Introduction to Computer Network Reading Notes

Introduction to Computer Network Reading Notes a large number of independent computers are connected to each other to form a computer network. Computer networks can be classified by transmission technology and network scale. 1. There are two types of transmission technologies: broadcast-type links and point-to-point links. Point-to-point transmission only has one sender and one receiver, and sometimes becomes an unicasting (unicasting). Each machine in the network receives the data transmission method, which is called broadcast. The packet sending mode for a group of machines is called multicast. 2. network scale, including the personal network, lan, man, and Internet. To reduce the complexity of network design, the vast majority of networks form a stack of layers or a stack of levels ), each layer is built on the basis of the next layer. The so-called Protocol refers to an agreement between the communication parties on how to communicate. An object that forms a corresponding level on different machines is called peer ). A collection of layers and protocols is called network architecture ). the specification of the network architecture must contain sufficient information so that the program or hardware designed for each layer can comply with relevant protocols. A group of protocols used by a specific system, that is, each layer of a protocol is called a protocol stack. Computer network hierarchy design Question 1: reliability. This includes two major problems: checking errors and correcting errors. 2. network evolution. The new design should be connected to the existing network. Because there are many computers on the network, each layer requires a mechanism in a specific message to identify the sender and receiver. This mechanism is called addressing and naming at the lower and higher layers. 3. Allocate resources. Statistics reuse, traffic control, congestion, real-time, and service quality. 4. network security. Confidentiality, authentication, and integrity. Connection-oriented services are modeled based on the telephone system. The sender's bar object (Data bit) is pushed to one end of the pipeline, and the receiver pulls them out at the other end of the pipeline. The connectionless service is modeled by the postal system. A service is officially stated by a group of primitives through which user processes access the service. LISTEN blocking operation. Wait for the incoming link request to CONNECT to the awaiting peer entity to establish a connection ACCEPT and ACCEPT the inbound connection request RECEIVE blocking operation from the peer entity, waiting for an incoming packet to be sent to a peer object to SEND a message DISCONNECT to terminate a connection service and a protocol relationship service refers to a group of primitives provided to the previous layer by a certain layer. The service defines which operations the layer is prepared to perform on behalf of its users, but it does not involve how these operations are implemented. Protocol is a set of rules that specify the format and meaning of packets or packets exchanged between peer entities on the same layer. Peer entities use protocols to implement their service definitions. They can freely change the protocols as long as they do not change the services presented to their users. It is worth using programming languages to compare these two concepts. A service is like an abstract data type and object in object-oriented language. It defines operations that can be performed on objects, but does not explain how to implement these operations. The Protocol is related to the specific implementation of the service. It is completely invisible to the users of the service. OSI Open System Interconnection Reference Model. Physical Layer, focusing on the original bit transmitted over a communication channel. The data link layer converts an original transmission facility into a line without missing inspection transmission errors. Network Layer to control the operation of subnets. How to route data packets from the source to the receiver. The Transport Layer receives data from the previous layer, splits the data into smaller units when necessary, and then transmits the data units to the network layer, make sure that these data units arrive at the other end correctly. The Session Layer allows users on different machines to establish sessions. The presentation layer focuses on the syntax and semantics of the transmitted information. The application layer contains various protocols that users usually need. TCP/IP Model Application Layer http smtp rtp dns transport layer tcp udp Internet layer ip icmp link layer dsl sonet 802.11 Ethernet TCP/IP reference model first, this model does not clearly distinguish between services, interfaces, and protocols. Second, it is not universal at all. It is not suitable for describing any protocol stack other than TPC/IP. Third, in the context of layered protocols, the link layer is not a layer in the general sense. It is an interface (between the network layer and the data link layer), and the difference between interfaces and layers is very important. Fourth, it does not distinguish between the physical layer and the data link layer. Fifth, although the IP and TCP Protocols are carefully designed and well implemented, there are many other local protocols that are self-developed.