1. DWDM and Internets’ Bandwidth Future
Yury Krotov and Elena Apter

2. Content Introduction Internet’s Growth Trends DWDM Physical Principles
DWDM Devices
TDM And WDM
DWDM and Network Protocols (SONET/SDH)
Conclusions
Q&A

3. Internet Traffic/Data Transmission Costs Trends
costs halved every 79 month
1995 – now every 9 month (DWDM)
traffic doubled every 21 months
every 9 months (TCP)
1998-now every 6 month (DWDM)
Same trend is expected to last until 2008

4. Internet Technology Trends
Source: Lawrence G. Roberts, Beyond Moore's Law: Internet Growth Trends,
COMPUTER JANUARY 2000, pp

5. Internet Bandwidth Use
consumer broadband adoption will be the real driver for Internet traffic growth over the next five years
By percent of all Internet traffic will be generated by consumers, while business users will account for the remaining 40 percent.

6. DWDM Applications
Source: AON

7. Source: CISCO DWDM tutorial
TDM and WDM
TDM-Time Division Multiplexing
WDM – Wave Division Multiplexing
Source: CISCO DWDM tutorial

8. Area of Application of DWDM
metro and long-haul networks
Source: CISCO DWDM tutorial

9. DWDM Principles

10. DWDM System Application
Transmitters
Receivers
Fiber amplifiers
DWDM multiplexers
DWDM demultiplexers

11. DWDM Optical Network Transmitter/receiver Multiplexer/Demultiplexer
Amplifier
Optical fiber

12. Transmitter Changes electrical bits to optical pulses
Is frequency specific
Uses a narrowband laser to generate the optical pulse
Infrared band

13. Tunable Laser
Requirements: precise wavelength ,narrow spectrum width,sufficient power,and control of chirp.
Semiconductor lasers satisfy the first three requirements:monochromatic Fabry-Perot, distributed feedback (DFB) etc.
Combiner sums1310 nm and laser wavelength.
SOA boosts the signal out.

14. Multiplexer\demultiplexer
Combines/separates discrete wavelengths

15. Multiplexing Prism refraction
Waveguide grating diffraction (each wavelength is diffracted at a different angle and therefore to a different point in space

16. Arrayed Waveguide Gratings
Optical waveguide router.
An array of curved-channel waveguides with a fixed difference in the path length between adjacent channels.
Different wavelength have maximal interference at different locations, which correspond to output ports.
Temperature sensitive.
Can be designed to perform M/D simultaneously.

17. Multilayer Interference Filters
Demultiplexing by cascading thin-film filters
Good stability and isolation between channels
Moderate cost
Impractical for large channel counts

18. Optical Amplifier
Pre-amplifier boosts signal pulses at the receive side
Post-amplifier boosts signal pulses at the transmit side
In line (ILA) provides signal recovery
Amplifiers add noise to the desired signal which limits the number of amplifications

19. Erbium-doped Fiber Amplifiers
Erbium,when excited, emits light around 1500 nm
Pump laser 980 nm or 1480 nm
Distance between optical amplifiers 120 km
Distance 500 km –signal recovery

20. Receiver Parameters Receivers use a photodiode.
PIN (positive-intrinsic-negative)photodiodes. Photon to electron ratio 1:1. Low cost and reliability.
Avalanche photodiodes (APDs)-provide gain through multiplication slower but more sensitive.

21. Transmission Challenges
Attenuation.
Chromatic dispersion.
Polarization mode dispersion.
Nonlinearities-cumulative effects from the interaction of light with the material through which it travels. Cannot be compensated, they are fundamental limiting mechanisms to the amount of data that can be retransmitted in optical fiber. The most important types of non linear effects are simulated Brillouin scattering, stimulated Raman scattering, self-phase modulation, and four- wave mixing.

22. Chromatic Dispersion
Chromatic dispersion is a measure of fiber delay for different wavelength.
It cause flattering and widening of the signal.
The faster the rate of transmission the greater the dispersion effects.
Some dispersion is required in DWDM networks. Newer fiber have just enough dispersion to eliminate cross-talk.

23. Compensation Modules SMF fiber has an average 17ps/nm/km of dispersion
A 10 Gb/s receiver can tolerate about 800 ps/nm of dispersion
A 500 km system generates 17X500=8500 ps/nm of dispersion
The DWDM system must compensate for dispersion to support 10-Gb/s transmission
2.5-Gb/s transmission is 16 times less sensitive

24. DWDM systems
In the short-haul network, PMD and nonlinear effects are not so critical as they are in long-haul systems, where higher speeds(OS-192 and higher) are more common. DWDM systems using optical signals of 2.5 Gbps or less are not subject to these nonlinear effects at short distances
In the long-distance network the majority of embedded fiber is standard single-mode with high dispersion in the 1550-nm window.
Dispersion can be mitigated to some extend, and some cost,using dispersion compensators.
Higher optical power introduces nonlinear effects.
Non-zero dispersion-shifted fiber takes advantage of the fact that a small amount of chromatic dispersion can be used to mitigate nonlinear effects such as four-wave mixing.

25. SONET/SDH SONET was developed in 1980’s by Bellcore
SONET/SDH is a TDM technology, optimized for voice data transmission
Long-haul networks are dominated by SONET/SDH
Base level STS-1: 51.8 Mbps. Higher level signals are integer multiples
Utilizes synchronous signals

26. Source: CISCO DWDM tutorial
SONET with DWDM
DWDM as a transport for TWM
Eliminates another SONET layer for combining different protocols
Source: CISCO DWDM tutorial

27. DWDM eliminates regenerators

28. Industry Leaders
Cisco – Cisco ONS 15808: up to 160 channels 40Gbps Dense Wavelength-Division Multiplexing (DWDM) system
Lucent
Nortel Networks
Alcatel
Fujitsu
ADVA

29. Future of Optical Market
The size of optical-networking equipment market (SONET, SDH, DWDM, DXC, and OXC) $10.1 b in 2002.
next-generation SONET and SDH will have the strongest growth, averaging 17% fro m 2002 to 2007
DWDM will have an 11- percent annual growth rate over that period
Source: KMI Research

30. Conclusions: Advantage of DWDM
Provides enormous bandwidth (theoretically ~25 Tbps). New computational model: slow computers/fast network
DWDM can transmit several different protocols and speeds over the same link
Provides cost saving due to elimination of regenerators
“Bandwidth on demand” – fast upgrade of existing networks. No additional equipment is needed

31. Conclusions: Future of DWDM
Video communication/video on demand
Reducing space between wavelengths
Expanding transmission range
DWDM will reach individual residencies

32. Q&A