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Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 61 but noticeable improvement in performance, with 1024 best for clean lines and smaller numbers better for noisy lines. When sending files over noisy phone lines not involving networks, the speed of error recovery may be increased by decreasing the values of the ZMODEM t and p numeric parameters. Information about YMODEM and ZMODEM protocol internals is provided in ymodem.doc and zmodem.doc, part of Omen Technology's ZMODEM Developer's Collection. 13.6.1 Receiver Window Size Override Some ZMODEM senders control the network window size to improve error recovery and/or overcome incorrect flow control configuration. The optimum size of this depends on the average error rate on the link, information that may not be available to the sender. ZMODEM-90(TM) allows the receiver to specify the window size, with the Wn option, overriding the sender's window size. SEE ALSO: Wn option 13.7 TERMINAL SERVERS Terminals on some timesharing systems are connected indirectly to the host with TERMINAL SERVERS operating over networks. Terminal servers often interfere with file transfers by "eating" control characters and/or losing data. Accessing a distant system using telnet on a local Unix system entails the same problems. If telnet does not work well, try rlogin with the -8 option. Set the escape character to ^P (control P) which is protected by ZMODEM. When terminal servers interfere with file transfers, server commands are often available to help the problem. When possible, enable the server and modems for hardware flow control in and out. Set the terminal server to telnet transparent mode. Some typical commands are "SET TERMINAL DOWNLOAD", "set session passall", and "SET TERMINAL NO ESC", but there is no standard set of commands suitable for all terminal servers. Normally these commands are given before attempting file transfers, but one user has reported that the command must be given after the file transfer is started(!). Until terminal server vendors improve the quality of their product, you may have to get on their case until they adequately support high performance file transfers. Escaping control characters with ZMODEM (sz -e) may help if the transfer gets stuck in the same place on every attempt. Professional-YAM and ZCOMM allow selection of which control characters need to be escaped. In extreme cases 7-bit transmission may be required (see the Professional-YAM/ZCOMM manual). If you encounter (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 62 problems with control characters you should identify which control characters are causing the problem. Please refer to the sz -T command in sz.doc for more help. Flow control between the server and modem is often defective. This rarely causes a problem in interactive applications whose short bursts (a screenfull at most) fit within the available memory buffers. Streaming protocols such as YMODEM-g, long packet SuperKermit, and ZMODEM can overload the available buffering. Some terminal servers support commands to enable hardware flow control such as "TERM FLOWCONTROL HARDWARE IN OUT"; this assumes the modem attached to the server is properly configured. If the terminal server is too brain damaged to support flow control, ZMODEM lets you fake it by setting a window size. Try sz -w2048 file... to enable software flow control. Experiment with different window sizes for best results. Terminal servers are designed to accept keyboard input from human operators. They may lose data when a program sends more data to the host faster than humans type. Some servers allow larger input buffers to support file uploads. If you can upload short files (less than 100 bytes) but not longer files, try sz -w1024 file... with your uploading program. (Not all programs support this option; use ZCOMM or Professional-YAM.) When both flow control and character transparency are problems, use sz -ew1024 file... as a starting point. Sometimes the terminal server software is defective and must be corrected. Please contact the network's vendor for corrective procedures. An alternative is to install direct serial ports for users desiring to upload files. We have also encountered problems when networking software fails to pass data after a large amount of data has been sent to the host. This has happened on a PPP internet connection which prevented uploads of large amounts of data via either FTP or a ZMODEM upload (via TELNET). The PPP connection grinds to a standstill and not even PING works. The same ZMODEM/TELNET combination easily uploaded ten times as much to a nearby machine connected by Ethernet. 13.7.1 PORT WATCHERS Some systems enforce a timeout which disconnects a user after several minutes of keyboard inactivity. Long, error free ZMODEM transfers do not generate keyboard activity (this is why ZMODEM is so efficient). Restricting the window size with (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 63 sz -w16384 file... option generates terminal input at regular intervals even when no error correction is needed. If problems persist, try setting a packet length. sz -l1024 file... (The default ZMODEM packet length is the file length.) The sz e and m options may be used in conjunction with the xmtxesc and zmrxesc string parameters to specify more control characters which cannot be passed over the serial line. SEE ALSO: zmtxesc, zmrxesc string parameters 13.8 7 Bit Environments ZMODEM-90 automatically detects 7 bit environments and adjusts accordingly. If the environment is known to be 7 bits, use the E option to provide 7 bit compatibility in minimum time. EXAMPLE: sz -E file.doc When transferring files with a large number of bytes with the 8th bit set, the P ("pack") option may be used to optimize 7 bit encoding. EXAMPLE: sz -P zipfile.zip 13.8.1 Manual ABORT If a ZMODEM transfer fails abruptly under exceptional conditions the program on the remote machine may be manually terminated by repeatedly typing Ctrl-X characters at it until the program exits. 13.9 XMODEM Family Protocols All XMODEM family protocols require an absolutely transparent data path from sender to receiver. Modems must not be configured for software flow control. 13.9.1 TRUE YMODEM(TM) Developed in 1981, YMODEM is finding its way into many communications programs. With Omen Technology's Enhanced Data Recovery(TM), YMODEM gives excellent efficiency, integrity, and fair robustness in many applications. True YMODEM transfers one or more files in a batch, without alteration or added garbage characters. True YMODEM also preserves the file date across multiple time zones. ZCOMM and the Unix(TM) rb and sb programs preserve the file modification date.[3] (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 64 13.9.2 YMODEM-1k The sb k option (1024 byte blocks) may be used to enhance throughput, especially when using timesharing systems, satellite links, or packet networks that can support the longer blocks. EXAMPLE: sb -k *.c *.h sends all .c and .h files in the current directory with 1024 byte blocks.