ipwdm
TRANSCRIPT
IP over WDM network
Fang Yu294 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 (OC768) Total link capacity = 160 *40G =6.4 Tbps
Current Typical Protocol Stacks
IP
ATM
SONET
WDM
N e tw o rk
P h y s ic a l
D a ta li n k
N e tw o rk
SONE
T
ATM
IPD a ta li n k
D a ta li n k
N e tw o rk
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 DCSLayer (DACS III)
DACS III DACS III
DACS IIIDACS 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)
ADMADM ADM
ADM
ADM
ADMADM
Fiber Conduit/Sheath
3/1 DCSLayer
SONET ADMLayer
Core ATM/IPLayers
ServiceLayers
MediaLayer
LACHCG
LA
LA
LA
LA
LA
LA
PHNX
PHNX
PHNXCHCG
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/OO/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-awareElectronic 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 le n g thc ro s s co n n e c t
L ig h tp a th s
IP ro u te 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 converters
1
2 3
New request 1 3
1
2 3
New request 1 3
With 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-switchesA 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
0.0010.01 0.02 0.03
Blo
ckin
g P
rob
abil
ity
0.04
FixedRouting
ReconfigurableRouting
0.05
X6
Call arrival rate
WDM ring, 20 nodesone transceiver/nodecall 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 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 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 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
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.