send

A send is the act of transmitting data from a source device or node to a destination across a communication channel. In electrical engineering, a send operation moves information as electrical signals, optical pulses, or radio waves, depending on the medium. The source initiates the transfer; the destination receives it. This is fundamental to every networked system, from industrial control networks to telecommunications infrastructure.

Sends differ by protocol and medium. In synchronous systems like CAN bus or Modbus RTU, a send follows strict timing and framing rules: data is packaged in frames with headers, checksums, and delimiters. Asynchronous serial sends use start and stop bits to mark boundaries. Ethernet sends package data into frames with MAC addresses and IP headers. Radio sends modulate information onto carrier waves at specified frequencies. Each send operation consumes electrical energy, introduces latency, and may experience interference or collision with other sends on shared media.

Send timing and buffering

A send is not instantaneous. The time from initiation to completion depends on data length, channel bandwidth, and protocol overhead. A microcontroller may queue a send operation in hardware or software; if the physical channel is busy, the send waits in a buffer. Buffer overflow, when sends arrive faster than the channel can transmit them, causes data loss or queuing delays. Real-time systems must account for worst-case send latency to guarantee response times.

Sends fail in characteristic ways. Noise or interference may corrupt the signal, requiring retransmission. Collisions occur when two nodes send simultaneously on a shared bus; higher-layer protocols (like CSMA/CD in Ethernet) manage recovery. Open circuits, short circuits, or impedance mismatches degrade signal quality. In radio systems, multipath fading and shadowing reduce range. Monitoring send success through acknowledgments and checksums is essential in safety-critical applications.

The term originates from telecommunications and radio practice, where "send" and "receive" describe the asymmetric halves of two-way communication. In modern networking, "transmit" and "send" are used interchangeably, though "send" appears more often in software APIs and control logic. The verb form "to send" is equally common in engineering parlance: "the PLC sends a command to the motor drive."