%!PS-Adobe-1.0 %%Title: DC.MSS.8 %%DocumentFonts: (atend) %%Creator: SY.FDC and Scribe 5(1500) %%CreationDate: 22 April 1988 17:05 %%Pages: (atend) %%EndComments % PostScript Prelude for Scribe. /BS {/SV save def 0.0 792.0 translate .01 -.01 scale} bind def /ES {showpage SV restore} bind def /SC {setrgbcolor} bind def /FMTX matrix def /RDF {WFT SLT 0.0 eq {SSZ 0.0 0.0 SSZ neg 0.0 0.0 FMTX astore} {SSZ 0.0 SLT sin SLT cos div SSZ mul SSZ neg 0.0 0.0 FMTX astore} ifelse makefont setfont} bind def /SLT 0.0 def /SI { /SLT exch cvr def RDF} bind def /WFT /Courier findfont def /SF { /WFT exch findfont def RDF} bind def /SSZ 1000.0 def /SS { /SSZ exch 100.0 mul def RDF} bind def /AF { /WFT exch findfont def /SSZ exch 100.0 mul def RDF} bind def /MT /moveto load def /XM {currentpoint exch pop moveto} bind def /UL {gsave newpath moveto dup 2.0 div 0.0 exch rmoveto setlinewidth 0.0 rlineto stroke grestore} bind def /LH {gsave newpath moveto setlinewidth 0.0 rlineto gsave stroke grestore} bind def /LV {gsave newpath moveto setlinewidth 0.0 exch rlineto gsave stroke grestore} bind def /BX {gsave newpath moveto setlinewidth exch dup 0.0 rlineto exch 0.0 exch neg rlineto neg 0.0 rlineto closepath gsave stroke grestore} bind def /BX1 {grestore} bind def /BX2 {setlinewidth 1 setgray stroke grestore} bind def /PB {/PV save def translate 100.0 -100.0 scale pop} bind def /PE {PV restore} bind def /SH /show load def /MX {exch show 0.0 rmoveto} bind def /W {0 32 4 -1 roll widthshow} bind def /WX {0 32 5 -1 roll widthshow 0.0 rmoveto} bind def %%EndProlog %%Page: 1 1 BS 0 SI 15 /NewCenturySchlbk-Bold AF 9591 8229 MT (EVALUATING RS-232 COMMUNICATION PACKAGES)SH 10 /NewCenturySchlbk-Roman AF 22511 11545 MT (Frank da Cruz, Christine Gianone)SH 18210 13522 MT (Columbia University Center for Computing Activities)SH 25310 14627 MT (New York, N.Y. 10027)SH 8 SS 33850 16492 MT (1)SH 10 /NewCenturySchlbk-Italic AF 26905 16837 MT (December 1987)SH /NewCenturySchlbk-Roman SF 8312 22647 MT (In most places where there are computers, nobody) 153 W( questions the need for data communication.)154 W 7200 23933 MT (The question is more likely to be how best to do) 66 W( it. In theory networks can do the job, typically PC)65 W 7200 25219 MT (LANs, perhaps interconnected by gateways to mainframe networks. But this) 1 W( arrangement presumes)2 W 7200 26505 MT (that equipment was) 197 W( purchased according to some consistent plan, with networking in mind. In)196 W 7200 27791 MT (practice, most organizations have a patchwork) 321 W( history of computer acquisition, resulting in a)322 W 7200 29077 MT (hodgepodge of PCs, minis, and mainframes for which compatible networking) 350 W( options are not)349 W 7200 30363 MT (available or affordable. Often, the only) 24 W( device these systems share in common is the humble RS-232)25 W 7200 31649 MT (asynchronous communication port. Even when comprehensive networking solutions) 1 W( exist, the cost of)SH 7200 32935 MT (attaching hundreds or thousands of PCs, at $500-$1500 per) 48 W( PC, to a Token Ring or Ethernet can be)49 W 7200 34221 MT (daunting. And) 468 W( those who want to dial in from home, or) 95 W( dial out to external services, must still be)94 W 7200 35507 MT (accommodated.)SH 8312 37822 MT (For these reasons, many organizations choose to connect PCs to their) 158 W( networks through use of)159 W 7200 39108 MT (RS-232 communication) 156 W( packages like Crosstalk, Blast, Relay Gold, Smartcomm, VTERM, Kermit,)155 W 7200 40394 MT (PC-Talk, ProComm, Red) SH( Ryder, HyperACCESS, or ASCII Pro. Hundreds of these products permeate)1 W 7200 41680 MT (the marketplace, and, if selected intelligently, they can fill) 151 W( the gaps in an organization's network)150 W 7200 42966 MT (effectively and inexpensively.) 251 W( The) 782 W( cost for PC-resident data communication programs typically)252 W 7200 44252 MT (ranges from $20 to $500 per PC, with) 85 W( some exceptions \050some are free, others cost more\051. And that)84 W 7200 45538 MT (makes these programs more affordable than most PC network connections.)SH 8312 47853 MT (Evaluating RS-232 communication packages can be a complicated) 200 W( process. The Cost must be)201 W 7200 49139 MT (weighed carefully against the needs of your organization. Reviews and surveys of) 129 W( communication)128 W 7200 50425 MT (packages appear frequently in the popular computer publications,) 102 W( and they can help. But surveys)103 W 7200 51711 MT (consisting mostly of charts in which, say, 100 popular software packages are) 64 W( compared on the basis)63 W 7200 52997 MT (of, say, 20 arbitrarily chosen) 37 W( features, are necessarily superficial. And many articles concentrate on)38 W 7200 54283 MT (frills and conveniences while giving short) 73 W( shrift to central issues like connection establishment and)72 W 7200 55569 MT (maintenance, terminal emulation, and file transfer. In this) 272 W( article we attempt to present the)273 W 7200 56855 MT (features of RS-232 communication packages in a way that will help you) 203 W( to assess their relative)202 W 7200 58141 MT (importance for yourself or your organization.)SH 10800 50 7200 69428 UL 6 SS 8090 70767 MT (1)SH 8 SS 8424 71076 MT (This is the original manuscript of the article that was published in Data Communications Magazine) 135 W( as "Shopping for)134 W 7200 72000 MT (Software That Lets PCs Chat With Mainframes", December 1987, pp.155-170.)SH ES %%Page: 2 2 BS 0 SI 12 /NewCenturySchlbk-Roman AF 30266 4423 MT (2)SH /NewCenturySchlbk-Bold SF 7200 8023 MT (WHAT IS AN RS-232 COMMUNICATION PACKAGE?)SH 10 /NewCenturySchlbk-Roman AF 8312 9995 MT (RS-232 communication packages are software programs) 90 W( that run on personal computers like the)91 W 7200 11281 MT (IBM PC, IBM clone,) 396 W( Apple II, or Macintosh, and communicate asynchronously with remote)395 W 7200 12567 MT (computers through RS-232-C serial ports, either directly or through modems. This) 169 W( distinguishes)170 W 7200 13853 MT (them from specialized) 133 W( products that emulate synchronous terminals in IBM mainframe, Wang, or)132 W 7200 15139 MT (similar environments, for which special adapters \050like an Irma board\051 and connections \050like coax\051) 10 W( are)11 W 7200 16425 MT (required, and which won't be discussed here.)SH 8312 18740 MT (There are two fundamental aspects) 389 W( to any PC communication package. One is terminal)388 W 7200 20026 MT (emulation, which allows you to connect your PC to) 117 W( a mini or mainframe as a terminal in order to)118 W 7200 21312 MT (conduct a timesharing session or to access an application on a central, shared) 64 W( system. The other is)63 W 7200 22598 MT (data transfer, which lets you exchange information between your PC and a mini or mainframe \050or)108 W 7200 23884 MT (another PC\051. For terminal emulation, PC-resident software is the only) 62 W( requirement. For error-free)61 W 7200 25170 MT (data transfer, however, a companion) 240 W( program is required on the other computer. The cost for)241 W 7200 26456 MT (commercial mini- or mainframe-based communication programs runs much higher than PC versions,)8 W 7200 27742 MT (typically ranging from $1000 to $100,000 \050again, with exceptions\051.)SH 12 /NewCenturySchlbk-Bold AF 7200 30937 MT (USER INTERFACE)SH 10 /NewCenturySchlbk-Roman AF 8312 32909 MT (The most immediately striking aspect of) 274 W( any program is the "user interface": the prompts,)275 W 7200 34195 MT (commands, menus, function keys, etc, with which you) 37 W( make your wishes known to the program, and)36 W 7200 35481 MT (the displays with which it makes the results known to you.)SH 8312 37796 MT (There are many styles of user interface: command line, interactive prompt) 72 W( and command, menus)73 W 7200 39082 MT (and arrow keys, mice and windows. The fundamental tradeoff is ease of) 26 W( learning versus ease of use.)25 W 7200 40368 MT (Ease of learning is important if many people will be using the package infrequently) 136 W( or if there is)137 W 7200 41654 MT (rapid personnel turnover, so that relatively little time need be) 49 W( "wasted" in learning and training. A)48 W 7200 42940 MT (user interface designed for ease of learning presents you with all) 38 W( the choices in menus. The penalty)39 W 7200 44226 MT (is that you are always presented with menus for everything, which slows) 70 W( you down needlessly once)69 W 7200 45512 MT (you have become expert.) 108 W( At) 495 W( the other extreme are programs that favor the expert, providing only)109 W 7200 46798 MT (terse and cryptic commands, sometimes with no) 65 W( way for a novice to get help at all, short of reading)64 W 7200 48084 MT (the manual. A compromise, "menu on demand", lets the expert issue rapid,) 71 W( terse commands, while)72 W 7200 49370 MT (still allowing the novice to see a menu at any point by entering a special help key.)SH 8312 51685 MT (There is an oft-neglected aspect of the user interface that falls into the "ease) 43 W( of use" category: can)42 W 7200 52971 MT (the package be used by people with disabilities like motor impairment, blindess, or) 36 W( deafness? If you)37 W 7200 54257 MT (can depress only a single key at) 384 W( a time, how can you enter complicated Ctrl-Alt-Shift key)383 W 7200 55543 MT (combinations? If) 456 W( your PC is) 89 W( connected to an ASCII-oriented speaking device or a Braille terminal,)90 W 7200 56829 MT (how can you decipher multicolor animated graphics screens? If you can't) 139 W( hear, how do you know)138 W 7200 58115 MT (when the package is beeping) 44 W( or whistling at you to signal some important event? Often, the fancier)45 W 7200 59401 MT (the user interface, the less it lends itself to use by the disabled.)SH 8312 61716 MT (Another item of minor importance, but whose absence can be a nuisance, is) 99 W( the ability to access)98 W 7200 63002 MT (system functions) 62 W( without actually leaving the program. If you want to change directories, list files,)63 W 7200 64288 MT (display a file,) 159 W( or delete a file, you should not have to exit the communication program, and then)158 W 7200 65574 MT (restart it afterwards. This) SH( can be time consuming, especially on floppy-disk-based systems, and even)1 W 7200 66860 MT (more so when settings -- or the connection itself -- must be reestablished.)SH 8312 69175 MT (Commercial communication packages) 26 W( tend to place great emphasis on the appearance and style of)25 W 7200 70461 MT (the user interface, primarily for marketing reasons. But for most people, the user) 82 W( interface should)83 W 7200 71747 MT (not be a key) 60 W( factor in evaluating a product. It only lets you specify the real work to be done, and it)59 W ES %%Page: 3 3 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30322 4286 MT (3)SH 7200 7886 MT (should take up a relatively small proportion of the total time) 358 W( you spend with the package.)359 W 7200 9172 MT (Ultimately, it is much more) 37 W( important to know whether the product can perform the required tasks,)36 W 7200 10458 MT (and how well.)SH 8312 12773 MT (CONNECTION ESTABLISHMENT AND MAINTENANCE)SH 8312 15088 MT (Perhaps the most important aspect of any communication package its set of mechanisms for)243 W 7200 16374 MT (establishing a connection, matching) 88 W( communication parameters to the communication medium and)87 W 7200 17660 MT (the system on the other end, monitoring the connection) 379 W( once established, and breaking the)380 W 7200 18946 MT (connection.)SH 12 /NewCenturySchlbk-Bold AF 7200 22141 MT (COMMUNICATION PARAMETER SETTINGS)SH 10 /NewCenturySchlbk-Roman AF 8312 24113 MT (Any communication program should) 138 W( allow you control over communication parameters like bits)137 W 7200 25399 MT (per second, parity, duplex, flow control, and the number of data, start and stop bits per) 106 W( character.)107 W 7200 26685 MT (Each of these parameters is important, and the lack of any particular option) 68 W( may prevent you from)67 W 7200 27971 MT (communicating satisfactorily with another computer. Before you select) 120 W( a communication package,)121 W 7200 29257 MT (you should be sure it supports all the communication parameters and settings required by all the)125 W 7200 30543 MT (computers you need to communicate with.)SH 8312 32858 MT (For example, most DEC minis and) 194 W( mainframes employ XON/XOFF full duplex flow control to)195 W 7200 34144 MT (prevent data) 96 W( overruns; if your PC communication package does not support XON/XOFF, then data)95 W 7200 35430 MT (transferred between it and) 157 W( the DEC system could be lost. IBM mainframe ASCII TTY linemode)158 W 7200 36716 MT (connections, on) 17 W( the other hand, are half duplex and exercise a line turnaround handshake discipline:)16 W 7200 38002 MT (if you transmit to the IBM mainframe before it has given you permission) 204 W( \050by sending a special)205 W 7200 39288 MT ("handshake" character, such as Control-Q\051, it will not accept) 5 W( your data. Certain popular mainframes)4 W 7200 40574 MT (and minis, as well as public data networks like Telenet) 62 W( and Tymnet, use even, odd, or mark parity,)63 W 7200 41860 MT (and will not recognize your characters unless the right parity is) 15 W( applied. And if your package cannot)14 W 7200 43146 MT (distinguish parity bits from data bits, the wrong characters) 3 W( will be displayed on your screen. Table 1)4 W 7200 44432 MT (shows typical RS-232 communication parameters for various systems.)SH /Courier SF 7200 46087 MT (______________________________________________________________________________)SH 7200 48149 MT (Computer Front) 4800 W( End) SH( Duplex Flow) 1200 W( Control) SH( Parity) 2400 W( Terminal)1800 W 7200 49180 MT (--------------- ---------) 600 W( ------ ------------) 1200 W( ------) 2400 W( --------)1800 W 7200 50211 MT (Data General MV) SH( None) 1200 W( Full) 4200 W( XON/XOFF) 3000 W( None) 4200 W( Dasher)3000 W 7200 51242 MT (DEC PDP-11) SH( None Full) 4200 W( XON/XOFF) 3000 W( None) 4200 W( VT52,VT100)3000 W 7200 52273 MT (DEC VAX) SH( None) 6000 W( Full) 4200 W( XON/XOFF) 3000 W( None) 4200 W( VT52,VT100)3000 W 7200 53304 MT (DECSYSTEM-20 PDP-11) 2400 W( Full) 3600 W( XON/XOFF) 3000 W( Even) 4200 W( VT52,VT100)3000 W 7200 54335 MT (Honeywell DPS8) SH( DN335) 1200 W( Half) 4200 W( XON) 1800 W( Handshake) SH( None) 2400 W( VIP7300,7800)3000 W 7200 55366 MT (HP-1000 None) 6000 W( Full) 4200 W( ENQ/ACK) 3000 W( None) 4800 W( HP262x)3000 W 7200 56397 MT (HP-3000 None) 6000 W( Half) 4200 W( XON) 1800 W( Handshake) SH( None) 2400 W( HP262x)3000 W 7200 57428 MT (IBM 370 Series) SH( 3705) 1200 W( TTY) SH( Half) 2400 W( XON) 1800 W( Handshake) SH( Mark) 2400 W( TTY)3000 W 7200 58459 MT (IBM 370 Series) SH( 7171) 1200 W( P.E.) SH( Full) 1800 W( XON/XOFF) 3000 W( Even) 4200 W( Various*)3000 W 7200 59490 MT (Prime minis) SH( None) 3600 W( Full) 4200 W( XON/XOFF) 3000 W( Mark) 4200 W( TTY,) 3000 W( PS300)SH 11400 61552 MT (P.E. = 3270 Protocol Emulator, TTY = ASCII Linemode Connection.)SH 9000 62583 MT (*Delivered with support for 13 popular terminals, configurable for more.)SH 18000 64645 MT (Table 1: Typical Communication Parameters)SH 7200 65676 MT (______________________________________________________________________________)SH /NewCenturySchlbk-Roman SF 8312 67991 MT (Some communication packages support only a limited range of transmission speeds.) 18 W( For) 312 W( instance,)17 W 7200 69277 MT (they may be designed to work only for dialup connections) 173 W( at speeds up to 1200 or 2400 bits per)174 W 7200 70563 MT (second \050bps\051. If you should ever need to connect two) 1 W( computers directly, you should not be artificially)SH 7200 71849 MT (limited to such low speeds. Even if dialups) 46 W( are the only connections you will ever make, you should)47 W ES %%Page: 4 4 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30322 4286 MT (4)SH 7200 7886 MT (be aware that new modems are appearing on the market that operate at speeds in excess of 9600 bps)10 W 7200 9172 MT (on ordinary voice-grade phone connections. For these) 95 W( reasons, any communication package should)96 W 7200 10458 MT (be able to operate at 9600 bps or higher. 9600) 116 W( bps is the highest speed supported by most minis,)115 W 7200 11744 MT (mainframes, and front ends today \050some support 19,200 bps\051. Micros like the) 98 W( IBM PC/AT and the)99 W 7200 13030 MT (Macintosh, however, can drive their RS-232 ports to speeds of 38,400 bps or higher,) 118 W( and two such)117 W 7200 14316 MT (PCs connected back to back can actually transfer) 6 W( data at these speeds. But the higher the speed, the)7 W 7200 15602 MT (more important it is to have an effective) 74 W( flow control mechanism supported by the systems on each)73 W 7200 16888 MT (end of the connection.)SH 12 /NewCenturySchlbk-Bold AF 7200 20083 MT (MODEM CONTROL)SH 10 /NewCenturySchlbk-Roman AF 8312 22055 MT (Unless your computers are hardwired together with dedicated) 555 W( lines, you probably use)556 W 7200 23341 MT (asynchronous dialup modems to establish connections) 148 W( with other systems. Modems communicate)147 W 7200 24627 MT (special control) 186 W( information with the PC via RS-232 modem signals like DTR, DSR, and CD \050see)187 W 7200 25913 MT (Table 2\051.) 110 W( Most) 497 W( communication packages can control and monitor these signals to detect when the)109 W 7200 27199 MT (connection is broken, or to) 113 W( break the connection and hang up the phone. If you use your package)114 W 7200 28485 MT (interactively, modem control is largely superfluous because you will notice when) 123 W( the connection is)122 W 7200 29771 MT (broken, or you will hang up the phone yourself when you are done with it.) 289 W( For) 857 W( unattended)290 W 7200 31057 MT (operation, on the other hand, modem control is important in) 61 W( avoiding the excessive phone bills that)60 W 7200 32343 MT (could result when the communication) 34 W( package does not notice that connections break and leaves the)35 W 7200 33629 MT (phone off hook all night.)SH /Courier SF 7200 35284 MT (______________________________________________________________________________)SH 8400 37346 MT (FG Frame) 1200 W( Ground)SH 8400 38377 MT (TD Transmitted) 1200 W( Data, from PC to modem)SH 8400 39408 MT (RD Received) 1200 W( Data, from modem to PC)SH 8400 40439 MT (RTS Request) 600 W( To Send, from PC to modem, used with half duplex modems)SH 8400 41470 MT (CTS Clear) 600 W( To Send, from modem to PC, ditto)SH 8400 42501 MT (SG Signal) 1200 W( Ground)SH 8400 43532 MT (DSR Data) 600 W( Set Ready, indicates modem is in data transmission mode)SH 8400 44563 MT (CD Carrier) 1200 W( Detect, indicates that modem is connected to other modem)SH 8400 45594 MT (DTR Data) 600 W( Terminal Ready, tells modem that PC is ready to communicate)SH 8400 46625 MT (RI Ring) 1200 W( Indicator, tells PC that the phone is ringing)SH 17400 48687 MT (Table 2: RS-232-C Asynchronous Modem Signals)SH 7200 49718 MT (______________________________________________________________________________)SH /NewCenturySchlbk-Roman SF 8312 52033 MT (Modems may be) 67 W( either external or internal. External modems are controlled in a consistent way)66 W 7200 53319 MT (according to RS-232-C, and rarely pose a problem to communications software. Although) 75 W( generally)76 W 7200 54605 MT (more expensive, external modems are interchangeable between different computers.) 348 W( Internal)972 W 7200 55891 MT (modems, on) 225 W( the other hand, are built specifically for certain computers, and sometimes require)226 W 7200 57177 MT (special handling by the software. A particular) 316 W( software package will not necessarily operate)315 W 7200 58463 MT (correctly with a specific internal modem \050check with) 198 W( the software vendor!