Daisy chain (electrical engineering)

In electrical and electronic engineering, a daisy chain is a wiring scheme in which multiple devices are wired together in sequence or in a ring, similar to a garland of daisy flowers. Other than a full, single loop, systems which contain internal loops cannot be called daisy chains.
Daisy chains may be used for power, analog signals, digital data, or a combination thereof.
The term daisy chain may refer either to large scale devices connected in series, such as a series of power strips plugged into each other to form a single long line of strips, or to the wiring patterns embedded inside of devices. Other examples of devices which can be used to form daisy chains are those based on USB, FireWire, Thunderbolt and Ethernet cables.
Signal transmission.
For analog signals, connections usually consist of a simple electrical bus and, especially in the case of a chain of many devices, may require the use of one or more repeaters or amplifiers within the chain to counteract attenuation (the natural loss of energy in such a system). Digital signals between devices may also travel on a simple electrical bus, in which case a bus terminator may be needed on the last device in the chain. However, unlike analog signals, because digital signals are discrete, they may also be electrically regenerated, but not modified, by any device in the chain.
Types.
Computer hardware.
Some hardware can be attached to a computing system in a daisy chain configuration by connecting each component to another similar component, rather than directly to the computing system that uses the component. Only the last component in the chain directly connects to the computing system. For example, chaining multiple components that each have a UART port to each other. The components must also behave cooperatively. e.g., only one seizes the communications bus at a time.
Network topology.
Any particular daisy chain forms one of two network topologies:
System access.
Users can daisy chain computing sessions together. Using services such as Telnet or SSH, the user creates a session on a second computer via Telnet, and from the second session, Telnets to a third and so on. Another typical example is the "terminal session inside a terminal session" using RDP. Reasons to create daisy chains include connecting to a system on a non-routed network via a gateway system, preserving sessions on the initial computer while working on a second computer, to save bandwidth or improve connectivity on an unstable network by first connecting to a better connected machine. A less wholesome purpose is camouflaging activity while engaged in cybercrime.