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LIDS
Future Optical Network Architecture
Vincent Chan, Asuman Ozdaglar, Devavrat Shah
MIT
NSF FIND Meeting Nov 2006
Vincent Chan
1
LIDS
Optical Networks
User
Local
Network
User
User
User
Freq.
Convert
Local
Traffic
Blocking
Filter
User
Opt
ic
Am al
p
User
Optical
Router/
switch
•WDM, Optical amplifiers  high rates, long reach
multicasting
•Optical routing and switching  power localization,
narrow casting, long reach, high utilization?
User
User
User
•Increase in capacities (major difference between fiber
bandwidth and link rates)  decrease in cost?
Can we trade bandwidth utilization for lower cost ?
Perhaps but with new architectures!
Vincent Chan
2
LIDS
Optical Network – Near future
•Optical switching – GMPLS bypass, load
balancing,
… Wide Area Optical Network
Future
•Packet processing cost dominates IP Route r
IP R outer
O p tic al
X - Co nn ect
WDM
I P R ou ter
IP
data ctrl
I P R outer
O p tical
X- Co nnec t
O ptical
X -Co nn ect
WDM
WDM
Other
data
IP Ro uter
O p tica l
X -C on nec t
Optica l
X-Connect
WDM
IP R outer
O ptical
X -C onnect
IP Ro uter
O ptical
X -C on nect
I P R ou ter
O ptical
X -Co nn ect
WDM
WDM
OXC
WDM
WDM
IP Ro uter
O p tical
X -C on nect
W DM
IP R outer
O ptical
X -C onnect
IP R outer
O ptical
X -C onnect
WDM
WDM
IP R outer
O ptical
X -C onnect
IP R outer
O ptical
X -C onnect
WDM
WDM
IP R outer
O ptical
X -C onnect
IP R outer
O ptical
X -C onnect
WDM
O ptical
X -C onnect
Vincent Chan
WDM
IP R outer
WDM
3
LIDS
Subscriber cost
102 103
104 105
106
Optical network evolution/revolution
and disruptive technologies
•1st disruptive technology - WDM fiber links
•2nd disruptive technology - optical switching
•3rd disruptive technology - direct optical access
•4th disruptive technology - new transport mechanisms
e-switched architecture
Computing
Optical switching
Fiber trunks
Increasing line speeds
1
10
Electronic access
Optical access
Dispersion managed
Limit of WDM/optical switching technology ?
1970 1974 1978 1982 1986 1990 1994 1998 2002 2006 2010 2014 2018 2020
Can we trade bandwidth utilization for lower cost ?
Vincent Chan
4
LIDS
Optical Networks
Wide area
CO
Metro/access Feeder
•Transport mechanisms
–flow switching
AN
Distribution Tree
AN
•Physical and logical
architecture
AN
•Routing: separate IP
and optical control
planes
•Very fast dynamics <
100mS
AN
Distribution Rings
AN
Access Node
•Scalable
•Low cost
Distribution bus
Vincent Chan
5
LIDS
Candidate Transport Mechanisms
scheduler
WAN
LAN
LAN
X
X
mux
OXC
X w dedicated
wavelength
channels
WAN
LAN
LAN
X
X
mux
X
Tell-and-Go / burst switching
(TaG)
OXC
X w dedicated
wavelength
channels
X
Optical flow switching
(OFS)
WAN
MAN
router
LAN
MAN
WAN
router
LAN
X
LAN
OXC
X w dedicated
wavelength
channels
WAN
router
MAN
WAN
MAN
Generalized multiprotocol
label switching (GMPLS)
Vincent Chan
MAN
router
MAN
Electronic packet switching
(EPS)
6
LIDS
Optical Flow Switching and Bypass
User 1
Network control
...
Router 1
User 2
...
Router 2
Router 3
WDM layer
•End-to end (user-to-user) flows
bypassing routers
•Very challenging IP/optical
control planes (<100ms)
•Architecture provide multiple
services including overlays.
•Supports virtualization
Decreasing cost
to scale
•Security? Optical
infrastructure isolation
Vincent Chan
7
LIDS
The Optical Network Architect’s Problem
IP R outer
T
O ptical
X -C onnect
WDM
IP R outer
IP R outer
Given
dynamic
traffic
matrices
O ptical
X -C onnect
O ptical
X -C onnect
WDM
WDM
IP R outer
O ptical
X -C onnect
WDM
IP R outer
O ptical
X -C onnect
WDM
IP R outer
•When failure occurs or
traffic changes, tunable
XCR & OXC take care of
maintaining or providing
new logical connection
via RWA
O ptical
X -C onnect
Derive desired
logical topology
(multiple,
dynamic)
Design sensible
fiber plant topology
Joint
optimization
IP R outer
IP Router
Optical
X-Connect
•When needed physical
topology fixed part of
LTD can be redone to get
better connections when
traffic changes
WDM
O ptical
X -C onnect
WDM
WDM
IP R outer
IP Router
IP R outer
IP Router
Optical
X-Connect
Optical
X-Connect
WDM
O ptical
X -C onnect
WDM
O ptical
X -C onnect
WDM
WDM
IP R outer
IP Router
Optical
X-Connect
O ptical
X -C onnect
WDM
WDM
IP R outer
IP Router
Optical
X-Connect
O ptical
X -C onnect
WDM
WDM
IP R outer
IP Router
• Physical topology is
made changeable by OXC,
slow or fast.
