计算机网络与互联网英语chap4
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Transmission of Information
Well-understood basics From physics
Energy Electromagnetic wave propagation
From mathematics
Coding theory
Transmission Media
The following two conditions must be met for the light rays in a fiber to be reflected back into the fiber without any loss due to refraction(折射):
➢ The core of the optical fiber has to have a larger index of refraction (n) than the material that surrounds it. The material that surrounds the core of the fiber is called the cladding.
Digital signal is a sequence of binary voltage pulses (0’s and 1’s).
Digital transmission avoids the noise problem by encoding the analog signal into digital form. The digitized version is then
Single-mode fiber has a much smaller core that only allows light rays to travel along one mode inside the fiber
Comparative of two fiber
input pulse
Multimode fiber
Transmission Media
Copper wire
Need two wires Possibilities
Twisted pair Coaxial cable
Optical fiber
Flexible Light “stays in”
Air / space
Used for electromagnetic transmission
Transmission is the communication of data by the propagation and processing of signals.
Bandwidth
Maximum times per second the signal can change
Terminology
100 Mbps over a segment length of 100m 2400 bps for up to 10 miles
Terminology
Analog data take on continuous values in a given interval, e.g. audio (human speech) or video.
Single-mode fiber
Single-mode fiber consists of the same parts as multimode
The outer jacket of single-mode fiber is usually yellow
Single-mode allows only one mode of light to propagate through the smaller, fiber-optic core
➢ The angle of incidence (入射角) of the light ray is greater than the critical angle (临界值) for the core and its cladding.
Total internal reflecti0 MHz
Cat 5
up to 100MHz Commonly pre-installed in new office
buildings Twist length 0.6 cm to 0.85 cm
UTP cable
The following are the types of cable connections used between internetwork devices:
same cable simultaneously eg. Cable TV
Coaxial cable
Table Categories of coaxial cables
Category RG-59 RG-58 RG-11
Impedance
Use
75 W
Cable TV
50 W
Thin Ethernet
白橙
白绿
➢ Router to PC
橙
绿
白绿
白橙
蓝 白蓝 绿 白棕
蓝 白蓝 橙 白棕
棕
棕
UTP connector
Coaxial cable
Bandwidth of about 500 Mbps More expensive than twisted pair transmits information
output pulse
input pulse
Single-mode fiber output pulse
fiber-optic component
Analog signal is a continuously
varying electromagnetic wave.
Used in early telephone systems.
Analog signals had the drawback that they attenuate (weaken) over long distances. Needed amplifiers to boost the signals. However, amplifiers distort the signal and introduce noise.
straight-through cable crossover cable
straight-through cable
Use for the following cabling: ➢ Switch to router ➢ Switch to PC or server ➢ Hub to PC or server
Light Emitting Diode (LED)
Cheaper Wider operating temp range Last longer
Injection Laser Diode (ILD)
More efficient Greater data rate
Wavelength Division Multiplexing
Stepped Index Multimode
Graded Index Multimode Single Mode
Detector: Photoelectric(光电) Diodes
Protective Sheat Cladding Core(fiber)
Total internal reflection
Digital data take on discrete values, e.g. text or integers.
Signals are electromagnetic representations of data.
Signaling is the physical propagation of the signal along a suitable medium.
折射角 包层 （低折射率的媒体）
入射角
纤芯 （高折射率的媒体）
包层 （低折射率的媒体）
Optical Fiber - Transmission Characteristics
Act as wave guide for 1014 to 1015 Hz
Portions of infrared and visible spectrum
白橙 橙 白绿
蓝 白蓝 绿 白棕
棕
白橙 橙 白绿
蓝 白蓝 绿 白棕
棕
Crossover cable
Use for the following cabling:
➢ Switch to switch
➢ Switch to hub
➢ Hub to hub
➢ Router to router
➢ PC to PC
Multimode fiber
The part of an optical fiber through which light rays travel is called the core of the fiber
These optical paths are called modes.
If the diameter of the core of the fiber is large enough so that there are many paths that light can take through the fiber, the fiber is called “multimode” fiber.
sent across the network.
Shielded twisted-pair cable (STP)
UTP cable
UTP Categories
Cat 3
up to 16MHz Voice grade found in most offices Twist length of 7.5 cm to 10 cm
baseband mode
bandwidth devoted to a single stream of data
broadband mode
bandwidth is divided into ranges each range typically carries separate coded information allows the transmission of multiple data streams over the
Twisted pair
Two insulated copper wires are twisted around each other
Twisted pairs often are bundled together and wrapped in a protective coating that allows the bundled cable to be buried
An infrared(红外) laser is used as the light source in single-mode fiber
has greater both the speed and the distance than multi-mode fiber.
single-mode fiber is often used for inter-building connectivity
50 W Thick Ethernet
Optical fiber
Use optical signals instead of electrical signals
Light sources : LED (Light Emitting Diode,发光二 极管）/Laser Diode
Optical Fibers
Twisting minimizes electromagnetic interference between pairs
Bandwidth up to 250 kHz for analog signals Digital signal data rates vary with distance
Well-understood basics From physics
Energy Electromagnetic wave propagation
From mathematics
Coding theory
Transmission Media
The following two conditions must be met for the light rays in a fiber to be reflected back into the fiber without any loss due to refraction(折射):
➢ The core of the optical fiber has to have a larger index of refraction (n) than the material that surrounds it. The material that surrounds the core of the fiber is called the cladding.
