어렵지만 다시 시작

• dial-up,
• landline (coaxial cable, fiber optic, copper wires),
• T-lines,
• Wi-Fi: IEEE 802.11 standard을 바탕으로 wireless devices 상호간 operatable(interoperability) 한 기기에 부여하는 TM
• stellite 
• cell phones.
  

dial-up internet access
dial-up internet access is form of internet access via telephone line(telephone network). the client uses a modem connected to a computer and a telephone line to dial into an ISP's node to establish a modem to modem link, which is then routed to internet.

• modern dial-up modems typically have a maximum theoretical speed of 56 kbit/s^[각주:1]
• 상용 전화선의 음성 데이터 처리와 model rate 사이의 상관관계

voice 주파수 대역 및 max frequency에 따른 nyquist frequency 는 8KHz 로 결정되었다. 샘플링되는 음성 신호의 quantization level은 256개 로서 2의 8승 개에 해당된다. 따라서 초당 처리 bit 는 8 KHz * 8 bits = 64 Kbits/sec.
오랫동안 64 Kbits/sec 로 통신을 하다가 음성신호의 전송은 8 bit가 아니라 7 bit로도 충분하다는 것을 발견하였다. 하지만 이미 8 bit의 규약으로 인프라(회선)가 건설되었기에 7 bit는 voice 전송을 위해 1 bit는 administration 목적을 위해 사용하고 있다. modem 의 경우 56 Kbit/s가 이론적인 최고 속도 (using the V.90 or V.92 protocol)

• broadband internet access

broadband internet access (or just broadband) is high data rate internet access - typically contrasted with dial-up access over a 56k modem. it is often called 'high speed' internet.

• DSL: ADSL (asymmetric digital subscriber line)

DSL is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL can be used at the same time and on the same telephone line with regular telephone, as it uses high frequency, while regular telephone uses low frequency.
ADSL is a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide.

landline


T-lines


Wi-Fi
Wi-Fi is a trademark for certified products based on the IEEE 802.11 standards. this certification warrants interoperability between different wireless devices. the term Wi-Fi is often used by the public as a synonym for WLAN; but not every wireless Lan product has a Wi-Fi certification, which may be because of certification costs that must be paid for each certified device type.

• Wi-Fi logo and practical example

(우) router, unicorn WB-1500N 의 제품상자에 표시되어 있는 Wi-Fi 로고

• Wi-Fi 에 대한 좀더 자세한 정보에 대해서는 별도의 posting을 통해 정리한다.

satellite


cell phone