Delay (engl. Delay ), latency, or latency occurs in the telecommunications than
- the time interval by which an event is delayed;
- the time between the occurrence of an event and the occurrence of an expected subsequent event;
- in radar technology as the electronic delay of the start of the time base , which is used to select a certain segment of the whole.
The events and their relationships must be specified precisely. An overall delay can be demonstrated in terms of the impulse response of a device or system . In analog systems, the total delay results from functions in the frequency domain (delay time).
Types of delay
Delay can arise in a number of ways. These are divided into four classes:
- The algorithmic delay results from the properties of the algorithm used to process or transmit the signal . It can only be influenced by changing the algorithm. Examples: voice data transmission in packets or interleaving in data transmission .
- The processing delay is determined by the time required to further process the signal. It can be reduced by using more computing power. Example: computation time of a MPEG - encoder .
- The serialization delay is the time it takes to completely send a data unit onto the medium. The following applies: Serialization delay = data volume / data rate.
- The propagation delay caused by signal propagation times in lines or air. This can be influenced within limits by selecting a different route. The following applies: propagation delay = distance in the medium / propagation speed. As a rule of thumb, 5 microseconds per kilometer can be assumed for the speed of propagation.
Delays in voice communication
The delay of the speech signal in the telephone network is an essential quality parameter for speech intelligibility, along with the echo, i.e. the attenuated reflected signal that travels back from the receiver to the transmitter. For this reason, various guidelines have been established.
For the national landline networks , the delay in Germany was set at a value of 25 ms end-to-end, since no active echo control measures are necessary up to this value in accordance with ITU-T recommendation G.131 “Control of talker echo”. The 25 ms were divided in such a way that the end devices can use 5 ms each and the network 15 ms (5 ms + 15 ms + 5 ms = 25 ms).
For international connections, the use of "echo suppressors" according to ITU-T recommendation G.164 or "echo cancellers" according to ITU-T recommendation G.165 is necessary due to the longer transit times .
In Internet telephony , the delay can be longer due to the technology and therefore the quality can be considerably worse. Depending on the codec used , packaging or de-packaging takes between 20 and 25 ms. Then there are the transfer times for the IP packets in the network.
According to ITU-T recommendation G.114 , real-time communication is no longer possible above a one-way delay time of 400 ms.
- Volker Jung, Hans-Jürgen Warnecke (Hrsg.): Handbook for telecommunications. Springer Verlag, Berlin / Heidelberg 1998, ISBN 978-3-642-97703-9 .
- Rolf Weiber: Diffusion of Telecommunications. Problem of the critical mass, Springer Fachmedien, Wiesbaden 1992, ISBN 978-3-409-16014-8 .
- Dieter Conrads: Telecommunications. Basics - Procedures - Networks, 5th edition, Friedrich Vieweg & Sohn Verlag, Wiesbaden 2004, ISBN 3-528-44589-0 .
- IT knowledge delay (accessed August 24, 2017)
- Wireless telecommunications system with a reduced delay for data transmission (accessed August 24, 2017)