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.