IP over WDM network
Fang Yu
294 Class Presentation
Outline
History of WDM networks
Current Internet: Multi-layer protocol stack
between IP and WDM layers
Future: IP directly over WDM
Challenge
Virtual Topology Reconfiguration
Multi-layer routing
One proposal: Optical Burst Switching technologies
History
In the late 70s
First fiber based optical transmission system
Before 1995
Mostly a single high-speed optical channel
All multiplexing done in electrical domain(TDM)
50Mb/s to 10Gb/s data services
After 1995
WDM allows simultaneously transmitting multiple high-speed
channels on different frequencies (Up to 160 wavelengths today)
40G per λ (OC768)
Total link capacity = 160 λ *40G =6.4 Tbps
Current Typical Protocol Stacks
IP
ATM
SONET
WDM
N e t w o r k
P h y s i c a l
D a t a l i n k
N e t w o r k
SONET
ATM
IP
D a t a l i n k
D a t a l i n k
N e t w o r k
WDM
Proprietary
(20-400 Gb/s)
OTS OTS OTS OTS OTS OTS
(OTS: Optical Transport
System)
Transport Layer Model
“Packet”
“Packet”
“Packet”
“Packet”
1/0 DCS
1/0 DCS
1/0 DCS
1/0 DCS
4E
4E
4E
4E
3/1 DCS
3/1 DCS
3/1 DCS
3/1 DCS
3/3 DCS
Layer (DACS III)
DACS III DACS III
DACS III
DACS III
ATM/IP
ATM/IP
ATM/IP
ATM/IP
DS1
(1.5 Mb/s)
DS3
(45 Mb/s)
DS3
(45 Mb/s)
OC48+
(2.5+ Gb/s)
ADM
ADM
ADM
ADM
ADM
ADM
ADM
Fiber Conduit/
Sheath
3/1 DCS
Layer
SONET ADM
Layer
Core ATM/IP
Layers
Service
Layers
Media
Layer
LA
CHCG
LA
LA
LA
LA
LA
LA
PHNX
PHNX
PHNX
CHCG
CHCG
CHCG
CHCG
CHCG
Wavelength Path
Crossconnect
Wavelength Mux Section
Crossconnect
Hard-
Wired
Disadvantage of Current Multi-
layer Protocol Stack
Inefficient
In IP over ATM over SONET over WDM network, 22%
bandwidth used for protocol overhead
Layers often do not work in concert
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
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 Multi-
layer Protocol Stack (Cont)
Functional overlap: So many layers are
doing the same thing
Routing
Protections
Slow speed
Electronic devices can not catch the transmission
speed available at optical layer
Latencies of connection
Historical Reason for Multi-layer
SONET over WDM
Conventional WDM deployment is using SONET as standard interface to higher
layers
IP over ATM
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
Electronic
Network
Electronic
Network
Electronic
Network
Electronic
Network
O/E/O
O/E/O
O/E/O
O/E/O
O/E/O
O/E/O
Optical Core
E/O
E/O E/O
E/O
Simplified Protocol Stacks?
IP
Frame Relay
ATM
SONET
WDM
IP
WDM
WDM-aware
Electronic layer
Current Typical Protocol Stack Simplified Protocol Stack
IP Directly Over WDM?
Establish high-speed optical layer connections
(lightpaths)
IP routers connected through lightpaths rather than
fiber
A
B C
D
E W a v e l e n g t h
c r o s s c o n n e c t
L i g h t p a t h s
I P r o u t e r
Challenge for IP over WDM
network
WDM-aware Electronic layer
Reconfiguration and load balancing
Protection and restoration
Optical flow switching
Network management/control
Cross-layer optimization
Reconfigurable (within milli-seconds) OXC
Wavelength Converters
No λ converters
1
2
3
New request
1 3
1
2
3
New request
1 3
With λ converters
WC
Virtual Topology Reconfiguration
Physical topology
Seen by optical layer
Virtual topology: a set of nodes interconnected by light-paths
(wavelength)
Seen by electronic layer
Reconfigure of light-paths in WDM network by
Changing the light path connectivity between electronic switches
Tuning of the transmitter wavelength and the frequency-selective-switches
A AB B
C D C D
Virtual Topology
Reconfiguration(Cont.)
Enable network to dynamically response to changing of traffic pattern
Load balancing
Efficiency
Issues:
Time scale of changes
Triggered by what mechanisms
IP routing properties (e. g. stability)
0.1
0.01
0.001
0.01 0.02 0.03
B
l
o
c
k
i
n
g
P
r
o
b
a
b
i
l
i
t
y
0.04
Fixed
Routing
Reconfigurable
Routing
0.05
X6
Call arrival rate
WDM ring, 20 nodes
one transceiver/node
call BW = 1 wavelength
Multi-layer Routing
IP layer routing is the bottleneck of present Internet
Solution: Routing long duration flows at lower layers
•
Conventional packet routing
•
Optical bypass of intermediate routers for high volume traffic
•
End-to end (user-to-user) flow of entire file bypassing routers
User 1 User 2
Router 1
Router 2
Router 3
WDM layer
. . .
. . .
Network control
LIDS
Switching all the packets in
optical layer?
Requires intelligence in the optical layer
Need to store packet during header processing
Optical buffers are extremely hard to
implement
1 pkt = 12 kbits @ 10 Gbps requires 1.2 µs of delay =>
360 m of fiber)
Optical Packet Switch still has a long way
to go………………………
Various Optical Switching
Technologies
Optical Burst Packet Switching
Retrospect the goal of IP over WDM:
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
Resources are allocated using one way reservation
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
The schemes differ in the way bandwidth release is
triggered.
In-band-terminator (IBT) – header carries the routing
information, then the payload followed by silenc e
(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
There is a time separation(offset time) between header
and data
Header and data are usually carried on different channels
Header goes through sophisticated electronic processing
Data is kept in optical domain
Conclusion
Current IP over ATM over SONET over WDM
network is inefficient and redundant
Future IP directly over WDM network
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
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.