and length of cables and fibers, and efficient use (and reuse)
of optical spectrum
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Optics vs. electronics
Optical domain
• photonic technology is well suited to certain simple (linear) signal-routing
and switching functions
• static photonic devices offer
• optical power combining, slitting and filtering
• wavelength multiplexing, demultiplexing and routing
• channelization needed to make efficient use of the enormous bandwidth of
the fiber
• by wavelength division multiplexing (WDM)
• many signals operating on different wavelengths share each fiber
=> optics is fast but dumb
=> connectivity bottleneck
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Optics vs. electronics (cont.)
Electrical domain
• electronics is needed to perform more complex (nonlinear) functions
• signal detection, regeneration and buffering
• logic functions (e.g. reading and writing packet headers)
• however, these complex functions limit the throughput
• electronics also gives a possibility to include in-band control information
(e.g. in packet headers)
• enabling a high degree of virtual connectivity
• easier to control
=> electronics is slow but smart
=> electronic bottleneck
P. Raatikainen
Switching Technology / 2004
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Optics and electronics
Hybrid approach:
• a multiwavelength purely optical network as a physical foundation
• one or more logical networks (LN) superimposed on the physical layer, each
– designed to serve some subset of user requirements and
– implemented as an electronic overlay
• an electronic switching equipment in the logical layer acts as a middleman
– taking the high-bandwidth transparent channels provided by the physical layer and
organizing them into an acceptable and cost-effective form
Why hybrid approach ?
• purely optical wavelength selective switches offer huge aggregate throughput
of few connections
• electronic packet switches offer large number of relatively low bit rate virtual
connections
• hybrid approach exploits the unique capabilities of optical and electronic
switching while circumventing their limitations
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Example LAN interconnection
• Consider a future WAN serving as a backbone that interconnects a large
number of high-speed LANs (say 10,000), accessing the WAN through
LAN gateways (with aggregate traffic of tens of Tbps)
• Purely optical approach
– each NAS connects its LAN to the other LANs through individual optical
connections ⇒ 9 999 connections per NAS
– this is far too much for current optical technology
• Purely electronic approach
– electronics easily supports required connectivity via virtual connections
– however, the electronic processing bottleneck in the core network does not
allow such traffic
• Hybrid approach: both objectives achieved, since
– LN composed of ATM switches provides the necessary connectivity
– optical backbone at the physical layer supports the required throughput
P. Raatikainen
Switching Technology / 2004
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Contents
• The Big Picture
• Network Resources
–
–
–
–
–
Network Links: Spectrum Partitioning
Layers and Sublayers
Optical Network Nodes
Network Access Stations
Electrical domain resources
• Network Connections
P. Raatikainen
Switching Technology / 2004
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Network links
A large number of concurrent connections can be supported on each network
link through successive levels of multiplexing
• Space division multiplexing in the fiber layer:
– a cable consists of several (sometimes more than 100) fibers, which are
used as bi-directional pairs
• Wavelength division multiplexing (WDM) in the optical layer:
– a fiber carries connections on many distinct wavelengths (λ-channels)
– assigned wavelengths must be spaced sufficiently apart to keep
neighboring signal spectra from overlapping (to avoid interference)
• Time division multiplexing (TDM) in the transmission channel sublayer:
– a λ-channel is divided (in time) into frames and time-slots
– each time-slot in a frame corresponds to a transmission channel, which
is capable of carrying a logical connection
– location of a time-slot in a frame identifies a transmission channel
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Fiber resources
Cable
Fibers
Wavebands
{ Transmission channel out
...
...
λ-channels in
...
λ-channels out
...
{ Transmission channel in
Space
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Wavelength
Time
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Optical spectrum
• Since wavelength λ and frequency f are related by f λ = c, where c is the
velocity of light in the medium, we have the relation
∆f ≈ − c ∆2λ
λ
• Thus, 10 GHz ≈ 0.08 nm and 100 GHz ≈ 0.8 nm in the range of 1,550 nm,
where most modern lightwave networks operate
• The 10-GHz channel spacing is sufficient to accommodate λ-channels
carrying aggregate digital bit rates on the order of 1 Gbps
- modulation efficiency of 0.1 bps/Hz typical for optical systems
• The 10-GHz channel spacing is suitable for optical receivers, but much too
dense to permit independent wavelength routing at the network nodes
- for this, 100-GHz channel spacing is needed.
