Is it necessary for the front end to learn blockchain

1. GT has no erc20 token on Ethereum

2. be necessary! The premise is that economic conditions permit
confinement in the confinement center is concive to maternal physical recovery. Confinement in the confinement center can prevent postpartum depression, and the baby can also be taken care of comprehensively. After childbirth, post-90s mothers are worried about skin yellowing, body deformation, pregnancy marks and so on. The confinement center has special nursing staff to take care of them, so they should be more careful.

3. TCP / IP protocol does not fully conform to OSI's seven layer reference model. The traditional open system interconnection reference model is a seven layer abstract reference model of communication protocol, in which each layer performs a specific task. The purpose of this model is to make all kinds of hardware communicate with each other at the same level. The seven layers are: physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer. The TCP / IP communication protocol adopts a four layer hierarchical structure, and each layer calls the network provided by its next layer to fulfill its own requirements. These four layers are: application layer: the layer of communication between applications, such as simple e-mail transfer (SMTP), file transfer protocol (FTP), network remote access protocol (telnet), etc. Transport layer: in this layer, it provides data transmission between nodes and communication services between applications. Its main functions are data format, data confirmation and loss retransmission. Such as transmission control protocol (TCP), user datagram protocol (UDP), etc., TCP and UDP add transmission data to the packet and transmit it to the next layer, which is responsible for transmitting data and determining that the data has been delivered and received. Interconnection network layer: it is responsible for providing basic packet transmission function, so that each packet can reach the destination host (but not check whether it is received correctly), such as Internet Protocol (IP). Network interface layer (host network layer): receive IP packets and transmit them, receive physical frames from the network, extract IP datagrams and transfer them to the next layer, manage the actual network media, and define how to use the actual network (such as Ethernet, serial line, etc.) to transmit data. TCP / IP protocol structure diagram
the main protocols are as follows: 1. IP internet protocol IP is the heart of TCP / IP and the most important protocol in the network layer. The IP layer receives the data packet from the lower layer (network interface layer, such as Ethernet device driver) and sends the data packet to the higher layer -- TCP or UDP layer; On the contrary, IP layer also transfers packets received from TCP or UDP layer to lower layer. IP packets are unreliable because IP doesn't do anything to confirm that the packets are sent in order or are not corrupted. IP packet contains the address of the host sending it (source address) and the address of the host receiving it (destination address). When high-level TCP and UDP services receive packets, they usually assume that the source address in the packet is valid. It can also be said that IP addresses form the authentication basis of many services, which believe that packets are sent from a valid host. IP confirmation contains an option called IP source routing, which can be used to specify a direct path between the source address and the destination address. For some TCP and UDP services, IP packets using this option seem to be delivered from the last system on the path rather than from its real location. This option exists for testing purposes, indicating that it can be used to spoof the system to make normally forbidden connections. Then, many services that rely on IP source address for confirmation will have problems and will be illegally intruded. 2. TCP if there are already sealed TCP packets in IP packets, then IP will "up" them to the TCP layer. TCP sorts packets and checks for errors, and realizes the connection between virtual circuits. TCP packets include sequence number and acknowledgement, so packets not received in order can be sorted, while damaged packets can be retransmitted. TCP sends its information to higher-level applications, such as telnet's server and client. Applications send information back to the TCP layer in turn, and the TCP layer sends them down to the IP layer, device drivers and physical media, and finally to the receiver. Connection oriented services such as Telnet, FTP, rlogin, X windows, and SMTP require a high degree of reliability, so they use TCP. DNS uses TCP (send and receive domain name databases) in some cases, but uses UDP to send information about a single host. 3. UDP is in the same layer as TCP, but it doesn't care about the order, error or retransmission of packets. Therefore, UDP is not used for connection oriented services that use virtual circuits. UDP is mainly used for query response oriented services, such as NFS. Compared with FTP or Telnet, these services need to exchange less information. Services that use UDP include NTP (Network Time Protocol) and DNS (DNS also uses TCP). Spoofing UDP packets is easier than spoofing TCP packets because UDP does not establish an initial connection (also known as handshake) (because there is no virtual circuit between the two systems), that is, UDP related services are at greater risk. 4. ICMP ICMP is located in the same layer as IP, which is used to transmit IP control information. It is mainly used to provide information about the path to the destination address. ICMP's "redirect" information informs the host of a more accurate path to other systems, while the "unreachable" information indicates that there is a problem with the path. In addition, if the path is not available, ICMP can terminate the TCP connection "gracefully". Ping is the most commonly used ICMP based service. 5. Port structure of TCP and UDP TCP and UDP services usually have a client / server relationship. For example, a telnet service process starts to be idle on the system, waiting for connection. The user uses the telnet client to establish a connection with the service process. The client program writes information to the service process, the service process reads the information and sends a response, and the client program reads the response and reports it to the user. Therefore, the connection is plex and can be used for reading and writing. How do multiple telnet connections between two systems confirm and coordinate with each other? A TCP or UDP connection uniquely uses the following four items in each message: the source IP address, the IP address of the sending packet. Destination IP address the IP address of the received packet. Source port the port of the connection on the source system. Destination port the port of the connection on the destination system. Port is a software structure, which is used by client program or service process to send and receive information. A port corresponds to a 16 bit number. Service process usually uses a fixed port, for example, SMTP uses 25, xwindows uses 6000. These port numbers are "well known" because these addresses and destination addresses are needed to communicate when establishing a connection to a particular host or service
reference model
TCP / IP protocol does not fully conform to OSI's seven layer reference model. The traditional open system interconnection reference model is a seven layer abstract reference model of communication protocol, in which each layer performs a specific task. The purpose of this model is to make all kinds of hardware communicate with each other at the same level. These seven layers are: physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer. The TCP / IP communication protocol adopts a four layer hierarchical structure, and each layer calls the network provided by its next layer to fulfill its own requirements. These four layers are: application layer: the layer of communication between applications, such as simple e-mail transfer (SMTP), file transfer protocol (FTP), network remote access protocol (telnet), etc. Transport layer: in this layer, it provides data transmission services between nodes, such as transmission control protocol (TCP), user datagram protocol (UDP), etc. TCP and UDP add transmission data to the packet and transmit it to the next layer. This layer is responsible for transmitting data and determining that the data has been delivered and received. Interconnection network layer: it is responsible for providing basic packet transmission function, so that each packet can reach the destination host (but not check whether it is received correctly), such as Internet Protocol (IP). Network interface layer: manage the actual network media, define how to use the actual network (such as Ethernet, serial line, etc.) to transmit data

