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Networks A collection of nodes interconnected by different types of links…

- - - - Application Architecture
        
        defines the structure of the application
        
        different concept than network architecture
        
        Peer to Peer
        minimal use of dedicated servers
        
        Peer
        
        no always on server
        
        communicate directly with each other
        
        peers request service from other peers
        
        peer connect intermittently
        
        no fixed IP address
        
        Self Scalability new peers allow for larger service capacity
        
        Client-Server Model
        client requests, always on server responds
        
        Server
        
        always on server
        
        permanent IP address
        
        data centers for scaling
        
        Client
        
        communicates w/server
        
        connected intermittently
        
        dynamic(not permanent) IP address
        
        don't communicate directly with other clients
        
        Hybrid Client-Server and P2P
        
        Examples
        -Skype
        -Instant messaging
      - Network Applications
        
        email
        
        remote login
        
        streaming
        
        P2P file sharing
        
        social media
        
        websites
        
        Creating a Network Application
        the program must:
        
        run on different end systems
        
        communicate over networks
      - Sockets
        where the messages are sent from & receive
        like a door
      - Addressing Process
        every message must have an identifier
        
        Identifier
        IP address
        port number
      - ALP
        application layer protocol
        
        Defines
        
        types of messages
        
        message syntax
        
        message semantics
        
        rules
        
        Types
        
        open
        ex: HTTP, SMTP
        
        proprietary
        ex: Skype
        
        HTTP
        
        Background
        
        Webpages have objects
        
        objects can be HTML, JPEG, audio, java applet
        
        Webpages have a base HTML-file
        
        Each object has a URL (uniform resource locator)
        
        URL has the host name and path name
        
        ex: www.someschool.edu/someDept/pic.gif
        
        www.someschool.edu is the host
        
        /someDept/pic.gif is the path name
        
        ALP for web
        
        uses Client-Server model
        
        client(browser): requests and displays objects
        
        server(web server): sends the objects requested
        
        HTTP Messages
        
        Request
        ASCII (human readable format)
        
        Request line
        
        GET, POST, HEAD
        
        Header lines
        
        Carriage return
        
        \r\n
        
        Body
        
        HTTP/1.0
        
        GET: input in URL field
        
        POST: input in entity body
        
        HEAD: asks server to send response message without requested object
        
        HTTP/1.1
        
        GET, POST, HEAD
        
        PUT: uploads file in entity body to path specified in URL field
        
        DELETE: deletes file specified in URL field
        
        Response
        
        Status line
        
        status code
        
        Header lines
        
        Carriage Return
        
        \r\n
        
        Data requested
        
        HTML file
        
        Response Codes
        200 OK
        301 Moved Permanently
        400 Bad Request
        404 Not Found
        505 HTTP Version Not Supported
        
        User-Server State: Cookies
        
        Cookie header line of HTTP response
        
        Cookie header line in next HTTP request
        
        Cookie file kept on user's host, managed by browser
        
        Back-end data base at website
      - Internet Transport Protocols
        
        Transport Services
        
        Data integrity (reliability data transfer)
        
        Timing (low delay times)
        
        Throughput (bits/time is high)
        
        Security (encryption)
        
        TCP
        
        Reliable Transport
        
        Flow Control
        
        Congestion Control
        
        Connection-oriented
        
        Does not have: timing, minimum throughput guarantee, security
        
        Adding Security
        
        SSL (older)
        Secure Socket Layer
        
        cleartext passwords sent into socket transverse internet encrypted
        
        TLS (newer)
        Transport Layer Security
        
        encrypted TCP connection
        
        data integrity
        
        end-point authentication
        
        HTTP & TCP
        
        client initiates TCP & creates socket
        
        server accepts TCP connection
        
        HTTP messages sent btwn browser & web server
        
        TCP connection closed
        HTTP is stateless: maintains no info about past client requests
        
        Non-persistent HTTP
        one object sent then TCP closed
        multiple objects -> multiple connections
        
        Steps
        
        HTTP client starts TCP connection to HTTP server
        
        HTTP server at host accepts connection
        
        HTTP client sends HTTP request message (asking for an object) to TCP socket
        
        HTTP server forms response message (message has object)
        
        HTTP server closes TCP connection
        
        HTTP client receives response message (message has object)
        
        Steps 1-6 are repeated for each object the HTTP client needs
        
        Response Time
        2RTT per object
        RTT = round trip time
        HTTP Non-P Response Time = 1 RTT(Steps 1&2) + 1 RTT(Steps 3&4) + file transmission time
        Browser often use parallel TCP connections to get requested objects
        
        Persistent HTTP
        multiple objects can be sent over one connection
        
        Details
        
        As little as 1 RTT for all objects
        
        Server leaves TCP connection open after sending response message
        
        After establishing connections clients can send request messages without needing to first make a connection
        
        UDP
        
        ?
        