\051. And, of course, two)199 W 7200 59749 MT (modems that are to communicate must support the same modulation techniques and speeds.)SH 8312 62064 MT (Some packages are designed to) 171 W( be used only with modems, and don't work properly when two)170 W 7200 63350 MT (computers are connected directly by) 438 W( a cable, unless certain modem signals are "faked" by)439 W 7200 64636 MT (cross-connections or jumper wires within) 30 W( the cable connectors. Such a fakeout cable is called a "null)29 W 7200 65922 MT (modem" or "modem eliminator" \050Figure 1\051, readily available from any computer supply house,) 115 W( and)116 W 7200 67208 MT (also available as an adapter that you can connect to your modem cable. But different systems) 67 W( may)66 W 7200 68494 MT (require different signals connected in different ways,) 160 W( so be prepared for some experimentation \050a)161 W 7200 69780 MT (breakout box will) 52 W( help\051. Your communication software package can relieve you of the tinkering if it)51 W 7200 71066 MT (can be configured to ignore modem signals altogether when you connect two computers directly.)SH ES %%Page: 5 5 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30322 4286 MT (5)SH /Courier SF 7200 7824 MT (______________________________________________________________________________)SH 15600 9886 MT (True Null Modem) SH( Minimal) 10200 W( Null Modem)SH 17400 10917 MT (\0508 wires\051) SH( \0504) 14400 W( wires\051)SH 15000 12979 MT (FG ----------- FG) SH( FG) 9600 W( ----------- FG)SH 15000 15041 MT (TD ----\134 /---- TD) SH( TD) 9600 W( ----\134 /---- TD)SH 19800 16072 MT (X X)19200 W 15000 17103 MT (RD ----/ \134---- RD) SH( RD) 9600 W( ----/ \134---- RD)SH 14400 19165 MT (RTS ----\134 /---- RTS) SH( RTS) 8400 W( -+) SH( +-) 3600 W( RTS)SH 19800 20196 MT (X |) 16800 W( |)3600 W 14400 21227 MT (CTS ----/ \134---- CTS) SH( CTS) 8400 W( -+) SH( +-) 3600 W( CTS)SH 14400 23289 MT (DSR -+) SH( +-) 3600 W( DSR) SH( DSR) 8400 W( -+) SH( +-) 3600 W( DSR)SH 17400 24320 MT (| |) 3600 W( |) 14400 W( |)3600 W 15000 25351 MT (CD -+--\134 /--+- CD) SH( CD) 9000 W( -+) 600 W( +-) 3600 W( CD)SH 19800 26382 MT (X |) 16800 W( |)3600 W 14400 27413 MT (DTR -+--/ \134--+- DTR) SH( DTR) 8400 W( -+) SH( +-) 3600 W( DTR)SH 17400 28444 MT (| |) 3600 W( |) 14400 W( |)3600 W 15000 29475 MT (RI -+) SH( +-) 3600 W( RI) SH( RI) 9600 W( -+) SH( +-) 3600 W( RI)SH 15000 31537 MT (SG ----------- SG) SH( SG) 9600 W( ----------- SG)SH 24000 33599 MT (Figure 1: Null Modems)SH 7200 34630 MT (______________________________________________________________________________)SH 12 /NewCenturySchlbk-Bold AF 7200 37825 MT (DIALER CONTROL)SH 10 /NewCenturySchlbk-Roman AF 8312 39797 MT (Many PCs are connected to) 184 W( the outside world only by telephone. "Smart modems", like those)185 W 7200 41083 MT (manufactured by) 142 W( Hayes, are able to dial the phone for you if they receive commands in the right)141 W 7200 42369 MT (format from the PC. This means) 148 W( that your communication package must understand the dialing)149 W 7200 43655 MT (language of the modem. Although the Hayes "AT" language has become) 46 W( a de-facto standard, not all)45 W 7200 44941 MT (autodial modems conform to it \050prominent counterexamples) 171 W( include DEC DF-series modems, and)172 W 7200 46227 MT (selected models from Racal-Vadic, US Robotics, and Ventel\051. Be sure your modem's dialing) 13 W( language)12 W 7200 47513 MT (is supported by your communication package.)SH 8312 49828 MT (Dialing software simplifies connection) 145 W( establishment, hiding the details of the dialing language)146 W 7200 51114 MT (from you. You tell the program what number to call, and let the software handle the details.) 47 W( Some)370 W 7200 52400 MT (packages go a step further and include a phone directory so that) 92 W( you don't even have to remember)93 W 7200 53686 MT (phone numbers, just the names of the places you want to call.)SH 8312 56001 MT (Dialer control and phone directories) 48 W( fall into the frill category for most users. It's not much more)47 W 7200 57287 MT (trouble to type "ATDT7654321" than it is to type "dial fred". For unattended operation,) 130 W( however,)131 W 7200 58573 MT (automatic dialing is) 66 W( an essential feature. If a dial command is lacking, then the same function can)65 W 7200 59859 MT (be performed by a script, described below.)SH 12 /NewCenturySchlbk-Bold AF 7200 63054 MT (DEBUGGING COMMUNICATION PARAMETERS)SH 10 /NewCenturySchlbk-Roman AF 8312 65026 MT (Often, we can only guess what the) 158 W( right combination of speed, stop bits, parity bits, data bits,)159 W 7200 66312 MT (duplex, and flow control might be for a particular connection. What if we guess wrong?) 54 W( What) 385 W( tools)53 W 7200 67598 MT (does the communication package give us to pin down the offending parameters?)SH 8312 69913 MT (Obviously, if the package) 55 W( lets us set these parameters independently, we can vary them until the)56 W 7200 71199 MT (connection works, but the combinations could be endless. Your communication package) 240 W( should)239 W ES %%Page: 6 6 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30322 4286 MT (6)SH 7200 7886 MT (include debugging tools to reduce the guesswork, like) 388 W( special display or logging of received)389 W 7200 9172 MT (characters, preferably including their 8-bit numeric values. If examination of the log reveals) 56 W( a byte)55 W 7200 10458 MT (with a numeric value of 193 \050= 11000001 binary\051) 40 W( where you would expect an ASCII "A" \050= 01000001)41 W 7200 11744 MT (binary\051, then you probably should be looking for 7 data bits with odd or) 87 W( mark parity rather than 8)86 W 7200 13030 MT (data bits with no parity.)SH 8312 15345 MT (A good communication) 72 W( package will also include a troubleshooting guide, like the one in Table 3,)73 W 7200 16631 MT (in which you can look up symptoms and find the corresponding diagnoses and prescriptions.)SH /Courier SF 7200 18286 MT (______________________________________________________________________________)SH 9600 20348 MT (SYMPTOM POSSIBLE) 15600 W( CAUSE) SH( CURE)3000 W 9600 22410 MT (Blank, dark screen.) SH( PC) 8400 W( turned off.) SH( Turn) 3000 W( on PC.)SH 9600 24472 MT (Total garbage on screen.) SH( Wrong) 5400 W( speed.) SH( Try) 4200 W( another speed.)SH 9600 26534 MT (Spurts of garbage on screen.) SH( Noise.) 3000 W( Hang) 7800 W( up and redial.)SH 9600 28596 MT (Uniform mixture of good and) SH( Parity.) 3600 W( Select) 7200 W( a different)SH 9600 29627 MT (bad characters on screen.) SH( parity.)16800 W 9600 31689 MT (Typed characters appear twice.) SH( Duplex.) 1800 W( Select) 7200 W( full duplex.)SH 9600 33751 MT (Typed characters don't appear.) SH( Duplex.) 1800 W( Select) 7200 W( half duplex.)SH 9600 35813 MT (Random gaps in screen text.) SH( No) 3600 W( flow control.) SH( Use) 1800 W( flow control,)SH 42000 36844 MT (or a slower speed.)SH 15000 38906 MT (Table 3: Sample Entries from a Troubleshooting Guide)SH 7200 39937 MT (______________________________________________________________________________)SH 12 /NewCenturySchlbk-Bold AF 7200 43132 MT (SAVING COMMUNICATION PARAMETERS)SH 10 /NewCenturySchlbk-Roman AF 8312 45104 MT (Once you have discovered the proper settings for communicating with) 98 W( a particular machine, you)97 W 7200 46390 MT (will want to have some way of saving them. To alleviate the tedium of setting five) 321 W( or ten)322 W 7200 47676 MT (communication parameters each time you connect to a given system, the package should allow)243 W 7200 48962 MT (settings to be collected together into "configurations" which may be saved under mnemonic names.)SH 8312 51277 MT (Some packages are delivered with a set of configurations for popular dialup services like)377 W 7200 52563 MT (Dow-Jones, Compuserve, MCI Mail,) 90 W( The Source, etc. These built-in configurations shield you from)89 W 7200 53849 MT (having to know anything about) 133 W( data communication parameters. But when you must establish a)134 W 7200 55135 MT (connection to a system the package doesn't know about -- like from) 293 W( your PC at home to the)292 W 7200 56421 MT (mainframe at work -- you should) 161 W( be able to manipulate the communication settings yourself and)162 W 7200 57707 MT (save them for future use. Once you've determined the) 52 W( appropriate settings for, say, your company's)51 W 7200 58993 MT (DEC VAX, IBM 3090, Harris) 7 W( 800, plus your local Telenet PAD, you only need mention the associated)8 W 7200 60279 MT (configuration name to set all the corresponding parameters at once.)SH 12 /NewCenturySchlbk-Bold AF 7200 63474 MT (SCRIPT LANGUAGE, UNATTENDED OPERATION)SH 10 /NewCenturySchlbk-Roman AF 8312 65446 MT (Just as a communication package may remember your communication settings or) 46 W( phone numbers)45 W 7200 66732 MT (for you, it can also allow repetitive interactive tasks, like login sequences, to be automated by) 22 W( means)23 W 7200 68018 MT (of "scripts". Scripts are little "programs" that look for specific outputs) 9 W( from the remote computer and)8 W 7200 69304 MT (provide appropriate responses. When the package, or the) 108 W( underlying system, allows a script to be)109 W 7200 70590 MT (executed at a predesignated time, then it is possible to) 162 W( carry on a canned dialog with no human)161 W 7200 71876 MT (operator present. For instance, you might program your) 9 W( PC to "wake up" at midnight, set the proper)10 W ES %%Page: 7 7 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30322 4286 MT (7)SH 7200 7886 MT (communication parameters and dial up your office) 63 W( mini, log in, deposit the day's transactions, fetch)62 W 7200 9172 MT (and print) 25 W( the day's mail, log out, and hang up. Script languages vary from the primitive and cryptic)26 W 7200 10458 MT (to full-blown programming languages complete with variables and conditional branching. Figure 2)82 W 7200 11744 MT (shows a simple script for dialing a Hayes modem to establish a) 3 W( connection to a Unix system and then)4 W 7200 13030 MT (logging in. It illustrates how a script can be used in place of built-in dialer control.)SH /Courier SF 7200 14685 MT (______________________________________________________________________________)SH 9600 16747 MT (set speed 1200) SH( Bits) 10800 W( per second)SH 9600 17778 MT (set parity none) SH( Parity)10200 W 9600 18809 MT (output AT\13413) SH( Wake) 12000 W( up the modem)SH 9600 19840 MT (input OK) SH( Look) 14400 W( for its "OK")SH 9600 20871 MT (output ATD7654321\13413) SH( Give) 7200 W( modem's dialing command)SH 9600 21902 MT (input CONNECT) SH( Look) 11400 W( for desired response)SH 9600 22933 MT (pause 1) SH( Wait) 15000 W( a second)SH 9600 23964 MT (output \13413) SH( Send) 13200 W( a carriage return)SH 9600 24995 MT (input login:) SH( Look) 12000 W( for login prompt)SH 9600 26026 MT (output chris\13413) SH( Send) 10200 W( user ID, followed by carriage return)SH 9600 27057 MT (input Password:) SH( Look) 10200 W( for password prompt)SH 9600 28088 MT (echo Connecting to Unix System...)SH 9600 29119 MT (echo Please type your password:)SH 9600 30150 MT (connect Let) 15000 W( the user take over)SH 20400 32212 MT (Figure 