[AG-TECH] Idea for creating "observer only" venues

S.Booth spb at epcc.ed.ac.uk
Mon Oct 25 07:08:10 CDT 2004

On Mon, 25 Oct 2004, Michael Daw wrote:

> We did a similar kind of thing for SC Global 2003 to create Observer venues.
> Stephen Booth of EPCC did the writing of the code, which uses the UCL
> libraries used for vic and rat.
> You can get the code from here:
> http://people.man.ac.uk/~zzcgumd/SCGlobal03/my_reflector.tar.gz
> The relevant bit of the code is in common/examples/rtp_reflect.
> Any specific questions beyond the simple, please direct straight to
> Stephen(!).

I guess I better elaborate on this a bit. What I wrote was a re-encrypting
reflector. Any traffic the reflector saw was re-transmitted using a
different (possibly null) encryption in a different venue.
The idea was to have a "viewer only" venue with the TTL set to 1.

The reflector transmits with the normal TTL. You restrict access to the 
sender venue so only legitimate senders get the encryption keys but let
anyone into the view only venue but unless they manually restart their
mbone tools with a higher TTL their own traffic does not leave the local
Its still a bit of a hack but it would be pretty difficult for somebody to
accidentally reset their TTL. 

The reflector is all pretty straightforward. The only tricky thing was
that the VIC RTP packets don't pass all the RTP format checks from the RAT
code so I had to do a brute force forwarding rather than use the high
level RTP code from libcommon.

|epcc| Dr Stephen P Booth             Project Manager           |epcc|
|epcc| s.booth at epcc.ed.ac.uk          Phone 0131 650 5746       |epcc|

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