Network frame

In networks, a frame is a unit of sending data. It is a successive series of bits, organized cyclically, that carry information and that allow this information to be extracted upon reception. It comes to be the equivalent of data packet or network packet, at the network layer of the OSI model.

Normally a frame will consist of header, data and tail. In the queue is usually some error checking. In the header there will be protocol control fields. The data part is what you want to transmit at a higher communication level, typically the Network Layer.

To delimit a frame, four methods can be used, the tracker:

1. by count of characters: at the beginning of the plot the number of bytes represents the beginning and end of the plots. STX is usually used (Start of Transmission: ASCII #2) to start and ETX (End of Transmission: ASCII #3) to finish. If arbitrary data are to be transmitted, escape sequences are used to distinguish the data from the control characters.
2. by bit sequences: in bit-oriented communications, a bit sequence can be used to indicate the beginning and end of a plot. The "guion" is usually used, 01111110, in transmission as long as five followed are filled with a zero; in reception provided that after five, one zero appears, it is eliminated.
3. for violation of the physical level: it is about introducing a signal, or signal level, that does not correspond to either a "1" or with a "0". For example if the physical encoding is bipolar you can use the level of 0 volts, or in Manchester Codification you can have the signal at high or low level throughout the bit time (avoiding the transition of characteristic levels of this system).
4. The de facto standard evolved into several official standards, such as:
   1. FR Forum (Partnership Association): Cisco, DEC, Stratacom and Nortel.
   2. ANSI: Frame-Relay policy source.
   3. ITU-T: also has technical regulations of Frame-Relay technology.