Digital signal is a sequence of binary voltage pulses (0’s and 1’s).
Digital transmission avoids the noise problem by encoding the analog signal into digital form. The digitized version is then
Single-mode fiber has a much smaller core that only allows light rays to travel along one mode inside the fiber
Comparative of two fiber
input pulse
Multimode fiber
Transmission Media
Copper wire
Need two wires Possibilities
Twisted pair Coaxial cable
Optical fiber
Flexible Light “stays in”
Air / space
Used for electromagnetic transmission
Transmission is the communication of data by the propagation and processing of signals.
Bandwidth
Maximum times per second the signal can change
Terminology
100 Mbps over a segment length of 100m 2400 bps for up to 10 miles
Terminology
Analog data take on continuous values in a given interval, e.g. audio (human speech) or video.
Single-mode fiber
Single-mode fiber consists of the same parts as multimode
The outer jacket of single-mode fiber is usually yellow
Single-mode allows only one mode of light to propagate through the smaller, fiber-optic core
➢ The angle of incidence (入射角) of the light ray is greater than the critical angle (临界值) for the core and its cladding.
Total internal reflecti0 MHz
Cat 5
up to 100MHz Commonly pre-installed in new office
buildings Twist length 0.6 cm to 0.85 cm
UTP cable
The following are the types of cable connections used between internetwork devices:
same cable simultaneously eg. Cable TV
Coaxial cable
Table Categories of coaxial cables
Category RG-59 RG-58 RG-11
Impedance
Use
75 W
Cable TV
50 W
Thin Ethernet
白橙
白绿
➢ Router to PC
橙
绿
白绿
白橙
蓝 白蓝 绿 白棕
蓝 白蓝 橙 白棕
棕
棕
UTP connector
Coaxial cable
Bandwidth of about 500 Mbps More expensive than twisted pair transmits information
output pulse
input pulse
Single-mode fiber output pulse
fiber-optic component
Analog signal is a continuously
varying electromagnetic wave.
Used in early telephone systems.
Analog signals had the drawback that they attenuate (weaken) over long distances. Needed amplifiers to boost the signals. However, amplifiers distort the signal and introduce noise.
straight-through cable crossover cable
straight-through cable
Use for the following cabling: ➢ Switch to router ➢ Switch to PC or server ➢ Hub to PC or server
Light Emitting Diode (LED)
Cheaper Wider operating temp range Last longer
Injection Laser Diode (ILD)
More efficient Greater data rate
Wavelength Division Multiplexing
Stepped Index Multimode
Graded Index Multimode Single Mode
Detector: Photoelectric(光电) Diodes
Protective Sheat Cladding Core(fiber)
Total internal reflection
Digital data take on discrete values, e.g. text or integers.
Signals are electromagnetic representations of data.
Signaling is the physical propagation of the signal along a suitable medium.
折射角 包层 （低折射率的媒体）
入射角
纤芯 （高折射率的媒体）
包层 （低折射率的媒体）
Optical Fiber - Transmission Characteristics
Act as wave guide for 1014 to 1015 Hz
Portions of infrared and visible spectrum
白橙 橙 白绿
蓝 白蓝 绿 白棕
棕
白橙 橙 白绿
蓝 白蓝 绿 白棕
棕
Crossover cable
Use for the following cabling:
➢ Switch to switch
➢ Switch to hub
➢ Hub to hub
➢ Router to router
➢ PC to PC
Multimode fiber
The part of an optical fiber through which light rays travel is called the core of the fiber
These optical paths are called modes.
If the diameter of the core of the fiber is large enough so that there are many paths that light can take through the fiber, the fiber is called “multimode” fiber.
sent across the network.
Shielded twisted-pair cable (STP)
UTP cable
UTP Categories
Cat 3
up to 16MHz Voice grade found in most offices Twist length of 7.5 cm to 10 cm
baseband mode
bandwidth devoted to a single stream of data
broadband mode
bandwidth is divided into ranges each range typically carries separate coded information allows the transmission of multiple data streams over the
Twisted pair
Two insulated copper wires are twisted around each other
Twisted pairs often are bundled together and wrapped in a protective coating that allows the bundled cable to be buried
An infrared(红外) laser is used as the light source in single-mode fiber
has greater both the speed and the distance than multi-mode fiber.
single-mode fiber is often used for inter-building connectivity
50 W Thick Ethernet
Optical fiber
Use optical signals instead of electrical signals
Light sources : LED (Light Emitting Diode,发光二 极管）/Laser Diode
Optical Fibers
Twisting minimizes electromagnetic interference between pairs
Bandwidth up to 250 kHz for analog signals Digital signal data rates vary with distance