Thursday, April 17, 2008, 6:28:40

Transcription

1 Wavelength Division Multiplexing By: Gurudatha Pai K gurudatha@gmail.com Thursday, April 17, 2008, 6:28:40

2 Overview Introduction Popular Multiplexing Techniques Optical Networking WDM An Analogy of Multiplexing SONET and SDH A Small Note on CWDM and DWDM 2

3 Introduction Enormous bandwidth available in optical fiber. Implies that a single optical carrier can be base band modulated at ~25,000 Gbps, occupying 25,000 GHz surrounding 1.55 nm, This bit rate is impossible for present-day optical devices to achieve. given that lasers, external modulators, switches or detectors have bandwidths < 100 GHz. So, a single high-speed channel takes advantage of an extremely small portion of the available fiber bandwidth. 3

4 Signal A Signal B Popular Multiplexing Techniques - TDM A 100-Gbps channel probably will be a combination of many M U L TI P L E X E R lower-speed signals, D E M UL TI PL E X E R Signal A These lower-speed channels are multiplexed together in time to form a higher-speed channel. This is time-division multiplexing Signal B (TDM). This can be accomplished in the electrical or optical domain, with each lower-speed channel transmitting a bit/packet t only in a Digital Baseband for given time slot. Signal C Transmission Signal C Generally, Digital or PAM signals are Multiplexed in Time. Results in higher bit rate, so corresponding increase in BW 4

5 Popular Multiplexing Techniques - FDM Analog signals, A number of Band Limited Base Band Signals frequency translated and sent over a single Channel Results in higher BW 5

6 Optical Networking - An Analogy of Multiplexing Packet containing stuff Payload Overheads High Speed Truck 6

7 Optical Networking Synchronous Transmission SONET - SDH All Equipments synchronized to the Network Clock. ANSI defined Synchronous Optical Network (SONET) for use in U S. ITU standardized on Synchronous Digital Hierarchy (SDH) for worldwide usage. SDH & SONET Traffic Interworking is compatible. India uses SDH First level of SONET hierarchy is referred to as Synchronous Transport Signal-1 (STS-1 for an electrical signal) Or Optical Carrier-1 (OC-1 for an optical signal) STS-1 / OC-1 corresponds to a bit rate of Mbps. STS-3 / OC-3 signal corresponds to STM-1 ( Mbps). 7

8 Advantages / Applications of SDH SDH offers higher Transmission rates, Offers more efficient Add / Drop / Cross connect functions. Incorporates powerful Network Management functions, which are Software controllable like Network Planning, Configuration Management, Fault Management, Performance Management, Security Management & Accounting Management functions. Enables easy identification of link / node failures and centralized maintenance. Wide variety of Interfaces to accommodate from other networks such as ISDN, ATM, LAN, TCP/ IP etc. Performs Multiplexing and Line Terminating functions. Allows dynamic allocation of bandwidth. 8

9 SONET Frame STM-1 Frame 155 Mbps ( Synchronous Transport Module-1) 125 µsec frame 270 x 9 bytes x 64 Kbps = STM 1 Payload floats in SDH frame (envelop). Pointer byte points to start of payload. Pointer and stuff byte 9 STM-1 frame o v er 9 Payload h e a d 270 can be dropped and inserted easily 9

10 An animation of WDM Optical Coupler λ 1 λ 1 λ2 λ2 λ3 λ3 λ4 λ4 Optic Fiber Cable Nortel's WDM System 10

11 Wavelength Division Multiplexing (WDM) Technology which multiplexes multiple optical carrier signals on a single optical Fibre by using different wavelengths (colors) of laser light to carry different signals. This allows for a multiplication in capacity. Duplex communications over a strand of Fibre. The true potential ti of optical Fibre is fully exploited when multiple beams of light at different frequencies are transmitted o n the same Fibre. This is a form of (FDM) but is commonly called WDM. WDM system enables single fiber to carry multiple high speed d ata streams with carrier frequencies in the order of 200 THz (1 500 nm) to 300 THz (1000 nm). By using Fused biconic tapered couplers, multiple wavelength signals are combined on same fiber. Due to fiber attenuation, periodic regeneration was done; Ne w generation Erbium Doped Fiber Amplifiers (EDFA) enable hig h-speed, long distance repeater less transmission. 11

12 Wavelength Demultiplexing Using an optical filter as illustrated in figure 12

13 DWDM Dense Wavelength Division Multiplexin g CWDM Coarse Wavelength Division Multiplexing Number of Wavelengths: 4 / 8 / 16 Channel Spacing: > 200 GHz (corresponds to 1.6 nm over the usable spectrum) Applications: Cost effective Metro Access & Enterprise netw orks. DWDM As Laser and Optical Filter Technologies improved, more signa l wavelengths could be combined on a single fiber. ITU has specified DWDM Band in the 1525 to 1565 nm range with suitable Channel Spacing. Number of Wavelengths: 32 / 40 / 80 / 100 Channel Spacing: 200 / 100 / 50 GHz (corresponding to 1.6 nm / 0.8 nm / 0.4 nm over the usable spectrum) Applications: High Capacity long haul (multiple sections of 100 KMs) backbone networks etc. 13

14 Thank You