[4] YMODEM and YMODEM-1k transfers can be received with the rb or F3 commands. YMODEM file transfers with Unix and VMS systems are discussed later in this chapter. Some programs claim to support YMODEM but actually use XMODEM with 1024 byte blocks. These programs do not meet the YMODEM Minimum Requirements defined by the YMODEM protocol. One can use ZCOMM's XMODEM sx -k and rc commands with these traditional programs. 13.9.3 YMODEM with OverThruster YMODEM and YMODEM-1k file downloading from networks and timesharing systems is slowed by response times. This slowing may be significant even when 1k blocks are used. With some systems, one can speed up YMODEM downloads by using the o option with the rb command to receive the file. Because OverThruster(TM) defeats error recovery, a line hit will usually abort a download. OverThruster(TM) may be used with X.PC or MNP error correcting link level protocols. EXAMPLE: rb -o SEE ALSO: O numeric parameter 13.9.4 XMODEM-1k The XMODEM-1k protocol transfers one file per command with 1024 byte blocks and a nominal 16 bit CRC. The file name must be entered for both the sender and the receiver. Programs lacking ZCOMM's Cybernetic Data Recovery(TM) logic are less likely to transfer data accurately under marginal conditions. XMODEM's use of every possible 8 bit code causes problems in some applications. ______________________________________________________________________ 3. Controlled by the d and z numeric parameters 4. ZCOMM switches to 128 byte blocks at the end of a file when the length warrants. (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 65 The end of the file may be padded by up to 127 or 1023[5] garbage characters. To send a file with XMODEM-1k: sx -k file1 To receive a file with XMODEM-1k: rc file1 13.9.5 XMODEM-CRC (with fallback) The XMODEM-CRC protocol transfers one file per command. The XMODEM-CRC protocol requires the receiving program to initiate an XMODEM-CRC transfer. The file name must be entered for both the sender and the receiver. Even with CRC-16, programs lacking ZCOMM's Cybernetic Data Recovery(TM) are less likely to transfer data under marginal conditions. XMODEM-CRC's use of every possible 8 bit code causes problems in some applications. The end of the file may be padded by up to 127 garbage characters. To send a file with XMODEM (or XMODEM-CRC): sx file1 To receive a file with XMODEM-CRC: rc file1 13.9.6 Classic XMODEM The original MODEM protocol, developed by Ward Christensen, is supported by a large and growing number of programs operating on a variety of micros and minis. The base level XMODEM protocol gives good results when used over low error rate direct telephone connections. XMODEM's short data blocks and use of every possible 8 bit code preclude its application in many environments. File transfers with this protocol add up to 127 garbage characters to transferred files. The XMODEM protocol can transfer one file per command. The file name must be entered at both the sender and the receiver. To send a file with XMODEM: sx file1 To receive a file with Classic XMODEM: rx file1 13.9.7 Relaxed XMODEM ZCOMM's XMODEM and YMODEM support has been optimized for maximum reliability with a wide variety of systems under a wide variety of conditions. The default XMODEM and YMODEM timeout parameterss are "relaxed" timings. They rarely need to be lengthened except under the most __________ 5. Some programs (including ZCOMM) limit this padding to 127 bytes. (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 66 sluggish of conditions. The zmodem t, T, and p numeric parameters (q.v.) control timeouts for XMODEM, YMODEM, and ZMODEM. The default values allow 10 seconds for a packet to appear and a 10 second pause within a packet before starting error recovery. EXAMPLE: zmodem pt200 pp150 :: Set more relaxed X/Y/ZMODEM timing For best reliability, Omen Technology does not recommend tightening these timings for XMODEM and YMODEM transfers on noisy lines. 13.9.8 XMODEM with OverThruster XMODEM file downloading from networks and timesharing systems is slowed by short blocks and long response times. With some systems, one can speed up downloads by using the ro command to receive the file. Because OverThruster(TM) defeats error recovery, a line hit will usually abort a download. With nearly error free connections, one can save enough time from the increased throughput to make up for the failed transfers. OverThruster(TM) may be used with X.PC or MNP error correcting link level protocols. EXAMPLE: ro file1 EXAMPLE: rb -o SEE ALSO: O numeric parameter 13.9.9 YMODEM-g: Traditional Overdrive The proliferation of error correcting modems has sparked a proliferation of YMODEM-g programs, more and more of which actually meet minimal YMODEM protocol specifications. YMODEM-g transmits 0 or more files per batch with an ACK-less variant of YMODEM-1k. The sender does not wait for individual data blocks to be acknowledged, allowing high speed transfers with error correcting modems. YMODEM-g assumes an error free communications channel. A single transmission error or character lost because of DOS or TSR interrupt latency ruins the entire transfer, and YMODEM-g does not support Crash Recovery(TM). ZCOMM supports True YMODEM-g with the sb and rb -g commands. EXAMPLE: sb *.old Sends files in the current directory with YMODEM or YMODEM-g protocol. The receiver controls whether YMODEM or YMODEM-g is used for the transfer. (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 67 EXAMPLE: rb -g Receives with YMODEM-g protocol. 13.9.10 XMODEM Mutants Misrepresented as YMODEM Despite continuing education efforts, a few lazy software providers insist on identifying their mutant XMODEM protocols as "ymodem". They choose to ignore the definition of YMODEM that Ward Christensen wrote when he coined the term YMODEM in his April 1985 message: (a) a record 0 containing filename date time and size (b) a 1K block size option (c) CRC-16. Use the XMODEM sx-k and rc commands to deal with these nonstandard programs. In case of questions, please refer to ymodem.doc, part of yzmodem.zoo for for the official YMODEM protocol. (Available in Omen's ZMODEM Developer's Collection.) 13.9.11 Qmodem-G/Streaming XMODEM The Qmodem program and certain bulletin boards provide an ACKless XMODEM mutant protocol selected with the Qmodem G protocol menu choice. The sx and rx -g commands support this mutant XMODEM. EXAMPLE: rx -g qmodem.fil 13.9.12 WXMODEM (People-Link) ZCOMM supports WXMODEM protocol downloads with the rw command. On the People-Link timesharing service, WXMODEM downloads are faster than XMODEM downloads. Throughput, reliability, accuracy, and amenities are not as good as ZMODEM or SuperKermit, but neither of these protocols are currently available on that system. WXMODEM adds up to 127 garbage bytes to transferred files. Omen Technology does not recommend WXMODEM for use over noisy phone lines. EXAMPLE: rw file1 13.9.13 MODEM7 Batch The MODEM7 batch protocol passes CP/M file names from the sending program to the receiver one character at a time. The compatibility, throughput, and reliability problems of this kluge prompted the development of YMODEM. Nonetheless, when it becomes necessary to transfer files with a program lacking more advanced protocols, MODEM7 batch is better than nothing. File names transmitted with the MODEM7 batch protocol must obey the restrictions of both 8 bit CP/M and DOS. The f option cannot be used with MODEM7 batch. Data transfer within MODEM7 batch uses XMODEM (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 68 protocol, and all of XMODEM's weaknesses discussed above apply to MODEM7 batch. MODEM7 batch does not preserve the modification date or exact file contents. EXAMPLE: s7 file1.ext *.baz sends files with MODEM7 batch. EXAMPLE: r7 receives one or more files with MODEM7 batch. 