2: Script Language Example)SH 7200 34274 MT (______________________________________________________________________________)SH /NewCenturySchlbk-Roman SF 8312 36589 MT (The "output" commands send the indicated text strings to the) 146 W( Unix system \050"\13413" is a code for)145 W 7200 37875 MT (carriage return\051, and the "input" commands search the incoming data for the indicated) 109 W( strings. If)110 W 7200 39161 MT (any of the input commands fail, the script is automatically) 21 W( terminated. This is an important feature)20 W 7200 40447 MT (of a) 17 W( script language. Suppose, for instance, you have a nightly script which sends your day's work to)18 W 7200 41733 MT (a mainframe and then deletes it from the PC's hard disk.) 188 W( If) 653 W( the data could not be successfully)187 W 7200 43019 MT (transmitted, then you certainly don't want the script to forge ahead stubbornly and destroy all) 52 W( your)53 W 7200 44305 MT (work.)SH 8312 46620 MT (Scripts are essential for unattended) 95 W( operation, and they are also useful in setting up procedures)94 W 7200 47906 MT (for relatively unskilled operators such as data) 303 W( entry clerks. For the typical interactive user,)304 W 7200 49192 MT (however, scripts are a minor convenience rather than a necessity.)SH 12 /NewCenturySchlbk-Bold AF 7200 52387 MT (TERMINAL EMULATION)SH 10 /NewCenturySchlbk-Roman AF 8312 54359 MT (The PC has increasingly replaced the terminal in many organizations. In addition to) 146 W( its other)145 W 7200 55645 MT (capabilities, a properly programmed PC can also act like \050"emulate"\051 a terminal, so that you can) 41 W( use)42 W 7200 56931 MT (it to conduct a dialog with a remote computer. Your keystrokes are) 4 W( sent out the communication port,)3 W 7200 58217 MT (and characters that arrive at the port are displayed on the screen. On half duplex, local) 225 W( echo)226 W 7200 59503 MT (connections, your keystrokes) 57 W( are also displayed on the screen. On full duplex connections, terminal)56 W 7200 60789 MT (emulation can be a) 54 W( tricky business because characters may arrive at the port at the same time that)55 W 7200 62075 MT (you are typing; communication programs vary in their ability to) 313 W( handle both events at once,)312 W 7200 63361 MT (especially at higher speeds.)SH 8312 65676 MT (It should be) 238 W( stressed that terminal emulation does NOT provide any sort of automatic error)239 W 7200 66962 MT (control, any more than a real terminal would. Bare characters are sent back and forth with)275 W 7200 68248 MT (absolutely no error recovery mechanism. If a package) 30 W( claims to supply error-checking data transfer,)31 W 7200 69534 MT (you should understand that this claim applies to) 117 W( its file transfer functions and not to its terminal)116 W 7200 70820 MT (emulator. A) 680 W( noisy) 201 W( telephone line would probably leave garbage on your screen during terminal)202 W ES %%Page: 8 8 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30322 4286 MT (8)SH 7200 7886 MT (emulation even though files could be transferred successfully.)SH 8312 10201 MT (In addition) 18 W( to sending and displaying characters, a terminal emulator also attempts to imitate the)17 W 7200 11487 MT (repertoire of special effects of some particular) 104 W( real ASCII video display terminal, such as the DEC)105 W 7200 12773 MT (VT100 series, the IBM 3101, the Televideo 920, the ADM3A, etc.) 176 W( This) 628 W( means that the program)175 W 7200 14059 MT (responds to screen control sequences sent by the host just as the real terminal) 45 W( would. For example,)46 W 7200 15345 MT (the ASCII sequence "ESC [ 5 ; 7 H" sent to a DEC VT100 positions the cursor at) 97 W( row 5, column 7;)96 W 7200 16631 MT ("ESC [ 0 J" clears the screen, and so a PC programmed to) 88 W( emulate a VT100 would understand the)89 W 7200 17917 MT (same sequences and) 15 W( perform the same actions. When emulating a terminal, the package should also)14 W 7200 19203 MT (provide some mapping between the terminal's function) 49 W( keys and the PC's, so that they transmit the)50 W 7200 20489 MT (same sequences. If the VT100 PF1 key sends "ESC O P", then the IBM) 199 W( PC's F1 key might be)198 W 7200 21775 MT (programmed to send the same sequence.)SH 8312 24090 MT (Today's video display terminals possess a formidable array of features) 116 W( for tabbing, highlighting,)117 W 7200 25376 MT (partitioning the screen, erasing and inserting) 30 W( text, positioning the cursor, drawing figures, changing)29 W 7200 26662 MT (colors, switching character sets, activating) 165 W( printers, etc, all controlled by host-transmitted escape)166 W 7200 27948 MT (sequences. A) 426 W( package may emulate such a terminal) 74 W( completely, or it may emulate a "subset" of its)73 W 7200 29234 MT (functions. Some) 350 W( terminals have features that cannot be emulated by certain PCs. For) 36 W( example, the)37 W 7200 30520 MT (DEC VT100 allows switching between 80- and 132-column) 84 W( modes, but an IBM PC can only display)83 W 7200 31806 MT (80 columns. To) 85 W( get 132 columns on a PC, a special board may be needed. Another example is the)86 W 7200 33092 MT (VT100's "smooth scrolling" feature, which allows a file to glide slowly) 113 W( along the screen -- the DEC)112 W 7200 34378 MT (Rainbow can do this, while the IBM PC cannot.)SH 8312 36693 MT (Emulation should be complete enough to allow you to access) 173 W( any desired software on the host)174 W 7200 37979 MT (which expects to control the appearance of the) 27 W( terminal's screen; full-screen text editors like EDT on)26 W 7200 39265 MT (VAX/VMS or GNU EMACS on a UNIX) 266 W( system are good tests. Another is IBM 3270 protocol)267 W 7200 40551 MT (emulation as performed by the IBM 7171 or other protocol converter. If) 74 W( emulation is not complete,)73 W 7200 41837 MT (you will see fragmented and jumbled screens, characters or lines overwriting each other, mysterious)38 W 7200 43123 MT (gaps and transpositions.)SH 8312 45438 MT (Terminal emulation is a very important) 186 W( function for people who engage in a lot of interactive)185 W 7200 46724 MT (dialog with a remote system, especially when screen control is) 64 W( involved. In this case, it is essential)65 W 7200 48010 MT (that the communication package be capable) 330 W( of emulating a terminal that the remote system)329 W 7200 49296 MT (supports, such as a DEC VT100) 8 W( or -200 series with a DEC VAX/VMS system, a Data General Dasher)9 W 7200 50582 MT (with DG minis, etc. \050see Table 1\051. Terminal emulation is less important for brief or) 65 W( non-interactive)64 W 7200 51868 MT (encounters, such as occasional sessions primarily for file transfer.)SH 12 /NewCenturySchlbk-Bold AF 7200 55063 MT (KEY REDEFINITION AND CHARACTER TRANSLATION)SH 10 /NewCenturySchlbk-Roman AF 8312 57035 MT (Since your PC keyboard may have a) 10 W( different layout than the emulated terminal, you may want to)11 W 7200 58321 MT ("move" the misplaced keys to their familiar locations) 27 W( \050no, you can't use pliers for this\051. For instance,)26 W 7200 59607 MT (the Escape \050ESC\051 key \050important to much host-resident software\051 is notoriously mobile, appearing) 22 W( in)23 W 7200 60893 MT (many different locations even) 11 W( on PCs from the same maker \050IBM and DEC spring to mind\051. If you're)10 W 7200 62179 MT (used to finding ESC immediately left of the "1", but your PC has) 80 W( "`" \050accent grave\051 in that position,)81 W 7200 63465 MT (you could redefine "`" to transmit ESC) 70 W( \050and vice versa\051. Similarly for function keys: the VT100 PF)69 W 7200 64751 MT (keys are on the right, whereas the IBM PC's F keys are on the left; some) 93 W( VT100 users may find it)94 W 7200 66037 MT (more convenient to assign the PF keys to the PC's numeric pad.)SH 8312 68352 MT (A package might also allow you to assign any arbitrary character string to a) 12 W( key, so that you could)11 W 7200 69638 MT (transmit commonly typed items like your) 164 W( name or login sequence with a single keystroke. Such)165 W 7200 70924 MT (many-to-one assignments are called "keyboard macros", and there are limits to the number of)276 W ES %%Page: 9 9 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30322 4286 MT (9)SH 7200 7886 MT (characters which may be represented by a single key.)SH 8312 10201 MT (Key redefinition is important if you switch frequently among terminals and) 155 W( PCs with different)156 W 7200 11487 MT (keyboard layouts; it means you) 108 W( don't have to retrain your fingers each time -- a blessing for touch)107 W 7200 12773 MT (typists. It) 454 W( is) 88 W( also helpful when switching the same PC between different hosts. If you are used to)89 W 7200 14059 MT (typing the Backspace key to erase a character, but one host uses ASCII) 156 W( Rubout for this function)155 W 7200 15345 MT (while another uses Control-H, you can assign the suitable character to the Backspace key.)SH 8312 17660 MT (Like communication settings, key definitions might take you some time and experimentation) 128 W( to)129 W 7200 18946 MT (perfect. Once) 638 W( you have configured your keyboard satisfactorily, you should be able to save your)180 W 7200 20232 MT (definitions for future use.)SH 12 /NewCenturySchlbk-Bold AF 7200 23427 MT (CHARACTER SETS)SH 10 /NewCenturySchlbk-Roman AF 8312 25399 MT (The ability to handle European) 82 W( and non-Roman character sets \050keyboard input as well as screen)83 W 7200 26685 MT (output\051 is important for those who deal in languages other) 91 W( than English. It is common practice in)90 W 7200 27971 MT (Germany and Scandanavia, for instance,) 111 W( to assign umlaut, slashed, or circled vowels to the ASCII)112 W 7200 29257 MT (bracket positions. PCs and host computers must agree upon these conventions in order for)345 W 7200 30543 MT (characters to be displayed as intended,) 278 W( rather than in Anglo-American ASCII. Translation of)279 W 7200 31829 MT (outbound and arriving characters is therefore an important function of the communication) 53 W( package.)52 W 7200 33115 MT (To be totally general, the package should not be restricted to 7-bit ASCII, but should allow for 8-bit)59 W 7200 34401 MT (international character sets, in line with ISO Recommendations 2022, 6937, et al.)SH 12 /NewCenturySchlbk-Bold