[tor-dev] SENDME cells

Gareth Owen gareth.owen at port.ac.uk
Thu Jul 3 10:36:03 UTC 2014

Just to answer my own question for any others.

I've played around with it a for a few days and it seems the intermediate
ORs don't maintain windows, it's only the edge nodes, maintaining a
circuit, and individual stream windows.

Hope someone can update the spec to be clearer on this to save others the
effort.  The offending sentence is:

*"The OP behaves identically, except that it must track a packaging window
and a delivery window for every OR in the circuit."*


On 1 July 2014 09:51, Gareth Owen <gareth.owen at port.ac.uk> wrote:

> (sorry re-post - forgot subject)
> Dear all
> I'm working on a tor research project and am having difficulty
> understanding the SENDME cells.  The tor spec acknowledges that it isn't
> particularly clear so I would welcome some clarification please.
> The spec says that *all* nodes in a circuit maintain a send and receive
> window, and that this window is decremented on each RELAY_DATA and
> incremented on each SENDME.  Cells that are neither of these do not affect
> the window size.  The problem I have understanding is, that only edge nodes
> will know whether a cell is a RELAY_DATA, the intermediate nodes only know
> that its a RELAY but not what type.  So, if only RELAY_DATA decrements the
> window size, and intermediate nodes cannot spot these, what point is there
> in intermediate nodes having a window?
> Any help greatly appreciated.
> Gareth
> ---
> Dr Gareth Owen
> Senior Lecturer
> School of Computing, University of Portsmouth
> W: ghowen.me

Dr Gareth Owen
Senior Lecturer
School of Computing, University of Portsmouth

Tel: 02392 846423
Web: ghowen.me
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