光通信网络 英文教案 第2部分

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Optical Comm Networks
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Optical Transmission System Concepts
Optical Transmission – Schematic Well-known advantages of optical comm: Weight and size, Material cost, No electrical connection, No electromagnetic interference, Distance between regenerators, Open ended capacity Information capacity – A 150 Mbps fiber connection gives just over 2000 digital telephone (64kbps) connections. Recently, NEC reported a successful experiment where 132 optical channels of 20 Gbps each were carried over 120 km (=2.64 Tbps).
Optical Communication Networks Part 1
Chapter 1. Introduction
Wang Wen-Fong
Introduction
The use of light to send messages is not new. Four milestones for optical comm: The invention of the LASER (late 1950’s) The development of low loss optical fibers (1970’s) The invention of the optical fiber amplifier (1980’s) The invention of the in-fiber Bragg grating (1990’s) Light is an electromagnetic wave and optical fiber is a waveguide – optical comm is not like electronic comm; while it seems that light travels in a fiber much like electricity does in a wire, this is very misleading. WDM (Wavelength Division Multiplexing) is a major step toward fully optical networking – WDM sends many independent optical channels on a single fiber.
Optical Comm Networks 5
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Optical Networking (cont’d)
Another major distinction between networks comes from the method by which switching is performed: Most networks (WAN) contain nodal points (=switches) where information is switched from link to link. Other networks (LAN/MAN) switch information by placing frames onto a shared medium to which many end users are connected. Optical networking is just beginning! Wide area optical switched networks (similar to the telephone network) could be built today as all of the required components are available. Optical packet switching is a long long way from reality and indeed may not ever be achievable.
edited by WWF, EE, NYUST
Optical Comm Networks
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Optical Networking
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Types of networks: The telephone network – Using one connection to allow per user but users makes arbitrary connections at will with other end users. Packet switching networks – Information is carried between end users in the form of packets; in these networks a single user is usually capable of communicating with a large number of other end users at the same time. Types of packet switched networks: Connection-oriented networks – the network paths are defined before information is transferred; information is always transferred along the predefined path. Connectionless networks – data frames are routed through the network based on a destination address carried within the data itself.
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edited by WWF, EE, NYUST
Optical Comm Networks
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edited by WWF, EE, NYUST
Optical Comm Networks
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Optical Transmission System Concepts
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Better security – It is possible to tap fiber optical cable. But it is very difficult to do and the addition loss caused by the tap is relatively easy to detect. Limitations of optical comm: Joining cables, Bending cables, Slow standards development, Optics for transmission only, Gamma radiation, Electrical fields, Sharks eat the ce cable