Vincent Chan
O ptical
X -C onnect
Optical
X-Connect
WDM
WDM
Logical topology realized by routing
and wavelength assignment, RWA
(dynamic part of LTD)
Design physical topology
– fixed part of LTD
100ms can be as fast as 5ms + 1 roundtrip time
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LIDS
Cost comparison of transport mechanisms
0
10
-1
Network cost per user per bps ($/user/bps)
10
-2
10
Replacement of electronic
NICs with optical transceivers
at end users
-3
10
Replacement of electronic
MAN transport with optical
MAN transport
-4
10
-5
10
-6
10 -4
10
OFS
EPS (optical transport)
EPS
GMPLS
TaG (OBS?)
-3
10
Bump and flattening curve represent
the addition of expensive optical
transceivers at end users
-2
-1
0
10
10
10
Bandwidth per active user (Gbps)
1
10
2
10
This plot assumes that there are 10,000 users per MAN, including both active and dormant users. It is
assumed that 10% of the number of users in each MAN are active (i.e. transmitting) at any instant in time.
It is also assumed that MAN and WAN routers run at 20% utilization.
Vincent Chan
9
LIDS
Large reconfigurable optical switches as architecture building blocks
Broadcast flow-switching 
All other colors for e-IP
Optical
switch
WAN
…
…
…
…
S
Optical
switch
Feeder Network
Achievable rate for input 2
2-inputs/2-outputs multicast rates
…
…
Distribution network
λ-converter Optical splitter
Optical splitter λ-converter
Optical Multi-cast
Optical tree aggregation
•Large optical switches used for aggregation
and multi/narrow-cast
Conventional
multicast
•Reconfigurable at mS rates
Optical multicast
for input 1
•Allows dynamic group formation for active
flow switching users
Optical multicast
for input 2
Optical multicast
for both inputs
•Optical multicast create new reachable
regions with networking coding
•Simplifies hardware
Vincent Chan
Achievable rate for input 1
10
LIDS
Routing & Wavelength Assignment
and Flow Control Algorithms
• Two main challenges in the design of routing and flow control
mechanisms:
– Design of distributed asynchronous algorithms that work with local
information
– Nonconvexities due to integrality constraints, and nonlinear
dependencies on the lightpaths owing to fiber nonlinearities.
• Previous Work: RWA problem formulated as a mixed integer-linear
program (computationally very hard)
• Two approaches:
– Multi-commodity flow formulation
– Statistical techniques for routing, scheduling and admission control
Vincent Chan
11
LIDS
Multi-commodity Flow Formulation
• Optimal multi-commodity flow
formulation
• fl : Total flow of link l
• The link cost function convex and
monotonically increasing
– Keep link flows away from link
capacity
– The link cost function piecewise
linear with integer breakpoints
• We proved in some topologies that
the relaxed problem has an
integer optimal solution and
provided an efficient algorithm to
find it.
Vincent Chan
12
LIDS
Algorithms based on state statistics
•
Algorithms need to operate at the granularity of flows
•
Primary network layer tasks in flow-level network
– Admission control
• Buffering, admitting or dropping flows arriving at network
• Interacts with Routing and Scheduling to make decisions
– Routing and wavelength scheduling
• Assign rates to end-hosts at network layer based on available
statistical information
• Given rate requirement by interacting with routing, it
allocates physical resources such as lightpaths and
wavelengths to end-hosts
Vincent Chan
13
LIDS
Trade-off between performance,
complexity and network dynamics
•
The algorithms utilize statistical information about network
– Dynamics of network affects the confidence in statistical information
– Complexity of feedback can reduce effect of dynamics
 Trade-off between complexity and effect of dynamics
•
The confidence in statistical information affects performance
– Less accurate statistical information will lead to wastage of resources
•
Thus, for algorithms operating in such network
– Trade-off between performance, complexity and network dynamics plays an
important role in design
•
Traffic statistics collection algorithms are essential in the network
performance
Vincent Chan
14
LIDS
•‘New technology’
•New transport mechanisms
•New architectures
•New applications
•Grows faster than Moore’s Law
•New opportunities
Vincent Chan
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