the reason why TCP / IP is a protocol family is that TCP / IP protocol includes TCP, IP, UDP, ICMP, rip, telnet FTP, SMTP, ARP, TFTP and many other protocols, which are collectively called TCP / IP protocol. Here we introce the English names and uses of some common protocols in the protocol family: TCP (Transport Control Protocol), IP (Internet Protocol), UDP (User Datagram Protocol), ICMP (Internet control message protocol) and SMTP (Simple Mail Transfer Protocol) Protocol SNMP (Simple Network Management Protocol) FTP (File Transfer Protocol) ARP (address resolution protocol) address resolution protocol from the perspective of protocol layered model, TCP / IP consists of four layers: network interface layer, inter network layer, transport layer and application layer. Among them: network interface layer, which is the lowest layer of TCP / IP software, is responsible for receiving IP datagrams and sending them through the network, or receiving physical frames from the network, extracting IP datagrams and giving them to the IP layer. The inter network layer is responsible for the communication between adjacent computers. Its functions include three aspects. 1、 After receiving the request, the packet is loaded into the IP datagram, the header is filled, the path to the destination machine is selected, and then the datagram is sent to the appropriate network interface. 2、 Processing input datagram: first check its validity, and then carry out pathfinding - if the datagram has arrived at the sink machine, remove the header and hand over the rest to the appropriate transport protocol; If the datagram has not arrived at the sink, the datagram is forwarded. 3、 Deal with path, flow control, congestion and other issues. The transport layer provides communication between applications. Its functions include: 1. Format information flow; 2、 Provide reliable transmission. In order to realize the latter, the transport layer protocol stipulates that the receiver must send back an acknowledgement, and if the packet is lost, it must be retransmitted. The application layer provides users with a set of common applications, such as e-mail, file transfer access, remote login and so on. Telnet uses telnet protocol to provide interfaces registered on other hosts in the network. Telnet session provides character based virtual terminal. File transfer access FTP uses FTP protocol to provide file function between machines in the network. We have learned the related concepts of OSI reference model. Now let's take a look at how TCP / IP protocol implements the network model compared with the seven layer protocol reference model. Layer functions in OSI: TCP / IP protocol family
application layer file transfer, e-mail, file service, virtual terminal, TFTP, HTTP, SNMP, FTP, SMTP, DNS, rip, telnet
presentation layer data format, code conversion, There is no protocol for data encryption
there is no protocol for session layer to release or establish contact with other nodes
the transport layer provides end-to-end interfaces TCP, UDP
the network layer selects routing IP, ICMP, OSPF, BGP, IGMP, ARP, RARP for data packets
the data link layer transmits addressable frames and error detection functions slip, CSLIP, PPP, MTU
the physical layer transmits data iso2110 and IEEE802 on the physical media in the form of binary data. Ieee802.2
data link layer includes hardware interface and protocols ARP and RARP