• In a waveband routing network, several λ-channels (with 10-GHz channel
spacing) comprise an independently routed waveband (with 100-GHz
spacing between wavebands).
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Wavelength partitioning of the optical
spectrum
λ-channel spacing for separability at receivers
Unusable spectrum
λ1
λ2
λm
...
f/λ
λ [GHz/nm]
10 GHz
0.08 nm
λ-channel spacing for separability at network nodes
λ1
λ2
λm
...
f/λ
λ
100 GHz/0.8 nm
P. Raatikainen
Switching Technology / 2004
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Wavelength and waveband partitioning
of the optical spectrum
10 GHz/
0.08 nm
λ1,1
λ2,1
λ10,1
...
100 GHz/0.8 nm
w1
100 GHz
w2
...
wm
f/λ
λ
100 GHz
200 GHz/ 0.16 nm
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Capacity of wavelength and waveband
routed networks
• Connections in optical networks usually require wavelength continuity, i.e.,
signal generated at a given wavelength must remain on that wavelength
from source to destination
• Due to the current state of technology, imperfections in signal resolution at
network nodes result in signal attenuation, distortion and cross-talk, which
accumulate along the path
=> channel spacing cannot be as dense in the network nodes as in the
end-receivers
=> loss of transport capacity
• Capacity losses can be avoided by switching wavebands (composed of a
number of wave lengths) instead of individual wavelengths
=> wavelength routed solutions have lower throughput than
waveband routed solutions
P. Raatikainen
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Network based on spectrum partitioning
λ 1, λ 2 ,..., λ m
Single waveband
λ1
λ 1,1 -λ
λ 10,1
w1
λ2
w2
λ 1,10 -λ
λ 10,2
...
...
λm
w2
w1
λ 1,m -λ
λ 10,m
wm
Wavelength-routed
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wm
Waveband-routed
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Contents
• The Big Picture
• Network Resources
–
–
–
–
–
Network Links: Spectrum Partitioning
Layers and Sublayers
Optical Network Nodes
Network Access Stations
Electrical domain resources
• Network Connections
P. Raatikainen
Switching Technology / 2004
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Layered view of optical network (1)
NAS
E
Access
Link
Network
Link
O
NAS
OA
OA
E
TP OT
O
OR RP
ONN
ONN
RP OR
OT TP
Fiber Section
Fiber Link
Optical/Wavelength Path
λ-channel
Optical Connection
Transmission Channel
Logical Connection
-E
-O
- OA
- ONN
P. Raatikainen
Electronic
Optical
Optical Amplifier
Optical Network Node
- OR
- OT
- RP
- TR
Optical Receiver
Optical Transmitter
Reception Processor
Transmission Processor
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Layered view of optical network (2)
VIRTUAL CONNECTION
LOGICAL PATH
Logical layer
LOGICAL CONNECTION
TRANSMISSION CHANNEL
OPTICAL
LAYER
OPTICAL CONNECTION
λ-CHANNEL
Physical layer
OPTICAL/WAVEBAND PATH
FIBER
LAYER
FIBER LINK
FIBER SECTION
Sub- layers
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Layers and sublayers
• Main consideration in breaking down optical layer into sublayers is to
account for
– multiplexing
– multiple access (at several layers)
– switching
• Using multiplexing
– several logical connections may be combined on a λ-channel originating
from a station
• Using multiple access
– λ-channels originating from several stations may carry multiple logical
connections to the same station
• Through switching
– many distinct optical paths may be created on different fibers in the
network, using (and reusing) λ-channels on the same wavelength
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Typical connection
Virtual Connection
ES
ES
Logical Path
LSN
LSN
LSN
Logical Connection
NAS
Optical Connection
Logical Connection
Optical Connection
NAS
NAS
OA
ONN
ONN
ONN
ONN
ONN
ES
LSN
NAS
ONN
OA
P. Raatikainen
ONN
OA
