HomePlug technology uses two basic frame formats. A Long Frame consists of a Start of Frame (SOF) delimiter, Payload and End of Frame delimiter (EOF). A Short Frame consists of a Response Delimiter and is used as part of the Stop-and Wait automatic repeat request (ARQ) process. ARQ mechanism causes retransmission of corrupt packets, thus reducing the packet error rate. All the delimiters share a common structure. A delimiter consists of a Preamble and Frame Control information field. The Preamble is a form of spread spectrum signal that is used to determine the start of a delimiter. This is followed by Frame Control information, which is encoded using a robust Turbo Product Code and can be detected reliably even at several dB below the noise floor.

Among other things, delimiters convey timing information that is used by MAC to determine the availability of the medium. The robust design of the delimiter helps the nodes to obtain a very high level of synchronization, thus reducing unintended collisions. The details of the various field contained in the Frame Control are given in Table 1. The Payload of the Long Frame delimiter is encoded based on the channel adaptation. The first 17 bytes ofthe payload contain the Frame Header. This field contains the source address, destination address and segmentation information.

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