In an optical fiber system, there are a minimum of five latency contributions. Two are created as the signal moves from the electrical domain to the optical; another contribution occurs as the signal travels down the optical fiber; and two more are created as the signal is converted from the optical domain back to the electrical.
Prior to entering the optical fiber, blocks of data bits—sometimes referred to as “words”—must be broken down into individual bits that can be more easily transported by the optical fiber.
This process is known as “serialization” and contributes to the end-to-end latency of the signal. Next, the signal must be converted from an electrical current to optical pulses of light. This process also contributes to overall latency.
Once inside the optical fiber, the signal takes time to go from one end to the other, resulting in transmission media latency. As the optical signal exits the other side of the fiber, it must be converted from optical energy back to electrical and from its deserialized format in bits, back to its original serialized form—words.
As this scenario reflects the most basic transmit path for an optical signal, we can say there are, at minimum, five contributions to latency in any optical fiber path.
Conversion latency is specific to the application, protocol, and active equipment involved. It is based on the design of the system and its contribution to overall latency is not affected by distance.
However, the latency contributed by the transmission media is a fixed value per unit length, so the longer the transmission line the greater the latency contribution. Systemic or total latency is the sum of all latency contributions and varies depending on the total length or distance of the transmission media.
Content sourced from paper by Joseph Coffey, senior principal engineer, CommScope