Transcript IP over WDM network

IP over WDM network
Fang Yu
294 Class Presentation
Outline
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History of WDM networks
Current Internet: Multi-layer protocol stack
between IP and WDM layers
Future: IP directly over WDM
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Challenge
Virtual Topology Reconfiguration
Multi-layer routing
One proposal: Optical Burst Switching
technologies
History
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In the late 70s
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Before 1995
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First fiber based optical transmission system
Mostly a single high-speed optical channel
All multiplexing done in electrical domain(TDM)
50Mb/s to 10Gb/s data services
After 1995
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WDM allows simultaneously transmitting multiple high-speed
channels on different frequencies (Up to 160 wavelengths
today)
40G per l (OC768)
Total link capacity = 160 l *40G =6.4 Tbps
Current Typical Protocol Stacks
IP
Network
Data link
ATM
Network
Data link
WDM
Physical
WDM
ATM
Network
SONET
SONET
IP
Data link
Transport Layer Model
“Packet”
1/0 DCS
“Packet”
“Packet”
“Packet”
4E
1/0 DCS
1/0 DCS
4E
LA
1/0 DCS
4E
4E
CHCG
Service
Layers
DS1
(1.5 Mb/s)
ATM/IP
ATM/IP
ATM/IP
ATM/IP
Core ATM/IP
Layers
DACS III
LA
3/1 DCS
DACS III
DS3
(45 Mb/s)
LA
PHNX
ADM
ADM
HardWired
LA
OTS
OTS
OTS
OTS
OTS
PHNX
CHCG
Wavelength Path
Crossconnect
OTS
(OTS: Optical Transport
CHCG
System)
CHCG
PHNX
SONET ADM
Layer
ADM
Proprietary
(20-400 Gb/s)
LA
CHCG
3/3 DCS
Layer (DACS III)
ADM
ADM
ADM
OC48+
(2.5+ Gb/s)
ADM
3/1 DCS
3/1 DCS
Layer
CHCG
DACS III
DACS III
3/1 DCS
LA 3/1 DCS
DS3
(45 Mb/s)
Fiber Conduit/
Sheath
Wavelength Mux Section
Crossconnect
Media
Layer
Disadvantage of Current Multilayer Protocol Stack
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Inefficient
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In IP over ATM over SONET over WDM network, 22%
bandwidth used for protocol overhead
Layers often do not work in concert
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Every layer now runs at its own speed. So, low speed
devices cannot fill the wavelength bandwidth.
When detecting of failure, different layers compete for
protection
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Optical layer detects failure almost immediately, restores error
in 2us to 60ms
SONET layer detects failure in 2.3–100 us, restores error in 60
ms
Disadvantage of Current Multilayer Protocol Stack (Cont)
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Functional overlap: So many layers are doing
the same thing
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Slow speed
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Routing
Protections
Electronic devices can not catch the transmission
speed available at optical layer
Latencies of connection
Historical Reason for Multi-layer
SONET over WDM
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IP over ATM
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IP packets need to be mapped into ATM cells before transporting over WDM
using SONET frame
OEO conversions at every node is easier to build than all optical switch
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Electronic
Network
Conventional WDM deployment is using SONET as standard interface to
higher layers
E/O
O/E/O
O/E/O
E/O
Electronic
Network
O/E/O
O/E/O
O/E/O
O/E/O
E/O
Electronic
Network
E/O
Optical Core
Electronic
Network
Simplified Protocol Stacks?
IP
IP
Frame Relay
ATM
SONET
WDM-aware
Electronic layer
WDM
WDM
Current Typical Protocol Stack
Simplified Protocol Stack
IP Directly Over WDM?
