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000214_news@newsmaster….columbia.edu _Wed Jun 17 02:01:40 1998.msg
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From: James Coe <jcoe@interlog.com>
Newsgroups: comp.protocols.misc,comp.bbs,alt.comp,alt.computer,alt.computer.security,aus.computers.sun,comp.bbs.misc,comp.dcom.modem,comp.protocols.tcp-ip,comp.protocols.tcpip,comp.protocols.ppp,comp.protocols.kermit.misc,comp.unix.sun,comp.unix.solaris,comp.unix
Subject: Z-Modem vs FTP: Is the following an accurate comparison?
Date: Tue, 16 Jun 1998 10:13:53 -0400
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Z-Modem vs FTP
Speed
Z-Modem is usually much faster than FTP. This is because most
implementations of Z-Modem use internal data compression routines and do
not perform Cyclic Redundancy Checks (CRC).
FTP is slower than Z-Modem since no data compression is used and CRC is
performed.
Error Checking/Reliability
Since Z-Modem does not use CRC routines, transmission errors are not
easily detected or corrected.
FTP has full error detection capabilities as well as very good error
recovery procedures.
Additional Purchasing
Z-Modem is not part of the standard Sun Solaris Operating System. Thus,
it must be purchased from some third party vendor.
FTP is part of the standard Sun Solaris configuration.
Customizing for GPS Needs
For the GPS system, Z-modem must be customized so that there is some
indicator that the file upload is complete and processing can proceed.
In order to do this, source code must be available.
FTP must also be customized in this way. Oasis customized the FTP
daemon so that the file will be transferred to a processing directory
when the file upload is complete.
Connection
In order to use Z-Modem, the user must dial into the UNIX box and be
connected as a �real� UNIX user. The user can then initiate a Z-Modem
protocol upload. Some sort of server software which allows terminal
access is necessary on the UNIX box.
In order to use FTP, the user connects to the PPP server and then
launches an FTP application. This application is connected as a FTP
user.
Security
Since the user is connected as a �real� UNIX user, there are fewer
restrictions that can be placed on them.
Since the user is connected as a �ftp� UNIX user, there are many
restrictions that can be placed on the account. For example, the ftp
account can be restricted such that they can only put the file on the
system. They will not be able to �get� files, change from their
directory, list files, etc.
Also, this method allows the use of 2-levels of authentication. That
is, the user must sign into their PPP account and then into their ftp
account. Both of these accounts could have different passwords (or even
different User ID�s) and the PPP account could use CHAP for password
authentication (password not sent �in the clear�).
UNIX Support
Since �real� UNIX accounts need to be created, a UNIX system
administrator is necessary to create and manage/maintain the UNIX user
accounts.
�FTP� UNIX accounts can be generated automatically.
PC Support
Z-Modem is much easier to support as it is just a terminal connection.
That is, no TCP/IP set-up is required.
FTP is more difficult to install and support since it requires Win95
dial-up networking to be configured.
General
Considering the speed and error issues, Z-Modem should only be used when
the file is large and can be easily resent. In our case, the maximum
size of a single transaction is only 150 kb and we expect a frequency
of � transaction per merchant per day.
FTP is better when file stability is necessary and speed is not an issue
as is true in our case. FTP is also preferable in terms of security,
availability and support on the UNIX side. The biggest drawback to FTP
appears to be the PC support issues.