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Security Virus Worm spyware Dos(Denail of Service) DDos botnet : 많은 컴퓨터에 바이러스를 심어둔다. 특정 상황에서만 바이러스가 동작하도록 명령한다. Packet sniffing : 중간에 정보를 catch IP spoofing : IP를 속인다 Man-in-the-middle attack : 중간에 정보를 가로채서 잘못된 정보를 보낸다 Packet sniffing broadcast media promiscuous network interface reads/records all packets (e.g., including passwords!) passing by Wireshark software is a (free) packet-sniffer IP spo..

Performance : Delay, loss throughput Performance in Networks 네트워크 성능 측정 기준 Throughput, delay, loss Throughput 네트워크를 통해 실제적으로 얼마나 많은 데이터를 보낼 수 있는가 "bit per second" Delay (Latency) 한 패킷을 목적지까지 보내는데 얼마나 시간이 걸리는가 Delay = transmission time + propagation delay + queueing delay + processing delay Four sources of packet delay 1. Processing delay 라우터에서 발생하는 지연 packet이 도착하면 에러가 났는지 확인 table을 통해 어디로 갈지 확인 ..

Video streaming and content distribution networks (CDNs) Internet Video video tarffic : major consumer of Internet bandwidth Netflix, Youtube : 37%, 16% of downstream residential ISP traffic ~ 1B YouTube users, ~ 75M Netflix users challenge scalibility - single mega-video server won't work heterogenity different users have different capabilities (e.g., wired versus mobile; bandwidth rich vershs ..

P2P Application Properties No central control, no central database No hierarchy Every node is both a client and a server The communication between peer is symmetric No global view of the system Scalability Availability for any peer Peers are autonomous System globally unreliable Robustness and security issues Napster : centralized directory original "Napster" design 1) peer가 연결되면, directory serv..