4. First, take the bus from Hangzhou to Ningbo south station, and then take the bus from Ningbo to Xiangshan. The ticket from Hangzhou to Ningbo is 55 yuan. If you are not in a hurry, you can take the 8:36 bus to Ningbo, and the ticket from Ningbo to Xiangshan is 35 yuan. If you take the 8:36 bus, you can take the 10:50 bus to Xiangshan. There are also trains from Hangzhou to Ningbo every 10 minutes from 6:00, and trains from Ningbo to Xiangshan every 20 minutes from 6:50

5. It's normal that disk C is small. If it's installed on Disk C, it will naturally take up part of Disk C space. If the client can't unload it in the normal way, it can use Tencent computer manager to unload it. It will help you solve all problems. If there are indivial programs that haven't been unloaded completely, it will automatically start the powerful cleaning mode to ensure that you can completely unload them

6.

use the software move tool in QQ computer manager to move the bitcoin client cache folder under Disk C to a large disk or mobile hard disk, so that it can be used anywhere at any time

7. Name and address of outlets: Tel.
Huainan Dongshan postal savings counter No.18-2 Dongshan Middle Road, Huainan 0554-6643720
Huainan Shungeng postal savings counter room 2, building 2, Shungeng Garden community, Longhu South Road 0554-2679143
Huainan railway station postal savings counter No.121 Shungeng Middle Road, Huainan 0554-2695750
Huainan Longhu postal savings counter no.44-1 Longhu South Road, Huainan 0554-2679432
Huainan Longhu postal savings counter/ >Postal savings counter in Qianfeng, Huainan 0554-2682941, 178 Chaoyang East Road, Huainan City
postal savings counter in Dongyuan District, Huainan 0554-6312819, south 10, ground floor, 3 commercial and residential building
postal savings counter in Chaoyang Road, Huainan 0554-6657942, 99-6 Chaoyang Middle Road, Huainan City
postal savings counter in Tianjiaan, Huainan 0554-3621587, 252 huaishun North Road, Huainan City
postal savings counter in Changchang Road, Huainan City 181 Power Plant Road 0554-3623170
Huainan huaishun North Road postal savings counter 360 huaishun North Road Huainan City 0554-3634594
Huainan Huaibin road postal savings counter 53 Huaibin road Huainan City 0554-3633244
huainantian power plant postal savings counter 0554-3668650
Huainan Dongfeng postal savings counter Tiandong bus station north 0554-3310829
Huainan Power Supply village postal savings counter Counter: Huainan huaishun South Road 169, 0554-2674394
Huainan huaishun South Road postal savings counter: Huainan huaishun South Road 304, 0554-2674824
Huainan textile factory postal savings counter: textile factory family members area 0554-2662814
Huainan Longyan postal savings counter: under the building of electrical appliances factory opposite the cinema, Huainan infrastructure Bureau 0554-6660596
Huainan Quanshan postal savings counter: Quanshan post office 0554-6413527
Huainan Quanshan post office Postal savings counter of Huainan No.3 railway station 0554-6414505, 50m to the east of the compound of Huainan No.3 railway station 0554-6640974, 200m to the north of laolongyan police station, Huainan No.96 postal savings counter, 0554-6642134, to the northeast of Railway New Village Club, Huainan Railway Village Counter 0554-6665144 opposite the east gate of Quanshan shopping mall
Huainan Xinghua postal savings counter 0554-6411647 in Xinghua shopping mall of Quanshan Dahua living area
Huainan Luohe postal savings counter Luohe post office 0554-3611194
Huainan Datong postal savings counter Datong Post Branch (turntable Street) 0554-2516552
Huainan Nanmenkou postal savings counter Nanmenkou post office 0554-2211402
Huainan huaiwang Village postal savings counter Wangfenggang postal branch 0554-5813400
Huainan Shijianhu postal savings counter opposite Longteng building, Wangfenggang North Road 0554-5813914
Huainan caijiagang postal savings counter caijiagang postal branch 0554-5677347
