Computer Networks

URL
    Uniform Resource Locater
    통합된 리소스 위치 지시자.
    17 messages for one URL Request
        6 IP address
        3 TCP connection
        4 HTTP request and ack
        4 TCP termination

HTTP
    Hyper Text Transfer Protocol

TCP
    Transmission Control Protocol

Connectivity
    Scale
    Link
    Nodes
    Point to point
    Multiple Access
    Switched Network
        Circuit Switched
        Packet Switched
    Packet Message
    Store and Forward

    Cloud
    Hosts
    Switches
    internetwork
    Router/Gateway
    Host-to-host Connectivity
    Address
    Routing
    Unicast/broadcast/multicast

Cost Effective Resource Sharing
    Multiplexing
    De-multiplexing
    Synchronous Time-Division Multiplexing

    FDM

    Statistical Multiplexing
        FIFO
        Round-Robin
        Pirorities
    
    LAN
        Local Area Networks
        A network connecting a group of devices in a “local” area, usually within the same building. 
        These connections are generally powered through the use of Ethernet cables, 
            which have length limitations, as the speed of the connection will degrade beyond a certain length.

        A WLAN, or wireless LAN, is a subtype of LAN. It uses WiFi to make the LAN wireless through the use of a wireless router.
    WAN
        Wide Area Networks
        covering any distance neccessary like internet

    MAN
        metropolitan area network
        These can cover an area as large as a city, linking multiple LANs through a wired backhaul.
            Citywide Wifi network    
    SAN
        System Area Networks
        high-performance, connection-oriented network that can link a cluster of computers
    
    About Network: https://www.c1c.net/blog/network-101/

Specification
    prose
    pseudo-code
    state tansition diagram: 다이어그램

Standard organization
    IETF
        Internet Engineering Task Force
        short term issue
        사실상 표준기구

    ITUT
        International Telecommunication Union Telecommunication Standardization Sector
        공식 표준기구

IRTF
    Internet Research Task Force
    Long term issue

Physical Layer
    handles the transmission of raw bits over a communication link

Data Link Layer
    collects a stream of bits called "frame"

Network Layer
    exchange "packet" btw nodes

Transport Layer
    implements a process to process channel
    exchange "message"

Session & Presentation
    provides a name space that is used to tie together 
        & format of data exchanged btw peers

Application Layer
    standardize common type of exchanges

An hour-glass shape = 모래시계 
1. NET NET NET NET
2. IP
3. TCP & UDP
4. FTP HTTP NV TFTP

Application Programming Interface
    sockets
        originally provided by Unix / C

        Interface btw an application and network
            create socket
            attach a socket to the network
            send and recv
            close socket
        
        Server
            bind 연결 설정
            listen 기다림
            accept 연결 후 수행

        Client
            connect 연결
        

 Bandwidth
    width of the frequency band
    number of bits per sec

    1Mbps: 1 * 10^6 = 1 * 2^20 
        <--> 1 * 10^(-6) seconds to transmit each bit
                = 1 microsec wide

Latency = Propagation + transmit + queue + processing
    propagation = distance / speed of light
    Transmit = size / bandwidth

Throughput = TransferSize / Transfer Time

Circuit Switching   
    전화
    Physical layer technology

Packet Switching
    datagram: indendent, Internet
        connectionless
        mostly used on network layer
        routing table, forwarding table에 따라 길 할당 at any time

    virtual circuit switching
        connection-oriented
        VCI: Virtual Circuit Indetifier
        permanent VC: 연결로 유지
        Switched VC: 연결로 할당
        new connection --> new VCI
    VCI 예제 다시!