Implement ARP/IP(including fragmentation and reassembly)/UDP/TCP protocol, provide BSD socket programming interface, support to run multiple application clients and servers at the same time. At present, it has been ported to the x86 operating system and ARM development board written by himself. Protocol stack characteristics Platform support Supports development and learning on Windows, Linux, and Mac platforms The C language uses the C99 standard and does not rely on a specific compiler The code is highly portable and can be easily ported to x86 and embedded platforms such as ARM Only the operating system needs to provide basic semaphore, mutex and time acquisition interface to support hardware It does not limit the specific network interface type, and supports other interface devices other than Ethernet Support to add multiple network interfaces (nics), IP packets will automatically be sent to the correct interface according to the routing table Support loopback interface, to achieve the local packet self-collection function features Standard Socket interface: Interfaces: socket, bind, connnect, close Interfaces: sendto, recvfrom, send, recv, read, write, setsockopt Concrete type SOCK_RAW: Allows applications to send and receive IP packets Sock_dgram-based: Allows applications to send and receive UDP packets Sock_stream-based (under development) : Allows applications to send and receive UDP packets multithreading Supports multi-threading operations on the same socket interface, that is, allows different threads to read and write at the same time Supports the creation of any number of applications at the same time, whether client or server Data packet Organize packets into multiple blocks of links to improve memory utilization efficiency Ethernet protocol: Supports Ethernet packet sending and receiving and packet processing Address resolution Protocol (ARP) Complete support for ARP query and response processes Supports the sending of gratuitous ARP packets Use a configurable size of ARP buffer