AF 7200 37596 MT (TEXT SCREEN MEMORY)SH 10 /NewCenturySchlbk-Roman AF 8312 39568 MT (A special advantage of emulating) 64 W( a terminal on a PC is that the PC may surpass the capabilities)63 W 7200 40854 MT (of the terminal. The PC's memory may be used to) 73 W( hold hundreds of lines that have scrolled off the)74 W 7200 42140 MT (top for later recall. Current or previous screens may) 28 W( be dumped to a disk file or printer at the touch)27 W 7200 43426 MT (of a button.)SH 8312 45741 MT (Screen print, dump, and rollback fall into) 110 W( the convenience category, and yet once you've become)111 W 7200 47027 MT (used to them, you wonder how you ever lived \050or at least, worked\051) 72 W( without them. How many times)71 W 7200 48313 MT (has some important message scrolled off your screen before you) 6 W( could read it? How many times have)7 W 7200 49599 MT (you typed hundreds of lines of text into a computer that crashes before you could save your work?)SH 12 /NewCenturySchlbk-Bold AF 7200 52794 MT (GRAPHICS)SH 10 /NewCenturySchlbk-Roman AF 8312 54766 MT (If your PC has a color monitor, your communication program should be) 97 W( able to set the fore- and)96 W 7200 56052 MT (background text screen colors. A well-chosen color scheme can reduce "operator fatigue") 345 W( or,)346 W 7200 57338 MT (conversely, can jolt you awake during the less exciting hours of your day.)SH 8312 59653 MT (In order to access graphics-oriented applications) 77 W( on your mainframe or mini such as SAS Graph,)76 W 7200 60939 MT (SPSS Graphics, Plot 10, TELL-A-GRAF, or) 157 W( various CAD packages \050not to mention certain dialup)158 W 7200 62225 MT (shopping services\051, the communication package must emulate a graphics terminal or standard)289 W 7200 63511 MT (known to the) 106 W( application, such as Tektronix 4010, 4014 or other model, DEC ReGIS, HPGL, GKS,)107 W 7200 64797 MT (GDDM, NAPLPS, etc.) 25 W( Graphics) 327 W( terminal emulation is only found in a few communication packages,)24 W 7200 66083 MT (usually as an extra-cost item, and) 95 W( for certain PCs \050like IBM\051 a special monitor and graphics board)96 W 7200 67369 MT (are also required.)SH 8312 69684 MT (In recent years, graphics tend to be done) 33 W( directly on the PC by such packages as Lotus, Macpaint,)32 W 7200 70970 MT (etc. It) 608 W( is normally not possible to connect one PC to another) 165 W( in order to access the remote PC's)166 W ES %%Page: 10 10 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30044 4286 MT (10)SH 7200 7886 MT (graphics applications, though certain highly specialized packages do allow this.) 89 W( You) 454 W( cannot expect)88 W 7200 9172 MT (to run Crosstalk from PC A to PC B, and expect Lotus on PC B to put a color pie) 102 W( chart on PC A's)103 W 7200 10458 MT (screen. More) 572 W( commonly, the graphics package exists on both PCs and their data files) 147 W( are moved)146 W 7200 11744 MT (from one computer to another using a file transfer protocol built into the communication package.)SH 12 /NewCenturySchlbk-Bold AF 7200 14939 MT (FILE TRANSFER)SH 10 /NewCenturySchlbk-Roman AF 8312 16911 MT ("...transfers your data over phone lines at the speed of light!") 70 W( was) 419 W( a claim that once appeared in)71 W 7200 18197 MT (an advertisement for) 9 W( a communication package. While it's true that electricity travels through wires)8 W 7200 19483 MT (at near light speed, it is not \050yet\051 true that one electron is equivalent) 76 W( to one bit of data. In fact, at)77 W 7200 20769 MT (the most common speed used for dialup data communication, 1200 bits per second, a single bit) 136 W( is)135 W 7200 22055 MT (pretty big -- about 150 miles) 51 W( long! A character \050generally represented in transmission by 10 bits\051 is)52 W 7200 23341 MT (1500 miles long; two characters, like "OK", would span the American continent.)SH 8312 25656 MT (Spurious advertising) 4 W( claims notwithstanding, transmission speed is a technological issue, but data)3 W 7200 26942 MT (transfer is a software) 11 W( issue: How to make effective use of the transmission medium? How to smooth)12 W 7200 28228 MT (over the differences between computers?)SH 8312 30543 MT (There are also several specific areas to watch out for. Can binary files be) 76 W( transferred? Can text)75 W 7200 31829 MT (file formats be converted to useful form between unlike systems? Can a group of files be sent in a)90 W 7200 33115 MT (single operation? Can filename collisions be avoided? Can a file transfer be cleanly interrupted?)SH 12 /NewCenturySchlbk-Bold AF 7200 36310 MT (ASCII VS ERROR-CHECKED PROTOCOLS)SH 10 /NewCenturySchlbk-Roman AF 8312 38282 MT (Communication packages offer two basic types of data transfer:) 177 W( "raw" and error-checked. The)176 W 7200 39568 MT (most common "raw" method is usually billed as "ASCII protocol". This means that) 72 W( the data is sent)73 W 7200 40854 MT (as-is, as ASCII characters,) 61 W( from one computer's communication port to the other. The advantage is)60 W 7200 42140 MT (simplicity. No) 338 W( special software need be resident on the remote computer, beyond its text editor, or a)30 W 7200 43426 MT ("type" or "copy" command. The disadvantages, however, explain why error-checked protocols have)110 W 7200 44712 MT (evolved, and are worth noting. The data sent using the ASCII) 71 W( protocol will be corrupted if there is)72 W 7200 45998 MT (noise on the communication line. Data will be lost if) 61 W( the receiving computer can't keep up with the)60 W 7200 47284 MT (sender. Binary) 512 W( \050non-textual\051 files generally) 117 W( cannot be transferred this way since many computers)118 W 7200 48570 MT (will ignore the "parity bit",) 326 W( or act upon control characters rather than accept them as data:)325 W 7200 49856 MT (Control-C, Control-S, and Control-Z are frequent culprits. And finally, this method works for only)105 W 7200 51142 MT (one file at a time.)SH 8312 53457 MT (A refinement of ASCII protocol incorporates XON/XOFF or some other flow control) 171 W( method, to)170 W 7200 54743 MT (reduce the chances of data loss. In) 121 W( this case, both computers must support the same flow control)122 W 7200 56029 MT (method, but corruption) 326 W( of the data \050including the flow control signals themselves\051 remains a)325 W 7200 57315 MT (problem, as does file delimitation and the restriction on binary files.)SH 8312 59630 MT (If you want reliable, correct, and) 21 W( complete transmission of files between computers, then you can't)22 W 7200 60916 MT (trust the job to ASCII or XON/XOFF) 11 W( "protocol". You'll need a communications package that includes)10 W 7200 62202 MT (a true error-correcting file transfer) 291 W( protocol. Error-checked data transfer requires cooperating)292 W 7200 63488 MT (programs on each) 112 W( end of the connection to exchange messages, called packets, according to agreed)111 W 7200 64774 MT (upon formats and rules, similar to how we behave on the telephone: I dial, your phone rings, you)129 W 7200 66060 MT (pick up and say hello, I identify myself, we take) 90 W( turns talking and if I didn't understand what you)89 W 7200 67346 MT (said then I ask you to repeat \050and vice versa\051, then we say goodbye, and then we hang) 56 W( up. And \050an)57 W 7200 68632 MT (important point\051) 10 W( we conduct the conversation in the same language. A file transfer protocol operates)9 W 7200 69918 MT (similarly: the two processes "connect" with each) 87 W( other, identify the files that are being transferred,)88 W 7200 71204 MT (request retransmission of lost or damaged packets, identify the end of the file, and) 98 W( then disengage)97 W ES %%Page: 11 11 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30044 4286 MT (11)SH 7200 7886 MT (from each other.)SH 8312 10201 MT (By the) 158 W( way, the fact that many newer modems provide error correction does not eliminate the)159 W 7200 11487 MT (need for file transfer software. An error-free data stream from modem to modem does) 21 W( not guarantee)20 W 7200 12773 MT (correct data from computer to computer. Issues of end-to-end) 75 W( flow control and error correction, file)76 W 7200 14059 MT (delimitation, and format conversion must still be addressed within the computers themselves.)SH 12 /NewCenturySchlbk-Bold AF 7200 17254 MT (XMODEM AND KERMIT)SH 10 /NewCenturySchlbk-Roman AF 8312 19226 MT (Two well known error-checking file transfer protocols are Xmodem and Kermit. Many commercial)17 W 7200 20512 MT (packages include one or both of these protocols \050sometimes) 69 W( alongside their own private, proprietary)70 W 7200 21798 MT (protocols\051, but there are also hundreds of public domain or freely sharable Kermit) 246 W( or Xmodem)245 W 7200 23084 MT (programs. In) 530 W( fact, the major advantage of Xmodem and Kermit is that they are ubiquitous. The)127 W 7200 24370 MT (protocol specifications are open and public, and large bodies of Kermit and Xmodem) 148 W( software are)147 W 7200 25656 MT (available. The) 780 W( cost to a large organization for these programs is minimal,) 251 W( compared with the)252 W 7200 26942 MT (per-CPU licensing fees required for commercial packages. Furthermore, chances are greater that) 70 W( a)69 W 7200 28228 MT (Kermit or Xmodem program will exist for any given computer.)SH 8312 30543 MT (In the case of Kermit programs, source code is included, which) 103 W( encourages their adaptation to a)104 W 7200 31829 MT (wide range of systems. Non-commercial Kermits can be) 94 W( had for more than 250 different machines)93 W 7200 33115 MT (and operating systems, ranging) 123 W( in size from the smallest micro to the largest supercomputer, and)124 W 7200 34401 MT (Kermit is included \050at no extra charge\051 in about) 79 W( 100 different commercial software packages. And,)78 W 7200 35687 MT (according to recent announcements from) 50 W( Telebit and AST, Kermit protocol is even beginning to find)51 W 7200 36973 MT (its way into silicon. Xmodem is also available for) 82 W( a wide variety of computers, but it was designed)81 W 7200 38259 MT (primarily for micro-to-micro links. It is most widely known by) 31 W( its commercial implementations, as a)32 W 7200 39545 MT (fixture in programs like Crosstalk.)SH 8312 41860 MT (Kermit, Xmodem, and other) 184 W( error-checking protocols are not equivalent. Kermit won't talk to)183 W 7200 43146 MT (Xmodem, and vice-versa. Each) 42 W( must be evaluated according to several criteria: Is there a version of)43 W 7200 44432 MT (the protocol available for all the systems that must communicate?) 