Frame (communications engineering)
Frames or frame designated in the field of communications technology and information processing ( Electronic Data Processing ) a repetitive timing structure , composed of a sequence of signals is carrying a dependent of their temporal position in the frame importance.
It is used when transmitting messages from a sender to one or more recipients . Both sender and receiver know the structure defined in the underlying transmission standard or protocol . By synchronization mechanisms , the receiver can detect the start of a frame within the incoming signal, which is the basis for meaningful recognition of the transmitted message - especially if the recipient without the knowledge of the beginning of "hook up" the transfer temporarily in the transmission can, such as when processing data streams .
In the context of the terminology of the OSI layer model , the term is used in a narrower sense. See data frame .
Examples:
- The frames of the television signal with their chronological sequence of synchronous and image information; Duration: 40 ms (with European analog television standards and neglecting the phase position of the color subcarrier, which changes from full screen to full screen). The television can be switched on at any time in a running program and synchronizes the image structure almost immediately.
- Data frames when transmitted via Ethernet .
- Frames within the MPEG-1 data such as MP3 - streams ; Duration: approx. 26.1 ms (MP3 at 44.1 kHz): Data processing can be started at any point in the stream; playback begins with the next frame, i.e. practically immediately.
- Data on audio CDs ; Duration of a frame: approx. 136 µs; Duration of a block: approx. 13.3 ms. After interruptions, the CD player can resume playback (in principle at any point).
- The data from 30 digital telephone calls are combined for transmission over a 2048 kbit / s line, see PCM30 ; Duration: 125 µs.
- The data telegram transmitted by the time signal transmitter DCF77 with the time information for the time of the following minute; Duration: one minute. The radio clock recognizes the beginning of the data telegram from the missing second pulse and can thus set itself without further action.
Often different data are also combined into a frame, the sequence of which in turn forms a frame. In order to be able to differentiate between the different frames in the documentation, they are given different names - for example “subframe”, “subframe”, “miniframe”, “block” or “superframe”.
Examples:
- A “full image” (English “frame”) of a PAL television signal consists of two “half images” (“fields”). These are in turn divided into 312.5 “lines”.
- A “block” of an audio CD consists of 98 “frames”. In addition to audio and correction data, each “frame” also contains so-called “subcode” data. The audio data of a “block” form 1/75 s audio material, while the “subcode” data of a “block” form eight “subchannels”. Each “subchannel” contains different information such as the beginning of the track, time information on the CD and, if applicable, CD-Text . "Block", "Frame" and "Subchannel" each represent a frame within the meaning of this article.