= End System
= Logical Switching Node
= Network Access Node
= Optical Network Node
= Optical Amplifier
Switching Technology / 2004
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Contents
• The Big Picture
• Network Resources
–
–
–
–
–
Network Links: Spectrum Partitioning
Layers and Sublayers
Optical Network Nodes
Network Access Stations
Electrical domain resources
• Network Connections
P. Raatikainen
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Optical network nodes (1)
• Optical Network Node (ONN) operates in the optical path
sublayer connecting N input fibers to N outgoing fibers
• ONNs are in the optical domain
1
• Basic building blocks:
2
– wavelength multiplexer (WMUX)
– wavelength demultiplexer (WDMUX)
N
– directional coupler (2x2 switch)
• static
input fibers
• dynamic
– wavelength converter (WC)
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1′′
2′′
N′′
output fibers
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Optical network nodes (2)
• Static nodes
– without wavelength selectivity
• NxN broadcast star (= star coupler)
• Nx1 combiner
• 1xN divider
– with wavelength selectivity
• NxN wavelength router (= Latin router)
• Nx1 wavelength multiplexer (WMUX)
• 1xN wavelength demultiplexer (WDMUX)
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Optical network nodes (3)
• Dynamic nodes
– without wavelength selectivity (optical crossconnect (OXC))
• NxN permutation switch
• RxN generalized switch
• RxN linear divider-combiner (LDC)
– with wavelength selectivity
• NxN wavelength selective crossconnect (WSXC) with
M wavelengths
• NxN wavelength interchanging crossconnect (WIXC)
with M wavelengths
• RxN waveband selective LDC with M wavebands
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Wavelength multiplexer and
demultiplexer
λ1
λ1
λ2
λ1,…,λ4
λ3
λ1,…,λ4
λ4
λ3
λ4
WMUX
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λ2
WDMUX
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Directional Coupler (1)
• Directional coupler (= 2x2 switch) is an optical four-port
– ports 1 and 2 designated as input ports
– ports 1’ and 2’ designated as output ports
• Optical power
– enters a coupler through fibers attached to input ports
– divided and combined linearly
– leaves via fibers attached to output ports
• Power relations for input signal powers P1 and P2 and
output powers P1′ and P2′ are given by
a11
1
P1′ = a11P1 + a12 P2
a21
P2′ = a 21 P1 + a22 P2
• Denote power transfer matrix by A
and power matrix by P = [Pi] =>
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1′′
a12
= [aij]
P’ = AP
2
2′′
a22
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Directional Coupler (2)
• Ideally, the power transfer matrix A is of the form
1 − α
A=
 α
α 
,
1 − α 
0 ≤α ≤1
• If parameter α is fixed, the device is static, e.g. with α = 1/2 and
signals present at both inputs, the device acts as a 2x2 star coupler
• If α can be varied through some external control, the device is
dynamic or controllable, e.g. add-drop switch
• If only input port 1 is used (i.e., P2 = 0),
1
the device acts as a 1x2 divider
• If only output port 1’ is used (and port 2’ is
2
terminated), the device acts as a 2x1 combiner
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1 −α
α
α
1 −α
1′′
2′′
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Add-drop switch
OT
OR
OT
Add-drop state
OR
Bar state
OR - Optical Receiver
OT - Optical Transmitter
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Broadcast star
• Static NxN broadcast star with N
wavelengths can carry
– N simultaneous multi-cast optical
connections (= full multipoint optical
connectivity)
1
λ1
2
λ2
3
λ3
λ1,…,λ4
4
λ4
λ1,…,λ4
• Power is divided uniformly
• To avoid collisions each input signal
1
must use different wavelength
2
• Directional coupler realization
– (N/2) log2N couplers needed
