Computer network Learning Notes

Hierarchical model of computer network:

From bottom to top: Physical layer, link layer, network layer, Transport layer, application layer

The physical layer (connecting the computer in the form of optical cables, radio waves, etc.) specifies the electrical characteristics of the network, and transmits 0 and 1 of the electrical Signal Link Layer Ethernet Protocol (which specifies the interpretation of electrical signals 0 and 1) a group of electrical signals consisting of a packet, called frames per frame including head and The Data Head section contains senders, receivers, data types, and other senders and receivers that identify MAC addresses with MAC addresses: that is, the network card address---Each NIC comes out of the factory with a unique MAC address in the world, with a length of 48 bits, usually in 12 hexadecimal digits.            The first 6 hexadecimal digits are the vendor number, and the last 6 are the vendor's NIC serial number.    Data is limited in length and is long enough to be split into multi-frame data transmission: Broadcast (within the same subnet) network layer (introducing a new address, differentiating whether the MAC address belongs to the same sub-network, is broadcasting, otherwise routing) to establish host-to-host communication. IP protocol (IPV4) IP address:0.0.0.0~255.255.255.255includes the network number and host number, the same subnet mask for the computer IP address network portion of the same sub-network: Computes the network number, as in the form "11111111.11111111.11111111.00000000 "(and IP address do &operation) IP packet: The "data" part of the "header" part of the Ethernet packet is mainly composed of the version, length, IP address and other information, the "data" part is the specific content of the IP packet.        ARP protocol: In the same sub-network, through the IP address to broadcast the MAC address Transport layer to establish "port-to-port" communication. Host+Port: Socket (socket) provides additional parameters: Port---to differentiate which program (process) the packets received on the network are actually used for the port number:0~65535, of which: 0~1023 The system occupies the UDP protocol header (send and Receive ports) and data, put into the "Data part" advantage of IP packets: simple, easy to implement the disadvantage: poor reliability, once the packet is issued, can not know whether the other party received the TCP protocol    There are confirmation mechanism advantages: ensure that the data does not lose the disadvantage: the process is complex, the implementation is difficult, consumes more resources the application layer stipulates various programs such as email, FTP, www and other data format DHCP protocol to provide users with dynamic IP address DNS protocol converts URLs to IP addresses

Computer network Learning Notes