chau@caen.engin.umich.edu (Hin Fai Chau) (01/22/91)
I have seen an ad in the January issue of Computer Shopper about the V.42bis
external modem by Zoom for a price of $189. It claims that it can achieve
9600 bd compressed through-put with a 2400 bd data-pump; fully V.42 COMPLIANT,
100% Hayes and MNP-5 compatible.
My questions are:
(1) How does it compare to the real 9600 baud modems in terms of performance
and usage?
(2) Does it require a special kind of software to operate?
(2) What do V.42, V.42bis, Hayes and MNP-5 mean?
(3) I have seen that some modems can be addressable with COM1, COM2, COM3 and
COM4. What are they?
(4) What is the limit of ordinary phone lines? Can it handle 9600 baud data
transmission?
(5) I assume some of you know X. I have a 386/33 IBM PC-compatible system at
home. What do you think the minimum baud rate necessary of a modem if I
want to run jobs "remotely" on DECs say, and display graphics "locally"
and efficiently on my PC screen via X window?
Please use my email address in your response if possible. Thanks.
-- H. Chaucirian@einstein.eds.com (Steve Cirian) (01/26/91)
In article <1991Jan21.164934.18031@engin.umich.edu>, chau@caen.engin.umich.edu (Hin Fai Chau) writes: > My questions are: > (1) How does it compare to the real 9600 baud modems in terms of performance > and usage? > (2) Does it require a special kind of software to operate? > (2) What do V.42, V.42bis, Hayes and MNP-5 mean? > (3) I have seen that some modems can be addressable with COM1, COM2, COM3 and > COM4. What are they? > (4) What is the limit of ordinary phone lines? Can it handle 9600 baud data > transmission? > (5) I assume some of you know X. I have a 386/33 IBM PC-compatible system at > home. What do you think the minimum baud rate necessary of a modem if I > want to run jobs "remotely" on DECs say, and display graphics "locally" > and efficiently on my PC screen via X window? 2) It shouldn't, but the modem on the other end must support the same compression scheme, or you will not see any increase in speed over 2400 bps. 2.5) Someone posted the following to comp.dcom.modems, but I unfortunately lost his name. =============================<CUT HERE>=============================== PEP Before even 2400 bps dialup modems received public acceptance, a company called Telebit Technologies was developing a 9600 bps modem based on a multicarrier modulation scheme. The Telebit TrailBlazer sends data at speeds from 0 to 8 baud on each of 511 carriers (spaced every 7.8 Hz from DC to 4 kHz) using Quadrature Amplitude Modulation (QAM). PEP stands for the Packetized Ensemble Protocol, which the TrailBlazer uses to correct errors, reassemble the data, and adjust the modems' operating parameters to achieve optimum performance. This was called Dynamically Adaptive Multicarrier QAM, or DAMQAM. Telebit later added MNP support for non-DAMQAM connections and PEP2 (a protocol with data compression) to what became known as the TrailBlazer Plus. MNP Microcom Networking Protocol, or MNP as it is called, consists of several layers of software protocols, often implemented within the modem itself, which detect and correct errors and provide improved throughput. MNP5 implements a form of dynamic data compression. It detects repeated patterns in the data stream and reduces redundancy in the transmissions. When transitting text files, this can significantly increase throughput but, when used on files which have already been compressed using run-length, Huffman, or Lempel-Ziv techniques, the overhead may actually reduce the effective data throughput. It is wiesest to disable MNP service class 5 when it is known that the majority of information to be transmitted is in compressed form. MNP5 may be used with any of MNP1 through MNP3, with or without MNP4. V.32 V.32 specified that echo cancellation be used to permit simultaneous communication in both directions. Echo cancellation with the necessary precision is complex, and the electronics to do it proportionately expensive. Recently, the mass production of V.32 chipsets has lowered the cost of V.32 modems significantly. HST Because V.32 was, at the time of its introduction, very expensive to implement, USRobotics derived from V.32 an asymmetrical modulation technique which provided a 9600 bps 'forward channel' and a 300 bps 'back channel'. This allowed the HST to send keystrokes, ACK packets, etc. back to the host without requiring that the high-speed carrier direction be reversed - but was incompatible with any other 9600 bps modulation technique. The HST used a variation of MNP for its error correction. V-9600 At the same time, Hayes was also developing a less expensive V.32 derivative. In stead of accepting a reduced speed backchannel, Hayes concentrated on refining the ping-pong technique used to simulate full duplex using a single carrier. The resulting product, the V-Series Smartmodem 9600, was also incompatible with other 9600 bps modulation techniques. HST 14.4 Faced with significant competition from inexpensive V.29 modems (some of which used powerful data compression techniques to achieve outstanding throughput), USRobotics increased their physical bit rate from 9600 to 14400 bps. The resulting 50% boost in throughput gave them a performance edge over most other manufacturers. This model of HST is often called the "HST fourteen-four". T2500 It was not long before owners of Telebit, USRobotics, and Hayes HST DS modems became concerned that their considerable investment in high Ultra speed modems did not always permit them to communicate at 9600 bps with others who had also spent a lot on high speed modems. This pressure, combined with the lowering cost of V.32 chipsets, led each manufacturer to introduce a 'dual standard' model, which was capable of communicating both with the manufacturer's own modems and with others which supported V.32. These were the Telebit T2500, The USRobotics Courier HST Dual Standard, and the Hayes V-Series Ultra Smartmodem 9600. V.42 In the mean time, the CCITT had been meeting to develop a standard for error correction between dialup modems. The result, recommendation V.42, included two protocols: LAP-M (the Link Access Protcol for Modems, derived from SDLC) and MNP. The latter, up to service class 4, was included as 'Annex A' to maintain compatibility with the large pool of existing MNP-equipped modems. V.42bis Aware also that MNP5 and other data compression techniques had become popular, the CCITT released recommendation V.42bis, which specified a data compression technique which would provide dramatic performance improvements where possible, but which would not become a burden when the information being sent was already well compressed. V.32bis Currently in the discussion phase, V.32bis may be released by February of 1991. It will describe a full-duplex carrier technique that will provide 14400 bps physical bit rate, effectively 'catching up' to the HST 14.4. Some manufacturers have already begun advertising V.32bis modems, but there is no gusrantee that they will be compatible with the final specification. =============================<CUT HERE>=============================== 3) COM1 and COM3 usually use the same interupt, as do COM2 and COM4. Usually you will only have one of COM1, COM2 and COM3, COM4, unless you buy a multiport expansion board (I do not know how they work in terms of defining ports). On my serial/parallel board determines which RS-232 ports are used via jumper settings. You then just tell your comm software which port your modem is connected to. 4) We have used Telebit modems, which are capable of 19.2Kbps, as do quite a few people in the Unix community, for a long time. I have heard of strategies to support even higher rates, on regular phone lines. 5) The more speed the better. You will need to run SLIP to use X with your PC acting as an X client. I am unsure of the details, but SLIP or PPP is available for the PC (I am not sure if this was for PCs running UNIX or DOS, but I believe DOS was also supported). You can ftp these, but I do not have an address. NOTE: Anything above 1200 baud is actually bps (bits per second). (i.e.- 2400bps). This is not a flame, just want to have everyone talking the same language. -- Steve Cirian ~ local girl: What does BRMC stand for? 750 Tower Drive ~ Johnny: Black Rebels Motorcycle Club Troy, MI 48007 ~ local girl: What are you rebelling against? (313) 265-5738 ~ Johnny: Whattya got?