1/2
1/
1/2
1/
3
λ1,…,λ4
1/N
1/
1/N
1/
1/N
1/
1/N
1/
λ1,…,λ4
1/2
1/
1/2
1/
1/2
1/
1/2
1/
4
1′′
2′′
3′′
4′′
1′′
2′′
3′′
4′′
broadcast star realized
by directional couplers
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Wavelength router
• Static NxN wavelength router with N wavelengths can carry
– wavelengths from the different inputs are routed so that identical
wavelengths do not enter the same outputs (Latin square principle)
– N2 simultaneous unicast optical
connections (= full point-to-point
λ ,…,λ4
λ1,…,λ4
optical connectivity)
1 1
1′′
λ
,…,
λ
λ
,…,
λ
1
4
1
4
• Requires
2
2′′
– N 1xN WDMUX’s
– N Nx1 WMUX’s
3
4
λ1,…,λ4
λ1,…,λ4
λ1,…,λ4
λ1,…,λ4
WDMUX’s
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WMUX’s
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Crossbar switch
• Dynamic RxN crossbar switch consists of
– R input lines
1
– N output lines
2
– RN crosspoints
• Crosspoints implemented by
3
controllable optical couplers
– RN couplers needed
4
• A crossbar can be used as
– a NxN permutation switch
(then R = N) or
– a RXN generalized switch
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1′
2′
3′
4′
crossbar used as
a permutation switch
L11 - 36
3′′
4′′
Permutation switch
1
1′
2
2′
3
3′
4
4′
output ports
1′ 2′ 3′ 4′
input ports
• Dynamic NxN permutation switch
(e.g. crossbar switch)
– unicast optical connections
between input and output ports
– N! connection states
(if nonblocking)
– each connection state can carry N
simultaneous unicast optical
connections
– representation of a connection state
by a NxN connection matrix
(exactly one connection “1” per each
row and column)
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1
1
2 1
1
3
1
4
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Generalized switch
• Dynamic RxN generalized switch (e.g. crossbar switch)
• Input/output power relation P’ = AP with
NxR power transfer matrix A = [aij], where
 1 , if switch (i,j ) is on
aij =  NR
0,
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otherwise
Switching Technology / 2004
1′′
1/N
1/
1/N
1/
1/N
1/
1/N
1/
1
2
3
2′′
3′′
1/
1/R
1/ 1/R
1/R
1/
1/R
1/
4
4′′
output ports
1′ 2′ 3′ 4′
input ports
– any input/output pattern possible (incl.
one-to-many and many-to one connections)
– 2NR connection states
– each connection state can carry (at most)
R simultaneous multicast optical
connections
– a connection state represented by a RxN
connection matrix
1
1 1
2 1
3
4 1
1
1 1
1
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Linear Divider-Combiner (LDC)
1′′
1
• Linear Divider-Combiner (LDC) is
δ δ11
δ41δ31 21
a generalized switch that
2
– controls power-dividing and
power-combining ratios
3
σ41
– less inherent loss than in crossbar
σ42
σ43
σ44
4
• Power-dividing and power-combining ratios
– δij = fraction of power from input port j directed to output port i’
– σij = fraction of power from input port j combined onto output port i’
• In an ideal case of lossless couplers, we have constraints
2′′
3′′
4′′
∑ δ ij = 1 and ∑ σ ij = 1
i
j
• The resulting power transfer matrix A = [aij] is such that
aij = δ ijσ ij
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LDC and generalized switch realizations
1
rx1
combiner
directional couplers
11
12
1r
...
22
2r
1xn
splitter
...
21
2
n
...
n1
δ - σ linear divider-combiner
1
2
n2
nr
r
Generalized optical switch
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Wavelength selective cross-connect
(WSXC)
• Dynamic NxN wavelength selective crossconnect
(WSXC) with M wavelengths
– includes N 1xM WDMUXs,
M NxN permutation switches, λ ,…,λ
λ1,…,λ4
4
1 1
and N Mx1 WMUXs
λ ,…,λ4
λ1,…,λ4
– (N!)M connection states
2 1
if the permutation switches
λ ,…,λ4
λ1,…,λ4
3 1
are nonblocking
λ ,…,λ4
λ1,…,λ4
4 1
– each connection state can
carry NM simultaneous
unicast optical connections
WDMUX’s
