Inter Frame Gap

Between Ethernet frames there must be an inter frame gap of at least 9,6 µs (96 bit times).

Ethernet repeaters only accept incoming frames in case of valid IFG time. Frames arriving within the IFG time are discarded.

These frames have to be retransmitted by the source station. Because the source adapter cannot detect that the frame has been discarded, retransmission has to be initiated by higher layer protocols providing data flow control (connection-oriented protocols). Because these protocols (LLC type 2, SPX, TCP, and others) expect frame acknowledgment (to be sent by the peer station) within certain time, retransmission will only be initiated in case that the acknowledgment timer expired. These ACK timers do not count in microsends rather than probably in seconds (especially under WAN conditions); the loss of frames cannot be detected as soon as in case of collisions. This will cause significant less performance.

If an Ethernet adapter transmits frames with an IFG less than 9,6 µs to a destination station beyond at least one repeater, many frames may be discarded by repeaters. This will cause many retransmissions resulting in bandwidth problems.

Normal Ethernet adapters cannot detect inter frame gaps being too short; therefore, protocol analyzers can only detect invalid IFGs using special measurement hardware.