13.9.14 Telink/FIDO The Telink protocol expands upon the MODEM7 batch kluge with a specially formatted block containing the length of the file and the local DOS time and date. All of the MODEM7 batch compatibility and reliability problems apply to Telink.[6] The zmodem Z numeric parameter or the z file transfer option may be used to correct the time/date stamping of files transferred between different time zones. EXAMPLE: zmodem pZ120; st file1.ext *.baz Sends the specified files with a 2 hour time zone adjustment. EXAMPLE: rt -z60 Receives one or more files with a 60 minute time zone adjustment. 13.9.15 SEAlink When transferring files with the CLINK 1.13 compatible programs, ZCOMM's rb and sb commands recognize SEAlink's modified Telink protocol. The rb command allows a transmitting SEAlink program to use sliding windows. Telink time zone and file name considerations apply to SEAlink. In addition, because SEAlink uses all 256 of the possible 8 bit codes for both data transfer and protocol management, some modems and networks that operate with XMODEM will not accommodate SEAlink. As with the MODEM7 and Clink protocols mentioned above, the SEAlink protocol is included for convenience in situations where the YMODEM and ZMODEM protocols are not implemented.[7] __________ 6. ZCOMM's rt and st commands were verified with Minitel 3.0 by Tom Jenning's Fido Software; other Programs may not produce the same results. 7. ZCOMM's SEAlink was verified with CLINK 1.13 by Systems Enhancement Associates. Other Programs may not produce the same results because of ambiguities in the SEAlink documentation and undocumented protocol variants. (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 69 EXAMPLE: zmodem pZ120; sb file1.ext *.baz Sends the specified files to a SEAlink program with a 2 hour time zone adjustment. EXAMPLE: rb -z60 Receives one or more files from a SEAlink program with a 60 minute time zone adjustment. (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 70 13.10 Kermit 13.10.1 ZCOMM Kermit Capabilities At a Glance Local operation..................Yes Remote operation.................Yes Transfers text files.............Yes Transfers binary files...........Yes Wildcard send....................Yes Filename collision avoidance.....Yes Can time out.....................Yes 8th-bit prefixing................Yes 8 bit serial data................Yes Sliding Windows..................Yes Long Packets.....................Yes Repeat count prefixing...........Yes Alternate block checks...........Yes Terminal emulation...............Multiple Communication settings...........Yes Transmit BREAK...................Yes IBM mainframe communication......Yes Transaction logging..............Yes Act as server....................no Talk to server...................Yes Advanced commands for servers....Yes Handle file attributes...........no Programmable reset string........Yes Kermit operates with a wide range of computer systems, including those whose restrictive terminal interfaces prevent XMODEM transfers. Kermit uses an encoding technique called quoting to represent control characters and (if necessary) parity bits with standard printable characters. It is one of the few asynchronous error correcting protocols that work properly with half duplex IBM front ends. Because of the overhead from character quoting, Kermit is less efficient (slower) than ZMODEM. Kermit can transfer one or more files per command, preserving the exact file length. EXAMPLE: kermit sb file1 file2 EXAMPLE: kermit rb 13.10.2 Incompatible Kermit Dialects When sending files with the Kermit Protocol, ZCOMM uses all 8 bits for the transfer unless a 7 bit parity mode (e.g., ena -7e) is used, the kermit 7 numeric parameter is non zero, or the other program requests 8th bit qouting. If ZCOMM is using a 7 bit parity mode (such as ena -7m), ZCOMM requests 8th bit (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 71 quoting unless the kermit 8 numeric parameter is non zero. -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Both programs must use the same parity for Kermit file transfers to succeed. -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- The Kermit protoocl does not specify an automatic means of forcing both the sender and receiver to use the same dialect. Some Kermit programs use various means to synchronize the dialects. Files cannot be transferred if the two programs disagree on parity handling, Such failures are quite commonplace. A common symptom is a transfer that starts up normally but always fails at the same block. Setting appropriate parity corrects these Kermit failures. ZCOMM's Kermit AutoDownload(TM) (enabled with the K term option) allows the term function to sense the beginning of a Kermit file download, make the proper determination on whether to use 8 bit serial data, and execute the file download without user intervention. 13.10.3 Kermit Performance Enhancements ZCOMM features Long Packet Kermit for increased throughput with suitable systems, including many that do not support sliding windows. ZCOMM allows Kermit long packets up to 1920 characters on DOS, up to 4096 on Unix systems. ZCOMM also supports Kermit with Sliding Windows. "Super-Kermit" transmits multiple packets before waiting for a response, increasing throughput with timesharing systems and networks. The maximum send packet length is set by the kermit l numeric parameter. EXAMPLE: k pl500 The maximum receive packet length is set by the kermit L numeric parameter. EXAMPLE: k pL500 Some Columbia University Kermit versions may not operate properly at full packet length. ZCOMM supports 12 bit Kermit checksums and 16 bit Kermit CRC for professional error detection performance. ZCOMM uses the most reliable Kermit error correction available. Shorter checksums may be forced by changing the kermit b numeric parameter. 13.10.4 MobyKermit ZCOMM's Kermit supports an optional smaller set of prefixed control characters with the MobyKermit(TM) accelerator. When used with Unix Ckermit 5A(189) or later, the following commands (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 72 should be included in your Unix .kermrc initialization file: set buffers 30000 30000 set window-size 7 set send packet-length 4096 set receive packet-length 4096 set block 3 set control unprefixed all set control prefixed 0 1 set transfer cancellation off set flow none set handshake none (or use hardware flow control) set file type binary set delay 0 13.10.5 Accessing Kermit Servers The commands to start up a Kermit server vary from system to system. Unix C-Kermit can be started in server mode with kermit -ix given to Unix or VMS. When the Kermit server is active, the ZCOMM get, send, and remote ... commands may be used. The ZCOMM finish command causes the remote Kermit server to exit to its operating system. 