Hi Hamish,

[Thus spake Hamish Moffatt unto Sunny Leung:]
 
 > v.34 allows for split speeds. This means that transmission and reception
 > of data can be carried out at different rates.

 HM> True, but not all manufacturers implement it. Supra did not have this
 HM> feature in their original V.34 ROMs, but added it in a later flash
 HM> revision. It's quite possible that other noname manufacturers haven't
 HM> bothered, then. 

You're right. I found some stuff on split speeds in John Navas' Modem
FAQ (http://web.aimnet.com/~jnavas/modem/faq.html):

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What are split/asymmetric speeds?



In the past, most standard modems were only capable of transmitting and

receiving at the same speed. (The exceptions were proprietary modems such

as the USR HST that used greatly different transmit and receive speeds.)

Since most connections were made at the maximum speed, there was little

reason to support different transmit and receive speeds.



With the advent of speeds up to 28800 bps that is no longer true. It's now

quite common to have a connection where at least one (and often both)

speeds must be limited to less than 28800 bps, and it's not uncommon to

find that a connection will support faster speed in one direction than the

other. (One reason is that send and receive channels are separated for

transmission between telephone switching offices.)



Having been designed to optimize performance over a wide variety of

conditions, V.34 includes an optional specification for asymmetric

(differing or split) transmit and receive speeds. For example, a connection

might support a transmit speed of 28800 bps but a receive speed of only

26400 bps; without split speed, the speed in both directions would have to

be limited to 26400 bps. For this reason split speed capability is a

worthwhile and desirable feature.



Not all V.34-compliant modems support split speeds. For example, at the

time of this writing most "glue 'n go" Rockwell V.34 clones, do not support

split speeds. On the other hand, others, including all USR V.34 modems

(Sportster 28800/33600 as well as the Courier V.34), Supra, and Motorola,

do support split speeds.

============================================================================

Sunny

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