DirecPC Protocols

Marshall Eubanks tme at multicasttech.com
Fri Nov 15 15:15:33 UTC 2002

This is AFAIK _not_ what DirectPC does, but have you taken a look at
RFC3077 and the UDLR draft

http://www.ietf.org/internet-drafts/draft-ietf-udlr-experiments-00.txt ?

This covers the complications of doing IP over very assymetric links as part of the IP, including
both multicast and TCP issues.

Marshall Eubanks

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.


T.M. Eubanks
Multicast Technologies, Inc
10301 Democracy Lane, Suite 410
Fairfax, Virginia 22030
Phone : 703-293-9624       Fax     : 703-293-9609
e-mail : tme at multicasttech.com

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