CS/정보통신과 컴퓨터네트워크

Chapter 4 Transmission Media

오오렌지 2022. 12. 27. 14:09

ㅋ 너무졸릴땐 복습을ㅜㅜ 

Transmission medium is the physical path between transmitter and receiver

전송매체는 transmitter과 receiver사이의 물리적인 통로이다.

 

   • Guided media – guided along a solid medium  // wired 

 

   • Unguided media – atmosphere, space, water   // wireless

 

   • Characteristics and quality of data transmission are determined by medium and signal

    데이터전송의 특성은 전송매체와 signal에 의해 결정된다. 

      - For guided, the medium is more important in determining transmission characteristics

       전송매체가 더 중요

      - For unguided, the bandwidth of signal produced by the antenna is more important

      unguided은 안테나에 의해 생성되는 시그널 대역폭이 더 중요하다.

          - Signals at lower frequencies are omnidirectional

         낮은주파수시그널은 전방향성 

         

         - Signals at higher frequencies are unidirectional

         높은 주파수 시그널은 단방향성 , 신호가 깨끗함 

   • Key design concerns are data rate and distance

 

frequency: 주파수 signal이 반복되는 rate ( perse, HZ )

bandwidth: 대역폭, 

Design Factors

 

   • Bandwidth

       -The greater bandwidth, the higher data rate

대역폭이 클수록 data rate가 높다

 

   • Transmission impairments

       - Attenuation, Attenuation distortion, delay distortion, noise

       신호감쇄, 신호감쇄+왜곡 , 지연+왜곡 , 잡음

       - Impairments limit the distance

       손상이 데이터의 거리에 영향을 미친다 

 

    • Interference

       - Interference from competing signals in overlapping frequency bands can distort or wipe out a signal

      특정 대역이 서로 중첩돼서 시그널들이 경쟁함 -> 신호간의 방해가 생긴다. 왜곡 wipe out 

 

    • Number of receivers

       - On a shared (multipoint) link, each attachment introduces some attenuation and distortion, limiting distance and/or data rate 

  shared (multipoint) link는 여러 장치들이 하나의 link를 공유할 수 있는데, 장치가 붙을때마다 신호감쇄와 왜곡이 일어날 수 있다. 이는 데이터전달거리와 data rate에 영향을 미칠 수 있음 이건 그냥 너무나 당연한 얘기

 

Electromagnetic Spectrum

Guided Transmission Media

 

• Twisted pair

• Coaxial cable

• Optical fiber

 

Transmission Characteristics of Guided Media

 

Delay 

 - Transmission Delay ()

 - Propagation Delay( 전파지연시간 ) ( Tprop )

  전파지연시간은 빛의속도 * 2/3 으로, 5 µs/km 인 상수값이다.

Twisted pair, Coaxial cable , Optical fiber 모두 대략 5 µs/km으로 동시에 도착하므로, 전송매체와는 상관없음.

Repeater Spacing 이 Optical fiber 쪽으로 갈수록 길어지는데 이것은 광섬유가 더 품질이 좋음을 의미한다. 

 

 

 

 

Twisted Pair

• Twisted pair is the least expensive and most widely used guided transmission medium

• Consists of two insulated copper wires arranged in a regular spiral pattern; A wire pair acts as a single communication link 하나의 쌍이 연결하나를 의미함 

• Pairs are bundled together into a cable

• Twisting and different twist length reduce crosstalk interference between adjacent pairs in a cable

• Typical twist length: 5 to 15 cm; Thickness of a wire: 0.4 to 0.9 mm

 

Twisted Pair - Applications

Twisted Pair는 보통 전화선에 쓰임 

 

• The most common medium for both analog & digital signals

• Telephone network 

  between house and local exchange (subscriber loop)

• Within buildings

  To private branch exchange (PBX) : 사설교환기, 분해교환기 

  For local area networks (LAN)

  Typically 100 Mbps

  Up to 10 Gbps

 

Twisted Pair - Pros and Cons

 

• Cheap

• Easy to work with

• Low performance

• Short range

 

Twisted Pair - Transmission Characteristics

 

• Analog transmission

   - Amplifiers are required every 5 to 6 km

• Digital transmission

   - Use either analog or digital signals

   - Repeaters are required every 2 or 3 km 

• Limited in distance, bandwidth and data rate

• Susceptible to interference and noise 4-11 Unshielded and Shielded TP

• Unshielded Twisted Pair (UTP)

 Ordinary telephone wire

 Cheapest

 Easy to install and work with

 Suffer from external electromagnetic interference • Shielded Twisted Pair (STP)  Metallic braid or sheathing that reduces interference  Provides better performance at higher data rates  More expensive  Harder to handle (thick, heavy)  Three configurations: FTP, F/UTP, S/FTP