WMUX’s
– representation of a connection
state by M NxN connection matrices optical switches
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Switching Technology / 2004
1′′
2′′
3′′
4′′
L11 - 41
Wavelength interchanging cross-connect
(WIXC)
• Dynamic NxN wavelength interchanging crossconnect
(WIXC) with M wavelengths
– includes N 1xM WDMUXs, 1 NM x NM permutation
switch, NM WCs, and N Mx1 WMUXs
– (NM)! connection states if
λ ,…,λ4
λ1,…,λ4
1 1
the permutation switch is
λ ,…,λ4
λ1,…,λ4
nonblocking
2 1
λ ,…,λ4
λ1,…,λ4
– each connection state can
3 1
carry NM simultaneous
λ ,…,λ4
λ1,…,λ4
4 1
unicast connections
– representation of a connection
WC’s
state by a NMxNM
WDMUX’s
WMUX’s
connection matrix
optical switch
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1′′
2′′
3′′
4′′
Waveband selective LDC
• Dynamic RxN waveband selective LDC with M wavebands
– includes R 1xM WDMUXs, M RxN LDCs, and N Mx1 WMUXs
– 2RNM connection states (if used
as a generalized switch)
w ,…,w4
w1,…,w4
1 1
– each connection state can
w ,…,w4
w1,…,w4
carry (at most) RM
2 1
simultaneous multi-cast
w ,…,w4
w1,…,w4
3 1
connections
w ,…,w4
w1,…,w4
4 1
– representation of a
connection state by a M RxN
connection matrices
WDMUX’s
WMUX’s
LDC’s
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Switching Technology / 2004
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Contents
• The Big Picture
• Network Resources
–
–
–
–
–
Network Links: Spectrum Partitioning
Layers and Sublayers
Optical Network Nodes
Network Access Stations
Electrical domain resources
• Network Connections
P. Raatikainen
Switching Technology / 2004
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1′′
2′′
3′′
4′′
Network access stations (1)
• Network Access Station (NAS) operates in the logical
connection, transmission channel and λ-channel sublayers
• NASs are the gateways between the electrical and optical
domains
e/o
• Functions:
– interfaces the external LC ports to
the optical transceivers
– implements the functions necessary
to move signals between the electrical
and optical domains
1
2
L
electronic wires
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a
a’
1′′
2′′
L′′
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optical fibers
L11 - 45
Network access stations (2)
• Transmitting side components:
– Transmission Processor (TP) with a number of LC input ports and
transmission channel output ports connected to optical transmitters
(converts each logical signal to a transmission signal)
– Optical Transmitters (OT) with a laser modulated by transmission
signals and connected to a WMUX (generates optical signals)
– WMUX multiplexes the optical signals to an outbound access fiber
• Receiving side components:
– WDMUX demultiplexes optical signals from an inbound access fiber and
passes them to optical receivers
– Optical Receivers (OR) convert optical power to electrical transmission
signals, which are corrupted versions of the original transmitted signals
– Reception Processor (RP) converts the corrupted transmission signals
to logical signals (e.g. regenerating digital signals)
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Elementary network access station
logical connection ports
e/o
OT
WMUX
TP
OT
ONN
OR
WDMUX
RP
OR
NAS
OR
OT
RP
TP
- Optical Receiver
- Optical Transmitter
- Reception Processor
- Transmission Processor
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access fiber pair
internodal fiber pairs
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Non-blocking network access station
logical connection ports
e/o
OT
WMUXs
TP
OT
ONN
OR
WDMUXs
RP
OR
NAS
access fiber pairs
internodal fiber pairs
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Wavelength add-drop multiplexer
(WADM)
WADM
WMUX
λ2
...
WDMUX
λ1
λm
λ1
OT
λ2
OR
OT
λm
OR
...
OT
OR
NAS
TP/RP
...
