Baotou bitcoin

5.

1Mbps=1000000bps

The unit of Mbps is bits per second (BPS), kilobits per second (kbps), or megabits per second (Mbps). The conversion relation is: 1kbps = 1024bps, 1Mbps = 1024 * 1024bps (sometimes 1kbps = 1000bps, 1Mbps = 1000000bps for simple calculation)

the data transmission rate reflects the information processing ability between terminal devices, which is the average value over a period of time

In computer science, bit is the smallest unit of information, which is called binary bit; It is generally represented by 0 and 1. A byte is called a byte. It consists of eight bits to represent a character in the computer

The conversion between

bit and byte is: 1byte = 8bit (or 1b = 8b); In practical application, the abbreviation is generally used, that is, 1bit is abbreviated as 1B (note that it is lower case letter b), 1byte is abbreviated as 1B (note that it is upper case letter b)

b is the abbreviation of bit, namely "bit", which is the smallest storage unit in information technology. One bit represents a "1" or "0". B is the abbreviation of byte, or "byte". It is a small storage unit in information technology. One English character takes up one byte, and one Chinese character takes up two bytes. The conversion between them is 1byte = 8bit, and their rate is 8

So 1Mbps (1 megabit per second) = 0.125m byte / S (0.125 megabyte per second) = 0.125m byte / s * 1024 = 128KB / S (128 kilobytes per second)

that is 1Mbps (megabit per second) = 1 / 8MB / S (one eighth megabyte per second)

in computer networks or network operators, generally, The unit of broadband rate is BPS (or B / s); BPS stands for bits per second, which means how many bits of information are transmitted per second. In practice, 1m bandwidth means 1Mbps [megabits per second (Mbps), not megabytes per second (Mbps)

Special tips for

< H2 > extended data

Mbps

(1) about the conversion between bit (bit) / second (s) and byte (byte) / S (s)

< P > the line unit is BPs, which means bit (bit) / second (s), note that it is a small letter B

the unit of rate displayed by users when downloading on the Internet is usually byte / S (second), note that it is capital B. The relationship between byte and bit is 1byte = 8bit

in addition to the increase of IP packet header and HTTP packet header e to network transmission protocol, the actual transmission rate of the line is about 10kbps when 1kbyte / s download rate is displayed. For example, when the download display is 50kbyte / s, the actual speed has reached 500kbps

(2) the rate of broadband service applied by users refers to the maximum theoretical rate that can be achieved technically. When users surf the Internet, they are also affected by the configuration of computer software and hardware, the location of the website they browse, the bandwidth of the opposite website, etc., so the rate of users surfing the Internet is usually lower than the theoretical rate

(3) theoretically, the theoretical rate of 2m (i.e. 2Mbps) broadband is 256Kb / S (i.e. 2048kb / s), and the actual rate is about 103-200kb / s The reason is caused by the user computer performance, network equipment quality, resource utilization, network peak, website service capacity, line attenuation, signal attenuation and other factors

The theoretical broadband rate of

4m (i.e. 4Mbps) is 512KB / s, and the actual rate is about 200-440kb / s

6. Is the header

in short, the IPv4 header adds the source IP address and the destination IP address to the data of the upper layer, as shown in the following

