Which layer in the osi model completes addressing and routing?

The "network layer" that completes addressing and routing in the osi model. The network layer mainly provides services for the transport layer. It can select the most appropriate path for packets through the communication subnet through routing algorithms, and can use IP addresses for addressing. The IP address is the network layer address that identifies each node. During the data transmission process, the target network address is calculated based on the target IP address and subnet mask, and then addressing is performed based on the target network address.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

The OIS reference model is divided into 7 layers. Their functions are:

• ①Physical layer: It is at the bottom of the OSI reference model. The main function of the physical layer is to provide physical connections for the data link layer using physical transmission media to transparently transmit bit streams.

• ②Data link layer: In this layer, data is framed and flow control is handled. This layer specifies the topology and provides hardware addressing;

• ③Network layer: This layer establishes the connection between two nodes through addressing, which includes routing through the Internet and relay data;

• ④Transport layer: Regular data transmission is connection-oriented or connectionless. Including full-duplex or half-duplex, flow control and error recovery services;

• ⑤ Session layer: Establish a terminal connection between two nodes. This service includes setting whether to establish a connection in full-duplex or half-duplex mode, although duplex mode can be handled in layer 4;

• ⑥Presentation layer: Mainly used Deals with the representation of information exchanged between two communication systems. It includes functions such as data format exchange, data encryption and decryption, data compression and recovery;

• ⑦Application layer: The application layer is the highest layer of the open system and directly provides services to the application process. of. Including virtual terminal, job transmission and operation, file transmission and access management, remote database access, graphics core system, open system interconnection management, etc.

#The "network layer" that completes addressing and routing selection in the osi model.

Network layer

The network layer is the third layer in the OSI reference model, between the transport layer and the data link layer It further manages the data communication in the network based on the data frame transmission function provided by the data link layer between two adjacent endpoints, and manages to transmit the data from the source end to the destination end through several intermediate nodes. This provides the most basic end-to-end data transmission service to the transport layer. The main contents include: virtual circuit packet switching and datagram packet switching, routing algorithm, congestion control method, X.25 protocol, Integrated Services Data Network (ISDN), Asynchronous Transfer Mode (ATM) and Internet interconnection principles and implementation.

The network layer mainly provides services for the transport layer. In order to provide services to the transport layer, the network layer must use the services provided by the data link layer. The main role of the data link layer is to solve the communication problem between two directly adjacent nodes, but it is not responsible for solving the communication problem when the data passes through multiple transfer nodes in the communication subnet. Therefore, in order to realize the communication between the two terminals, The transparent transmission of data between systems allows the source data to transparently reach the destination through multiple transfer nodes in the communication subnet via the optimal path, so that the transport layer does not need to care about the network topology and the communication medium used. and switching technology, the network layer must have the following functions:

• Packet and packet switching: encapsulate the data messages received from the transport layer into packets (Packet, also known as "packet" ) and then transmitted down to the data link layer.

• Routing: Selecting the most appropriate path for a packet through the communication subnet through a routing algorithm.

• Network connection multiplexing: Create logical links for the transmission of packets between nodes in the communication subnet, and multiplex multiple network connections on one data link ( Time division multiplexing technology is often used).

• Error detection and recovery: Generally, the header checksum in the packet is used for error checking, and the acknowledgment and retransmission mechanism is used for error recovery.

• Service selection: The network layer can provide datagram and virtual circuit services for the transport layer, but the network layer of the Internet only provides datagram services for the transport layer.

• Network management: Manage the data communication process in the network, try to transmit the data from the source to the destination through several intermediate nodes, and provide the most basic end-to-end data for the transport layer Delivery Service.

• Traffic control: Traffic control is achieved through traffic shaping technology to prevent performance degradation of the communication subnet caused by excessive traffic.

• Congestion control: When the data traffic of the network exceeds the rated capacity, network congestion will occur, causing the network's throughput capacity to drop sharply. Appropriate control measures are therefore required for diversion.

• Network interconnection: Connect one network to another network to achieve cross-network communication between users.

• Fragmentation and reassembly: If the packet to be sent exceeds the allowed length of the protocol data unit, the network layer of the source node will fragment the packet. After the fragments arrive at the destination host, The network layer of the destination node is then reassembled into the original packet.

Routing

The communication subnet provides the possibility of multiple transmission paths for the network source node and destination node sex. After receiving a packet, a network node must determine the path to transmit to the next node, which is routing. In the datagram mode, the network node has to make a selection for each packet route; in the virtual circuit mode, the route only needs to be determined when the connection is established. The strategy that determines routing selection is called a routing algorithm.

Many technical factors must be considered when designing routing algorithms. First, we need to consider whether to choose the shortest route or the best route; second, we need to consider whether the communication subnet uses virtual circuits or datagram operation; third, we need to use a distributed routing algorithm, that is, each node is To select the next route for arriving packets, a centralized routing algorithm should be used, that is, the central node or the originating node determines the entire route; fourth, the source of network information such as network topology, traffic and delay must be considered; fifth, Determine whether to use a static routing strategy or a dynamic routing strategy.

Addressing

Use ip address for addressing. The network layer is the third layer, which completes the end-to-end data transmission service of data packets from the source to the destination node. The IP address is the network layer address that identifies each node. During the data transmission process, the target network address is calculated based on the target IP address and subnet mask, and then addressing is performed based on the target network address.

Each router that passes through forwards data in this way according to the best route until it reaches the target network. The target node uses a Layer 2 address to address the target node, thereby realizing data forwarding to the target node.

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