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Establish high-speed optical layer connections
(lightpaths)
IP routers connected through lightpaths rather than
fiber
IP router
B
C
E Wavelength
crossconnect
Lightpaths
A
D
Challenge for IP over WDM
network
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WDM-aware Electronic layer
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Reconfiguration and load balancing
Protection and restoration
Optical flow switching
Network management/control
Cross-layer optimization
Reconfigurable (within milli-seconds) OXC
Wavelength Converters
3
2
3
2
WC
No l converters
1
New request
1 3
With l converters
1
New request
1 3
Virtual Topology Reconfiguration
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Physical topology
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Virtual topology: a set of nodes interconnected by light-paths
(wavelength)
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Seen by optical layer
Seen by electronic layer
Reconfigure of light-paths in WDM network by
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Changing the light path connectivity between electronic switches
Tuning of the transmitter wavelength and the frequency-selectiveswitches
A
B
A
B
C
D
C
D
Virtual Topology
Reconfiguration(Cont.)
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Enable network to dynamically response to changing of traffic
pattern
 Load balancing
Fixed
0.1
Routing
 Efficiency
0.01
Reconfigurable
Routing
X6
WDM ring, 20 nodes
one transceiver/node
call BW = 1 wavelength
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Issues:
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0.001
Time scale of changes
Triggered by what mechanisms
IP routing properties (e. g. stability)
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0.02
0.03
0.04
Call arrival rate
0.05
Multi-layer Routing
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IP layer routing is the bottleneck of present Internet
Solution: Routing long duration flows at lower layers
User 1
...
Router 1
Network control
Router 2
User 2
...
Router 3
WDM layer
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•
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Conventional packet routing
Optical bypass of intermediate routers for high volume traffic
End-to end (user-to-user) flow of entire file bypassing routers
LIDS
Switching all the packets in
optical layer?
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Requires intelligence in the optical layer
Need to store packet during header
processing
Optical buffers are extremely hard to
implement
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1 pkt = 12 kbits @ 10 Gbps requires 1.2 s of
delay => 360 m of fiber)
Optical Packet Switch still has a long
way to go………………………
Various Optical Switching
Technologies
Optical Burst Packet Switching
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Retrospect the goal of IP over WDM:
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Avoid electronic bottlenecks
Decrease the cost by simplifying the
multiple layer architecture
OBS is one proposal of how to realize
such a network
Optical Burst Switching
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Resources are allocated using one way
reservation
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Sender sends a request
Sender sends burst without waiting for an
acknowledgement of its reservation request
Switch does preparation for the burst when getting
the request
Bursts can have variable lengths
Burst switching does not necessarily require
buffering
Various OBSs
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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.
Main Characteristics of Optical
Burst Switching
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There is a time separation(offset time) between header
and data
Header and data are usually carried on different
channels
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Header goes through sophisticated electronic processing
Data is kept in optical domain
Conclusion
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Current IP over ATM over SONET over WDM network
is inefficient and redundant
Future IP directly over WDM network
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Advantages
 Less latency
 Automatic provisioning
 Higher bandwidth utilization
Challenge of packet directly over WDM network
 Optical buffer
Optical burst switch is one of the proposed techniques to IP
over WDM network
Reference
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John Strand, “Optical Networking and IP over Optical”, Feb 4, 2002
Kumar N. Sivarajan, “IP over Intelligent Optical Networks”, Jan 5, 2001
Gaurav Agarwal, “A Brief Introduction to Optical Networks”, 2001
Yang Lihong, “Optical Burst Switching”, CMU networking seminar presentation
Vincent W. S. Chan, “Optical Networks: Technology and Architecture”
Eytan Modian, “WDM-Based Packet Networks”, IEEE Communication Magazine,
March 1999
Ornan (Ori) Gerstel, Rajiv Ramaswami,, “Optical Layer Survivability—An
Implementation Perspective”, IEEE Journal on selected areas in
communications, October 2000
Eytan Modiano, Aradhana Narula-Tam, “Survivable lightpath routing:a new
approach to the design of WDM-based networks”, IEEE JSAC,April 2002
R. Ramaswami and K. N. Sivarajan, Optical Networks: A Practical Perspective,
San Francisco: Morgan Kaufmann, 1998.