Overview of core basic knowledge of computer network

The first chapter--Overview Computer network Performance Index 1. Rate, transmission data rate, also known as data rate, bit rate, units are: b/S, kb/s, MB/s, tb/s 2. Bandwidth, the highest transfer rate, which is the highest rate, with the same unit rate 3. ThroughputThe amount of data per unit of time through a network channel or interface, in units B, KB, Mb, Gb, Tb 4. Delay, transmission delay (time required for the host or router to send data), propagation delay (the time it takes to transmit the electromagnetic wave in the channel), processing delay, queue delay 5. Delay Bandwidth Product= Propagation delay * Bandwidth 6. Roundtrip time RTT 7, utilization of channel utilization and network utilization Computer network Architecture OSI:Open System Interconnect Basic Reference Model, open Systems Interconnection Reference model protocol:The rules, standards, or conventions established for data exchange in the network are called network protocols. Benefits of Tiering:1, each layer independent, the big problem into a number of independent small problems 2, good flexibility, as long as the interface is not changed, the internal implementation can be modified without affecting the upper and lower layer 3, the structure is easy to separate 4, easy to implement and maintain 5, promote standardization work Five-layer structure (seven-layer structure is to add a presentation layer under the application layer to the session layer, more is a theoretical structure, actually more than five-layer structure representation)1, the Application Layer 2, the Transport Layer 3, the network layer 4, the data Link Layer 5, the physical layer
Chapter II-Physical layer the primary task of the physical layer is to identify some of the features associated with the Transport media interface, including: 1, mechanical characteristics 2, electrical characteristics 3, functional characteristics 4, process characteristics How information interacts1, simplex Communication 2, half duplex communication 3, full duplex communication Channel Multiplexing Technology1, Frequency division take-users in the same time to occupy different resources 2, Division multiplexing-users at different times occupy the same resources 3, wavelength division multiplexing-Optical Frequency Division multiplexing 4, Code Division multiplexing
Chapter Three--Data link layer Data Link:In addition to a physical line representing the physical layer, but also includes a number of communication protocols to control data transmission, the combination of the two is the data link Network adapter:The Data Link layer protocol is usually implemented by the network adapter, which realizes the function of the data link layer and the physical Layer two layer. Its main function is to realize the computer and the external network communication. Protocol Data Unit for the Data Link layer:Frame Point-to-point data link Communication steps (Point-to-point data links, data links using broadcast channels are two main data links):1, Node A in the network layer of the node to the IP datagram to add the header and the tail package into frame 2, node A to the encapsulated frame through the physical layer link to Node B 3, Node B in check the received frame error-free, to the network layer of the B node, otherwise, discard this frame the three basic issues to be addressed in the Data Link layer protocol:1, package into frame--frame start character Soh, Terminator EoT 2, transparent transmission-prevent the transmission of text in the case of SOH or EOT, resulting in false start or end of error 3, error detection-Extensive use of CRC cyclic redundancy detection PPP Point-to-Point ProtocolThe data link layer is the most used protocol, he provides unreliable datagram services, because the data link layer does not have to provide more than the network layer IP protocol functions, so PPP protocol does not need to error correction, no serial number, no flow control, simple is the main requirements of PPP protocol and the maximum characteristics Ethernet:The most widely used LAN specification today, using CSMA/CD technology and operating at 10m/s rates on a variety of cables CSMA/CD Protocol:Carrier monitoring multi-point access/collision detection
CSMA/CD Core points:
1, "Multi-point access", many computers connected to a bus with multi-point access, at the same time only one computer can occupy the bus to transfer data
2, "Carrier monitoring", each station (computer) must constantly detect whether the channel is transmitting data, not occupied in order to get the right to send
3, "Collision detection", the side of the sending side monitoring, if the detection of a bus has two stations simultaneously transmit data, immediately stop the transmission
MAC Address:Physical Address of Ethernet Network Bridge:can be forwarded, filtered frames, can be connected to different physical layers, Mac sub-layer and different Ethernet, the data link layer can be extended Ethernet, the disadvantage is to increase time delay. hubs:Can forward bitstream, work on physical layer, extend Ethernet in physical layer