        Does not have: reliability, flow control, congestion control, timing, throughput guarantee, security, connection setup
- - - - End systems(hosts)
        at the edge
        run programs (email, web...)
    - - PAN
        personal area network
        ex: bluetooth, USB
        range of a person
      - MAN
        metropolitan area network
        ex: cable
        range of a city
      - LAN
        local area network
        ex: WiFi, ethernet
        range of a building
      - Satellite
        270 ms end-end delay
      - WAN
        wide area network
        ex: cellular, landline phone
        range of a country/continent
    - - Packet-Switching
        
        forwards packets from one router to the
        next thru links from source to designation
        
        uses interconnected routers
        
        Host
        breaks application message into packets
        
        L = packets length (bits)
        
        R = link transmission rate
        
        Link Capacity
        max link transmission rate
        
        Store-and-Forward
        entire packet must arrive at router before router can pass packet to next link
        
        Alternative Core
        circuit switching
        dedicated resources
        used in telephone networks
    - - Internet Protocol Stack
        
        Application
        supports network applications
        ex: FTP, SMTP, HTTP
        
        Transport
        process data transfer
        ex: TCP, UDP
        
        Network
        routes data from source to destination
        ex: IP
        
        Link
        data transfer btwn neighboring network elements
        ex: Ethernet, PPP
        
        Physical
        bits on a wire
    - - Internet Structure
        
        end systems connect to internet with access ISP
        
        access ISP must be interconnected so hosts can send packets
        
        ex: residential, company, university
        
        due to economics and national laws it is very complicated
        
        O(N^2) connections if every access ISP was connected to each other directly
        
        result: all access ISP are interconnected but not directly
        
        Example Internet Structure
        ISP A,B,C = Sprint, AT&T
        CPN = Google, Bing
        
        Content Provider Network (CPN)
        
        ISP A
        
        IXP internet exchange point
        
        ISP C
        
        4 more items...
        
        Access ISP
        
        Access ISP
      - History of the Internet
        I am assuming I wont need to know this
    - - Bit
        propagates btwn transmitter/ receiver pairs
      - Physical Link
        what lies btwn transmitter and receiver
      - Types
        
        Guided
        signals in solid media
        
        Twisted Pair(TP)
        two insulated copper wires twisted in helix form(think DNA)
        signals are carried as the difference in voltage btwn the two wires
        used for ethernet and landlines
        
        Coaxial Cable
        two concentric copper conductors
        better shielded than TP(less external noise)
        longer distances w/ greater transmission rate
        bidirectional
        broadband, multiple channels on a cable
        used in cable televison
        
        Fiber optic cable
        glass fiber carrying light pulses (1 pulse=1 bit)
        high speed
        low errors, external noise has no effect, distance doesn't increase errors
        
        Unguided
        signals propagate freely
        no physical wire
        
        electromagnetic waves (most common), acoustic waves, magnetic induction(close range)
        
        environment can impact electromagnetic waves ex: reflection, obstructed by objects, other external factors
- - - - Queueing Delay & Loss
        if more packets are arriving than can be processed/output (more in than out)
        these 'excess' packets will be waiting in the router buffer
        if buffer 'overflows' packets may be lost
        
        Packets in
        
        Router
        
        Packets out
        
        Throughput
        
        Throughput Rate
        bits/time
        rate that the receiver receives data from sender
        
        instantaneous, rate at given moment
        
        average, rate over time
        
        Bottleneck Link limits the average throughput
        in router A example link Y is the bottleneck
        in router B example link X is the bottleneck
        
        Source
        
        2 more items...
        
        Traffic intensity L*a/R = .....
        
        0 queueing delay is small
        
        1 queueing delay is large
        
        >1 more packets arriving than can be process (infinite delay)
    - - L/R = bit/(bit/sec)
      - 2L/R = bits/(bits/sec)
        end-end delay (if propagation delay = 0)
    - - d/s = m/(m/s)