Understand signal and optical fiber, number system conversion, IP division
1. Signal and fiber
1.1 Signal
Signal : information, signal, data
The signal is divided into digital signal and analog signal.
Signal distortion causes during transmission : noise, attenuation (weak signal)
Advantages of digital signal : strong anti-interference ability, long transmission distance and quality assurance
Repeater : filter noise and amplify signal power
1.2 Optical fiber
Optical fiber features : high transmission bandwidth, long transmission distance, strong anti-interference ability
The transmission of light pulses in optical fibers uses the principle of total reflection of light
Fiber classification: single-mode fiber , multi-mode fiber
1.2.1 Features of optical fiber
1.2.2 Twisted pair connection specification:
Generally useful are 1, 2, 3, 6 (receive, send)
1.3 Wireless transmission
Wireless transmission medium: radio wave, microwave, infrared, laser, etc.
Radio waves: electromagnetic waves in the radio frequency band that propagate in free space (air and vacuum)
Propagation characteristics: the lower the frequency, the smaller the propagation loss and the longer the coverage distance
The higher the frequency, the larger the system capacity and the longer the coverage distance
Radio waves are classified according to their propagation characteristics: ground wave propagation, sky wave propagation, straight line propagation
2. Number system conversion
2.1 Unit conversion
We generally say that the unit of 100M and Gigabit network is bps (bit rate, that is, bit/s, bit/s). For example, we say that the transmission speed of network cards or optical fibers is 100M, which means 100Mbps. In practical applications (download tools such as Xunlei), the transmission unit used is byte/s (Byte/s).
8bit=1byte
1024byte=1KB
1024KB=1MB
1024MB=1GB
1024GB=1TB
1024TB=1PB
1024PB=1EB
1024EB=1ZB
1024ZB=1YB
2.2 Number system conversion
2.2.1 Computer System
Decimal number
（1010) 10，1010D，1010
Octal number
（1010）8，1010O
Binary number
(1010)2，1010B
Hexadecimal number
(1010)16，1010H，0X1010
In the number system, there is another rule, that is, the N base must be one in every N.
The characteristic of decimal numbers is that every decimal is one. E.g:
Cato
2.2.2 Number system conversion
Convert decimal to binary:
Method 1: Invert the remainder
| method one | Inverted remainder | |
|---|---|---|
| 125/2 | Can not be eliminated | 1 |
| 62/2 | Divide | 0 |
| 31/2 | Can not be eliminated | 1 |
| 15/2 | Can not be eliminated | 1 |
| 7/2 | Can not be eliminated | 1 |
| 3/2 | Can not be eliminated | 1 |
| 1/2 | Can not be eliminated | 1 |
| 0 | ||
| 125=1111101B |
Method 2: Subtract full 1
Binary number to octal number : 3 digits to one conversion
Binary number conversion to hexadecimal number : 4-bit one conversion
8-bit binary number
| 10101000 | 168 |
|---|---|
| 10101100 | 172 |
Three, IP division
3.1 IP address
3.1.1 Know IP
IPv4 consists of 32-bit binary numbers, generally expressed in dotted decimal notation
IPv6 is composed of 128 bits, which are generally represented by colons in hexadecimal notation
The IPv4 address consists of two parts: the network part (NETWORK) and the host part (HOST)
For example: 192.168.0.25
Network part: 192.168.0
Host part: 25
3.1.2 IPv4 private network address and public network address
A public network address refers to a globally unique IP address on the Internet. November 26, 2019 is a memorable day in the era of the human Internet. Nearly 4.3 billion IPv4 addresses worldwide have been officially exhausted.
IP addresses are divided into five categories: A, B, C, D, and E:
Class A address range: (0xxxxxxx), 1.0.0.1~126.255.255.254
Class A address = network part + host part + host part + host part
(Classified boundary) The default subnet mask is /8, which is 255.0.0.0
Class B address range: (10xxxxxx), 128.0.0.1~191.255.255.254
Class B address = network part + network part + host part + host part
(Classified boundary) The default subnet mask is /16, which is 255.255.0.0
Class C address range: (110xxxxx), 192.0.0.1~223.255.255.254
Class C address = network part + network part + network part + host part
(Classified boundary) The default subnet mask is /24, which is 255.255.255.0
Class D address range: (1110xxxx), 224.0.0.1~239.255.255.254
Address used for multicast communication
Class E address range: (11110xxx), 240.0.0.1~255.255.255.254
Reserved address for scientific research
To 127 at the beginning of the IP addresses on behalf of the machine (except the broadcast address 127.255.255.255), 127.0.0.1 is the native loopback address
169.254.0.0~169.254.255.255 The address assigned when the DHCP service fails
DHCP service is to automatically obtain IP service
Private network
Private network addresses refer to the IP addresses of internal networks or hosts. IANA (Internet Assigned Numbers Agency) stipulates that the following IP addresses are reserved for private network addresses, and are not allocated on the Internet, but can be used within an organization or company. The private address specified in RFC1918 is as follows:
Class A private address: 10.0.0.0~10.255.255.255 /8
Class B private address: 172.16.0.0~172.31.255.255 /12
Class C private address: 192.168.0.0~192.168.255.255 /16
3.2 32 binary bit subnet mask
3.2.1 "And"
The network part of the IP address corresponding to the subnet mask is represented by 1
The host part of the corresponding IP address is represented by 0
Such as: 255.240.0.0/12
Converted to binary 11111111.11110000.00000000.00000000
Subnet mask 11111111.11110000.00000000.00000000
IP address and subnet mask are used for "and" operation to get the network address
0 and any number are equal to 0
1 and any number are equal to any number itself
Example:
192.168.1.189/26
11000000.10101000.00000001.10111101 IP address
111111111.111111111.111111111.11000000 Subnet mask
Get:
11000000.10101000.00000001.10000000 network address
which is:
192.168.1.128
Set all the host bits to 1 to get the broadcast address
The broadcast address changes the last 0 bits of the subnet mask in the obtained network address to 1
11000000.10101000.00000001.10111111 Broadcast address
192.168.1.191
3.3 Subnetting
Example: 10.0.0.0/8
Network segment composition: network address, available IP, broadcast address
Example: 192.168.1.189/24
Network number: 192.168.1.0
Available IP: 192.168.1.1~192.168.1.254
Broadcast address: 192.168.1.255
to sum up:
Number of subnets=2^n, where n is the number of bits in the subnet, for example: /26, n=26-24=2
Number of hosts (available IP)=2^N-2, where N is the number of bits in the host part: N=32-26
192.168.1.189/26
11000000.10101000.00000001. 10 111101 IP address
(The number of digits in the subnet is in bold positions 26-24)
| 192.168.1.0 | /24 | /25 | /26 | /27 | /28 | /29 | /30 | /31 | /32 |
|---|---|---|---|---|---|---|---|---|---|
| Subnet mask | 0 | 128 | 192 | 224 | 240 | 248 | 252 | 254 | 255 |
| Number of subnets | 1 | 2 | 4 | 8 | 16 | 32 | 64 | 128 | 256 |
| Number of IP | 256 | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
| Available IP | 254 | 126 | 62 | 30 | 14 | 6 | 2 | 1 | 1 |
192.168.1.100/32 表示为一个固定IP