Wireshark-dev: Re: [Wireshark-dev] Query regarding pdus
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From: Sake Blok <sake@xxxxxxxxxx>
Date: Sun, 19 Nov 2006 21:31:44 +0100
On Sun, Nov 19, 2006 at 12:41:10PM -0500, Andrew Schweitzer wrote:
> > I wanted to know what exactly is a PDU. Where is the length of the pdu 
> > defined in the PDU.
> 
> I believe a PDU is a "Protocol Data Unit". I believe it is the 
> application layer packet that has been wrapped into TCP or UDP, or the 
> "payload" of TCP or UDP. It's length is specified by whatever protocol 
> is used to fill that payload, so it varies from protocol to protocol.

A pdu is not specifically linked to protocols atop tcp or udp. For
example, think of a BPDU (Bridge Protocol Data Unit). Which sits just
on top op de data-link layer.

>From wikipedia:

In telecommunications, the term protocol data unit (PDU) has the following meanings:

1. Information that is delivered as a unit among peer entities of a network and that may contain control information, address information, or data.
2. In layered systems, a unit of data that is specified in a protocol of a given layer and that consists of protocol-control information of the given layer and possibly user data of that layer. For example: Bridge PDU or iSCSI PDU

	  Source: from Federal Standard 1037C 

(http://en.wikipedia.org/wiki/Protocol_data_unit)


Cheers,


Sake