13.10.6 Kermit Caveats Some versions of Kermit translate files as they are sent, by default! Typical modifications include CR/LF to NL transformations and CPMEOF stripping. Before transferring binary files, such editing must be disabled with SET FILE TYPE BINARY or similar commands given to the other program. The demonstration in Chapter 10 includes several Kermit server access and file transfer commands. If the Kermit protocol doesn't work with IBM mainframe communications, incorrect ASCII/EBCDIC translate tables may be the problem. Some mainframe "front ends" require special characters or a break signal to recover from transmission errors ("line hits"). The kermreset string parameter (q.v.) may be programmed with the required sequence. SEE ALSO: kermreset string parameter When downloading files from some versions of Kermit, best results may sometimes be obtained by starting ZCOMM's kermit receive before typing the carriage return that starts the sender on the remote. If the other program includes an adjustable initial delay, you can save time by setting it to zero. SEE ALSO: kermit d numeric parameter SEE ALSO: K term option (Kermit AutoDownload(TM)) (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 73 13.11 Transferring Files with Unix Systems 13.11.1 Terminal Servers / Port Multiplexers Some Unix systems are accessed via a port multiplexer or other network. Some of these interfere with data transmission. In some cases it has been necessary to contact the manufacturer to obtain undocumented instructions or software updates to make the multiplexers or networks suitable for file transfers. These systems may require additional control characters to be escaped. The sz command e option may be used to escape all control characters. SEE ALSO: e option Individual control characters can be escaped with the zmtxesc string parameter. SEE ALSO: zmtxesc string parameter Sometimes it is necessary to use 7-bit transfers with the E or EP options. EXAMPLE: sz -EP bigkahuna.zip 13.11.2 Remote Access via Telnet Sometimes one wishes to access a distant host by calling into a nearby Unix system. The Unix telnet program may be used to access other hosts. When using telnet, the -8 option should be used to enable an 8 bit path. The telnet escape character should be set to Control-P, a character which is protected by standard ZMODEM. EXAMPLE: telnet -8 -e ^P localhost 13.11.3 Flow Control on Unix Systems It is a pleasure to upload and download files from Unix at high speed without errors with today's faster modems. Unfortunately, many Unix systems are not properly configured for flow control. On improperly configured systems it will be necessary to restrict the window size with -w 4096 to prevent buffer overruns. Try different numbers to get the best results. Better yet, get the flow control fixed. 13.11.4 Uploading Files to Unix Systems Files may be sent to Unix systems conveniently and quickly with ZMODEM. Unix flavors of Professional-YAM support the full ZMODEM-90(TM) feature set including Intelligent Crash Recovery(TM) and selective transfers with the rz (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 74 command, a hard link to the /usr/bin/yam program. If the Unix system is operating with 7 bits, the sender's zmodem d parameter may have to be increased to allow the rz program time to change Unix to 8 bits for the transfer. SEE ALSO: zmodem d numeric parameter Traditional Unix systems limit serial input buffering to a few hundred characters or less. This is sometimes too small to prevent data loss and retransmissons when operating at high speeds. On SCO Unix 3.2.4 this bufering can be increased by increasing the TTYHOG and NCLIST kernel parameters. 13.11.5 The rz and sz Programs Professional-YAM is the fastest Unix ZMODEM upload program. Pro-YAM uses a minimum of CPU resources for uploads. Pro-YAM provides the best ZMODEM technology and feature set available., but it may not be available on a particular system. The rz program, part of the rzsz package, may be used to support a subset of Pro-YAM's ZMODEM features. If rz is not installed on the target Unix system, unpack the rzsz.zoo file on your MSDOS system with: booz x rzsz.zoo given from the DOS prompt.[8] Next, the command source zupl.t calls the zupl.t script to upload the bootstrap file minirb.c, compile it, and use it to upload the remainder of the source files. After the rest of the files have been uploaded, compile rz.c and sz.c using the directions given in the README file and in the C source files. The rz and sz manual pages may be formatted with a make doc command. The undos program may be used to remove carriage returns in files uploaded to Unix machines. 13.11.6 Downloading Files from Unix Systems To download files from Unix(TM) systems, use the Unix sz command to send the desired files to ZCOMM. To Unix keyboard: sz file ... ZCOMM's ZMODEM AutoDownload(TM) takes care of the rest for you, saving unnecessary keystrokes. If one or more of the files already exists on the destination disk, use sz -y file ... instead, to replace the old copies on your computer. __________ 8. On Unix systems with Professional-YAM installed, the rzsz source files and man pages are installed in the /usr/src/command/rzsz directory, or on the distribution diskette in the file /tmp/yamusrc.tar.Z. (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 75 Another useful option sends only the files that exist on both computers (Y), and furthermore sends only those that are newer (n): sz -Yn file ... When files are long and transmission slow, you can save time by compressing them first. The zoo program, available for DOS, Unix, and VMS, may be used to compress file(s) before transmission. Other suitable programs include compress, zip, and gzip. Omen Technology products support ZMODEM compression with the Z option. All Omen Technology products support compression by Run Length Encoding (RLE). Unix flavors of Professional-YAM also support LZW compression. Unix source files normally do not contain carriage returns used by CP/M and DOS. Some CP/M or DOS programs, such as C compilers, do not require carriage returns in the source files. Others, such as the Microsoft Macro Assembler, become quite confused by such files, although such files fully meet the requirements of the ASCII standard. Carriage Returns may be added before downloading with the todos or tocpm programs. Carriage returns may be added during the transfer with the sz -a option. Carriage Returns may be added after the transfer by some program editors, including uEMACS. Short files (less than 64kb) may be converted using ZCOMM's read and create commands to pass the data through ZCOMM's capture buffer. Text files may also be downloaded using the capture buffer if sz has not been installed on the Unix machine. If a file or set of files are to be transported between two Unix systems, it may be helpful to place them in a tar or cpio archive (and possibly compress the archive) before transmission. This procedure will preserve the Unix file modes and modification times, and bypass pathname restrictions imposed by DOS. As with rz, Unix Professional-YAM is linked to sz to support the full ZMODEM-90(TM) feature set. Otherwise the separate Unix sz program may be obtained as described in the previous subchapter. 