[+] Security [+]/네트워크
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Wired LANs : Ethernet[+] Security [+]/네트워크 2020. 11. 27. 20:40
Ethernet One of the most widely used wired LAN technologies Operates in Data-Link-Layer and Physical Layer Family of networking technologies that are defined in the IEEE 802.2 and 802.3 standards Supports data band witdhs of 10, 100, 10,000, 40,000, and 100,000 (100Gbps) Ethernet standards Define Layer 2 protocols and Layer 1 technologies Two separate sublayers of the data link layer to operate ..
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MAC(Media Access Control)[+] Security [+]/네트워크 2020. 10. 20. 17:04
Random Access(Contention) No station is superior to another station and none is assigned control over another ALOHA Potential collision allow multiple access After accept request packet, receiver immediately sends ACK All stations try to resend their frames after time out period If collision occur, Ignore the packet Slotted ALOHA divided the time into slots of T second and force the station to s..
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PPP (Point to point Protocol)[+] Security [+]/네트워크 2020. 10. 17. 18:04
PPP (Point to Point Protocol) majority of home user use simple error control : discarding and resending no flow control Framing Address field fixed 11111111 (broadcast address) Protocol field defines what is being carried dafault 2 bytes long Payload field maximun 1500 bytes FCS field CRC Transition Phase Dead state of start no active carrier and the line is quiet Establish when one of the two n..
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HDLC (High-Level Data Link Control)[+] Security [+]/네트워크 2020. 10. 16. 23:26
FSM (Finite State Machine) Machine with a finite number of states Simple protocol niether flow nor error control receiver can immediately handle any frame it receives the receiver can never be overwhelmed with incoming frame Stop and Wait protocol use both flow and error control The sender sends one frame at a time and waits for an ACK before sending the next one Add CRC to each frame If the tim..
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데이터 링크 제어 DLC(Data Link Control)[+] Security [+]/네트워크 2020. 10. 15. 00:20
Framing When a message is carried in one very large frame, even a single-bit error would require the retransmission of the whole frame fixed-size framming there is no defining the boundaries of frame the size itself can be used a delimiter example : ATM, WAN Variable size framming Character-Oriented framming carried 8-bit character (such as ASCII) To seperate one frame from next one, an 8-bit fl..
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오류 검출과 교정(Error Detection and Correction)[+] Security [+]/네트워크 2020. 10. 13. 19:08
Error Detection and Correction 1. Types of Errors The term of single bit error means that only 1 bit of given data is changed The term burst error means 2 or more bits in the data have changed 2. Block coding Divided message into block, each of k-bits, called dataword Add r redundant bits to each block to make the length n=k+r The resulting n-bit blocks are called codeword 3. Hamming distance Th..
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데이터 링크 계층 (Data-Link Layer)[+] Security [+]/네트워크 2020. 9. 10. 13:16
Data Link Layer 1. Nodes and Links Communication at the data link is note to note 2. Services node is responsible for delivering a datagram to the next node each node may be using different protocol with different frame format each node need to encapsulate and decapsulate 3. Framing Definitely, The first service provided by data-link layer is framing (encapsulate, decapsulate) 4. Flow Control De..
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TCP/IP 와 UDP/IP[+] Security [+]/네트워크 2020. 6. 15. 21:33
어느 화창한 6월의 오후, 나는 여느 때와 같이 코딩을 하며 시간을 보내고 있었다. 머신러닝으로 학습된 모델을 API로 만들어 원격으로 요청할 수 있게 끔 하는 작업이었는데, 연구실 PC는 유동 IP를 사용하고 있어서, 고정 IP를 발급 받아야 외부에서 접근할 수 있다고한다. 근데 IP발급 요청을 작성하는 칸에 무슨 외계어 마냥 맥주소, 통신방식, 단말종류 어쩌구 저쩌구 이해할 수 없는 용어들이 홍수처럼 쏟아지니, 대충 기본값으로 채워서 신청했다. 그리고 몇일 뒤 발급받은 IP로 통신을 해보니.... 될리가 있나.... 마감기한이 얼마 남지 않아서, 고정IP를 발급받은 교수님 PC에서 서버를 급하게 실행했다. 교수님께서는 정보보안을 한다는 애가 네트워크도 몰라서 되겠냐 하셨고 무지함과 무력함을 용납할 수..