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Re: //gs LocalTalk Port
Dan Bethe wrote:
> Nathan Mates wrote:
>
> > For regular modem transmissions, then the 57600 bps speed
> > applies. Appletalk is done via a less-standard mode (asychronous vs
> > synchronous) not 'spoken' by the standard 16550[A] serial chips found
> > on non-Apple boxen. Same kind of quirk as the MFM vs GCR floppy disk
> > I/O, etc that prevents compatability by using unusual combos of
> > less-standard chips.
Can everyone please use the correct terms, or this is going to get
confusing.
"AppleTalk" is a protocol stack that runs over a variety of
communications mechanisms.
"LocalTalk" is the specific implementation of AppleTalk running over
RS-422 (or something derived from it) at 230400 bps using FM modulation
and HDLC-like framing, with half duplex communication, potentially
multi-drop (with the right cabling).
(The name "AppleTalk" originally meant both the protocol stack and the
physical media, but that was before AppleTalk phase 2 and other network
types were supported, which was some time around 1987.)
> Oh, so if I did Appletalk between a //gs and a Linux pc, it would work
> at a maximum of 57600bps?
You could run AppleTalk over an asynchronous serial connection, but it
wouldn't be the same thing as LocalTalk, and you couldn't physically
connect a PC running Linux to the IIgs serial port and expect it to
work.
(The AppleTalk Remote Access protocol allows AppleTalk to work over
modems and serial links, but there is no support for it on the IIgs.)
> But if I did Appletalk with a //gs and a //gs or Mac, then it would be at
> a happy 230kbps?
Yes, LocalTalk would be running at that speed.
> Is there any way to increase that speed if we're using a //gs and a
> Linux pc? Get an Appletalk card for the PC?
That is probably the easiest option (it might be called an AppleTalk
card, but it is really a LocalTalk card), assuming there is software
support for it.
Another solution might be an Ethernet connection (running EtherTalk),
with an EtherTalk-to-LocalTalk bridge of some kind (e.g. LocalTalk
Bridge running on a Macintosh, or a dedicated external box).
> Also I'm curious about using more than 2 hosts. If I have Phonenet
> adaptors, are those just as directly hardware-compatible as a straight
> serial cable? Do I need any additional special software drivers? Or
> can I just hook up multiple Apple hosts and start sharing data? Does
> this setup have to change if I want to add a printer?
LocalTalk is designed to work on a daisy-chained cabling system. When
you use Phonenet boxes (or Apple's LocalTalk cabling system) all that
happens is the transmit signals from all nodes are mixed together and
received by all nodes. The protocol deals with avoiding transmit
collisions (with some help from the SCC chip).
If you use a plain serial cable, each device receives transmissions from
the other one, so the whole thing works fine. (The computer doesn't
receive its own transmission, but this is not required by the protocol,
and is completely ignored anyway.)
> At my house, we have two //gs's, a Linux PC, an Imagewriter //, and we
> might add a Mac or two and another printer.
> Okay here's another level of complexity. Can I also do tcp/ip across
> this Phonenet link?
Yes. You need to run the MacIP protocol, which encapsulates IP frames
using one of the AppleTalk subprotocols. Support for this is built into
Open Transport on the Mac. The IIgs could participate in theory, if the
drivers are ever released.
Using MacIP does not interfere with other uses of the AppleTalk protocol
(e.g. printing, file sharing).
It might cause some problems with other uses of TCP/IP on the Mac: if
you are not running any routing software, then you can only have one
active TCP/IP connection, so you can communicate over MacIP, or via PPP,
or via Ethernet, just not more than one at the same time.
> Basically like you do with Ethernet? Could I use the Linux PC as an
> internet connection via TCP/IP modem to an ISP, and also as a
> masquerading gateway to the rest of the in-house hosts?
For TCP/IP connections, yes. LocalTalk is pretty slow, so I'd suggest
Ethernet would be better for this, if you have the necessary hardware.
The Mac is quite capable of running AppleTalk over LocalTalk and TCP/IP
over Ethernet at the same time.
This would give you a network looking something like this, at a minimum
(add extra computers as required to either network):
LocalTalk
(AppleTalk only)
-------- ------
| | |
ImWrII IIgs Mac Linux - modem ---> ISP
| |
----------
Ethernet
(TCP/IP only)
Without adding any special software, this cuts the Linux box off from
the printers, and prevents the Linux box from acting as a server for the
IIgs (and difficult for it to be an AppleTalk server for the Mac).
Several options are available, all of which allow the Linux box to act
as an AppleShare server and to talk to LocalTalk printers:
1. Run LocalTalk Bridge software on the Mac. (LocalTalk Bridge is
commercial software sold by Apple, but it appears to be difficult to
obtain at present. There is a freeware program called LaserWriter
Bridge which only allows Postscript printers to be hooked up on the
LocalTalk side, so it isn't much use in this case.)
LocalTalk
(AppleTalk only)
-------- ------
| | |
ImWrII IIgs Mac Linux - modem ---> ISP
| |
----------
Ethernet
(TCP/IP and AppleTalk)
2. Add a LocalTalk card in the Linux box.
(a) You could drop the Ethernet, if you don't need the extra speed, and
use MacIP to talk TCP/IP between the Macs and Linux.
LocalTalk
(AppleTalk and TCP/IP via MacIP)
-------- -----------------
| | | |
ImWrII IIgs Mac Linux - modem ---> ISP
(b) You could have both networks in parallel. If Linux has any
AppleTalk bridging capability in this configuration, you could
disconnect any Ethernet-capable Macs from LocalTalk, and run AppleTalk
over the Ethernet instead.
LocalTalk
(AppleTalk only)
-------- -----------------
| | ? |
ImWrII IIgs Mac Linux - modem ---> ISP
| |
----------
Ethernet
(TCP/IP and AppleTalk?)
3. Add a hardware bridge between the Ethernet and LocalTalk networks,
and use AppleTalk on the Ethernet. (In this case, you could disconnect
any Ethernet-capable Macs from LocalTalk.)
LocalTalk
(AppleTalk only, possibly also TCP/IP via MacIP)
-------- ------
| | |
ImWrII IIgs Bridge Mac Linux - modem ---> ISP
| | |
----------------
Ethernet
(TCP/IP and AppleTalk)
I've never used Linux, so I don't know what its AppleTalk support is
like, but the rest of it is well defined.
--
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand