A computer network connects independent computers to share resources. It consists of nodes, servers, and networking devices linked by transmission mediums like cables. Data communication is the exchange of data between devices via a transmission medium. It has five components: the message, sender, receiver, transmission medium, and protocols governing the communication. For effective data transmission, networks must meet criteria like performance, reliability, and security. Performance depends on factors like transit time. Reliability is measured by failure frequency and recovery time. Security involves protecting data access and integrity. Point-to-point links connect two devices exclusively, while multipoint links are shared between multiple devices.