Re: TCPIP/MacIP and Appletalk

[andrew.roughan@writeme.com (Roughana)]

I asked Ewen about this issue and he allowed me to post his response
as a followup for the benefit of everyone.

Cheers,
Andrew

Ewen Responds:
====

andrew.roughan@writeme.com (Roughana) wrote in message:
>> I have no idea if Spectrum's Zmodem was designed to be used with
>> TCP/IP or not.

The problem with using the Internet for X/Y/Zmodem is that there 
might well be delays that arise in the middle of the data packets 
being received. As the integrity of X/Y/Zmodem is primarily designed 
round timeouts, this causes problems and so slow transfers.

You can of course remove the timeouts, but if a piece of data is 
lost, the download will never complete. If you increase the timeouts, 
the process may well take far too long to complete.

Basically X/Y/Zmodem are not best suited to the Internet, unless you 
have a good fast and loss free path to your ISP. FTP is better, as it 
does not involve timeouts.

>> Spectrum's handling of special characters passed across the Telnet
>> connection with Zmodem

Spectrum handles the full 8-bit character set for Telnet, but this 
assumes the host is also supporting the 8-bit path.

Problems with Zmodem under TCP/IP I suspect will all come down to the 
character timeout factor. Kermit is a better solution if FTP cannot 
be used, as long as the host that is connected to can handle full 
8-bit Kermit, with extended packets, and or sliding windows. It is 
then faster than Zmodem. Unfortunately many ISPs cannot handle the 
full Kermit implementation.

I do know that ProTerm Mac does not have the same problems with 
Zmodem and a Telnet connection, but there may well be other factors 
at work with that program running on a Mac.