Calculate Ethernet framing overhead and its impact on effective throughput.
Every Ethernet frame carries fixed overhead beyond the payload: an 8-byte preamble for clock synchronization, a 14-byte header (destination MAC, source MAC, type/length), a 4-byte Frame Check Sequence for error detection, and a 12-byte Inter-Frame Gap that separates consecutive frames on the wire — totaling 38 bytes per frame. This overhead is constant regardless of payload size, so it represents a larger percentage loss for small frames than for large ones, directly reducing the effective throughput available for actual data below the link's rated speed.
Ethernet framing overhead
overhead = preamble(8) + header(14) + FCS(4) + IFG(12) = 38 bytes/frame
The 8-byte preamble (plus start frame delimiter) synchronizes the receiver's clock before the frame proper begins; the 14-byte header holds destination MAC, source MAC, and EtherType/length; the 4-byte Frame Check Sequence is a CRC used to detect transmission errors; and the 12-byte Inter-Frame Gap is idle time enforced between frames, totaling 38 bytes of non-payload data per frame.
The 38-byte overhead is fixed per frame regardless of payload size, so a 64-byte minimum-size frame loses over 37% of its wire time to overhead, while a 1500-byte frame loses only about 2.5%. Workloads dominated by small packets (VoIP, gaming, many small API calls) therefore see proportionally lower effective throughput than large, bulk transfers.
No — it's idle time (minimum 96 bit-times) enforced on the wire between the end of one frame and the start of the next, not data within the frame itself. It is still counted as overhead because it consumes link time that cannot carry payload, reducing achievable throughput exactly like the other components.