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A frame check sequence (FCS) is an
The FCS is often transmitted in such a way that the receiver can compute a running sum over the entire frame, together with the trailing FCS, expecting to see a fixed result (such as zero) when it is correct. For Ethernet and other IEEE 802 protocols, the standard states that data is sent least significant bit first, while the FCS is sent most significant bit (bit 31) first. An alternative approach is to generate the bit reversal of the FCS so that the reversed FCS can be also sent least significant bit (bit 0) first. Refer to for more information.
A frame check sequence (FCS) is an error-detecting code
In information theory and coding theory with applications in computer science and telecommunication, error detection and correction (EDAC) or error control are techniques that enable reliable delivery of digital data over unreliable communi ...
added to a frame
A frame is often a structural system that supports other components of a physical construction and/or steel frame that limits the construction's extent.
Frame and FRAME may also refer to:
Physical objects
In building construction
*Framing (co ...
in a communication protocol
A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics and synchroniz ...
. Frames are used to send payload data
In computing and telecommunications, the payload is the part of transmitted data that is the actual intended message. Headers and metadata are sent only to enable payload delivery.
In the context of a computer virus or worm, the payload is ...
from a source to a destination.
Purpose
All frames and the bits, bytes, and fields contained within them, are susceptible to errors from a variety of sources. The FCS field contains a number that is calculated by the source node based on the data in the frame. This number is added to the end of a frame that is sent. When the destination node receives the frame the FCS number is recalculated and compared with the FCS number included in the frame. If the two numbers are different, an error is assumed and the frame is discarded. The FCS provides error detection only. Error recovery must be performed through separate means. Ethernet, for example, specifies that a damaged frame should be discarded and does not specify any action to cause the frame to be retransmitted. Other protocols, notably the Transmission Control Protocol (TCP), can notice the data loss and initiate retransmission and error recovery.Implementation
The FCS is often transmitted in such a way that the receiver can compute a running sum over the entire frame, together with the trailing FCS, expecting to see a fixed result (such as zero) when it is correct. For Ethernet and other IEEE 802 protocols, the standard states that data is sent least significant bit first, while the FCS is sent most significant bit (bit 31) first. An alternative approach is to generate the bit reversal of the FCS so that the reversed FCS can be also sent least significant bit (bit 0) first. Refer to for more information.
Types
By far the most popular FCS algorithm is acyclic redundancy check
A cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to digital data. Blocks of data entering these systems get a short ''check value'' attached, based on ...
(CRC), used in Ethernet and other IEEE 802 protocols with 32 bits, in X.25 with 16 or 32 bits, in HDLC
High-Level Data Link Control (HDLC) is a bit-oriented code-transparent synchronous data link layer protocol developed by the International Organization for Standardization (ISO). The standard for HDLC is ISO/IEC 13239:2002.
HDLC provides bot ...
with 16 or 32 bits, in Frame Relay
Frame Relay is a standardized wide area network (WAN) technology that specifies the physical and data link layers of digital telecommunications channels using a packet switching methodology. Originally designed for transport across Integrated Se ...
with 16 bits, in Point-to-Point Protocol (PPP) with 16 or 32 bits, and in other data link layer protocols
Protocol may refer to:
Sociology and politics
* Protocol (politics), a formal agreement between nation states
* Protocol (diplomacy), the etiquette of diplomacy and affairs of state
* Etiquette, a code of personal behavior
Science and technology
...
.
Protocols of the Internet protocol suite tend to use checksum
A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify data ...
s.
See also
*Syncword
In computer networks, a syncword, sync character, sync sequence or preamble is used to synchronize a data transmission by indicating the end of header information and the start of data. The syncword is a known sequence of data used to identi ...
References
{{DEFAULTSORT:Frame Check Sequence Link protocols Logical link control Packets (information technology)