13 W( Can) 303 W( the protocol accommodate all)12 W 7200 45718 MT (the communications parameters required for the systems, and for the communication) 109 W( medium? Is)110 W 7200 47004 MT (the performance acceptable? Is the software affordable?)SH 8312 49319 MT (Xmodem is more properly called the Christensen protocol after its) 142 W( designer, Ward Christensen,)141 W 7200 50605 MT (who originally) 3 W( intended it only for communication between CP/M micros. Ward put his original 1977)4 W 7200 51891 MT (MODEM program into the public domain, and it was modified by others over the years,) 111 W( and some)110 W 7200 53177 MT (protocol features were added, resulting in protocol) 101 W( variants with names like MODEM2, MODEM7,)102 W 7200 54463 MT (XMODEM, YMODEM, ZMODEM, etc.)SH 8312 56778 MT (The Kermit file transfer protocol was originally developed) 176 W( in 1981 at the Columbia University)175 W 7200 58064 MT (Center for Computing Activities for CP/M, MS-DOS, the DECSYSTEM-20, and IBM mainframes)190 W 7200 59350 MT (with VM/CMS; that is, for use in the) 122 W( micro-to-mainframe environment. It was shared freely with)121 W 7200 60636 MT (other institutions, with sources and documentation) 88 W( included. Everyone was, and is, permitted and)89 W 7200 61922 MT (encouraged to copy and share, to make improvements, and to contribute new versions.)SH 8312 64237 MT (Kermit and Xmodem both transfer files between computers in blocks of data, or) 138 W( packets. Both)137 W 7200 65523 MT (protocols require a) 170 W( program running on each computer to compose, send, read, decipher, and act)171 W 7200 66809 MT (upon the packets. Each packet is error-checked through the use of calculated) 246 W( checksums, and)245 W 7200 68095 MT (retransmission is requested when packets have incorrect checksums. Deadlocks are broken) 253 W( by)254 W 7200 69381 MT (timeouts and retransmission. Missing or duplicate packets are) 299 W( caught using packet sequence)298 W 7200 70667 MT (numbers. Both) 340 W( protocols are half-duplex stop-and-wait: the next packet is not sent until the) 31 W( current)32 W 7200 71953 MT (packet is acknowledged. Kermit and Xmodem packets are illustrated in Figure 3.)SH ES %%Page: 12 12 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30044 4286 MT (12)SH /Courier SF 7200 7824 MT (______________________________________________________________________________)SH 7200 9886 MT (Xmodem:)SH 7200 10917 MT (+-------+-------+-------+------------------+-------+)SH 7200 11948 MT (| SOH) SH( |) 1200 W( BLOCK |-BLOCK | DATA \050128 bytes\051 | CHECK |)SH 7200 12979 MT (+-------+-------+-------+------------------+-------+)SH 7200 15041 MT (All fields are 8-bit binary:)SH 7200 17103 MT (SOH is) 2400 W( ASCII Control-A \050SOH, Start of Header\051.)SH 7200 18134 MT (BLOCK is) 1200 W( the 8-bit binary "block" \050packet\051 number, 1-127 \050recycles\051.)SH 7200 19165 MT (-BLOCK is) 600 W( 255 minus the block number \0501's complement of block number\051.)SH 7200 20196 MT (DATA is) 1800 W( exactly 128 bytes of unencoded 8-bit data \050a CP/M disk block\051.)SH 7200 21227 MT (CHECK is) 1200 W( an 8-bit binary checksum.)SH 7200 23289 MT (Kermit:)SH 7200 24320 MT (+-------+-------+-------+-------+----------+-------+)SH 7200 25351 MT (| START | LEN) SH( |) 1200 W( SEQ) SH( |) 1200 W( TYPE | DATA.... | CHECK | )SH 7200 26382 MT (+-------+-------+-------+-------+----------+-------+)SH 7200 28444 MT (Each Kermit packet field except DATA is a single character. Each field)SH 7200 29475 MT (except START is composed only of printable ASCII characters. The packet is)SH 7200 30506 MT (normally terminated by a carriage return.)SH 7200 32568 MT (START is usually Control-A \050SOH\051, but can be redefined.)SH 7200 33599 MT (LEN is) 1200 W( the packet length, 0-94, encoded as a printable ASCII character.)SH 7200 34630 MT (SEQ is) 1200 W( the packet sequence number, 0-63 \050recycles\051, printable.)SH 7200 35661 MT (TYPE is) 600 W( the packet type, S F D Z B Y N, etc.)SH 7200 36692 MT (DATA is) 600 W( a file name, file data, etc, depending on TYPE, printable ASCII.)SH 7200 37723 MT (CHECK is an 8-bit checksum, folded into 6 bits as a printable character.)SH 19800 39785 MT (Figure 3: Xmodem and Kermit Packets)SH 7200 41847 MT (______________________________________________________________________________)SH /NewCenturySchlbk-Roman SF 8312 44162 MT (The differences between Xmodem and Kermit are worth noting. First,) 54 W( Xmodem uses 8-bit binary)53 W 7200 45448 MT (bytes in its packet fields, and therefore requires an 8-bit transparent communication link.) 32 W( It) 343 W( cannot)33 W 7200 46734 MT (function, even for text files, when parity is in use. Similarly, when any device in the communication)27 W 7200 48020 MT (path is sensitive) 111 W( to control characters such as Control-Z or Control-S \050which occur in the Xmodem)112 W 7200 49306 MT (packet control fields\051, Xmodem packets are subject to interference. For) 37 W( this reason, Xmodem cannot)36 W 7200 50592 MT (operate in conjunction with XON/XOFF or other) 117 W( in-band flow control. Kermit, on the other hand,)118 W 7200 51878 MT (encodes its packets as lines of text, and therefore does not have these restrictions.)SH 8312 54193 MT (Second, Xmodem packets are) 8 W( sent only in one direction. The responses are bare unchecked control)7 W 7200 55479 MT (characters such as Control-F for acknowledgement,) 229 W( Control-U for negative acknowledgement, or)230 W 7200 56765 MT (Control-X for cancel. Corruption of) 134 W( Xmodem responses into other valid responses is possible, and)133 W 7200 58051 MT (can cause a file transfer to terminate prematurely. Kermit uses fully error-checked) 56 W( packets in both)57 W 7200 59337 MT (directions, and is therefore more robust in the face of transmission errors.)SH 8312 61652 MT (Third, Xmodem uses fixed-length) 145 W( packets. There is no length field. If a file's length is not an)144 W 7200 62938 MT (exact multiple of 128 bytes, then extra bytes will be transmitted. Furthermore, if a) 225 W( computer,)226 W 7200 64224 MT (multiplexer, or other device cannot handle bursts of 132 characters,) 136 W( Xmodem packets will not get)135 W 7200 65510 MT (through. Kermit) 634 W( packets include a length field. Packets can be) 178 W( adjusted to accommodate small)179 W 7200 66796 MT (buffers, and a short packet can be sent at the end, so there is no confusion about the exact end of file.)SH 8312 69111 MT (Fourth, Xmodem includes) 148 W( no mechanism for transmitting the file's name, and therefore has no)147 W 7200 70397 MT (way of sending multiple files in a single session. Kermit does this routinely.)SH ES %%Page: 13 13 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30044 4286 MT (13)SH 8312 7886 MT (Fifth, Xmodem makes no distinction between text and binary files. But since the conventions) 58 W( for)59 W 7200 9172 MT (representing text files on different systems can vary, the results of an Xmodem) 170 W( text-file transfer)169 W 7200 10458 MT (between unlike systems can be surprising. Kermit specifies a common) 70 W( intermediate representation)71 W 7200 11744 MT (for text) 75 W( files during transmission, so that incoming text files can always be stored in a useful form.)74 W 7200 13030 MT (However, this places the burden on the user to select text or binary transfer mode.)SH 8312 15345 MT (Finally, both the Xmodem and Kermit protocols have seen a number of extensions over) 45 W( the years.)46 W 7200 16631 MT (Xmodem has no formal or) 172 W( consistent way to negotiate the presence or absence of given features,)171 W 7200 17917 MT (whereas feature negotiation is built into the basic Kermit) 227 W( protocol. A pair of variant Xmodem)228 W 7200 19203 MT (programs will not necessarily be able to communicate, whereas any pair of Kermit programs will)149 W 7200 20489 MT (automatically fall back to the greatest common) 303 W( set of options. Xmodem and Kermit protocol)304 W 7200 21775 MT (extensions include:)SH /Symbol SF 9242 23228 MT (\267)SH /NewCenturySchlbk-Roman SF 9980 XM (Multiple files. MODEM7 and YMODEM can transfer multiple files in) 143 W( a single batch,)142 W 9980 24333 MT (Xmodem can't. Multiple file transmission is built into the basic Kermit protocol.)SH /Symbol SF 9242 26091 MT (\267)SH /NewCenturySchlbk-Roman SF 9980 XM (The ability to pass 8-bit data through a 7-bit channel. Xmodem can't.) 74 W( Kermit) 427 W( supplies)75 W 9980 27196 MT (this as a negotiated feature \050commonly available\051.)SH /Symbol SF 9242 28954 MT (\267)SH /NewCenturySchlbk-Roman SF 9980 XM (Alternate checksums. Xmodem-CRC uses) 127 W( a 16-bit cyclic redundancy check for greater)126 W 9980 30059 MT (reliability, and tries to adapt itself to 8-bit-checksum-only Xmodem programs) 67 W( automati-)68 W 9980 31164 MT (cally. Kermit) 456 W( supplies an optional 12-bit) 89 W( checksum, and a 16-bit CRC, negotiated with)88 W 9980 32269 MT (automatic fallback to the single character checksum.)SH /Symbol SF 9242 34027 MT (\267)SH /NewCenturySchlbk-Roman SF 9980 XM (File transfer interruption. Both Xmodem and Kermit allow file transfer) 451 W( to be)452 W 9980 35132 MT (interrupted cleanly. Kermit also includes) 24 W( the ability to cancel the current file in a group)23 W 9980 36237 MT (and proceed to the next one.)SH /Symbol SF 9242 37995 MT (\267)SH /NewCenturySchlbk-Roman SF 9980 XM (Compression. Kermit) 378 W( programs may) 50 W( negotiate compression of repeated bytes. Xmodem)51 W 9980 39100 MT (lacks a compression option.)SH /Symbol SF 9242 40858 MT (\267)SH /NewCenturySchlbk-Roman SF 9980 XM (Long packets.) 