Hello, I'm Samantha!
In the last course, I learned the functions and protocols of the transmission layer, and this week I learned the functions and common protocols of the network layer.
The network layer is between the transmission layer and the data link layer. It further manages the data communication in the network on the basis of the transmission function of data frames between two adjacent endpoints provided by the data link layer, and manages to transmit data from the source end to the destination end through several intermediate nodes. This provides the most basic end-to-end data transfer service to the transmission layer.
The functions of the network layer are as follows:
1. Shield network differences and provided transparent transmission. Different networks have different specification requirements. The network layer is to solve the difference and find a network communication specification that can be followed by different networks, so that different networks can recognize each other and accept each other's network requests.
2. Provide routing for inter-network communication. Route selection is the process of selecting an optimal path to the destination node in a communication subnetwork with multiple nodes according to certain principles and route selection algorithms. The policy for determining routing becomes the routing algorithm.
3. Packet encapsulation and decapsulation. At the sender, the protocol header and/or protocol tail information of the corresponding layer must be added to the data header at each layer from top to bottom. The protocol header and/or protocol tail information encapsulated at the previous layer must be removed at each layer from the bottom to the top.
4. Congestion control. Congestion control is used to avoid transmission delay or deadlock of data in the network transmission path.
In the TCP/IP protocol suite, the network layer protocols include IP protocol, ARP protocol, ICMP protocol (Internet Control Packet Protocol), IGMP protocol (Internet Group Management Protocol), and the like.
1. Internet Protocol (IP). It is a network layer protocol that provides an unreliable service. It simply sends packets from the source node to the destination node as quickly as possible, but does not provide any reliability guarantee. The IP protocol is a connectionless protocol. Connectionless means that no connection between the IP address and the peer destination address needs to be established before packets are sent. If the upper layer has data to be sent to the IP, it is compressed into IP packets and sent out. It is used by both TCP and UDP, and each set of data for TCP and UDP is transmitted over the Internet through the IP layer in the end system and each intermediate router.
2. Address Resolution Protocol (ARP). Any time a host has an IP data packet to send to another host, it needs to know the logical (IP) address of the receiver. However, IP addresses must be encapsulated into frames to pass through the physical network. This means that the sender must have the physical (MAC) address of the receiver, and therefore the logical address-to-physical address mapping needs to be completed. The ARP protocol can receive the logical address from the IP protocol, map the logical address to the corresponding physical address, and then deliver the physical address to the data link layer.
3. Internet Control Message Protocol (ICMP). ICMP is a subsidiary protocol of the IP protocol. A new network needs to be tested first to verify whether the network is normal. However, the IP protocol does not provide reliable transmission. If a packet is lost, the IP protocol cannot inform the transmission layer of whether the packet is lost and the reason for the packet loss. Therefore, we need the ICMP protocol to implement this function. It is used to send control packets between IP network devices to transmit error, control, and query information.
The ICMP protocol is used to check whether the IP packet reaches the destination address and notify the reason why the IP packet is discarded during transmission. Transfers control messages between IP hosts and routers. Control messages refer to the messages of the network itself, such as network connectivity, host reachability, and route availability. Although these control messages do not transmit user data, they play an important role in transmitting user data.
4. Internet Group Manage Protocol (IGMP). IGMP is an Internet Group Management Protocol that is used to multicast a UDP packet to multiple hosts. It lets all systems on a physical network know which multicast group the host is currently in. The multicast router needs this information in order to know which interfaces the multicast packet should be forwarded to.
The above is my summary of this course. There may be some problems. I hope that I can review my knowledge and enhance my understanding. I also hope that you can point out the mistakes and shortcomings in this course and learn from each other. Thank you dear all!