13.12 VAX/VMS File Transfers Most of the comments made above about Unix file transfers apply to VMS as well. Many VAX/VMS systems attach terminals with terminal multiplexers just as nasty as those used with Unix systems. They require fixes similar to those described above for Unix systems.. Automatic uploads to VMS may require setting the zmodem d (delay) numeric parameter to give time for the VMS rz program to properly initialize. (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 76 SEE ALSO: zmodem d numeric parameter EXAMPLE: zmodem pd15 13.12.1 Version 4 rz/sz Omen provides VMS flavors of version 4 rz and sz precompiled in rzsz.tlb, a VMS "text library". Version 4 rz supports most ZMODEM-90 features including Crash Recovery, compression, and MobyTurbo. Binary uploads write files with a default VMS 512 byte fixed length record format. EXAMPLE: sz biglib.tlb Sending to VMS with the i option selects the VMS Stream_LF record format. Stream_LF preserves the exact file length and data contents when read by C programs. EXAMPLE: sz -i vmsemacs.exe Sending to VMS with the I option causes the VMS receiver to use variable length binary records. VMS Kermit-32 and some other programs understand this record format. Text files uploaded with the a option are written in variable length records with CR carriage control. EXAMPLE: sz -a emacs*.c Version 4 VMS sz supports standard VMS wild card and directory recursion syntax. EXAMPLE: $ sz -qa [*...]*.prn sends all accessible .prn files on the system in ASCII mode. The VMS sz q option suppresses the initial tally of the number of files and their lengths. This tally can take some time when a large number of files and directories are invloved. The f option may be added to send directory names as well. If you use Kermit to upload the rzsz.tlb file to VMS, command the receiving Kermit program to SET FILE TYPE FIXED. (Some VMS Kermit programs may require SET FILE TYPE BLOCK.) Otherwise Kermit will garble the data. (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 77 13.13 GEnie File Transfers The General Electric Consumer Information Service service (GEnie) uses ZMODEM-90(TM) for efficient downloads. GEnie's ZMODEM server selects ZMODEM RLE Compression or MobyTurbo(TM) for optimum download speed on each file. GEnie uses a large network to provide callers with local access numbers. This requires technical tradeoffs to control data flow in the network. If you have a reliable, error-free connection to GEnie, download speeds can be improved by increasing GEnie's ZMODEM window size. EXAMPLE: genie24 speed 4800 249-8365/mnp set adlopts "W16384" Startup on Genie ZMODEM AutoDownloads can be speeded up by disabling Security Verification. EXAMPLE: ena -yZ :: Disable ZMODEM Security verification The sx file.exe command is used for XMODEM-CRC uploads to GEnie. When uploading with XMODEM-CRC, Wait for GEnie's "READY FOR INPUT, start your XMODEM upload." message, and then wait for the XMODEM-CRC C to appear before issuing the sx command. Issuing the sx command before the C appears may corrupt the uploaded file. A number of GEnie access scripts are provided in scripts.zoo with filenames starting with ge. The main GEnie login script is provided in phones2.t witin scripts.zoo. 13.14 BIX File Transfers BIX (Byte Information Exchange) supports ZMODEM-90 and Kermit file transfers. The Tymnet phone number in the bix telephone directory entry should be changed for your calling area. Other scripts are provided to handle BIX mail and conferences. When setting up a new BIX account, give the command call bix,new to force a login to the BIX new account program. Be sure to select ZMODEM downloads and uploads with the BIX "OPTIONS" menu choice. Set the Zcomm adlopts string variable to m or mr to enable MobyTurbo and ZMODEM Crash Recovery. When uploading over Tymnet or other networks, it may be necessary to set the zmodem w numeric parameter to a value between 2048 and 8192 (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 78 for best upload performance. The optimum value depends on load and the particular node you dial in to. EXAMPLE: z pw6144 BIX's transfer time predictions are about 40 per cent too pessimistic for ZMODEM transfers. A number of BIX scripts are included in SCRIPTS.ZOO. 13.15 CompuServe File Transfers B+ Protocol is used by the CompuServe Timesharing Service through the CompuServe, Tymnet, and Telenet networks. B+ Protocol file transfers are initiated by the CompuServe computer. The B+ Protocol file transfer protocol is well supported by this timesharing service. Under typical conditions, the B+ Protocol saves 35 per cent or more in file transmission time and connect charges compared to XMODEM protocol transfers. The c or C term option must be set with ena -c or ena -C to allow the B+ protocol to seize control and transfer files. The adlopts string parameter allows the y and v file transfer options to be specified for B+ protocol transfers. The w numeric parameter controls the block length used by the CompuServe B+ Protocol. A longer length increases throughput, but may overload some networks, resulting in excessive retransmissions or failed transfers. The maximum B+ block length is 1024 data bytes. A value of 0 (the default) allows the Compuserve computer to control the block length. A negative value controls the upload block length but still allows Compuserve to control the download block length. Uploads to Compuserve using longer block lengths are sensitive to poor flow control, especially when error correcting modems (MNP, etc.) are used. If B+ uploads fail or require excessive retransmissions, correct the flow control arrangements, disable the modem's error correction, or try a smaller upload block size. The data contents of successfully transferred files are not affected by this parameter. Some networks may garble data when B+'s streaming causes ZCOMM to respond to incoming data concurrently with incoming data. The o numeric parameter can be set to 0 to disable streaming (send-ahead). CompuServe B+ controls all file transfer operations (except permission to overwrite files) from the timesharing system. Waiting for long files to download can be boring. You can start the (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 79 transfer and walk away from the computer, but CompuServe will stay connected for 15 minute$ after the transfer is finished if you don't come back when the download finishes. This expense can be avoided by typing ALT-Q once the protocol transfer has started. ALT-Q tells ZCOMM to disconnect as soon as the protocol transfer is completed, stopping the connect charges. An alternative method is to control the transfers with a script, using either ejryam or the less sophisticated cissig and dow.t scripts included with the software distribution. When "browsing" through CompuServe's software "downloading section" libraries, the kcisdl.t script file and ZCOMM allow you to download a file with a single keystroke: F3. Installation instructions are provided in that file. 13.16 User Exit Processing The onclosetx and oncloserx string parameters provide a facility to perform user defined file related functions ("user exits") immediately after each file is closed, while the protocol is still active. Wild card filename expansionss are not allowed in this context. The oncloserx string parameter may be used to perform user commands or call a script once for each file received with a file transfer protocol. EXAMPLE: set oncloserx @crc %rname; obey "!