Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!att!pacbell.com!tandem!netcom!gandrews
From: gandrews@netcom.COM (Greg Andrews)
Newsgroups: comp.dcom.modems
Subject: Re: Inside info on Telebit spoofing?!?
Summary: It's simpler than that.
Message-ID: <1991Apr20.032353.27408@netcom.COM>
Date: 20 Apr 91 03:23:53 GMT
References: <7229.280E4283@zswamp.uucp>
Organization: Netcom - Online Communication Services  UNIX System {408 241-9760 guest}
Lines: 26

In article <7229.280E4283@zswamp.uucp> root@zswamp.uucp (Geoffrey Welsh) writes:
>
>   I could imagine a Trailblazer stripping all the framing and providing the 
>ACKs, and then sending the data into the PEP or MNP as if the host had simply 
>done a binary dump to the serial port.  The receiving modem would take the 
>raw data after the PEP/MNP processing and send it via UUCP-g to the receiving 
>computer.
>

Why bother?  It would be another order of magnitude more work to have to
strip out the protocol stuff and re-generate it at the receiving end.  Heck, 
the computer has done all the hard work already.  Just check the basic stuff
like the packet is not out of sequence and the checksum compares okay and
ack it.  The receiver's modem only has to feed the packet to the computer 
and get the ack.

The fact that the sender's modem provides the ack locally and the receiver's
modem absorbs the ack locally (and the sender's modem ensures that its buffer
stays full) is what makes spoofing work across a PEP connection.


-- 
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|  Greg Andrews   |       UUCP: {apple,amdahl,claris}!netcom!gandrews    |
|                 |   Internet: gandrews@netcom.COM                      |
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