Uday wrote:
>
> We have a D-Link 128K external TA connected to a P-IV system running
> RedHat Linux 8.0 (kernel 2.4) using serial comms port (16550 UART). At
> present i connect to the inet by manually dialling the TA using
> minicom and then running pppd -detach /dev/ttys0. Whatsoever i've
> done, i m unable to get 128K Rx speed. The average Rx is just around
> 52k - 60kbps (6-7KBps).
I don't know current details for external isdn cards but at the time I
made my desicion, the situation was as follows:
ISDN provides 2 communication lines of 64000 bits/second (the B channels
used for communication) and 1 line of 16000 bits/second for connection
setup and such, optionally to be used for communication. In the end, all
communication goes over 2 wires in the connection. The 2 lines can each
be used for data (full 64000 bits/second) or for speach (and fax,
analogue modum emulation and such). btw: you never know which link is
used and who cares, in the end they go over the same line.
Internal ISDN devices are seen as network cards. The connection is
handled buy hisax, the isdn driver for linux, it can do channel bundling
and such. The data stream still goes like a network connection, only at
64.000 or 128.000 bits/second. Details: there are 8 bits used in a byte
hence 8.000 bytes per second is (theoretically) possible. Then, I don't
use kbits and kBytes here since K = 1000 with telco-protocols and K=1024
with comuter protocols, which can make a difference...
External ISDN devices (with serial connection to computer) act as modems
to the PC (at... command set) but retranslate that to the data line. The
computer just sees a modem that can do a 'high' speed. Over the (single)
isdn data line, there goes 64.000 bits/second, 8.000 bytes/second. Over
the serial line between the ta and the computer, goes the 8000
bytes/second but in a 10 bits/byte hence using 80.000 bits/second. Add
to that the handling of the modem, like the xon-xoff handshaking for the
buffers and such and you see there is not much room for aditional data
while aproaching the limit of the uart (115000 bits/second?)
Hence, there is not much gain in channel bundling, handled by an
external isdn-ta. Except when fitted with an additional serial
connection. So it is save to say that your external TA cannot handle
channel bundling, except if it is fitted with an other serial
conneciton. Then, from the computer side, just hook that one to an other
serial port in your machine and define an other modem and use channel
bundling as if using multiple modems.
So if you like to use channel bundling, best use an internal isdn
device. THe cheapest ones (passive isdn) are the best. I just bought an
other one for 30 euros, doing just what I like.
>
> The TA supports 128K for which i've to use AT%A2=6 (MLPPP), also the
> portspeed is set to 230400bps in the pppd options, which the TA
> supports. The dial command : ATD172225 and my ISP uses PAP
> authentication (pap-secrets - OK). While i have no problems while
> connecting or afterwards, the connection is stable but the only
> bottleneck is the 60k downlink that i m getting.
.... I've never seen those devices, then again, once I found even the
most basic internal device (now long gone Teles 16.3 cards) can do
decent channel bundling, I never looked at external devices...
>
> I've calculated the Rx throughput by checking the /var/log/messages to
> record the pppd startup time and the ifconfig to record the Rx data
> received (in BYTES and not bits). ifconfig ppp0 reports no or very few
> (2-5) packet errors. About 50-60 WinXP clients have been configured to
> access proxy services which squid (2.5 stable) provides.
>
> When i tried ATD172225&172225, the TA reported error. I tried putting
> spaces around & but couldn't suceed. I have no telephones connected to
> the TA. But when i connected a phone to both the ports 1 after
> another, i found both the lines busy (silence). intrestingly, as
> mentioned in the manual "the BACP/BOD functionality will automatically
> freeup 1-b channel when the user picks up the receiver" i didn't get
> any such result. both the lines remain silent without getting any
> dailtone. Are bot the channels really being used? This setup is at
> our college. I've convinced the admin there to use linux+squid over
> WinXP+NAT. the performance is better in linux as compared to WinXP but
> Rx still is low on both the OSes.
Best you can do is get an internal isdn device. It avoids all the ppp
and modem stuff and can do just what you like at the klick of a button.
In the linux world, SuSE is one of the developers of the isdn drivers,
hence you get state of the art with a SuSE distribution.
>
> The responses I receive after entering AT commands are :
> PROTOCOL : MLPPP 128k
> CONNECT 230400
>
> I've tried using a shell script "pppd connect 'chat -v ......" for
> connection. but all in vain.
>
> what am i missing? is anything wrong?
> ready to post ne other required details,
> just ne suggestions are welcome.
> thnx in advance
>
> - uday
>
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