Editing Frame (networking)

{{Short description|Data transmission unit}}
A '''frame''' is a digital [[data transmission]] unit in [[computer networking]] and [[telecommunications]]. In [[packet switched]] systems, a frame is a simple container for a single [[network packet]]. In other telecommunications systems, a frame is a repeating structure supporting [[time-division multiplexing]].

A frame typically includes [[frame synchronization]] features consisting of a sequence of bits or symbols that indicate to the receiver the beginning and end of the [[Payload (computing)|payload data]] within the stream of symbols or bits it receives. If a receiver is connected to the system during frame transmission, it ignores the data until it detects a new frame synchronization sequence.

==Packet switching==
In the [[OSI model]] of computer networking, a frame is the [[protocol data unit]] at the [[data link layer]]. Frames are the result of the final layer of [[Encapsulation (networking)|encapsulation]] before the data is transmitted over the physical layer.<ref>{{cite web|url=http://www.tcpipguide.com/free/t_DataLinkLayerLayer2.htm |title=Data Link Layer (Layer 2) |publisher=The TCP/IP Guide |date=2005-09-20 |access-date=2010-01-31}}</ref> A frame is "the unit of transmission in a link layer protocol, and consists of a link layer header followed by a packet."{{Ref RFC|1122}} Each frame is separated from the next by an [[interframe gap]].  A frame is a series of bits generally composed of frame synchronization bits, the [[Network packet|packet]] payload, and a [[frame check sequence]].  Examples are [[Ethernet frame]]s, [[Point-to-Point Protocol]] (PPP) frames, [[Fibre Channel frame]]s, and [[ITU-T V.42|V.42]] modem frames.

Often, frames of several different sizes are nested inside each other.  For example, when using [[Point-to-Point Protocol]] (PPP) over [[asynchronous serial communication]], the eight bits of each individual byte are framed by start and stop bits,<ref>
David S.Lawyer and Greg Hankins.
"Serial HOWTO".
Section [http://www.tldp.org/HOWTO/Serial-HOWTO-20.html "20.4 Forming a Byte (Framing)"].
2011.
quote:
"... a start bit and a stop bit to mark the beginning and end of a byte. This is called framing ...
Don't confuse this type of framing with the framing used for a packet of bytes on a network."
</ref><ref>
MATLAB External Interfaces.
Section [http://www.ece.northwestern.edu/local-apps/matlabhelp/techdoc/matlab_external/ch_seri8.html "Serial Data Format"].
quote:
"... one start bit...  parity bit ... stop bit[s] ... called framing bits because they frame the data bits."
</ref> the payload data bytes in a network packet [[Network packet#Framing|are framed]] by the header and footer, and several packets can be framed with [[High-Level Data Link Control#Asynchronous framing|frame boundary octets]].{{Ref RFC|1661|quote=A packet is usually mapped to a frame; the exceptions are when data link layer fragmentation is being performed, or when multiple packets are incorporated into a single frame.}}

==Time-division multiplex==
In telecommunications, specifically in [[time-division multiplex]] (TDM) and [[time-division multiple access]] (TDMA) variants, a frame is a cyclically repeated data block that consists of a fixed number of time slots, one for each logical TDM channel or TDMA transmitter. In this context, a frame is typically an entity at the physical layer. TDM application examples are [[SONET/SDH]] and the [[ISDN]] circuit-switched B-channel, while TDMA examples are [[Circuit Switched Data]] used in early cellular voice services. The frame is also an entity for [[time-division duplex]], where the mobile terminal may transmit during some time slots and receive during others.

== See also ==
* [[Application-layer framing]]
* [[Datagram]]
* [[Jumbo frame]]
* [[Multiplexing|Multiplex techniques]]
* [[Overhead bit]]

== References ==
{{Reflist}}

{{DEFAULTSORT:Frame (Telecommunications)}}
[[Category:Computer networks]]
[[Category:Link protocols]]
[[Category:Packets (information technology)]]
[[Category:Units of information]]

[[it:Ethernet#Frame]]