the IPv4 header has 12 required fields and optional IP option fields, which are located before the data to be sent. If you use the existing libraries or other components of IP layer, you don't need to consider most fields in the header, but the program code needs to provide the source and destination addresses
1, Version (4 bits)
the IP protocol version has been revised many times. Rfc0791 in 1981 describes IPv4, and rcf2460 introces IPv6
2. Header length (4 bits)
header length is the length of header data, expressed in 4 bytes, that is, 32 bytes. The header length is variable. The required fields use 20 bytes (header length is 5, IP option field has up to 40 additional bytes (header length is 15)
3. Service type (8 bits)
this field gives the method that the sending process suggests the router how to handle the packet. Maximum reliability, minimum latency, maximum throughput and minimum overhead can be selected. Routers can ignore this part
4. Datagram length (16 bits)
this field is the sum of header length and data bytes, in bytes. The maximum length is 65535 bytes
5. Identifier (16 bits)
the original data host assigns a unique datagram identifier to the datagram. When a datagram is sent to the destination address, if the router divides the datagram into pieces, then each piece has the same data identifier
6. Flag (3 bits)
two of the flag fields are related to newspaper
bit 0: not used
bit 1: not a newspaper. If this is 1, the router will not fragment the datagram. The router will try its best to transmit the datagram to the network that can receive the whole datagram at one time; Otherwise, the router will give up the datagram and return the error message, indicating that the destination address is unreachable. IP standard requires that the host can receive datagram within 576 bytes. Therefore, if you want to transfer the datagram to an unknown host and confirm that the datagram has not been abandoned e to its size, you should use the datagram less than or equal to 576 bytes
bit 2: more news. If the bit is 1, the datagram is a piece, but not the last piece of the partitioned datagram; If the bit is 0, the datagram is not partitioned, or it is the last one
7. Segment offset (13 bits)
this field identifies the location of the segment in the segmented datagram. Its value is in 8 bytes, the maximum is 8191 bytes, corresponding to the offset of 65528 bytes
for example, the 1024 bytes to be sent are divided into 576 and 424 bytes. The offset of the first piece is 0, and the offset of the second piece is 72 (because 72) × 8＝576
8. Lifetime (8 bits)
if the datagram does not reach its destination within a reasonable time, the network will abandon it. The time to live field determines when the datagram is discarded
the survival schele indicates the remaining time of the datagram, and each router will rece its value by one, or decrease the time needed to calculate and deliver the datagram. In fact, the time for routers to process and deliver datagrams is generally less than 1s, so this value does not measure the time, but the number of hops between routers or the number of network segments. The initial lifetime of the computer sending the datagram is set
9. Protocol (8 bits)
this field specifies the protocol used in the data part of the datagram, so the IP layer knows where to send the received datagram. TCP protocol is 6, UDP protocol is 17
10. Header check sum (16 bits)
this word terminal makes the receiver of datagram only need to check the error in IP header, but not the content or message in data area. The check sum is calculated by the numerical value in the header. The header check sum is assumed to be 0. The Ethernet frame, TCP message segment and the options in UDP datagram all need message error detection
11. The source IP address (32 bits)
indicates the sender of the datagram
12. The destination IP address (32 bits)
indicates the destination of the datagram.

7. TTL is a value in IP protocol packet, which tells the network router whether the packet should be discarded because it has been in the network for too long. There are many reasons why the package cannot be delivered to the destination within a certain period of time. For example, an incorrect routing table may result in an infinite loop of packets. One solution is to discard the packet after a period of time, and then send a message to the sender, who decides whether to resend it. The initial value of TTL is usually the system default value, which is the 8-bit field in the packet header. The original idea of TTL is to determine a time range, beyond which packets will be discarded. Since each router has to rece the TTL domain by at least one, TTL usually represents the maximum number of routers that a packet can pass through before it is discarded. When the count reaches 0, the router decides to discard the packet and send an ICMP message to the original sender< The default value of TTL in Windows 95 / 98 is 32. It is suggested to set this value to 128 when it is difficult to reach a node. Both Ping and tracerouter use TTL values to try to reach a given host or track a route to that host. Traceroute sets the TTL value of the packet to a small value, so that it is discarded continuously by each router on the way to the destination. The time between sending packets and receiving returned ICMP packets is used to calculate the time from one router to another<

using multiplexed IP protocol, TTL value represents a range of packets to be forwarded. There are the following conversions: 0, limited to the same host 1, limited to the same subnet 32, limited to the same node 64, limited to the same region 128, limited to the same continent 255,

because the default TTL values of different operating systems are different, it is said that the type of target system can be judged by the returned TTL values, which is correct, But it is not the function of TTL, just an application of understanding TTL. The value of TTL can be modified. Some special systems (such as NIDS) will define special TTL values to deny illegal access to data. When we execute the ping command, we can use the - I parameter to specify the TTL value. You can set TTL to 0, and the packet will be discarded immediately. Sometimes we execute a ping command, but when it's busy, it's busy with another address, with an English prompt (generally meaning that TTL is invalid), which means that before the packet reaches the destination (that is, when it returns to the IP location), the TTL carried by the packet is 0 or less than the TTL allowed by the next network segment, and the packet has been discarded by the route