IP over WDM network potx

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.