Wireshark-dev: [Wireshark-dev] New DVB_CI dissector: Discussion as to approach
From: Bill Meier <[email protected]>
Date: Thu, 10 Feb 2011 14:20:12 -0500
(Extracts of comments on Bug #5654 copied to wireshark-dev for further discussion)

(From Martin Kaiser)
I would like to submit a dissector for the DVB Common Interface. It's a
protocol between a PCMCIA module and a DVB receiver that is implemented in the vast majority of DVB-compliant devices (TVs, DVD/Bluray recorders).

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(From Bill Meier)
I see that this dissector is coded to dissect
DVB-CI bytes received as the payload of UDP
(in a manner somewhat similar to that used by packet-gsmtap).

I also see that there's a program (not part of this patch)
which is used to read a log file containing DVBCI bytes
and send them out to the local loopback interface as the
payload of UDP on port 50221.

I'm wondering if an alternative approach wherein the DVBCI
bytes are stored in (say) a pcap format file
(with a special "DVBCI DLT") should be considered.

(A conversion to pcap format can be done quite easily with text2pcap).

(With this approach, only the actual DVB-CI bytes would be
dissected/displayed (without the dummy Ethernet/IP/UDP layers)).

(I think that this is the general approach used by packet-radiotap)

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(Response from Martin Kaiser to Bill Meier questions)

> Before discussing further, it would be helpful to know a bit
> more about how the DVB-CI bytes are actually captured.
>
> Are there different solutions ? (different vendors, etc ?)

There's some vendors of commercial capturing tools. The tools I've seen come bundled with some software that can display and export the captured data.
...

Some companies also built their proprietary tools purely for internal use. As they write their own drivers, it should be feasible to output the captured information as a pcap file.
> Is additional information available ? (e.g., timestamps ?)

First of all, the tools log the direction of the data transfer (host->module or module->host). I converted this into a direction byte that I put in front of the actual data transfer.
Do you know of a better way to encode the direction in a pcap file or 
should I keep the direction byte? (If we go for pcap files and a new 
DLT, we should agree on this before I can apply for a DLT value).
...

Usually, you have timestamps relative to the beginning of the capture. I
understand that they can be set in a pcap file.


The DVB-CI physical layer consists of 4 registers to access data and status infos. Some tools can log all access to these registers.
Apart from the command interface, there's a transport stream interface 
to route the digital tv data stream through the DVB-CI module. There's 
tools that can log infos about changes of this routing.

[Response from Bill Meier will be in a follow-up EMail].