Article Directory
Introduction
The entire content of this blog is an individual summary based on the instructor, and whether it is useful or not varies from person to person.
Chapter 1 Overview
1. The predecessor of the Internet is ARPANET in the United States. Corresponding to page 5 of the textbook
2. Two communication methods: client-server and peer-to-peer connection. Corresponding to page 11 of the textbook
3. Data exchange Three exchange methods and their characteristics:
Circuit exchange: The bit stream of the entire message continuously goes from the source point to the end point.
Message exchange: The entire message is first transmitted to the neighboring node, and after all the messages are stored, the forwarding table is searched and forwarded to the next node.
Packet switching: A single packet (this is only a part of the entire message) is transmitted to the adjacent node, stored and then searched for the forwarding table, and forwarded to the next node.
Corresponds to page 17 of the textbook .
4. Computer networks are classified according to the scope of the network:
(1) Wide area network WAN. The range of action is usually tens to thousands of kilometers
(2) Metropolitan Area Network MAN. The operating distance is about 5~50km
(3) WAN LAN. Limited to a small area (such as about 1km) the size of a school or factory.
(4) Wide area network PAN. The range is very small, about 10m.
Corresponds to page 20 of the textbook.
5. Seven performance indicators of computer networks
(1) rate (2) bandwidth (3) throughput
(4) delay
calculation formula of
transmission delay calculation formula of propagation delay
(5) delay bandwidth product (6) round trip The utilization rate of time RTT(7)
corresponds to pages 21 to 26 of the textbook.
6. The three key inputs of the protocol and their meanings:
(1) Syntax, that is, the structure or format of data and control information;
(2) Semantics, that is, what kind of control information needs to be sent, what action to complete, and what response to make;
(3) Synchronization, that is, a detailed description of the sequence of events.
7. The relationship between service and protocol:
Under the control of the protocol, the communication between two peer entities enables this layer to provide services to the upper layer. To implement this layer protocol, you also need to use the services provided by the layer below.
Corresponding to page 34 of the textbook
Chapter 2 Physical Layer
1. Four characteristics of the physical layer:
(1) Mechanical characteristics: specify the shape and size of the connector used in the interface, the number and arrangement of pins, and fixing and locking devices.
(2) Electrical characteristics: Specify the range of voltages that appear on each line of the interface cable.
(3) Functional characteristics: specify the meaning of a certain level of voltage appearing on a certain line.
(4) Process characteristics: specify the order of occurrence of various possible events for different functions.
2. Three basic interaction modes of the channel
(1) Simplex communication: There can only be communication in one direction and no interaction in the opposite direction.
(2) Half-duplex communication: Both parties of communication can send information, but not both parties can send at the same time (of course, they can not receive at the same time).
(3) Full-duplex communication: Both parties of communication can send and receive information at the same time.
3. The characteristics of guided transmission media
①. Twisted-pair
transponder: Transforms one form of signal into another. In the early days, it was a peripheral device, and now it is a component on the network card, which is mainly responsible for receiving and sending signals.
Repeater: Allows the cable to extend farther, breaking the transmission distance limit of UTP 100 meters, but cannot filter traffic. The main function is to regenerate the signal (de-drying, amplifying).
Hub: Multi-port repeater, allowing many devices to connect , Can be used as the center of the star topology, but still can not filter traffic.
Shielded twisted pair STP: with metal shielding
unshielded twisted pair UTP
②. Optical
fiber Optical fiber is the transmission medium of optical fiber communication.
The advantages of optical fiber: (1) Very large communication capacity (2) Small transmission loss and long relay distance. (3) Good anti-lightning and electromagnetic interference performance. (4) No crosstalk interference and good confidentiality. (5) Small size and light weight.
Multi-mode fiber and single-mode fiber
Multi-mode fiber: There can be multiple incident light rays transmitted in one fiber.
Single-mode fiber
If the diameter of the fiber is reduced to only one wavelength of light, the fiber is like a waveguide, which allows the light to propagate forward without causing multiple reflections.
4. The content and difference of channel multiplexing technology Multiplexing
is a basic concept in communication technology. It allows users to use a shared channel for communication, reducing costs and improving utilization.
(1) Frequency division multiplexing Divide
the entire bandwidth into multiple parts. After users are allocated a certain frequency band, they will occupy this frequency band from beginning to end during the communication process.
All users of frequency division multiplexing occupy different bandwidth resources at the same time.
(2) Time-
division multiplexing Time- division multiplexing divides time into sections of time-division multiplexing frames of equal length. Each time division multiplexed user occupies a fixed number of time slots in each TDM frame.
All users of time division multiplexing occupy the same bandwidth at different times.
(3) Statistical time-division multiplexing The
statistical time-division multiplexing STDM frame is not a fixed allocation of time slots, but a dynamic allocation of time slots as needed. Therefore, statistical time division multiplexing can improve the utilization rate of the line.
(4) Wavelength
division multiplexing Wavelength division multiplexing is optical frequency division multiplexing. Use an optical fiber to transmit multiple optical carrier signals simultaneously.
(5) Code division multiplexing
After class 2-16,
there are four stations for code division multiple access CDMA communication. The chip sequence of the four stations is:
A: (-1-1-1+1+1-1+1+1) B: (-1-1+1-1+1+1+1-1)
C : (-1+1-1+1+1+1+1-1-1) D: (-1+1-1-1-1-1+1-1)
Now we have received such a chip sequence: (- 1+1-3+1-1-3+1+1). Ask which station sent the data? Does the station sending the data send 1 or 0?
5. The difference between the two interfaces RJ45 and RJ11
Chapter 3 Data Link Layer
1. The basic unit of information transmission on the data link layer is called a frame.
2. Three main points of the CSMA/CD protocol: corresponding to page 86 of the textbook
(1) "Multipoint Access"
(2) "Carrier Sense"
(3) "Collision Detection"
Chapter 4 Network Layer
1. The common dividing the IP address corresponding to the textbook page 119
(. 1) Class A, Class B and Class C network ID address are 1, 2 and 3 bytes long, and the network ID foremost There are 1 to 3 category bits, and their values are specified as 0, 10
, and 110 respectively. (2) The host number fields of Class A, Class B, and Class C addresses are 3, 2, and 1 byte long, respectively.
(3) Class D addresses (the first 4 bits are 1110) are used for multicast
(4) Class E addresses (the first 4 bits are 1111) are reserved for future use.
2.127.0.0.1 is the loopback address. Corresponding to page 120 of the textbook
3. IP address assignment range: Corresponding to Table 4-2 on page 121 of the textbook
3. IPv4 address is composed of 32-bit binary values
IPv6 address is composed of 128-bit binary values
Hardware address is composed of 48-bit binary values
4 .Although the RFC document does not stipulate that a string of 1s in the subnet mask must be continuous, it is highly recommended to use consecutive 1s in the subnet mask to avoid possible errors. Corresponding to page 137 of the textbook
Chapter 5 Transport Layer
Chapter 6 Application Layer
1. The corresponding transport port number of each protocol 2.
The function of
DNS 3. The classification of domain name servers
4. Who uses iterative recursion
5. The basic working principle of
FTP 6. The working process of the World Wide Web and FTP
7. The 3 stages of
SMTP communication 8. UA 4 functions