WADM combined with NAS
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Contents
• The Big Picture
• Network Resources
–
–
–
–
–
Network Links: Spectrum Partitioning
Layers and Sublayers
Optical Network Nodes
Network Access Stations
Electrical domain resources
• Network Connections
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End System
• End systems are in the electrical domain
• In transparent optical networks, they are directly
connected to NASs
– purpose is to create full logical connectivity
between end stations
• In hybrid networks, they are connected to LSNs
– purpose is to create full virtual connectivity
between end stations
a
a’
access wires
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Logical Switching Node (LSN)
• Logical switching nodes (LSN) are needed in hybrid networks,
i.e. in logically routed networks (LRN)
• LSNs operate in the electrical domain
• Examples of LSNs are
– SONET digital cross-connect systems (DCS)
– ATM switches
1
1′′
2′′
2
– IP routers
N
input wires
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N′′
output wires
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Logically routed network
End systems
Logically
switching
node
LS
Logical layer
NAS
LSN
ONN
Physical layer
LSN - Logically Switching Node
LS - Logical Switch
NAS - Network Access Station
ONN - Optical Network Node
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Contents
• The Big Picture
• Network Resources
• Network Connections
– Connectivity
– Connections in various layers
– Example: realizing full connectivity between five
end systems
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Connectivity
• Transmitting side:
– one-to-one
• (single) unicast
– one-to-many
• multiple unicasts
• (single) multicast
• multiple multicasts
• Receiving side:
– one-to-one
• (single) unicast
• (single) multicast
– many-to-one
• multiple unicasts
• multiple multicasts
• Network side:
– point-to-point
– multipoint
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Connection Graph (CG)
• Representing point-to-point connectivity between end systems
transmitting
side
1
4
2
3
Connection graph
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receiving
side
1
1
2
2
3
3
4
4
Bipartite representation
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Connection Hypergraph (CH)
• Representing multipoint connectivity between end systems
transmitting
side
1
E1
1
2
E2
4
3
receiving
side
1
2
E1
2
3
E2
3
4
Connection hypergraph
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hyperedges
4
Tripartite representation
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Contents
• The Big Picture
• Network Resources
• Network Connections
– Connectivity
– Connections in various layers
– Example: realizing full connectivity between five
end systems
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Connections in various layers
• Logical connection sublayer
– Logical connection (LC) is a unidirectional connection between
external ports on a pair of source and destination network
access stations (NAS)
• Optical connection sublayer
– Optical connection (OC) defines a relation between one
transmitter and one or more receivers, all operating in the same
wavelength
• Optical path sublayer
– Optical path (OP) routes the aggregate power on one waveband
on a fiber, which could originate from several transmitters within
the waveband
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Notation for connections in various
layers
• Logical connection sublayer
– [a, b] = point-to-point logical connection from an external port on station a
to one on station b
– [a, {b, c, …}] = multi-cast logical connection from a to set {b, c, …}
• station a sends the same information to all receiving stations
• Optical connection sublayer
– (a, b) = point-to-point optical connection from station a to station b
– (a, b)k = point-to-point optical connection from a to b using wavelength λk
– (a,{b,c,…}) = multi-cast optical connection from a to set {b,c,…}
• Optical path sublayer
– 〈a, b〉 = point-to-point optical path from station a to station b
– 〈a, b〉k = point-to-point optical path from a to b using waveband wk
– 〈a, {b, c, …}〉 = multi-cast optical path from a to set {b,c,…}
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Example of a logical connection between
two NASs
Logical connection [A,B]
NAS
NAS
TP
RP
Transmission channel
Electrical
Electrical
Optical connection (A,B)λ
OT
Optical
1
λ-channel
λ1 ... λm
OR
λm ... λ1
WMUX
Optical
WDMUX
Optical path <A,B>w
1
w1
ONN
w2
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ONN
ONN
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Contents
• The Big Picture
• Network Resources
• Network Connections
– Connectivity
– Connections in various layers
– Example: realizing full connectivity between
five end systems
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Example: realization of full connectivity
between 5 end systems
1
5
2
4
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3
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Solutions
• Static network based on star physical topology
– full connectivity in the logical layer (20 logical connections)
– 4 optical transceivers per NAS, 5 NASs, 1 ONN (broadcast star)
– 20 wavelengths for max throughput by WDM/WDMA
• Wavelength routed network (WRN) based on bi-directional ring physical
topology
– full connectivity in the logical layer (20 logical connections)
– 4 optical transceivers per NAS, 5 NASs, 5 ONNs (WSXCs)
– 4 wavelengths (assuming elementary NASs)
• Logically routed network (LRN) based on star physical topology and
unidirectional ring logical topology
– full connectivity in the virtual layer but only partial connectivity in the logical
layer (5 logical connections)
– 1 optical transceiver per NAS, 5 NASs, 1 ONN (WSXC), 5 LSNs
– 1 wavelength
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Solution markings
End station
Logical switching node, e.g. ATM switch
Network access station
Wavelength switching equipment, e.g. star coupler or
wavelength selective cross-connect
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Static network realization
1
1
1
2
5
2
5
2
3
4
4
3
4
5x5 broadcast star
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3
5
LCG
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Wavelength routed network realization
3x3 WSXC
1
1
1
2
2
5
5
2
3
4
3
4
4
5
3
LCG
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Logically routed network realization
1
LSN
1
1
2
5
5
2
2
3
4
4
4
3
3
5x5 WSXC
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5
LCG
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L11 - 68
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