Interpacket gap
Interpacket Gap (abbreviation IPG , also English Interframe Spacing IFS , Interframe Gap IFG ) describes the minimum time interval between two packets sent on the transmission medium in computer networks . There are several reasons to keep this minimum distance; these can be of a technical nature (e.g. Ethernet ) or a consequence of the underlying network protocol (e.g. WLAN according to the IEEE 802.11 standard ).
Ethernet
The minimum waiting time between two transmitted Ethernet packets is generally 96 bit times - for example at 10 Mbit / s 9.6 microseconds. When receiving , it is possible that shorter pauses occur:
- with 40 and 100 Gigabit Ethernet at least 8 bit times (1 byte)
- with 2.5, 5, 10 and 25 Gigabit Ethernet at least 40 bit times (5 bytes)
- with Gigabit Ethernet at least 64 bit times (8 bytes)
- No shortened pause is defined for Fast Ethernet , the standard is 96 bit times (12 bytes)
- with 10 Mbit / s Ethernet a minimum of 47 bit times
WLAN according to IEEE 802.11
In the WLAN standard there are several different interframe spacings of different lengths. These are used to enable priorities for different types of data frames and transmitting stations.
One distinguishes
- SIFS ( Short Interframe Spacing ): The time that must have passed before an acknowledgment frame (ACK), “Clear to Send” packet (CTS) or a response to polling is sent . Since the receipt of every regular unicast data frame in particular has to be confirmed using ACK , SIFS is the most frequently used interframe spacing.
- PIFS ( Point Coordination Function Interframe Spacing ): The time that must have passed before the point coordinator (e.g. the access point ) sends PCF information .
- DIFS ( Distributed Coordination Function Interframe Spacing ): The time that must have passed before a regular data frame can be sent.
- EIFS ( Extended Interframe Spacing ): The time that must have passed before sending after a detected collision.
The following applies: SIFS <PIFS <DIFS <EIFS.
Typical values for media access control in WLANs are around 10 µs for SIFS and around 50 µs for DIFS.
Fiber Channel
With Fiber Channel , a sequence of primitives is necessary between successive frames, which is sometimes called the interframe gap . The sequence consists of at least six primitives IDLE|IDLE|R_RDY|R_RDY|IDLE|IDLE. Each primitive consists of four channel words, each 10 bits in the 8b / 10b -coded variants (1–8 Gbit / s).