1. Future Optical Network Architecture
Vincent Chan, Asuman Ozdaglar, Devavrat Shah
MIT
NSF FIND Meeting Nov 2006
Vincent Chan

2. Optical Networks Can we trade bandwidth utilization for lower cost ?
WDM, Optical amplifiers  high rates, long reach multicasting
Optical routing and switching  power localization, narrow casting, long reach, high utilization?
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

3. Optical Network – Near future
Optical switching – GMPLS bypass, load balancing, …
Packet processing cost dominates
Vincent Chan

4. 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
Subscriber cost
e-switched architecture
Computing
Optical switching
Electronic access
Fiber trunks
Increasing line speeds
Optical access
Dispersion managed
Limit of WDM/optical switching technology ?
Can we trade bandwidth utilization for lower cost ?
Vincent Chan

5. Optical Networks Wide area Metro/access
Physical and logical architecture
Transport mechanisms –flow switching
Routing: separate IP and optical control planes
Very fast dynamics < 100mS
Scalable
Low cost CO AN
Metro/access
Feeder
Distribution Tree AN AN AN AN
Distribution Rings
Access Node
Distribution bus
Vincent Chan 1 1

6. Candidate Transport Mechanisms
scheduler
WAN
WAN
LAN
LAN
LAN
LAN X X X
OXC X
OXC X
w dedicated wavelength
channels X
w dedicated wavelength
channels
mux X
mux X
Tell-and-Go / burst switching (TaG)
Optical flow switching (OFS)
WAN
LAN
MAN
router
LAN
MAN
router
WAN
router X
WAN
router
OXC
LAN
MAN X
w dedicated wavelength
channels
MAN
WAN
MAN
MAN
Generalized multiprotocol label switching (GMPLS)
Electronic packet switching (EPS)
Vincent Chan

7. Decreasing cost to scale
Optical Flow Switching and Bypass
Network control
User 1
User 2
. . .
. . .
Router 1
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
Security? Optical infrastructure isolation
Decreasing cost to scale
Vincent Chan

8. Design physical topology
The Optical Network Architect’s Problem T
Given dynamic
traffic matrices
Derive desired logical topology (multiple, dynamic)
Design sensible fiber plant topology
Design physical topology
– fixed part of LTD
Logical topology realized by routing and wavelength assignment, RWA (dynamic part of LTD)
When failure occurs or traffic changes, tunable XCR & OXC take care of maintaining or providing new logical connection via RWA
When needed physical topology fixed part of LTD can be redone to get better connections when traffic changes
Physical topology is made changeable by OXC, slow or fast.
Joint optimization
100ms can be as fast as 5ms + 1 roundtrip time
Vincent Chan

9. Cost comparison of transport mechanisms
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

10. Large reconfigurable optical switches as architecture building blocks
Large optical switches used for aggregation and multi/narrow-cast
Reconfigurable at mS rates
Allows dynamic group formation for active flow switching users
Optical multicast create new reachable regions with networking coding
Simplifies hardware
Vincent Chan

11. 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

12. 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

13. 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

14. 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

15. New transport mechanisms New architectures New applications
‘New technology’
New transport mechanisms
New architectures
New applications
Grows faster than Moore’s Law
New opportunities
Vincent Chan