%mv %rname /tmp" When each file is received, the crc command calculates and displays a CRC for the file. Then the !% command calls the mv program to move the file just received to the /tmp directory. The "%" in the "!%" command causes the rest of the command string to be processed for string substitutions. The onclosetx string parameter may be used to perform user commands or call a script once for each file sent with a file transfer protocol. Wild card file name expansions may not be used in onclosetx. EXAMPLE: The following causes each successfully sent file to be moved to the /done directory. set onclosetx @if !d? obey "!%mv %rname /done" SEE ALSO: rname, tname, drive, pwd string parameters, ?, d? test conditions User exits will cause protocol timeouts if their scripts take too long to finish. Since both Zcomm and the remote machine are still executing file transfer protocols when user exits are called, user (C) 1994 Omen Tech Inc Chapter 13 Protocol File Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 80 exit scripts can not reference the serial port. (C) 1994 Omen Tech Inc Chapter 13 Message Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 81 14. MESSAGE TRANSFERS 14.1 Downloading Messages ZCOMM is flexible capturing output from other systems. The trick is to make the remote send the information without too much embellishment. When downloading files without a file transfer protocol, set the timesharing system to send tabs as tab characters without expanding them to spaces. Turn off fill characters. These extra characters waste time and money and ZCOMM doesn't need them. ZCOMM's s and S term options can be used to strip control characters and escape sequences from the capture download. EXAMPLE: t -s file If the remote system responds to XOFF and XON, E term option may be enabled to allow Error Containment(TM) to reduce the number of characters garbled by "line hits". EXAMPLE: t -E7e file1 uses Error Containment to download file1 from a system using 7 bits even parity. Error Containment works best when even or odd parity is available. SEE ALSO: E, j, S, s term options 14.1.1 XON/XOFF Files of arbitrary length may be transferred if the remote supports flow control with the ASCII XOFF and XON control characters. Output from most timesharing services may be captured to a file using this method. To download a file with XON/XOFF flow control: t file1 14.1.2 DC2/DC4 (^R/^T) Some bulletin boards support file downloads by issuing a DC2 to open a capture buffer, sending the file, and terminating the capture with DC4. ZCOMM does not support this "protocol" directly. The review t and b commands can be used to strip excess characters from the circular buffer before writing the file to disk. This "protocol" can be implemented with Turbodial(TM) script commands: EXAMPLE: pat 1c "\022" "@kill; create capture.fil" pat 2c "\024" "close" (C) 1994 Omen Tech Inc Chapter 14 Message Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 82 14.1.3 Data Dump Sometimes no flow control is available. The fget * command allows ZCOMM to accept a continuous stream of data at a maximum data rate determined by the hardware and software environment. With a hard disk, excellent results have been obtained with a 4.77 mHz PC accepting graphics dumps at 9600 bps. EXAMPLE: fget file1 At slower speeds or with a fast computer, the term function j option* may be used for nonstop file capture. EXAMPLE: t -j file1 The fget command does not provide a progress display. While this allows the fastest possible data capture (38400 bps on a suitable computer), sometimes there is no handy way to monitor the flow of data. The term function I (super-image) option may be used to capture a binary file, provided CRT emulation is disabled with a display dumb command or by enabling v option. EXAMPLE: display dumb; t -Ij file1 The fax directory entry in PHONES2.T gives another example of how ZCOMM's data capture options may be used to capture binary data. 14.2 Uploading Messages It is often possible to upload files using the f command with one or more term options (such as w or p, possibly in combination with t). Message uploads are more reliable if you keyboard enab flow before connecting through Telenet. If using Tymnet, type ^R^X just before the host computer name to enable flow control with XOFF and XON. Check with your network's documentation for further details or updates to this information. It often helps to use "half duplex" ( h term option) with the computer echo disabled when uploading files to the computer. This saves the computer from wasting precious time echoing characters. Another tactic is to avoid uncorrected message transfers during peak hours. Telephone usage peaks during midday with a resulting increase in noise induced line hits. Timesharing computers and communications networks are more likely to drop characters due to buffer overloading during high traffic periods as well. (C) 1994 Omen Tech Inc Chapter 14 Message Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 83 14.2.1 Paced Some systems accept characters only at a certain rate, a slow speed for each character and possibly a pause at the end of each line. Depending on the particular system, data transfer may have to pause briefly at the end of the line,[1] or wait for a particular character to signify readiness to accept the next line. There may be an additional delay after that[2] before the remote is able to accept more data. EXAMPLE: f -p file1 uploads file1 with a wait for the linefeed echo at the end of each transmitted line. EXAMPLE: pg63; f -p file1 Sets the prompt character to decimal 63 ("?") and sends the file with a wait for "?" after each transmitted line. As with the fpute command, the remote system must be commanded to open and close the file. 14.2.2 Throttle Another method of slowing message uploads is the throttle, activated by t term option. Throttle artificially slows Zcomm's character transmission to allow more time for the receiving system to digest each character. The speed of transmission with t