DWDM and Internets’ Bandwidth Future Yury Krotov and Elena Apter

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

Internet Traffic/Data Transmission Costs Trends 1970-1995 costs halved every 79 month 1995 – now every 9 month (DWDM) 1970-1980 traffic doubled every 21 months 1980-1998 every 9 months (TCP) 1998-now every 6 month (DWDM) Same trend is expected to last until 2008

Internet Technology Trends Source: Lawrence G. Roberts, Beyond Moore's Law: Internet Growth Trends, COMPUTER JANUARY 2000, pp. 117-119

Internet Bandwidth Use consumer broadband adoption will be the real driver for Internet traffic growth over the next five years By 2007 60 percent of all Internet traffic will be generated by consumers, while business users will account for the remaining 40 percent.

DWDM Applications Source: AON

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

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

DWDM Principles

DWDM System Application Transmitters Receivers Fiber amplifiers DWDM multiplexers DWDM demultiplexers

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

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

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.

Multiplexer\demultiplexer Combines/separates discrete wavelengths

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

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.

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

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

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

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.

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.

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.

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

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.

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

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

DWDM eliminates regenerators

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

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

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

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

Q&A