Short Interframe Space (SIFS), is the amount of time in
microsecond
A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available.
A microsecond is equal to 1000 n ...
s required for a
wireless interface to process a received
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 (con ...
and to respond with a response frame. It is the difference in time between the first symbol of the response frame in the air and the last symbol of the received frame in the air. A SIFS time consists of the delay in receiver
RF,
PLCP delay and the
MAC processing delay, which depends on the
physical layer
In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first and lowest layer; The layer most closely associated with the physical connection between devices. This layer may be implemented by a PHY chip.
The ...
used. In
IEEE 802.11
IEEE 802.11 is part of the IEEE 802 set of local area network (LAN) technical standards, and specifies the set of media access control (MAC) and physical layer (PHY) protocols for implementing wireless local area network (WLAN) computer commun ...
networks, SIFS is the
interframe spacing prior to transmission of an
acknowledgment, a
Clear To Send (CTS) frame, a
block ack frame that is an immediate response to either a block
ack request frame or an A-MPDU, the second or subsequent
MPDU
In telecommunications, a protocol data unit (PDU) is a single unit of information transmitted among peer entities of a computer network. It is composed of protocol-specific control information and user data. In the layered architectures of c ...
of a fragment burst, a station responding to any polling a by
point coordination function
Point coordination function (PCF) is a media access control (MAC) technique used in IEEE 802.11 based WLANs, including Wi-Fi. It resides in a point coordinator also known as access point (AP), to coordinate the communication within the network. ...
and during contention free periods of
point coordination function
Point coordination function (PCF) is a media access control (MAC) technique used in IEEE 802.11 based WLANs, including Wi-Fi. It resides in a point coordinator also known as access point (AP), to coordinate the communication within the network. ...
.
Implications for Software Radio
Because most Software-Defined Radios use a host computer for processing, the SIFS imposes a difficult to achieve time constraint, as the latency for most SDR systems for the signal to traverse from the radio to the host and back to the radio, and vice versa, exceeds the SIFS requirements.
While in some cases it is possible to achieve SIFS requirements for testing, the practical approach is almost always to leverage the FPGA portion of processors common to many commercial SDRs.
See also
* DIFS –
DCF Interframe Space The IEEE 802.11 family of standards describe the DCF protocol, which controls access to the physical medium. A station must sense the status of the wireless medium before transmitting. If it finds that the medium is continuously idle for DCF Inter ...
* RIFS –
Reduced Interframe Space
Reduced Interframe Space (RIFS) is one of the new features introduced in IEEE 802.11n to improve its efficiency. RIFS is the time in micro seconds by which the multiple transmissions from a single station are separated. RIFS is used when no SIFS se ...
* PCF –
Point coordination function
Point coordination function (PCF) is a media access control (MAC) technique used in IEEE 802.11 based WLANs, including Wi-Fi. It resides in a point coordinator also known as access point (AP), to coordinate the communication within the network. ...
** PIFS –
PCF Interframe Space
Point coordination function (PCF) is a media access control (MAC) technique used in IEEE 802.11 based WLANs, including Wi-Fi. It resides in a point coordinator also known as access point (AP), to coordinate the communication within the network. ...
* EIFS –
Extended interframe space
Extended Interframe space (EIFS) is used in IEEE 802.11 based WLANs. If a previously received frame contains an error then a station has to defer EIFS duration instead of DIFS before transmitting a frame. This is because, although this station was ...
References
{{IEEE standards
IEEE 802.11