Niall O Broin
niall at magicgoeshere.com
Sat Sep 9 14:22:48 IST 2000
Sat, Sep 09, 2000 at 02:25:13AM +0100, Paul Jakma wrote:
> > routers are I think all heading for a about £1K in price. The serial port
> > TAs (I think they are a most ridiculous class of device)
> why? telcos have always presented lines to customers as serial
ISDN TAs connected to a PC's serial port offend my engineer's soul. ISDN is
a synchronous technology. There are no start and stop bits (so 1000 bits
down an ISDN line = 125 bytes of data, whereas 1000 bits of data down an
RS-232 cable = 100 bytes of data). So, a PC using a serial TA is busily
converting an 8 kbyte/s data stream into asynchronous serial data, which is
being re-converted into synchronous data by the TA. This leads to poorer
latency figures with a serial TA than with a PCI/ISA ISDN card.
And if you want to use channel bonding, and you have an ISP to support it,
you're simply wasting your money with a serial TA. Two channels of ISDN =
128 kbps =~ 13kbps more than a normal PC serial port can support
(115200 kbps, though of course you can buy faster serial ports).
The clincher for me (to drag this back on topic) is that for a Linux user,
excluding routers, the choice is between a serial TA (costs at least £300)
and an ISDN card (costs at least £30) where the card is to my mind a better
solution, engineering-wise, and with ISDN4Linux correctly installed (as it
is by default with SuSE Linux) it is a piece of piss to get going (except if
you're trying to use Esat as an ISP, and don't expect any help from them).
Just my 0.02 Euros worth, and one of my hobbyhorses.
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