Re: Request for new DLT value for Wireshark Dissector

[Guy Harris <guy () alum mit edu>]

On Jan 20, 2011, at 3:05 AM, Schemmel, Hans-Christoph wrote:

> The format of the additional header is:
>
> | Header_Size | Msg_ID | Freq_ID | Start_Pos | End_Pos |  Flag  | ... | Msg_ID |
> Freq_ID | Start_Pos | End_Pos |  Flag  | Direction | MUX_Frame
>
> Header_Size (1 Octet): Total length of the addtional header
> Msg_ID (1 Octet): ID of the PPP packet
> Freq_ID (1 Octet): ID of the PPP packet part, if the PPP packet is split into
> several parts
> Start_Pos (1 Octet): Beginning of the PPP packet in the information field of the
> MUX frame
> End_Pos (1 Octet): End of the packet in the information field
> Flag (1 Octet): If "Flag" is set, this is the last part of the fragmented/split
> packet
> Direction (1 Octet): Direction of the Mux frame: GSM Modem -> Host or Host ->
> GSM Modem

So are any of those fields optional?  For example, is the fragment ID optional?  If so, what indicates whether it's 
present?  If nothing is optional, why is the header size not always 7?
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