(2748) Tue 23 Jul 91 0:17 By: Edwin Halsema To: Henry Hache Re: Re: Confussion St: ------------------------------------------------------------ @MSGID: 2:285/102.2 36b32205 @PID: PM 2.05 Hello Henry, in a message to Ricky Meleschi you wrote: HH> On a more apropriate topic: HH> I've tried over the past month to figure out hst terminology. When I HH> get one answer another contridicts it. Hi there, let me jump in and try to make the confusion even bigger. 8^) HH So here are my questions for the last time: HH> 1. What is HST? HST = High Speed Transfer, this is a US Robotics proprietary protocol with a speed of 14400/450 bps. So one channel sends at 14400 bps and receives at 450 bps (300 bps for the older HST models!). But because the HST modem can do line reversals it can switch these channels, i.e. while uploading a file you're sending at 14400 and receive the ACK's or NACK's at 450 bps. But when you're downloading your are receiving at 14400 and send your ACK's or NACK's at 450 bps. Because nobody else is allowed to use this protocol you can only make a HST CONNECT with another HST modem. With other brands you will only connect at max. 2400 bps (unless you have a HST DS, this takes us to question: HH> 2. What is DS (Dual Standard)? This is a modem with both the HST protocol and the V32, and for the newest models, the V32bis protocol. With this modem you can also connect with none-HST modems at speeds above 2400 bps, if that modem also supports V32(bis) of course. :-) HH> 3. " " v.32 This is a CCITT protocol for a connection at 9600 bps (9600/9600), so 9600 bps for both channels. V32bis is a CCITT protocol for a connection at 14400 bps (14400/14400). HH> 4. " " v.42 Is an error correction protocol, not unlike MNP levels 1 to 5, but smarter. This protocol is mostly used at speeds from 1200 bps and above, this protocol is also called 'LAPM error control'. HH> 5. " " v.42bis This is a protocol for datacompression, like MNP level 5, but also smarter. If you are sending an uncompressed ASCII file the modem does on-line compression, look at it as ZIPPING or LHARC'ing a file while sending it. HH> 6. How can I transfer at 38K? (compression!) 38400 bps is a so called DTE speed, with other words, the speed between the modem and the computer and has nothing to do with the actual link-rate, this is the speed between the two modems. Because of the V42bis protocol you can send data at higher speeds to the modem thn the modem sends it to the other modem, because of the compression. 38400 bps is most of the time only useful when sending an uncompressed ASCII file. Because then the modem can compress the date very efficient and then you can get cps rates as high as 3000 to 3400. (3Kb to 3.5 Kb data send per second) HH> 7. " " " " " 19.2K? But most of the time you will down/upload already compressed files. V42bis notices this and does not try to decompress/compress the file. MNP-5 is not so smart and tries to compress the already compressed file and ends up with an expanded file => loss of cps-rate. So a speed of 19200 bps between the modem and computer is 90% of the time enough because the modem can only send the data to the other modem at max. 14400 bps. Locking your modem at 38400 bps and then sending only compressed files will not give you any speed improvement, oh well, maybe 5 to 10 cps. HH> 8. Anything else I forgot? Know what ASL (Adaptive Speed Levelling) is? Know the difference between Baud and bps? And the difference between bps and cps? And... and.... :^) HH> Thanks! Well, I hope I helped you to unravel the mysteries of High Speed Modeming a bit for you. Greetings from a warm and sunny Holland. [ Edwin *8-D ] --- Point Manager 2.05 @PATH: 9102/2 285/102 1 280/0 512/0 241/0 310/11 260/1 13/13 @PATH: 260/228 212 * Origin: Explore illusive Tir-Na-Nog, Mega-Net HST-DS Travels (2:285/102.2)