256 W( YMODEM) 789 W( allows 1K-byte fixed-length packets for greater efficiency.)255 W 9980 41963 MT (Kermit extensions permit variable-length packets up to about) 326 W( 9K, negotiated with)327 W 9980 43068 MT (automatic fallback to regular-length packets.)SH /Symbol SF 9242 44826 MT (\267)SH /NewCenturySchlbk-Roman SF 9980 XM (Sliding windows. Kermit) 456 W( programs may negotiate simultaneous and continuous)455 W 9980 45931 MT (transmission of packets and their) 55 W( acknowledgments on full-duplex links, with a window)56 W 9980 47036 MT (of up to 31) 173 W( unacknowledged packets, and selective retransmission of lost or damaged)172 W 9980 48141 MT (packets. \050This) 634 W( option is not yet widespread among Kermit implementations\051. Sliding)179 W 9980 49246 MT (windows are not possible in Xmodem) 130 W( because its responses carry no sequence number)129 W 9980 50351 MT (\050an Xmodem variant called) 224 W( WMODEM simulates sliding windows, but only works if)225 W 9980 51456 MT (there are no errors\051.)SH /Symbol SF 9242 53214 MT (\267)SH /NewCenturySchlbk-Roman SF 9980 XM (File attributes. YMODEM transmits a file's name, size, and creation date. Xmodem)163 W 9980 54319 MT (does not. Kermit always transmits) 153 W( the name, and the ability to communicate a wide)154 W 9980 55424 MT (range of other file attributes may be negotiated \050but, like sliding windows, this is not) 22 W( yet)21 W 9980 56529 MT (a widely implemented Kermit feature\051.)SH /Symbol SF 9242 58287 MT (\267)SH /NewCenturySchlbk-Roman SF 9980 XM (Checkpoint/restart. ZMODEM) 648 W( includes the ability) 185 W( to restart a file transfer after the)186 W 9980 59392 MT (connection was broken. Neither Xmodem nor Kermit have this ability.)SH 8312 61707 MT (Kermit also differs from Xmodem) 194 W( by including a "file server" mode of operation, in which the)193 W 7200 62993 MT (remote Kermit program receives all its instructions from the PC Kermit in packet form. This)244 W 7200 64279 MT (simplifies operation considerably. Kermit servers can transfer files, as well as perform) 75 W( a variety of)74 W 7200 65565 MT (file management functions -- deletion, directory listing, changing directories, etc.)SH 8312 67880 MT (Implementations of Kermit) 439 W( can be had for most PCs, minis and mainframes. Xmodem)440 W 7200 69166 MT (implementations are found mostly on) 229 W( PCs, rarely on minis and mainframes. Basic Xmodem is)228 W 7200 70452 MT (somewhat more efficient than basic Kermit,) 33 W( because the packets are slightly longer and there is less)34 W 7200 71738 MT (encoding overhead. The situation is reversed) 175 W( when Kermit can do compression, long packets, or)174 W ES %%Page: 14 14 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30044 4286 MT (14)SH 7200 7886 MT (sliding windows.)SH 8312 10201 MT (Most commercial RS-232 communication packages claim to include Xmodem, Kermit, or) 62 W( both. In)63 W 7200 11487 MT (general, the commercial Xmodem implementations include none) 209 W( of the MODEM7, YMODEM, or)208 W 7200 12773 MT (ZMODEM options, but often do include support for CRCs. Thus,) 48 W( they can transfer only a single file)49 W 7200 14059 MT (at a time, and only through transparent 8-bit communication channels. The) 180 W( commercial Kermit)179 W 7200 15345 MT (implementations vary from the bare-bones to the very advanced, but all) 245 W( can transfer text files)246 W 7200 16631 MT (through 7-bit links, and can handle multiple files in a single operation. It is) 111 W( not always apparent)110 W 7200 17917 MT (from vendor literature exactly which options are supported,) 15 W( so if any of these issues are important to)16 W 7200 19203 MT (you, you should call the vendor and ask about them. After all, one of the advantages) 55 W( of commercial)54 W 7200 20489 MT (offerings over public domain software is telephone support.)SH 12 /NewCenturySchlbk-Bold AF 7200 23684 MT (OTHER ASYNCHRONOUS PROTOCOLS)SH 10 /NewCenturySchlbk-Roman AF 8312 25656 MT (Xmodem and Kermit are not the only two asynchronous) 425 W( communication protocols in the)426 W 7200 26942 MT (marketplace. Others) 760 W( include UUCP, Blast, MNP, X.PC, Poly-Xfr, DX,) 241 W( Compuserve, FAST, and)240 W 7200 28228 MT (DART. Most) 400 W( of these protocols are proprietary, which means that the protocol specification itself) 61 W( is)62 W 7200 29514 MT (secret, or licensed, and they are found) 278 W( primarily in commercial packages. They often include)277 W 7200 30800 MT (advanced capabilities like checkpoint/restart, bidirectional file transfer, and sliding windows.)SH 8312 33115 MT (But all proprietary protocols have the same drawbacks: you must buy commercial) 172 W( packages in)173 W 7200 34401 MT (order to use them, and if there) 26 W( is not a package available for a certain computer that you need it for,)25 W 7200 35687 MT (you're out of luck. Of the commercial packages, Blast probably comes) 20 W( closest to Kermit in covering a)21 W 7200 36973 MT (wide variety of systems,) 44 W( and exceeds Kermit in many design and performance areas. The drawback)43 W 7200 38259 MT (is the cost: $250 for) 246 W( the PC version, $450 for a PDP-11 version, and more for larger minis or)247 W 7200 39545 MT (mainframes. And) 474 W( since the Blast protocol is) 98 W( inherently full duplex, a special "Blast box" front end)97 W 7200 40831 MT (must be purchased for half duplex systems. Kermit, on the other hand, may be used with either) 28 W( full)29 W 7200 42117 MT (or half duplex systems, and the cost is minimal.)SH 12 /NewCenturySchlbk-Bold AF 7200 45312 MT (SUMMARY)SH 10 /NewCenturySchlbk-Roman AF 8312 47284 MT (Here is a checkoff list that you can use to evaluate and compare communication packages.) 32 W( Before)341 W 7200 48570 MT (purchase, you should decide which features are important to you,) 321 W( and then determine which)322 W 7200 49856 MT (packages have these features. Check the vendor literature, or call the vendor directly.)SH ES %%Page: 15 15 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30044 4286 MT (15)SH /Courier SF 7200 7824 MT (______________________________________________________________________________)SH 7200 9886 MT (CONFIGURATION)SH 7200 11948 MT (Make and model of your computer:______________________________________________)SH 7200 14010 MT (Operating system and version:_________________________________________________)SH 7200 16072 MT (Memory:___________\050K\051 Floppy) 600 W( drives:_________ Hard Disk Capacity: _______\050M\051)SH 7200 18134 MT (Communications interfaces:____________________________________________________)SH 7200 20196 MT (Modem make and model:____________________________ [ ] Internal [ ] External)SH 7200 22258 MT (Name of communications package:_______________________________________________)SH 7200 24320 MT (Communications package vendor:_________________________ Phone:________________)SH 7200 26382 MT (Package memory size:___________\050K\051 Package disk occupancy:________________\050K\051)SH 7200 28444 MT (Before proceeding, be sure that the communication package is compatible with)SH 7200 29475 MT (your computer's configuration!)SH 7200 30506 MT (______________________________________________________________________________)SH 7200 32568 MT (COST)SH 7200 34630 MT (\050a\051 What is the unit cost of the package?) SH( $_____________)13200 W 7200 36692 MT (\050b\051 Is source code included, so that you can make changes)SH 9600 37723 MT (and fix bugs? Is there is an additional charge for)SH 9600 38754 MT (source code? Cost of source code, if you want it:) SH( $_____________)5400 W 7200 40816 MT (\050c\051 Is copying allowed? If so, go directly to \050f\051.)SH 7200 42878 MT (\050d\051 How many PCs will you need it for? _____________)SH 9600 43909 MT (Is there a volume discount? If so, enter discounted cost: $_____________)SH 7200 45971 MT (\050e\051 If a site license is available, what does it cost?) SH( $_____________)5400 W 7200 48033 MT (\050f\051 Enter best total price for PC versions . . . . . . . . . . $_____________)SH 7200 50095 MT (\050g\051 Do you also need minicomputer or mainframe versions?)SH 9600 51126 MT (If so, enter total cost for mini or mainframe versions . . $_____________)SH 9600 52157 MT (\050Figured as above\051)SH 7200 54219 MT (\050h\051 Total cost to your organization . . . . . . . . . . . . . $_____________)SH ES %%Page: 16 16 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30044 4286 MT (16)SH /Courier SF 7200 7824 MT (______________________________________________________________________________)SH 7200 10917 MT (DOCUMENTATION, TRAINING, AND SUPPORT)SH 7200 12979 MT (Is the manual...)SH 7200 14010 MT ([ ]) 600 W( thick and unmanagable?)SH 7200 15041 MT ([ ]) 600 W( thin and cryptic?)SH 7200 16072 MT ([ ]) 600 W( just right?)SH 7200 18134 MT (How important is the manual?)SH 7200 19165 MT ([ ]) 600 W( Must be consulted frequently)SH 7200 20196 MT ([ ]) 600 W( Occasional lookups required)SH 7200 22258 MT ([ ]) 600 W( Does the manual have a good index and table of contents?)SH 7200 24320 MT ([ ]) 600 W( Is training available?)SH 7200 26382 MT ([ ]) 600 W( Is training necessary?)SH 7200 28444 MT ([ ]) 600 W( Is telephone support available and included in the package price?)SH 7200 30099 MT (______________________________________________________________________________)SH 7200 33192 MT (WHAT IS YOUR PRIMARY USE FOR THE PACKAGE?)SH 7200 35254 MT ([ ]) 600 W( Long interactive remote sessions. Communication parameter settings,)SH 10200 36285 MT (terminal emulation, and key definition are the most important features.)SH 7200 38347 MT ([ ]) 600 W( Infrequent remote sessions mainly for the purpose of data transfer.)SH 10200 39378 MT (Concentrate on the user interface, script language, and file transfer)SH 10200 40409 MT (protocol.)SH 7200 42064 MT (______________________________________________________________________________)SH 7200 45157 MT (COMMUNICATIONS PACKAGE FEATURES)SH 7200 47219 MT (Each of the features listed below should be evaluated according to your needs.)SH 7200 48250 MT (The lack of a certain feature is not critical if you know you will never need)SH 7200 49281 MT (that feature. Items may be rated as follows:)SH 10800 51343 MT (X - I don't care about this feature.)SH 10800 52374 MT (Y - I need this feature, and the package has it.)SH 10800 53405 MT (N - I need this feature, but the package doesn't have it.)SH 7200 55467 MT (A single "N" may be sufficient to disqualify the package, depending on how)SH 7200 56498 MT (important the feature is to you. If you don't know whether the package)SH 7200 57529 MT (provides a feature you need, call the vendor and ask.)SH ES %%Page: 17 17 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30044 4286 MT (17)SH /Courier SF 7200 7824 MT (______________________________________________________________________________)SH 7200 10917 MT (USER INTERFACE)SH 7200 12979 MT ([ ]) 600 W( Is help available at all times?)SH 7200 15041 MT ([ ]) 600 W( Does the user interface favor the novice user? \050Menus at all times\051)SH 7200 17103 MT ([ ]) 600 W( Does it favor the expert user? \050No menus\051)SH 7200 19165 MT ([ ]) 600 W( Is the package equally convenient for both novice and expert? \050Menu on)SH 10200 20196 MT (demand\051)SH 7200 22258 MT ([ ]) 600 W( Can canned procedures be set up for unskilled users? \050Scripts, command)SH 10200 23289 MT (files\051)SH 7200 25351 MT ([ ]) 600 W( Can local operating system functions be accessed without leaving the)SH 10200 26382 MT (package?)SH 7200 28444 MT ([ ]) 600 W( Can the package be used by the disabled?)SH ES %%Page: 18 18 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30044 4286 MT (18)SH /Courier SF 7200 7824 MT (______________________________________________________________________________)SH 7200 10917 MT (COMMUNICATION PARAMETER SETTINGS \050always important\051)SH 7200 12979 MT (Bits/Second: 0,110,300,1200,2400,4800,9600,19200,etc. Maximum:__________)600 W 7200 15041 MT (Duplex)SH 7200 16072 MT ([ ]) 600 W( Full \050e.g. for DEC minis\051)SH 7200 17103 MT ([ ]) 600 W( Half \050e.g. for IBM mainframes\051)SH 7200 19165 MT (Echo)SH 7200 20196 MT ([ ]) 600 W( Remote \050e.g. for DEC minis\051)SH 7200 21227 MT ([ ]) 600 W( Local \050e.g. for IBM mainframe linemode connections\051)SH 7200 23289 MT (Data Bits)SH 7200 24320 MT ([ ]) 600 W( 5 \050Baudot\051)SH 7200 25351 MT ([ ]) 600 W( 7 \050ASCII\051)SH 7200 26382 MT ([ ]) 600 W( 8 \050national characters\051)SH 7200 28444 MT (Stop Bits)SH 7200 29475 MT ([ ]) 600 W( 1) SH( \050for) 1200 W( most connections\051)SH 7200 30506 MT ([ ]) 600 W( 1.5 \050rarely used\051)SH 7200 31537 MT ([ ]) 600 W( 2) SH( \050used) 1200 W( only for 110 bits per second or less\051)SH 7200 33599 MT (Parity Selection)SH 7200 34630 MT ([ ]) 600 W( None \050all bits used for data\051)SH 7200 35661 MT ([ ]) 600 W( Even \050required by some mainframes, front ends, public networks, etc\051)SH 7200 36692 MT ([ ]) 600 W( Odd \050ditto\051)SH 7200 37723 MT ([ ]) 600 W( Mark \050ditto\051)SH 7200 38754 MT ([ ]) 600 W( Space \050rarely used, but sometimes handy\051)SH 7200 40816 MT (Character Set Selection)SH 7200 41847 MT ([ ]) 600 W( 5-bit Baudot \050used in Telecommunication Devices for the Deaf\051)SH 7200 42878 MT ([ ]) 600 W( 7-bit US ASCII \050most common in English-speaking countries\051)SH 7200 43909 MT ([ ]) 600 W( 7-bit "national ASCII" \050Norwegian, German, etc\051)SH 7200 44940 MT ([ ]) 600 W( 8-bit "extended ASCII" \050e.g. use of IBM PC 8-bit character set\051)SH 7200 45971 MT ([ ]) 600 W( Support for international standard non-Roman character sets)SH 7200 47002 MT ([ ]) 600 W( User-definable or downloadable character sets)SH 7200 49064 MT (Flow Control Selection)SH 7200 50095 MT ([ ]) 600 W( X-on/X-off \050e.g. with DEC computers\051)SH 7200 51126 MT ([ ]) 600 W( ENQ/ACK \050e.g. with Hewlett-Packard computers\051)SH 7200 52157 MT ([ ]) 600 W( RTS/CTS \050for half duplex modems\051)SH 7200 53188 MT ([ ]) 600 W( Half duplex line turnaround handshake \050e.g. with IBM mainframes\051)SH 7200 54219 MT ([ ]) 600 W( Other:________________________________)SH 7200 55250 MT ([ ]) 600 W( None \050can flow control be turned off?\051)SH 7200 57312 MT (Debugging)SH 7200 58343 MT ([ ]) 600 W( Special display of all received and transmitted characters)SH 7200 59374 MT ([ ]) 600 W( Logging of all received and transmitted characters)SH 7200 61436 MT ([ ]) 600 W( Can you collect communication settings into recallable configurations?)SH ES %%Page: 19 19 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30044 4286 MT (19)SH /Courier SF 7200 7824 MT (______________________________________________________________________________)SH 7200 10917 MT (CONNECTION ESTABLISHMENT)SH 7200 12979 MT (Support for RS-232-C asynchronous modem signals \050RTS, CTS, DSR, CD, DTR, RI\051:)SH 7200 15041 MT ([ ]) 600 W( Does the package monitor Carrier Detect \050CD\051 and Data Set Ready \050DSR\051)SH 11400 16072 MT (from the modem?)SH 7200 17103 MT ([ ]) 600 W( Does the package assert Data Terminal Ready \050DTR\051?)SH 7200 18134 MT ([ ]) 600 W( Can the package drop DTR to hang up the phone?)SH 7200 19165 MT ([ ]) 600 W( Does the package respond to Ring Indicator \050RI\051 so that it can be called)SH 11400 20196 MT (from outside?)SH 7200 21227 MT ([ ]) 600 W( If you have a half duplex modem, does the package support RTS/CTS?)SH 7200 23289 MT ([ ]) 600 W( Does your PC have an internal modem?)SH 7200 24320 MT ([ ]) 600 W( Does the package support this internal modem?)SH 7200 26382 MT (Dialer Control:)SH 7200 27413 MT ([ ]) 600 W( Does your modem provide automatic dialing?)SH 7200 28444 MT ([ ]) 600 W( What dialing language is used by your modem? ________________________)SH 7200 29475 MT ([ ]) 600 W( Does the package support automatic dialing?)SH 7200 30506 MT ([ ]) 600 W( Does the package support your modem's dialing language?)SH 7200 31537 MT ([ ]) 600 W( Does the package provide a phone directory?)SH 7200 33599 MT ([ ]) 600 W( Can the package operate over direct connections, without modems? That)SH 10200 34630 MT (is, can it be told to ignore CD and DSR? \050If not, you will need the)SH 10200 35661 MT ("fakeout" \050minimal\051 null-modem cable from Figure 1\051.)SH 7200 37723 MT (Script language for automatic login, unattended operation:)SH 7200 38754 MT ([ ]) 600 W( Access to all necessary package commands from script language.)SH 7200 39785 MT ([ ]) 600 W( Conditional execution/termination of script commands.)SH 7200 40816 MT ([ ]) 600 W( Fancy script programming features \050variables, labels, goto's, etc.\051)SH 7200 41847 MT ([ ]) 600 W( Unattended operation \050e.g. late at night, when phone rates are low\051.)SH 7200 43909 MT ([ ]) 600 W( Can the program be suspended and resumed without dropping the connection?)SH ES %%Page: 20 20 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30044 4286 MT (20)SH /Courier SF 7200 7824 MT (______________________________________________________________________________)SH 7200 10917 MT (TERMINAL EMULATION:)SH 7200 12979 MT (What terminal\050s\051 does the package emulate? ___________________________________)SH 7200 15041 MT ([ ]) 600 W( Is the maximum speed for full duplex terminal emulation sufficient for)SH 10200 16072 MT (your needs?)SH 7200 18134 MT ([ ]) 600 W( Does the package emulate a terminal that is supported by the computers)SH 10200 19165 MT (you wish to communicate with?)SH 7200 21227 MT ([ ]) 600 W( Is the terminal emulated fully enough for use with all desired software)SH 10200 22258 MT (applications on these computers?)SH 7200 24320 MT ([ ]) 600 W( Is any special hardware \050like a 132-column board\051 required in the PC?)SH 7200 26382 MT ([ ]) 600 W( Does the package support fore- and background colors?)SH 10200 27413 MT (\050Do you need them?\051)SH 7200 29475 MT ([ ]) 600 W( If a graphics terminal is emulated, does your application support it?)SH 7200 31537 MT ([ ]) 600 W( Screen rollback \050view screens that have scrolled away\051)SH 7200 33599 MT ([ ]) 600 W( Screen dump \050save current or previous screens in PC files\051)SH 7200 35661 MT ([ ]) 600 W( Printer control \050copy displayed characters to printer;print whole screen\051)SH 7200 37723 MT ([ ]) 600 W( Print or save text screens in alternate character sets)SH 7200 39785 MT ([ ]) 600 W( Print or save graphics screens)SH 7200 41847 MT ([ ]) 600 W( Function keys)SH 7200 43909 MT ([ ]) 600 W( Key redefinition)SH 7200 45971 MT ([ ]) 600 W( Keystroke macros)SH 7200 48033 MT ([ ]) 600 W( Translation of displayed characters, alternate character sets)SH 7200 49688 MT (______________________________________________________________________________)SH 7200 52781 MT (FILE TRANSFER PROTOCOLS)SH 7200 54843 MT ([ ]) 600 W( ASCII \050this is not an error-correcting protocol\051)SH 7200 56905 MT ([ ]) 600 W( XON/XOFF \050this is not an error-correcting protocol\051)SH 7200 58967 MT ([ ]) 600 W( Xmodem)SH 7200 61029 MT ([ ]) 600 W( Kermit)SH 7200 63091 MT ([ ]) 600 W( Proprietary \050Blast, MNP, etc\051:____________________________________)SH 7200 65153 MT ([ ]) 600 W( Other: ___________________________________________________________)SH 7200 67215 MT ([ ]) 600 W( Do the systems you're communicating with support the same protocol\050s\051?)SH 7200 69277 MT ([ ]) 600 W( Does the package transfer both text and binary files?)SH 7200 71339 MT ([ ]) 600 W( Do text files arrive on the target computer in useful form?)SH ES %%Page: 21 21 BS 0 SI 10 /NewCenturySchlbk-Roman AF 30044 4286 MT (21)SH /Courier SF 7200 7824 MT (XMODEM OPTIONAL FEATURES)SH 7200 9886 MT ([ ]) 600 W( Modem7-style transfer of multiple files)SH 7200 11948 MT ([ ]) 600 W( Xmodem-CRC for more reliable error checking)SH 7200 14010 MT ([ ]) 600 W( Ymodem 1K packets for increased efficiency \050half duplex\051)SH 7200 16072 MT ([ ]) 600 W( Ymodem filename transmission)SH 7200 18134 MT ([ ]) 600 W( Checkpoint/restart \050Zmodem\051)SH 7200 20196 MT ([ ]) 600 W( Wmodem continous transmission \050full duplex\051)SH 7200 22258 MT ([ ]) 600 W( Do the computers you wish to communicate with support the same)SH 10200 23289 MT (Xmodem options?)SH 7200 24944 MT (KERMIT OPTIONAL FEATURES)SH 7200 27006 MT ([ ]) 600 W( 8-bit data through 7-bit links \050e.g. links with parity\051)SH 7200 29068 MT ([ ]) 600 W( Repeated character compression for improved efficiency)SH 7200 31130 MT ([ ]) 600 W( 12-bit checksum, 16-bit CRC, for more reliable error checking)SH 7200 33192 MT ([ ]) 600 W( File transfer interruption)SH 7200 35254 MT ([ ]) 600 W( Long packets \050up to 9K\051 for improved efficiency \050half duplex\051)SH 7200 37316 MT ([ ]) 600 W( Sliding windows for improved efficiency \050full duplex\051)SH 7200 39378 MT ([ ]) 600 W( Transmission of file attributes)SH 7200 41440 MT ([ ]) 600 W( Server operation)SH 7200 43502 MT ([ ]) 600 W( Remote host commands and file management)SH 7200 45564 MT (______________________________________________________________________________)SH ES %%Trailer %%Pages: 21 %%DocumentFonts: NewCenturySchlbk-Roman NewCenturySchlbk-Bold NewCenturySchlbk-Italic Courier Symbol