Each frame contains between one and forty four cells which must all be for the same association. For each cell two octets of FAS are carried.
The frame carries the required ethernet source and destination addresses, and
an ethernet protocol identifier of 0x6660
This information is followed by a two octet field which together with the
destination ethernet address form the VCI of the frame. This two octet
field is called the ``associd''.
For historical reasons only ten bits of the two octet field are significant. They are all eight bits of the first octet and bits six and seven of the second octet. The other six bits of the second octet should be set to zero.
The frame header is displayed in table 1.
The frame header is followed by a frame control structure. It consists of one octet which contains the number of cells in the frame. This has a value in the range one to forty four. This octet is followed by a reserved octet which has value zero. These fields are followed by forty four pairs of octets which contain the FAS for each of the forty four cells in the frame. Note that these fields are always present even for a frame of less that forty four cells. For cells which are not present the FAS octets may contain any value. The de facto standard FAS for EDL Cells present is a variant of SAR1 where the part-full bit is never used. Consult the SAR document for details.
The payload contains between one and forty four cells of thirty two octets each.