term option is controlled by the t numeric parameter. EXAMPLE: f -t secret.msg Really slow systems may require both throttle and pacing to send data efficiently without loss. EXAMPLE: f -tp turkey.slo 14.2.3 Uploading to IBM Mainframes Text files can be uploaded to IBM mainframes using the P (upper case) term option. When the P term option is activated, ZCOMM will wait for an XON (^Q) after sending each line. With this special option, the term function will not time out waiting for the XON, no matter how long it takes for the IBM front end to send it. If, for some reason, the front end fails to send the XON, (or if it is garbled in transmission), Ctrl-Q may be keyboarded. EXAMPLE: f -P file1 __________ 1. Controlled by the p numeric parameter 2. Controlled by the q numeric parameter (C) 1994 Omen Tech Inc Chapter 14 Message Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 84 SEE ALSO: P term option, Kermit protocol 14.2.4 Uploading Messages to Bulletin Boards The greatest file transfer challenge is to upload a file to a bulletin board message system running on a tiny microcomputer. Bulletin board message systems have a rich variety of operating sequences and timing dependencies matched only by the proliferation of incompatible dialects of Basic and Pascal. Message upload from files to bulletin boards reduces connect time and $welling of the Phone Bill. Unattended message transfer saves the user's time, especially if the board is difficult to access. The t, p and w term options and the g, p, t, and q numeric parameters allow disk files to be uploaded to such systems. The basic program cbbsck.bas may be used (perhaps with modifications) to check that a message file does not violate the restrictions of the message system being uploaded to. A C version is also available. EXAMPLE: f -pt file1 14.2.5 Uploading to CompuServe SIGS A file may be uploaded to a CompuServe SIG (Special Interest Group) editor with p term option and the g numeric parameter set to colon. When the file has been transferred, hit ENTER to send a blank line to terminate message entry. EXAMPLE: set eolstr "\r."; pp1000; pg58; f -p FILE Is useful for uploading a prepared message to Compuserve's bulletin boards. This setting for eolstr inserts a carriage return and period after each line to prevent the CompuServe software from reformatting the message. EXAMPLE: pp1000, pg58, and f -p FILE transmits FILE waiting for the prompt character ":" before sending each line after the first. An alternative is to set the SIG "FIL" option, which calls the EDIT editor. The cisupl script file referenced by phones2.t uses the SIG "FIL" editor option. Compuserve nodes often drop characters when files are uploaded at full speed in full duplex. This can be avoided by using h term option (local echo) and turning off Compuserve's echo. (C) 1994 Omen Tech Inc Chapter 14 Message Transfers Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 85 14.3 Fpute: Echoplex Uploads Text files can often be uploaded reasonably efficiently using the fpute command.* Fpute waits for an echo to each character sent to the remote. Fpute provides modest throughput without loss of data for systems with terminal ports designed for keyboard data entry. The maximum speed with fpute is limited to about 1/3 the normal character rate by echo delays. There is no error correction with fpute, but character by character handshaking prevents lost data caused by buffer overflow. If possible, TABS should be set to echo as TAB characters and not as spaces. Before the fpute command is given, the remote system must be instructed to enter data from the "terminal" to a file. After the file has been sent, the remote system must be instructed to close the file. EXAMPLE: fpute file1 (C) 1994 Omen Tech Inc Chapter 14 Flow Control Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 86 15. FLOW CONTROL All of us must sometimes tell people to "slow down" lest they overload us with information faster than we can write it down. "Wait!" is a Flow Control Signal for the English language. When the receiving ZCOMM complains about Garbled Data Subpacket or Line Status Register 01 you should suspect a flow control problem. When buffered modems, timesharing systems, networks, or computers of differing speeds are involved, a machine readable "Wait!" signal is required. Flow control is sometimes necessary to display long messages without skipping over the good parts. If you see pieces of text missing from messages but don't see the usual funny characters caused by line noise, you have a flow control problem. File transfers that use long blocks or streaming protocols may not work well unless slower parts of the system regulate the speed of transmission to prevent loss of data. With ZMODEM, SuperKermit, and other streaming protocols, inexplicable retransmissions of data blocks, often at regular intervals, indicate flow control failure. If you wish to keep things simple, the sending computer should not operate at a higher interface speed than the slowest link in the network. Otherwise precautions must be taken to prevent data loss with interactive operations and unnecessary retransmissions with streaming file transfer protocols. ZCOMM, ZCOMM, and DSZ default to software flow control with XON and XOFF characters.[1] When used with modems that require hardware flow control, the handshake command (q.v.) should be used to specify which hardware lines are to be used for flow control. Non transparent software flow control is incompatible with Emacs editors, XMODEM and YMODEM transfers. XMODEM and YMODEM require complete transparency to all 256 8 bit codes. An XMODEM transfer that always fails at the same block results from non transparent flow control. When XMODEM-1k and YMODEM-1k are used, the network must assert flow control, or handle bursts of 1040 characters without data loss. When X.25 or hardware CTS is unavailable, flow control that does not "eat" any characters may be used with XMODEM and YMODEM. When buffers fill up, an XOFF should be emitted. An XON should be __________ 1. The PCDOS flavor enables "handshake both" when selecting a port with an active Clear To Send (CTS) signal that was previously initialized to a speed greater than 2400 bps (C) 1994 Omen Tech Inc Chapter 15 Flow Control Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 87 sent when the buffer has emptied. Otherwise, the network should neither generate nor eat XON or XOFF characters. On Telenet, this is obtained by setting CCIT X3 5:1 and 12:1 in the PADs (Packet Assembler Disassembler) at both ends of the network. Packets should be forwarded when the packet is a full 128 bytes, or after a moderate delay (3:0,4:10). Set parameter 5 to 1 at both ends AFTER one is connected to the remote modem. (Sorry, these commands must be given each time you connect to a modem in the far city!) <ENTER>@<ENTER> set 5:1<ENTER> rst? 5:1<ENTER> cont<ENTER> ZMODEM and Kermit protect all 4 XOFF and XON characters, commonly used network control characters and trigger strings. ZMODEM and Kermit are compatible with many networks that do not support XMODEM