Internet Access Technologies - Kasetsart University
Transcript of Internet Access Technologies - Kasetsart University
Internet Access Technologies
Chaiporn Jaikaeo
Department of Computer EngineeringKasetsart University
01204325 Data Communications and Computer Networks
Based on lecture materials from Data Communications and Networking, 5th ed.,Behrouz A. Forouzan, McGraw Hill, 2012.
Revised 2018-10-04
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Outline• Telephone lines
•Dial-up modems
•Digital Subscriber Line (DSL)
•Cable TV networks
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Access Technology• Internet access technology◦ A data communications system that connects an Internet subscriber
to an ISP (Internet Service Provider)
◦ Such as a telephone company
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Narrowband vs. Broadband•Both refer to access technologies◦ Narrowband → typically 128 kbps
◦ Broadband → typically 1 Mbps
•Narrowband access technologies◦ Dial-up telephone line
◦ Leased line
•Broadband access technologies◦ Digital Subscriber Line (DSL)
◦ Cable modem
◦ Wireless/Mobile broadband: Satellite, 3G/4G, WiMAX
Notes: no exact speed boundary
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Local Loop• Local loop describes the physical connection between a
telephone company Central Office (CO) and a subscriber◦ Consists of twisted pair and dialup call with 4 KHz of bandwidth
Downstream
Upstream
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Telephone Lines• Traditional telephone lines can carry frequencies between
300 and 3300 Hz
•All this range is used for transmitting voice◦ A great deal of interference and distortion can be accepted without
loss of intelligibility
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Dial-Up Modems
Modem
stands for Modulator/Demodulator.
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T Lines and Analog Signals
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PCM: Quantization
1 2 3 4 5 6 70
Input
2
4
6
Output
•Converts continuous values of data to a finite number of discrete values
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Quantization Error•Assume sine-wave input and uniform quantization
◦ nb is the number of bits per sample
•Known as the 6 dB/bit approximation
See also: http://en.wikipedia.org/wiki/Quantization_error#Quantization_noise_model
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56K Modems• Support 56 kbps
downlink
•Uplink is limited to ~33.6 kbps due to quantization noise
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Digital Subscriber Line (DSL)•Provides higher-speed access to the Internet
• Supports high-speed digital communication over the existing local loops
• The existing local loops can handle bandwidths up to 1.1 MHz.
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ADSL•ADSL – Asymmetric Digital Subscriber Line◦ Downstream bit rate > upstream bit rate
◦ Designed for residential users
◦ Unsuitable for businesses
•ADSL operates on existing local loops◦ Local loops can handle up to 1.1 MHz of bandwidth
◦ The distance limit is ~18,000 feet
◦ The system uses a data rate based on the condition of the local loop line
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Bandwidth Division in ADSL
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Discrete Multi-Tone Modulation•Or DMT, based on OFDM (Orthogonal Frequency-Division
Multiplexing) technique
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Allocation and modulation of each channel are determined adaptively
4 kHz
Bandwidth Division
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•Voice – Channel 0
• Idle – Channels 1-5
•Upstream – Channels 6-30◦ 24 data channels, 1 control channel
◦ 1.44 Mbps (max) upstream bit rate
◦ Actual bit rate: 64 Kbps to 1 Mbps
•Downstream – Channels 31-255◦ 224 data channels, 1 control channel
◦ 13.4 Mbps (max) downstream bit rate
◦ Actual bit rate: 500 Kbps to 8 Mbps
Bandwidth Division
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ADSL Customer Residence
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DSL Access Multiplexer•Or DSLAM
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Other DSL Technologies•HDSL – High-bit-rate DSL
•VDSL – Very-high-bit-rate DSL
• SDSL – Symmetric DSL
•ADSL2
•ADSL2+
• See also◦ http://en.wikipedia.org/wiki/Digital_subscriber_line
Source: AWARE. ADSL2 and ADSL2+ The new ADSL standard.
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Cable TV Networks• Started as a video service provider, then moved to the
business of Internet access
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Hybrid Fiber-Coaxial Network•Or HFC
•Bidirectional communication is achieved
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Data Transfer over CATV• Standard: DOCSIS (Data Over Cable Service Interface
Specification)
•Division of coaxial cable band by Cable TV
• Theoretical downstream data rate up to 10 Gbps
• Theoretical upstream data rate up to 1-2 Gbps
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Cable Modem
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Cable Modem Transmission System•Or CMTS
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Fiber To The x (FTTX)•Optical broadband network architectures
Fiber-to-the-node
Source: Wikipedia
Fiber-to-the-curb
Fiber-to-the-building
Fiber-to-the-home