The first chapter concept of computer network

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Concept:
    LAN: Coverage is small, own money to buy equipment, bandwidth fixed, self-maintenance
        LAN network cable less than 100 meters;
        Bandwidth: The switch is 100M, that is, each interface is 100M
         Access Layer switches: Switches <---> pcs, ports, small bandwidth
        converged layer switches: switch sinks <---> switch "connect", small port, large bandwidth
        specification of LAN should be layered.
    WAN: Wider than LAN, bandwidth is not fixed (pay rent bandwidth), by the ISP maintenance
    Internat:isp, own room, Provide Internet access services to Internet users
        ISP: Internet service operator,
         two-wire room:
    computer Data communication process:
        MAC: Decide who to scare to.
        IP Address: Determine source and target
        Routers: one IP address per interface, one MAC address
        packet:
         Data frame:

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OSI Reference Model: should be shown net chain

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Application layer: All programs that can generate network traffic
Presentation layer: Whether to encrypt before transmission, or compression processing, binary, ASCII, etc.
Session Layer: Trojan, differentiate and manage different session programs and Windows
Transport Layer: Reliable transmission (transmission + acknowledgement), unreliable transmission, flow control (sliding window mechanism)
Network layer: Choose the best path, plan IP address
Data Link layer: The start and end of a frame. Transparent transmission (Escape recovery), error checking
Physical layer: Interface standard (physical standard), electrical standard, how to transfer data faster

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ISO troubleshooting: From low to high, one layer at a line of error

Physical Layer:
is connected (connected state)--
Transmitted packets and received packets--network cable, Crystal Head (two rounds, two receipts, total 8)
Data Link Layer:
Does not apply to the MAC address of the network card, but by modifying the registry, using a different MAC address
ADSL Overdue fee
Network negotiation Inconsistent
The computer is connected to the wrong VLAN
Network layer:
No gateway configured
Network Address settings error, subnet mask
No network at the specified address on the router
Application layer:
OSI Reference Model and network security:
1. Physical Layer Security:
Cannot allow others to access their network at will
2. Data Link Layer Security:
ADSL, WiFi account password;
Vlan
Switch-bound Mac
3. Network Layer Security:
Use ACLs on routers to control access
4. Application Layer Security:
App No bugs
The performance index of computer network:

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1) Rate: The rate at which a host on a computer network transmits data bits on a digital channel, also known as date or bit rates, Unit b/s,kb/s,mb/s,gb/s
0,1:bit
2) Bandwidth: The highest data rate that digital channels can transmit in the field of Datacom, Unit b/s,kb/s,mb/s,gb/s
3) Throughput: The amount of data in a network per unit of time, Unit b/s,mb/s
4) Delay:
Send delay:
Transmit delay = data block length (bit)/channel bandwidth (bite/sec)
Propagation delay: Line
Processing delay:
Queue delay:

Propagation Speed:
Fiber: 20.5wkm
Copper Wire: 23.1wkm
But the fiber supports a smaller transmit rate, but the copper wire does not support

5) Delay Bandwidth product:
Delay Bandwidth Product = propagation delay x Bandwidth
The implication is that if the data is sent at the maximum bandwidth, and then the first bit arrives at the destination, the number of bits sent, and the number of these bits is now transmitted in the tunnel, that is, the maximum number of bits that can be accommodated on a link.

        6) Round trip: RTT (round-trip time)
             start sending data from sender to sender to send to receive acknowledgement
             test: Ping time =**ms
        7) Network utilization:
             Channel Utilization: Data elapsed time/(have, no) data elapsed time
             Network utilization: Channel utilization weighted average
             network utilization is closer to 1 o'clock, the time delay increases infinitely;
            D = d0/(1-u )
                D0: Time delay when the network is idle;
                D: Network Current latency
                U: Channel utilization

First chapter concept of computer network