Shulou(Shulou.com)06/01 Report--

1. Network communication process:

The network in daily use can be simplified into the following topology:

Among them, the green circle is the router, and the blue part is not the switch.

2. Network layering:

The OSI 7-layer model, the textbook 5-layer model, and the 4-layer implementation of the TCP/IP protocol stack (actual network implementation) are compared as follows:

Among them, the last layer in the TCP/IP protocol stack combines the data link layer and the physical layer, which is called the network interface layer. At the same time, hierarchical subdivision is carried out within the network layer.

The role of each layer in the OSI 7-layer model can be simply understood as:

Application layer: all programs that generate network traffic

Presentation layer: whether encryption or compression is performed prior to transmission Binary ASCII

Session layer: establish session, can be used to check ***(netstat -n)

Transport Layer: Reliable Transmission Flow Control Unreliable Transmission

Network layer: responsible for selecting the best path planning IP address

Data Link Layer: Start and End of Frame Transparent Transmission Error Check

Physical Layer: Interface Standards Appliance Standards How to transmit faster speeds over physical links

3. The process of data transmission on the network:

1) Packaging process:

2) Unpacking process:

4. Network troubleshooting guidelines (principle: start from the bottom):

Physical layer:

Check the network connection status, send and receive data packets (if only send but not receive, it may be the crystal head problem of the network cable (the network cable has 2 thin wires for sending and 2 for receiving))

Data Link Layer:

MAC conflict, ADSL arrears, switch port network speed negotiation failure (default is automatic negotiation, if mandatory, 100M and 1000M may fail to negotiate), computer connected to the wrong VLAN

Network layer:

IP address, subnet mask, gateway incorrectly configured, router not configured with route to destination network

Application layer:

Application Configuration Error

5. Network security:

Physical layer: timely remove network cable connections that do not belong to the local area network (if the 10th floor of a building is leased to other companies, the 10th floor switch network connection can be removed at this time)

Data link layer: ADSL account, VLAN switch port binding MAC address

Network layer: ACL is used on routers to control packet traffic (some machines can not access the Internet)

Application Layer: The application has no vulnerabilities

6. Computer network performance indicators:

Rate: The rate at which a host connected to a computer network transmits data bits over a digital channel, also known as data rate or bit rate. (Single bit: b/s, kb/s, Mb/s, Gb/s)

Bandwidth: In the field of data communication, the highest data rate that can be transmitted by digital channels (units: b/s, kb/s, Mb/s, Gb/s)

3) Throughput: the amount of data passing through a network in unit time (units: b/s, kb/s, Mb/s, Gb/s)

4) Delay:

Transmission delay: data block bit length/channel bandwidth

Propagation delay: channel physical length (m)/signal propagation rate on the channel (m/s)

Processing delay:

Queue delay:

5) Delay bandwidth product: propagation delay x bandwidth

6) Round-Trip Time (RTT): The time from when the sender sends data to when the sender receives the acknowledgement from the receiver

7) Utilization:

Channel utilization: with data transit time/(with + without data transit time)

Network utilization: weighted average of channel utilization (since delay increases with channel utilization)

Note: This series of articles is notes taken from watching Professor Han Ligang's computer network foundation course.

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