Frame (networking)




A frame is a digital data transmission unit in computer networking and telecommunication. 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 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.




Contents






  • 1 Packet switching


  • 2 Time-division multiplex


  • 3 See also


  • 4 References





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 before the data is transmitted over the physical layer.[1] A frame is "the unit of transmission in a link layer protocol, and consists of a link layer header followed by a packet."[2] 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 packet payload, and a frame check sequence. Examples are Ethernet frames, Point-to-Point Protocol (PPP) frames, Fibre Channel frames, and 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,[3][4] the payload data bytes in a network packet are framed by the header and footer, and several packets can be framed with frame boundary octets.[5]



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




  • Data link layer

  • Datagram

  • Jumbo frame

  • Multiplex techniques

  • Overhead bit

  • Protocol data unit



References





  1. ^ "Data Link Layer (Layer 2)". The TCP/IP Guide. 2005-09-20. Retrieved 2010-01-31..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}


  2. ^ "RFC 1122: Requirements for Internet Hosts — Communication Layers". IETF. October 1989. p. 18. doi:10.17487/RFC1122. RFC 1122. https://tools.ietf.org/html/rfc1122#page-18. Retrieved 2010-06-07. 


  3. ^
    David S.Lawyer and Greg Hankins.
    "Serial HOWTO".
    Section "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."


  4. ^
    MATLAB External Interfaces.
    Section "Serial Data Format".
    quote:
    "... one start bit... parity bit ... stop bit[s] ... called framing bits because they frame the data bits."


  5. ^
    RFC 1661 "The Point-to-Point Protocol (PPP)"
    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."









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