Optical networking Emilie CAMISARD GIP RENATER Optical technologies engineer Advanced IP Services
Agenda Optical fibre principle Time Division Multiplexing (TDM) Wavelength Division Multiplexing (WDM) Optical Equipments Thursday, 20 October 2005 ATHENS 2005 2
Optical fibre principle Total reflection of light in the core: n core >n cladding Step-Index Fibre Glass cladding r Core n Graded-Index Fibre r n Thursday, 20 October 2005 ATHENS 2005 3
Modes in fibres Mode = Reflection angle in fibre Multimode fibre: Single-mode fibre: Single angle but several colours if wanted! Thursday, 20 October 2005 ATHENS 2005 4
Fibre types and applications Multimode: large core (62.5 µm) to propagate several modes. Used for LANs. Single-mode: small-core fiber (8-9 µm) through which only one mode will propagate. Used for large networks (500m- more than 1000 km). Plastic Optical Fibres (POF): applications in cars, lighting, medicine and Local Area Networks. Silica glass fibres: large networks, better propagation => our topic today. Thursday, 20 October 2005 ATHENS 2005 5
Optical Networking Pros Weak attenuation Large bandwidth Electromagnetic disturbances immunity Spectral multiplexing Advantages of implementation Thursday, 20 October 2005 ATHENS 2005 6
Signal losses Absorption: due to silica nature and OH -. Losses: cable curve, junctions, fibre inhomogeneousness. Dispersion: Chromatic: light speed depends on its wavelength. Signal pulse spreads out (λ= 1550 nm, Dt= 17 ps/nm/km) Intermodal: propagation duration depends on mode, i.e. the light reflection angle in the fibre. The smaller the angle, the shorter the duration. (for 1 km, between 2 extreme modes: 75 ns) PMD (Polarization Mode Dispersion): polarization of electromagnetic signals change in function of physical characteristics of the fibre. Non-linear effects: at a high transfer rate, several wavelengths in a same fibre cause interferences. Thursday, 20 October 2005 ATHENS 2005 7
Attenuations in fibre α (db/km) 10 Rayleigh scattering Impurity influence (metal ions, OH-) Infra-red absorption 5 0.6 0.8 1.0 1.2 1.4 1.6 1.8 λ (µm) Thursday, 20 October 2005 ATHENS 2005 8
Wavelength windows ultraviolet visible infra-red C L bands 700 900 1200 1400 1700 nm 850 1310 1550 1625 1st window 2nd 3rd 4th Thursday, 20 October 2005 ATHENS 2005 9
Multiplexing techniques TDM (Time Division Multiplexing) Data (kb) a b c a b t (µs) WDM (Wavelength Division Multiplexing) Frequency (Hz) Thursday, 20 October 2005 ATHENS 2005 10 c b a t
TDM: Synchronous Digital Hierarchy (SDH) End of 80s International signal standardization Simplified data extraction Standardized network architecture and management Signals are made of STM frames (Synchronous Transport Module). Thursday, 20 October 2005 ATHENS 2005 11
STM-1 frame 125 µs 1 byte (64 kbit/s capacity) 9 rows 9 columns 261 columns SOH VC (Virtual Container) (Section Overhead) Thursday, 20 October 2005 ATHENS 2005 12
STM-4 frame 4x9 bytes 4x261 bytes RSOH AUpointers 9 rows 4 VC MSOH New Virtual Container 125 µs MSOH: Multiplexing SOH RSOH: Regeneration Section Overhead AU(G): Administrative Unit (Group) Thursday, 20 October 2005 ATHENS 2005 13
SDH: hierarchical levels Data rate 155 Mb/s 622 Mb/s 2.5 Gb/s 10 Gb/s 40 Gb/s Frame STM-1 STM-4 STM-16 STM-64 STM-256 Interface complexity and cost increase with data rate Thursday, 20 October 2005 ATHENS 2005 14
Wavelength Division Multiplexing (WDM) Division of optical spectrum in sub-channels. λ1 on fibre a λ2 on fibre b MUX 3 lambdas in 1 fibre DE MUX λ1 λ2 λ3 on fibre c λ3 Thursday, 20 October 2005 ATHENS 2005 15
Two WDM examples CWDM (coarse) Example with 8 λ 1470 1490 1510 1530 1550 1570 1590 1610 nm C-band L-band DWDM (dense) => More than 100 λ on C and L-bands 1510 1530 1565 1625 nm Supervision channel Thursday, 20 October 2005 ATHENS 2005 16
DWDM grid Defined by IUT-T G.692 standard, λ are referenced in function of the absorption stripe of acetylene (1553.524 nm). Central frequency (THz) for =100 GHz 196.10 196.00 195.90 195.80 Central wavelength (nm) 1528.77 1529.55 1530.33 1531.12 192.20 192.10 1559.79 1560.61 Thursday, 20 October 2005 ATHENS 2005 17
CWDM (coarse) WWDM (wide) DWDM (dense) Wavelengths <16 4 Several tens to more than 100 Channel wideness 20 nm 24.5 nm 0.4 or 0.8 nm Equipments characteristics Non-cooled lasers Non-cooled lasers Stabilized laser temperature, importance of reception precision Applications, span Short distances, <150 km 10000Base-LX (802.3ae) 200m-10km in function of the fibre Metro or long haul networks (from 100 to more than 1000 km) Cost cheap: 30 to 40% less than DWDM cheap expansive Thursday, 20 October 2005 ATHENS 2005 18
Several means of data transporting ATM cell IP packet SDH WDM Solutions with ATM are becoming obsolete. IP+SDH= POS (Packet Over SDH [or SONET in America: Synchronous Optical Network]). Nowadays, optical IP interfaces are on the market. Thursday, 20 October 2005 ATHENS 2005 19
SDH layer equipments ADM (Add/Drop Multiplexer): data multiplexing, concatenation and demultiplexing (STM frames building). DXC (Digital Cross-Connect): rearranging data affluent in containers, data mixing. Thursday, 20 October 2005 ATHENS 2005 20
Optical layer equipments (1/2) OADM : Optical Add & Drop Multiplexer fibre preamp WDM demux λ1 λ2 λ3 λ4 λ5 STM-n WDM mux + VOA booster fibre Channel termination Thursday, 20 October 2005 ATHENS 2005 21
Optical layer equipments (2/2) OXC: Optical CrossConnect. Lambda management, regeneration and signal routing. Input fibre 1 Output fibre 1 2 types: Input fibre M MxN OXC switch O-E-O : switching via an optical-to-electronic transformation of signals. O-O-O : photonic switching. Output fibre N Thursday, 20 October 2005 ATHENS 2005 22
O-O-O technologies MEMS:Micro-Electro- Mechanical-Systems: silicon plates with controlled mirrors. Bubble technology: waveguides are filled with liquid. Bubbles refract light in different directions in function of the signal wavelength. Electro-holography: crystals create holograms that can deviate optical signals. Thursday, 20 October 2005 ATHENS 2005 23
Thank you! Any questions? Thursday, 20 October 2005 ATHENS 2005 24