Re: A puzzled maintainer with questions regarding DLT_ values

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

On Feb 3, 2011, at 8:47 AM, M.Baris Demiray wrote:

> Hello again,
>
> I have solved almost all the problems that I mentioned below and now I
> am sure that I should ask for a new DLT value for STANAG 5066 [1] MAC
> (Medium Access Control Sublayer) PDUs. Currently I am able to dissect
> these PDUs using DLT number 147 (USER0) using Wireshark 1.4.3 and I'd
> like to have this dissector and corresponding DLT value in the main
> stream.
>
> I might add that STANAG 5066 SIS layer is already defined in Wireshark
> [2] yet it can only dissect the packets transferred between STANAG
> 5066 and its clients.

OK, that answers the questions I asked in my previous message.

> Now, what I propose is to have the same
> functionality for the interface between STANAG 5066 and HF modem as
> well. What else should I provide regarding this protocol to ask for a
> DLT value?

So that protocol is presumably the one mentioned in the isode.com white paper:

        At the modem level, STANAG 5066 uses packets (DPDUs) of a size appropriate to the modem speed. At 1200 
bits/second 128 bytes will be used, which is much less than the typical Unit Data. Benefits of using smaller DPDUs 
include:

                • Acknowledgement is done for each DPDU, so if data loss occurs when transmitting a DPDU, only that 
DPDU (and not the whole Unit Data) need to be retransmitted.
                • When higher precedence Unit Data arrives is sent for transmission by a STANAG 5066 server, sending 
can begin after transmission of the current DPDU (i.e., there is no need to wait for the full Unit Data transmission).
Acknowledgements, often referred to as ARQ (Acknowledgement ReQuest), are used for Reliable Unit Data and are made for 
each DPDU. In order to minimize the number of turnarounds, sending of acknowledgements is delayed. A typical sequence 
with two radios might be:

                • Radio 1 transmits to Radio 2 for 127 seconds; it sends a number of DPDUs.
                • Radio 2 transmits to Radio 1 for 127 seconds; it sends acknowledgments for the DPDUs received from 
Radio 1; then it sends some DPDUs.
                • Radio 1 transmits to Radio 2 for 127 seconds; it sends acknowledgements for the DPDUs received from 
Radio 2; then it works out which DPDUs failed to transmit last time and resends them; then it sends more DPDUs.

with the packets for the MAC layer being the DPDUs.  Is that correct?

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