family protocols, including some that claim network compatibility. For PADs that do not accept "rst?", use: <ENTER>@<ENTER> set 4:2,5:1,12:1<ENTER> cont<ENTER> For best Telenet download throughput, parameter 64 (advance ACK) should be set to 7. The parameter 0 is a dummy argument that distinguishes Telenet parameters from CCIT parameters. <ENTER>@<ENTER> set 0:0,64:7<ENTER> cont<ENTER> Sometimes Telenet flow control stops data transmission when the network buffers are not yet full. If you often see "STOPPED" flashing in the status line (DOS versions), or if you see the modem send data light pause in a ZMODEM or SuperKermit file send, poor flow control may be the culprit. Such slowdowns are typical when a network is overloaded. If this condition persists, the network should take steps to reduce the congestion. Turning OFF network flow control and activating ZMODEM's or SuperKermit's protocol flow control may increase throughput under these conditions. Instead of or in addition to XON/XOFF flow control, the sending program's ZMODEM w numeric parameter can restrict the window size to a value that does not overload the network. A zmodem pw2048 command restricts the window size (maximum number of bytes in transit) to 2048. This causes the sz command to trigger the receiver's acknowledgement every 512 bytes (one fourth the value of the ZMODEM w numeric parameter). The sender monitors these responses and suspends transmission when necessary to restrict the window to the specified size. Until a network dependent lower limit is reached, lower window sizes improve the speed of error recovery at the expense of slight increases in protocol overhead. When the window size becomes less than the number of characters sent within the network's transit time, throughput falls off rapidly. Frequent protocol acknowledgements slow down high speed pseudo full duplex modems (US Robotics HST, Telebit (C) 1994 Omen Tech Inc Chapter 15 Flow Control Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 88 TrailBlazer) and should be avoided. ZMODEM-90(TM) allows the receiver to specify the window size with the -Wn option where n is the desired window size. EXAMPLE: set adlopts W8192 requests an 8192 byte window size. Some modems and networks can be configured to flush (discard the contents of) their buffers when a break signal is received. If this is possible, error recovery with ZMODEM transfers may be speeded up by setting the ZMODEM b parameter to 1, which sends a break whenever the ZMODEM sending program gets a retransmission request. Network and Flow Control (FC) Compatibility ______________________________________________________________________ | Network | Interactive | XMODEM | WXMODEM | S-KERMIT | ZMODEM | |________________|_____________|________|_________|__________|________| |No Network | YES | YES | YES | YES | YES | |8 bit, no FC | NO | YES | YES | YES(1) | YES(1) | |Transparent FC | YES | YES | YES | YES | YES | |Non Transparent | YES | NO | NO | YES | YES | |7 bit | YES | NO | NO | YES | YES(2) | |________________|_____________|________|_________|__________|________| (1) Window size must be restricted to avoid buffer overrun if the network cannot transfer data at full speed. (2) Requires ZMODEM-90(TM) 7-bit support 15.1 Got ZRPOS Errors Got ZRPOS indicates the receiving program has detected a transmission error and has requested retransmission. In other words, ZMODEM is doing its job of detecting and correcting missing and garbled data. If this happens with error correcting modems, or more often than observed line noise would suggest, the receiver's error messages must be studied. "Line Status Register 01" messages indicate a flow control problem. "Line Status Register 02" messages suggest a receiver problem with interrupt latency. Otherwise, the sender may have a flow control problem in one of four areas: + Between the sending program and its modem. If using an interface speed higher than the transmission speed, or modem to modem error correction (MNP, LAPB, PEP, etc.), check that the modem and the sending program are configured for the same flow control methods. Omen Technology's software is faster than most other programs, and may expose flow control problems not seen with slower software. (C) 1994 Omen Tech Inc Chapter 15 Flow Control Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 89 + Between the sending modem and the network. Correcting this requires "handshake both" to allow the sending program to honor both hardware (CTS) flow control from the modem and software flow control (XON/XOFF) from the network. + Between parts of the network, or between the host computer and its terminal server(s). We have received a number of reports of problems with Cisco terminal servers. + Between the receiving modem and the receiving program. This can happen at high transmission speeds when the receiver has specified a large I/O buffer size with the B numeric parameter. Excessive interrupt latency from extended memory ramdisks or disk caches, and poorly written hard disk drivers also wreak havoc on streaming protocols but do not affect start-stop protocols (XMODEM, etc.). Problems with extended memory disk caches may cause errors at regular intervals; check the receiver's error messages. To work around these problems, give the "handshake slow" command to the receiver. (C) 1994 Omen Tech Inc Chapter 15 Running ZCOMM Version 18.18 TurboDial 2.41 Universal Line Printer Edition ZCOMM User Manual 90 16. RUNNING ZCOMM Before running ZCOMM, the keyboard Caps Lock should be turned off. ZCOMM commands and most arguments must be entered in lower case. 16.1 Running ZCOMM from DOS ZCOMM is called from DOS as ZCOMM [DPORT=n] [command ...] The following special commands may be given from the command line only. DPORT=n is an optional override to the default comm port. If another program is using the default comm port, ZCOMM may be told to use another port to prevent interference. SEE ALSO: DPORT environment variable Command may be any desired combination of ZCOMM commands. Command line arguments to ZCOMM must be in lower case except as noted. EXAMPLE: C>ZCOMM call cissig invokes ZCOMM and executes the commands in the "cissig" telephone directory entry. EXAMPLE: C>ZCOMM DPORT=2 call othersys Selects COM2 before initializing the serial port 16.1.1 DOS Environment Variables DOS environment variables are set with the DOS set command in the form SET VARIABLE=VALUE given in a batch file or at the DOS prompt. NOTE: There must not be any spaces before or after the "=" sign. If you set many environment variables, DOS will quietly forget some of them unless you tell DOS to make more room for them. You can issue the DOS "set" command by itself to check the accuracy of DOS environment variables. ZCOMM searches the DOS Environment for the following variables: CBSIZE overrides the default allocation for the circular buffer.** If memory is limited, the DOS command SET CBSIZE=3000 will leave more memory for DOS Gateway or other programs. CBSIZE may be set as high as 65500. EXAMPLE: C>SET CBSIZE=65000 (C) 1994 Omen Tech Inc Chapter 16 Running ZCOMM