s. Socket interfaces are a set of system calls. Most operating systems define socket as a structure with the following fields (see Figure 26.3): Family: This field defines the protocol group like IPV4, IPV6, or UNIX domain protocols. Type: This field defines the type of the socket. Socket type can be raw socket, stream socket, or datagram socket. Protocol: This field defines the protocol used. It can be TCP for connection oriented communication and UDP for connectionless communication. Socket Communication Family Protocol Local socket address Remote socket address Figure 26.3 Socket structure. Application program Stream socket Datagram socket Raw socket interface interface interface Physical and data link layers Figure 26.4 Types of socket. Local socket address: This field is a combination of the local IP address and the port address. It is the socket address of the local application program. Remote socket address: This field defines the combination of the remote IP address and the port address. It is the remote socket address of the remote application program. There are three types of sockets (see Figure 26.4): Raw socket: Sockets that directly use the IP services are referred to as raw sockets. Neither the stream socket nor the datagram sockets are used by some protocols like ICMP or OSPF that directly uses the IP services of raw socket. Stream socket: Stream sockets are used with connection oriented protocol like TCP. It uses pairs of stream sockets to connect an application program with another application program on the network. Datagram socket: Datagram sockets are used with connectionless protocol like UDP. It sends messages from one application program to another appli- cation program on the network using pairs of datagram sockets. Fundamentals of EMS, NMS and OSS/BSS The two types of transport protocols commonly used for socket communication: TCP provides a reliable, connection oriented, and flow controlled sequenced channel of communication. Stream sockets are used with connection oriented protocols lik