Analog Signal Periodic Signal 같은 패턴이 주기적으로 반복된다. Sine wave 진폭, 주파수(f, [Hz]), 주기(T, [s]) f = 1/T and T = 1/f 주파수가 크면 직진성 좋고(벽에 부딪혀), 주파수가 낮으면 회전성이 좋다
digital data(0101...) -> digital signal (descrete level)Convert binary data into digital signalsData element : unit of digital data. = bitSignal eleme
Most basic analog-to-digital conversion schemesample analog dataQuantize signalsEncode signals into digital bitsteam주기적으로 signal amplitude를 읽는다.주기는 내가
Digital data can be encoded using these 3 characteristicsAmplitudeFrequencyPhaseData element : bitSignal element : the smallest unit of signal that re
발신자가 bit 0(1)을 보낸다.수신자는 발신자가 1(0)을 보냈다고 생각하거나,이게 무슨 bit인지 확인을 못해오류의 정도를 어떻게 판단할 것인가"01101100" -> "01101101" : 1-bit errorThe size of data block depend
Block Coding block coding은 physical layer에서 연속적인 0을 방지하기 위해 사용되었다. error detection/correction에서도 사용된다. dataword : a block of original message codewor
Suppose we want to sent five 4-bit numbers: 7, 11, 12, 0, 6Add all numbers and place the sum as the last number: 7, 11, 12, 0, 6, 36The receiver check
Complexity and power of CRC can be controlled by selecting "divisor(generator)"Use Modulo-20 + 0 = 0, 0 + 1 = 1, 1 + 0 = 1, 1 + 1 = 00 - 0 = 0, 0 - 1
bit는 연속적으로 들어오기 때문에, 들어오는 bit stream을 의미있는 block of data로 나누는 것이 가장 먼저 해야 할 일이다. FramingFixed number of bits. 장점이기도 하다. 모든 frame bit가 정해져있다.No delimet
Error를 검출한 이후에, what should the receiver do?ACK(Acknowledgement) frame 만약 frame이 성공적으로 수신되었다면, 수신자는 발신자에게 ACK frame을 보낸다.발신자가 ACK frame을 받았다면, 보낸 fram
한 번에 한 명씩 말해라 "randomness"를 이용해서 충돌을 피한다If two people start to talk at the same time, they both stop, wait for a moment, and start to talk againIf th
충돌을 피하기 위해 random number를 이용하지 않는다.전송 전에(before transmission), node가 time slot을 예약(reserve)한다.There is a reservation slot befoe data slots, where node
Channelization / FDMA / TDMA / CDMA / Walsh table
Wireless Channel / Pathloss / Receiver sensitivity / SNR / Fading / Modulation / Channel Coding / MIMO / OFDM
Internet address / Classful addressing / Subnetting / Classless addressing / Prefix routing / Route aggregation
IP / Header / VER / HLEN / Service / Total length / Identification / Flags / Fragmentation offset / Time to live / Protocol / Header checksum / Option
Network Layer / Forwarding / Routing
Routing / Distance vector / RIP / Link state / OSPF
BGP / Routing / iBGP / eBGP / Policies
ARP / DHCP / ICMP / NAT
Scheduling / FIFO / Priority Queue / Round Robin / Fair Queuing / Weighted Fair Queuing / Traffic Shaping / Token Bucket
Transport Layer / Process-to-Process communication / Port / Socket / Error control
UDP / Header / Operation / Application / Benefit
TCP / Segment / Connection / Number / Function / Header
Connection setup / teardown / Sliding window / size / control / Flow control / Silly window syndrome / Congestion control
Timeout / Proper RTO / RTT Estimation / Fast Retransmission / Fast Recovery
Cryptography