Macintosh Sisters - FAQs
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FAQ's - Modems and Cables

What kind of modem will work with my Macintosh?
Any *external* Hayes compatible modem will work with your Macintosh. There are too many to list or review here. The USENET newsgroup comp.dcom.modems is a good place to ask questions about the many different external Hayes compatible modems. Such modems can be used with any computer (Macintosh, UNIX box, MS-DOS PC, Amiga, etc) with a serial port (e.g.: Macintosh modem port) interface. However, there *are* modems that are designed specifically for use with the Macintosh. Examples include internal Powerbook modems, ADB modems, and internal NuBus modems.

Note that modems for the Macintosh Performa apparently can only plug into the Macintosh Performa because of an extra pin which they posesses (there is a corresponding extra hole on the Performa serial port connector into which this pin fits). As a result, the bundled Global Village FAX modem can only plug into the Performa. Other modems can of course also plug into the Performa; the extra pin only prevents plugging the Performa-specific modem into other Macs.

Assuming you wish to use an external modem, your only other hardware consideration is to find an appropriate hardware-handshaking cable to connect it to your Macintosh.

Various special modems exist with unique features; the most notable type is the dual FAX/modem. For more information, visit comp.dcom.modems or your local dealer: there are simply too many products to describe here.


What kind of cable do I need to use my external modem with my Macintosh? 

Most modems have a female DB-25 (25 pin) connector labelled RS-232C on their backsides. All Macintoshes since the Mac Plus except for the Imac use a mini DIN-8 (8 pin) connector for the two serial ports (modem and printer). Earlier models use the larger DB-9 (9 pin) connector. Finding a hardware handshaking cable for any 14.4K+ configuration at most computer accessory store should not be very difficult and typically sale $15.00 (10 ft) via mail order. Note some older modem cables are -not- hardware-handshaking and can cause such problems as repeated transmission errors, a drop in the transfer rate, and possibly an aborted transmission.

What do V.32, V.42, bis, MNP, etc mean?

Because these topics are universal telecommunications issues, they are more fully discussed in comp.dcom.modems. However, a short description of some of the more common abbreviations and buzzwords is given below.

<<An excellent article on the subject of modems, including a guide to buying high-speed modems, is available from InfoMac and its mirror sites as the file info-mac/comm/info/modem-guide-11.hqx.>>


Buzzword What it typically means?

bit : binary digit; amount of information necessary to distinguish between two equally likely events (such as the value of a binary digit)

byte : eight bits; size of a single ASCII character

bps : bits per second

baud : one analog signal state change; people usually use baud and bps interchangeable, although most modern modems can encode multiple bits per baud

Bell 103 : 300 bps U.S. Standard

Bell 212A : 1200 bps U.S. Standard

LAP/M : Link Access Protocol/Modem.

MNP : Microcom Networking Protocol (Proprietary)

MNP5 : MNP extension; 2 to 1 data compression.

V.32 : 9600bps, 4800bps

V.32bis : 14.4Kbps, 12Kbps, 9600bps, 7200bps, 4800bps

V.32terbo : psuedo-standard extending V.32bis to 16.8, 19.2 kbs

V.34 : 28,800 bps, 14,400 bps, 9,600 bps, 2,400 bps

V.Fast : Interim version of V.34; sometimes used as a nickname for V.34

V.FC : proprietary Rockwell protocol used before V.34 was approved as a standard

V.42 : MNP 4 and LAP/M modem to modem error correction

V.42bis : LAP/M and 4-to-1 data compression.

X2/K56flex : Two incompatable proprietary formats for 56K Dependent on a digital equipment which some areas do not have.

V.90 : standard for 56K modems

Note: Some V.FC modems do not work with V.34 modems at 28,800 bps.

FAX standards

V.21 : 300 bps FAX

V.27ter : 4800 bps FAX

V.29 : 9600 bps FAX

V.17 : 14400 bps FAX

How fast can the Macintosh serial ports really go?

Orignally the MacOS supported up to an asynchronous data rate of 57600 bps though the serial hardware could support much higher transfer rates externally clocked (as much as 16 times synchronously). The AV and Powermac introduced a different SCC clock and DMA based serial driver which allowed 115,200 and 230,400 bps.

While the ability to achive these speeds was useful in the days of communications software (see [3.1]) its importance dwindled with the introduction of Intenet communications and PPP. The reason is that many non-text files on the Internet are already compressed which renders the built in MNP5 and V.42bis compression methods virturally useless. In addition due to limiations in equipment and phone line quality even a 56K modem rarely gets a sustained throughput over 50K.

For these reasons the modem scripts that come with Open Transport have 57600 bps as the maximum serial speed for a modem.

How can I disable call-waiting when using my modem?

This varies depending on your local phone company, but often, if you preced the phone number you wish to tone dial with "*70," (omit the quotes but not the comma), you can disable call-waiting FOR THAT CALL ONLY.

In the United Kingdom, the code to use is #43#.
In New Zealand, the code to use is *52.
If you are using Telecom Australia,
ATDT#43#,;H Will turn call-waiting OFF
ATDT*43#,;H Will turn it back ON again.



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