Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!samsung!umich!sharkey!tygra!mich-ns!tech From: tech@mich-ns.UUCP (Mich. Network Sys. TECH SUPPORT) Newsgroups: comp.dcom.modems Subject: Re: Inside info on Telebit spoofing?!? Message-ID: <32@mich-ns.UUCP> Date: 24 Apr 91 23:17:27 GMT References: <7229.280E4283@zswamp.uucp> Reply-To: tech@mich-ns.UUCP Organization: Michigan Network Systems, Detroit, MI Lines: 57 In article <7229.280E4283@zswamp.uucp> root@zswamp.uucp (Geoffrey Welsh) writes: " " Does anyone know what the data stream fed to the line looks like after a "Telebit has gone into spoofing mode? " Basically, what spoofing does is eliminate the need for the ACK to traverse the phone line. The sending modem receives data from the DTE and pumps it out to the phone line as fast as it can and sends an ACK back to the DTE without having to receive one from the remote end. The remote (receiving) modem tosses out all ACK's that its DTE sends it in response to an incoming packet. This reduces the latency involved in whereby the sending system has to wait for an ACK from the remote for a packet just sent before sending another one. All of Telebit's features (Spoofing and PEP) are designed to optimize a link over a normal phone line. PEP utilizes as much of the bandwidth as possible, given the line quality and can dynamically change its utilization based on changing line conditions. Spoofing eliminates the latency involved with the "send-wait" mentality of most protocols. As for error correction: Thats done at a lower level by PEP's CRC-16. " 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. " " This might not be the most elegant or safest approach, but it would mean "easy inter-manufacturer compatibility. Data should remain safe, since MNP or "LAP-M would be entrusted with delivering the binary data verbatim, and each "modem could take care of the protocol spoofing with its own home machine. " Thats it. Error correction protocols eliminate the need for ACK/NAK. Telebit takes advantage of this. " This might also make it *theoretically* possible to tell machine A to send "using Kermit and machine B to receive using XMODEM, since the data stream in "between would be raw and spoofing would be a local issue only. " " Don't ask me how the modem is supposed to recognize the protocol if both "ends don't interact enough to indicate a transfer reliably, this is just an "uneducated dream. " Protocol spoofing is enabled on either end by the setting of certain S- registers. The modems can also detect which method the other modem is using and will use that as well if it is enabled locally. -- Michigan Network Systems Technical Support Division 1-800-736-5984 BBS: +1 313 343 0800 TELEBIT DIGIBOARD WESTERN DIGITAL 3COM SCO INTERACTIVE UNIX MICROPOLIS ADAPTEC