Huainan Kuangji road postal savings counter Caixin road postal office 0554-5713924
Huainan fangcaoyuan postal savings counter North Gate of fangcaoyuan market 0554-5670890
Huainan South lijiazi postal savings counter east of lijiazi town government 0554-5861015
Huainan Bagongshan postal savings counter Bagongshan post office 0554-5618204
Huainan bijiagang postal savings counter 30 meters north of bijiagang bus station 0554-5611610
Huainan Shanwang postal savings counter Shanwang town post office 0554-5215119
Huainan Dingshan postal savings counter Bagongshan post office new building 0554-5617954
Huainan Dingshan postal savings counter South Yuanzhuang postal savings counter Yuanzhuang postal branch 0554-4973001
Huainan Baiyun postal savings counter 100 meters east of Yuanzhuang shopping mall 0554-4973036
Huainan Bihai postal savings counter, Bihai new village, Panji District 0554-4972847
branch name and address telephone
Huainan Pansan postal savings counter, family home of Pansan mine 0554-4851718
Huainan New Street postal savings counter, No. 3, Panji middle road 0554-49749 52
Huainan Pan'er postal savings counter Pan'er living area 0554-4711244
Fengtai County Nongshui road postal savings counter Chengguan Nongshui road 0554-8627933
Fengtai County Dashan postal savings counter Dashan town Fengshou roadside 0554-8911624
Fengtai County Guqiao postal savings counter Guqiao town Caishi street 0554-8391414
Fengtai County Guiji postal savings counter Guiji Township Guiji street 0554-8011573
Fengtai County Ma Fengtai County Maoji postal savings counter No.1 Maoji street, Maoji District 0554-8271194
Fengtai County Daxing postal savings counter Daxing Township Daxing street 0554-8561004
Fengtai County Xiaji postal savings counter No.99 Xiaji street, Xiaji Township 0554-8281384
Fengtai County Dingji postal savings counter Dingji Township Dingji Laoji street 0554-8551345
Fengtai County Qian Temple postal savings counter qianmiao street, qianmiao Township 0554-8311004
Fengtai County Zhangji postal savings counter Zhangji town Zhenxing street 0554-8111296
Fengtai County Shangtang postal savings counter Shangtang Township Yimin street 0554-8461022
Fengtai County Huaibin road postal savings counter Chengguan Town Huaibin road 0554-8627931
Fengtai County Zhongshan Street postal savings counter No. 077 Zhongshan Street South Road, Chengguan town 0554-8627932
Fengtai County Gudian street, Gudian Township 0554-8361001
Xueyuan Road, Chengguan Town, Fengtai County 0554-8627930
Dongzhu street, Xinji Town, Xinji County 0554-8161294

8. Xiamen north station to Xiamen city to take BRT (Bus Rapid Transit) line 1, in addition, there are multiple buses to the city
the specific routes are:
BRT line 1 North Station first wharf. To T4 Hanglou, you can take this to T4 Hanglou station, to Shuangshi middle school high school, to Qianpu Convention and Exhibition Center, you can take the Dongfang villa station to transfer; To Xiamen railway station, Wucun bus station, to the eye hospital, you can take to Sibei station, to Zhongshan Road, you can take the first pier to transfer to the link car. To Xiamen University, you can take this bus to the first pier and take bus No.29 or No.2 to Xiamen University. This bus is the most convenient and fast way to downtown
from the North Station of 950 road to the University of science and Technology (Siming campus) to Xiamen University, you can take this on Zhongshan Road
953 north station railway station (Wucun bus station)
949 North Station international trade new town to the exhibition center, you can take this
957 North Station Sibei bus station

9.

bus line: No.1 fast bus → No.26 bus, the whole journey is about 33.0km

1. Walk about 600m from Xiamen north station to Xiamen North Station

2. Take No.1 fast bus, pass 20 stops, and reach Ershi station

3. Walk about 80m, and reach Ershi station

4. Take No.26 bus, pass 6 stops, and reach municipal government station

5. Walk about 80m, and reach Xiamen