Wireshark · Ethereal-dev: Re: [Ethereal-dev] OSI Session dissector in the works

[Guy Harris <guy@xxxxxxxxxxxx>]

On Tuesday, September 2, 2003, at 12:19 AM, Sid Sid wrote:

> I started OSI Session dissector. It works well for unsegment PDUs but 
> for segmented PDUs it is not so simple.
> Can anybody advise me - how I should manage this:
> For example, we've two low level PDUs(TPKT in our case). Let's say 
> each low level TPKT pdus have TWO high level OSI Session PDUS inside:
> 1. First TPKT Pdu/First Session PDU inside - end of the some segmented 
> Session PDU.
> 2. First TPKT Pdu/Second Session PDU inside - first block of the next 
> segmented Session PDU.
>
> 3. Second TPKT/First Session PDU inside - it continues second Session 
> PDU from first TPKT.
> And so on.

So by "TPKT PDU" do you mean a TPKT PDU that contains an OSI TP (COTP 
or CLTP) PDU?

If so, is the segmentation being done at the transport or session layer?

If it's being done at the transport layer, note that reassembly of 
segmented transport PDUs is done by the COTP dissector, so your session 
dissector shouldn't have any reason to worry about segmented PDUs.

If there's segmentation being done at the session layer, then you'd 
have to do reassembly in your dissector.