CS/컴퓨터네트워크

Link Layer Services Link Layer 1 subnet & 4 L2-switch (no IP addr, no MAC addr) Link Layer (Layer 2) nodes: hosts and routers links: communication channels that connect adjacent nodes along communiation path - wired & wireless links layer-2 packet == frame that encapsulates datagram Data Link Layer (Layer 2) has responsibility of transferring datagram from one node to physically adjacent node ov..

ICMP ICMP (Internet Control Message Protocol) ICMP: Internet Control Message Protocol used by hosts & routers to communicate network-level information error reporting 중간 라우터에서 incoming pkt에 문제 발생 시, ICMP msg를 생성하여 해당 pkt의 src host로 전송한다. network-layer above "IP": ICMP msgs carried in IP datagrams ICMP mesageL type + code + first 8 bytes of IP datagram causing error 최종적으로 해당 패킷을 만든 프로세스가 사용하는 포트 ..

Hierarchical Routing Autonomous Systems (AS) Autonomous Systems (1 AS ~= 1 ISP ~= domain) collection of networks with same routing policy, under single ownership identified by a unique 32-bit integer AS number (ASN) ASN is managed by the Internet Assigned Numbers Authority (IANA) routers in the same AS run same routing protocol: intra-AS routing protocol (OSPF, RIP..) Gateway router: locates at ..

Overview Two approaches to structuring network control plane 1) per-router control (traditional routing algorithms) Routing algorithm classification Link State routing algorithm: Dijkstra's algorithm Distance Vector algorithm: Bellman-Ford algorithm Hierarchical routing Routing protocols RIP, OSPF (IGP; interior gateway) / BGP (EGP; exterior gateway) 2) logically centralized control SDN controll..

IPv6 IPv6 Addressing IPv6 Motivation 32-bit address space soon to be completely allocated header format helps speed processing/forwarding header changes to facilitate QoS IPv6 Addressing 128-bit address: 16-bit씩 끊어서 콜론(:)으로 분리하여 표현 x:x:x:x:x:x:x:x IPv6 Datagram Format flow label: identify datagrams in same "flow" next header: identify the protocol to which the data field of this datagram will be..

Datagram format & Fragmentation IPv4 Datagram Format IP Header: 20바이트 IPv4 Fragmentation IPv4 Fragmentation at router large IP datagram divided(fragmented) at routers (UDP datagram -> at host) one datagram -> several datagrams reassembled only at final destination "host" (not router) before they reach the transport layer (Layer 4) using IP header IP header bits used to identify, order related fr..

Network Layer Network Layer Network Layer (Layer 3) Layer 3의 main mission: source host가 보내는 데이터를 destination host까지 전달하는 것 👉 host-to-host communication Most complex layers Network layer protocls in every host(only data plane) & router(data & control plane) data plane = forwarding / control plane = routing Delevering segment from sending to receiving host sending host: encapsulates segments(Layer..

Principles of Congestion Control Congestion Congestion occurs when too many sources (sending hosts) sending too much data too fast for network to handle queuing delays, lost packets in router's output buffers Causes and cost of congestion at router buffer in the network Link Bandwidth -> delay Finite output buffer at routers -> delay, loss Multi-hop -> more work to achive the same throughput, un..

UDP: connectionless transport UDP UDP: User Datagram Protocol connectionless: no call setup -> no delay before data delivery doesn't care errors at receiver -> just error-check UDP datagram can be lost or delivered out-of-order to app UDP doesn't control over what data is send & when -> App can send its data as fast as it wants used in streaming multimedia apps (loss tolerant, rate sensitive), D..

CDN DASH Streaming stored video playing while downloading challenge: scale, heterogeneity of clients 👉 solution: distributed, smart client progressive: 점진적(Progressive)으로 내 컴퓨터에 다운로드하여 플레이 되는 방식 adaptive: 비디오를 chunk로 나누어 전송 DASH (Dynamic, Adaptive Streaming over HTTP) server divides video file into multiple chunks -> each chunk stored, encoded at different rates manifest file: provides URLs for ..