DirecPC Protocols

Thu Nov 14 23:15:57 UTC 2002

Well there are some two way dish solutions for consumers now that don't
need a dial-uplink.  I think dishnetwork has such a thing as does direct
tv.  Doesn't help much but does help people in remote areas.

On Thu, 14 Nov 2002, Crist J. Clark wrote:

>
> I've been looking for some technical descriptions on how DirecPC works
> from a TCP/IP point of view. Does anyone out there have some
> references? I have not been able to find anything too detailed, and
> from what I have been told, they are not too forthcoming when
> contacted directly.
>
> I know the rough outline. The customer sends out traffic over a normal
> PPP link (since the customer has no uplink to the DirecPC satellite)
> to a separate ISP. The traffic has a spoofed source address set to
> some DirecPC server at their ground site(s). Thus, the third-party
> target's response goes to DirecPC who send it over their satellite
> link back to the customer using the wide satellite pipe instead of the
> narrow PPP pipe.
>
> But I'm curious about the details. First things first, anyone know how
> the DirecPC link is established? That is, how the customer tells
> DirecPC what his IP address is? I assume this must all happen over the
> PPP-link, or at least the two-way PPP-link is used for bootstrapping.
> Now once things are going, what kind of predictive ACKing games does
> DirecPC play?
>
> The reason I am curious is that I'm trying to figure out what kinds of
> things ISPs, or any Internet access provider (say the user is dialing
> into a corporate RAS), can do to break or accomodate DirecPC. The
> obvious things that come to mind are egress filtering and NAT. In
> addition to any technical information that can help me figure this out
> for myself, experience others have had with these same problems would
> also be helpful.
>
> Thanks a lot for any help.
> --
> Crist J. Clark                     |     cjclark at alum.mit.edu
>                                    |     cjclark at jhu.edu
> http://people.freebsd.org/~cjc/    |     cjc at freebsd.org
>