Data transmission can occur over short or long distances. There are three main factors to consider: transmission direction, transmission method, and data synchronization. Data transmission can be serial, with one bit sent at a time over a single channel, or parallel, with multiple bits sent simultaneously over multiple channels. Serial transmission works well for long distances but is slower, while parallel transmission is faster but over shorter distances. Transmission can also be simplex (one-way), half-duplex, or full-duplex. Simplex utilizes the full channel capacity but lacks two-way communication.