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Chap 10. Cellular Wireless networks - 움직이면서 끊김없이 통신하고 싶음 → wide-area mobile Internet의 해결방안 - widespread deployment/use (배치/사용) : mobile-broadband-connected devices > fixed-broadband-connected devices devices (5:1 in 2019) : 4G availability: 97% of time in Korea (90% in US) - 최대 transmission rates: 100’s Mbps - technical standards: 3rd Generation Partnership Project (3..

Chap 10. Cellular Wireless networks - all use CSMA/CA for multiple access, and have base-station and ad-hoc network versions *CSMA: Carrier Sense Multiple Access - 상황을 보고 쉬거나, 여러사람이 접근하도록 해준다. 보내기 전에 들어보고 signal level이 어느정도 이하이면 보내고 아니면 보내지 않는다. 대기하고 다시 듣고 전송 *CA: Collision Avoidance - hidden problem 해결 > wireless host communicates with base station - base station = access p..

Chap 10. Cellular Wireless networks - wireless (mobile) phone 가입자 수 >>> fixed (wired) phone 가입자 수 (10:1 in 2019) - mobile-broadband-connected devices >>> fixed-broadband-connected devices (5:1 in 2019) : 4G/5G cellular networks now embracing Internet protocol stack, including SDN *2가지 어려운 점 1) wireless: communication over wireless link - 거리, 주파수 대역(d, f)..

Chap 9. WAN Technology and Protocols > Switching nodes : provide a switching facility that move data between nodes (노드들 간의 스위칭 제공) > Stations : network에 붙어있는 모든 devices > Nodes : 통신을 지원(제공)하는 모든 switching devices *Stations와 굳이 나누지 않아도 되는 용어 > Communications network : nodes의 집합 > Switched communication network : station에서 network로 들어오는 데이터는 node에서 node로 전환되어 destination에 routing된다. < 대략..

Chap 7. Data Link Control Protocols > application > transport > network > link: data transfer between neighboring network elements - Ethernet, WiFi, ppp > physical : Directly connected, wire-like : Losses & errors, but no out-of-sequence frames : Applications - Direct Links; LANs; Connections across WANs > Data Links Services - Framing - Error ..

Chap 7. Data Link and Control Protocols : directly connected, wire-like : Losses, and errors : no out-of-sequence frames : 적용 - direct links, LANS, Connections across WANs 예) PPP, HDLC, Ethernet LAN, IEEE 802.11(Wifi) LAN > Services - Framing (Frame synchronization) - Flow control - Error control - Addressing - Control and data - Link Maintenance - Multiplexing - ..

Chap 6. Error Detection and Correction : transmission(전송)과 reception(수신) 사이에 비트가 변경되면 오류가 발생 – 1 전송 → 0 수신 – 0 전송 → 1 수신 > Single bit errors : 1 bit를 변경하는 isolated error. 주변 bits에게는 영향 x : white noise에 의해 발생 > Burst errors : 첫 번째와 마지막 비트 및 임의의 수의 중간 비트가 오류로 수신되는 연속적인 sequence : impulse noise, fading in a mobile wireless environment에 의해 발생 : data rates ↑ → error의 효과 ↑ ..

Chap 5. Data Encoding : public telephone system : analog signals를 receive, switch, transmit 하도록 설계 : 주파수 범위 - 300Hz ~ 3400Hz : subscriber locations의 digital signals를 처리하는 데 적합 x : modem(modulator-demodulator)을 사용하여 digital data -> analog signal / analog signal -> digital data 1) ASK (Amplitude Shift Keying) 0 - 중간 ..

Chap 5. Data Encoding - Encoding : 통신 채널을 통해 전송할 수 있는 형식으로 데이터를 변환하는 process 예) Text to binary code - Modulation (변조) : carrier signal을 부호화된 데이터를 전송하도록 변경하는 process - Signal spectrum : A good signal design은 transmitted power를 transmission bandwidth의 중간에 집중 - Clocking : transmitter와 receiver를 external clock 또는 sync mechanism과 동기화 - Error detection :..

Chap 4.Transmission Media 1) Bandwidth (대역폭) : bandwidth ↑ → data rate ↑ 2) Transmission impairments : attenuation, limit the distance 3) Interference : Overlapping frequency bands can distort or wipe out a signal Interference 4) Number of Receivers : receivers ↑ → attenuation ↑ Guided transmission media Wireless transmission Wireless propagation Line..