The fourth chapter--Network layer IP AddressFor knowledge See IP address classification and subnet mask http://blog.csdn.net/zhangliangzi/article/details/51263337 Address Resolution Protocol ARP:Resolves the IP address of the host and router to the hardware address. ARP mechanism:Each host has an ARP cache, which has a local area network host, the router's IP address to the Hardware address mapping table, and this mapping table is also frequently updated dynamically. Internetwork Control Message Protocol ICMP:Provide the host or router with information, report errors, or abnormal conditions. ICMP message type:1. Error report message 2, inquiry message ICMP application:Using the ping command, the application layer crosses the transport layer directly using the ICMP protocol echo request and the Echo reply message to test the connectivity between the hosts. Router packet forwarding algorithm (Network layer operation):The IP address of the destination host is extracted from the datagram header, according to the IP address class (A, B, C, D), extracting the network address 1, if the network address n is the network address connected to the router, the datagram is delivered directly to the destination host of the network. (This includes the network interface software through the ARP protocol to convert the IP address into a MAC address, the datagram encapsulated into a link-layer Mac frame, through the physical layer line to send this frame to the destination host process) 2, if the network address is not connected to the router network address, then query the route table 2.1, if the route A specific host route in the table that has a destination address for the datagram, the datagram is sent to the next hop route specified by the routing table 2.2, if there is a route to the destination network address n in the routing table, the datagram is sent to the next hop route specified in the routing table 2.3, if the routing table Has a default route, the datagram is sent to the default route 2.4 in the routing table, reporting packet forwarding errors
Fifth-Transport layer Overview:Although the IP layer sends packet data to the destination host, strictly speaking, the two host communication in the computer network is actually the application process communication on two hosts, the endpoint of the communication is not the host but the application process on the host. The network layer provides logical communication between hosts, and the transport layer provides logical communication between ports. The main features of UDP:1, UDP is non-connected Transport layer protocol, send data without establishing a connection, reliability is reduced but improve efficiency 2, UDP is to provide the best delivery service 3, UDP is message-oriented, that is, send a message at a time, do not merge, do not split, but if the data is too long will be in the network layer IP shard transmission, affect the network layer efficiency 4, UDP can not avoid network congestion data loss, but to ensure the stable rate of transmission data 5, UDP support a pair of one or one-to-many, many-to-many communication 6, UDP header shorter than 8 bytes, more than TCP 20 bytes (including fixed word length) reduced overhead. UDP header field:1, the source port 2, the destination port 3, the length, the datagram length 4, the checksum, verifies the transmission information whether is wrong, has the mistake to discard The main features of TCP:1, TCP is a connection-oriented transport layer protocol. TCP connection must be established before using TCP, just like a phone call, after the call 2, the TCP connection is point-to-point, only two Port 3, TCP provides reliable service, error-free, not lost, not duplicated, ordered to arrive, and transport layer below are unreliable efforts to provide the best service. 4, TCP provides full-duplex communication, both ends of the communication with send cache and receive cache, can be sent or received at idle 5, TCP-oriented byte stream Socket (SOCKET)= IP Address: port number TCP message header field:
The main header field explains:1. Serial number: The first byte of the data section of the message segment occupies the position of the entire packet data segment 2, confirm the number: expected to receive the next segment of the message sequence number (such as: the previous message segment ordinal bit 600, the data section length is 100, after the correct reception, this expected to accept the data serial number 700) 3, Window Size: Indicates the amount of data allowed to be sent, dynamically changing 4, checksum: Verifying data integrity and correctness 5, emergency pointers: Indicate the end position of the emergency data in this paper, note: When the window is 0 o'clock can also send emergency data 6 Control bits explained: 1, the ACK reply function, occupies 1 bits; the confirmation Number field is valid only when ack=1, ack=0, the confirmation number is invalid 2,