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

2

Outline• Telephone lines

•Dial-up modems

•Digital Subscriber Line (DSL)

•Cable TV networks

3

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

4

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

5

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

6

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

7

Dial-Up Modems

Modem

stands for Modulator/Demodulator.

8

T Lines and Analog Signals

9

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

10

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

11

56K Modems• Support 56 kbps

downlink

•Uplink is limited to ~33.6 kbps due to quantization noise

12

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.

13

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

14

Bandwidth Division in ADSL

15

Discrete Multi-Tone Modulation•Or DMT, based on OFDM (Orthogonal Frequency-Division

Multiplexing) technique

16

Allocation and modulation of each channel are determined adaptively

4 kHz

Bandwidth Division

17

•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

18

ADSL Customer Residence

19

DSL Access Multiplexer•Or DSLAM

20

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.

21

Cable TV Networks• Started as a video service provider, then moved to the

business of Internet access

22

Hybrid Fiber-Coaxial Network•Or HFC

•Bidirectional communication is achieved

23

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

24

Cable Modem

25

Cable Modem Transmission System•Or CMTS

26

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