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From: steve@johnson.jvnc.net ("Steven L. Johnson")
Newsgroups: comp.protocols.tcp-ip.ibmpc
Subject: Re: TCP/IP over modem (I need SERIOUS help here)
Message-ID: <359@johnson.jvnc.net>
Date: 26 Mar 91 22:34:59 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 80

>1)  Is there any truth to what I've heard?  Can I run TCP/IP over a
>modem?

Yes, two ways.  First, and most common, is SLIP (Serial Line Internet
Protocol).  Second, is PPP, the newer Point to Point Protocol.  I
currently run dial-up SLIP access from a Compaq 286 box to the
Internet (NSFnet backbone node at Princeton).

>2)  Aside from speed, what differences will I notice between this
>implementation and an "ethernet-ed" IBM running "TELBIN / TN3270" and
>"FTP"?

Well, theory says that SLIP is a full IP access.  But in actual practice
many of the IBM-PC programs won't run because they make assumptions
that all IP datagrams will have a 14 byte ethernet header tacked onto
the front, or that the ARP protocol is available.  It is my understanding
(although no experience) that some versions of TELBIN and TN3270 do support
the Packet Driver type 6 packets (i.e. SLIP).  I don't believe that
the commercial packages (from FTP, Sun, B&W, etc) suffer from these
problems.

This 'compatibility problem' would go away if someone wrote a packet
driver that accepted etherenet frames (PD type 1) from the user and
converted them to SLIP frames for network transport, and hacked fake
ethernet id and ARP service.  I've had limited discussions with people
to implement this functionality, but have seen little interest.

I included this discussion, because I'm sure someone will tell you that
you can just use the SLIP packet driver and everything will work.  It
doesn't, unless the program specifically has slip packet driver support.


>3)  What software do I need and what's the installation process like?

I've used Phil Karn's KA9Q package successfully.  It is free for
Ham Radio people and universities; a license is needed for other use.
Full source is available, a big plus.  Telnet support is very weak; it
works but no terminal emulations.

If you find versions of telbin, ftpbin, tn3270 that support slip packet
formats, you can get the slip driver itself from sun.soe.clarkson.edu.

Alternatively of course there are the commercial packages.

The installation varies from package to package, and many people have
reported frustration with all of the packages.  The error messages
are not necessarily intuitive.

>4)  Do I need the cooperation of a current internet machine for me to
>access the internet and, if so, what does that machine need to provide
>me with?

You need the cooperation of a machine.  Many people run SLIP on a
unix box connected to the Intenet.  I haven't done this.  I have
connected directly to a Cisco router and a Cisco terminal server
which directly supported SLIP access.  These of course had to be
configured to route packets for my IP address (also security
config'ed also).  Since I purchased this service, the Internet side
was all done for me (thank goodness).

I imagine that the procedure varies highly dependent on the type of
service (single IP address or network gateway), and what type of
machine you're tying into on the Internet side.

>5)  Do I need any TECHNICAL knowledge of TCP/IP packet structure,
>ethernet, internet, etc. or is a good working knowledge of IBM and
>internet USAGE sufficient?

To install and use SLIP on the PC side, I wouldn't think so.  But to
resolve problems, someone will.  It depends on if there is any SLIP
experience on the machine you connect to, and how willing they are
to tackle PC problems.

>6)  Do I really want to do this????  (Don't bother answering this one -
>the questions above are what I really need!)

In my case, I both wanted to and did.  It provides me with a flexible
and cost effective access to the Internet.

-Steve