Re: Low latency IP direct connection over ISDN

Am 14.11.2012 00:37, schrieb Matthias-Christian Ott:
> On 2012-11-12 02:42, Birger Harzenetter wrote:
>> On Sun, 11 Nov 2012 19:20:07 +0100, Matthias-Christian Ott
>> <[email protected]> wrote:
>>
>>> I want to connect two sites in Germany with minimal latency under low
>>> bandwidth requirements. Both sides have numbers with the same area code.
>>
>> Same area code only helps if it's the same telco, off course.
> 
> It would be Deutsche Telekom I guess (at one location I can confirm
> this, at the other location would have to find out if they transitioned
> to an IP-based solution already or something similar), although I
> couldn't find any offerings for leased ISDN lines that I would have to
> configure an on-demand (dialled) connection or have to take a much more
> expensive 2 Mbit/s leased line which probably requires expensive
> equipment as well which is perhaps obsolete in a few years (I'm
> currently in the planning stage for the project, so I don't want to
> spend money on hardware or make contracts and just want to find out if
> the current situation could be improved with any easy and inexpensive
> alternative solution).
> 
>>> Can latency be improved via ISDN (I've read contradicting statements
>>
>> Definitely.
> 
> Do you have some exemplary numbers (you could save me several hours of
> work setting up two newly installed computers with old ISDN cards just
> to perform a short test)?
> 

Hmm the absolute latency is low, only few ms (<5). But since the bitrate
is low and you have FIFOs and packets the latency between sending and
receiving is bigger.
If I remember correctly a normal ping (without special options), give
about 25 ms (RAW IP mode).
The advantage compared to DSL is, that this latency is constant as long
the connection is established.
Off course these numbers expect, that the line on both sides is a
classical ISDN line, and not a broadband based line which terminates in
a special NTBA.

ISDN from DTAG is at least supported until 2019 so far I know.

>> But even if the call takes the long way, the latency will be MUCH lower.
> 
> Why (I'm not really familiar with how current telecommunication networks
> are built; you read contradicting things about this on the internet)
> shouldn't ISDN and IP be transferred over the same lines?

No, if you have a classical ISDN line. Yes if you have a IP based line.
On a IP based line the ISDN latency should be a little bit better as
with DSL (because QOS priorisation), but bigger as on a classic line.

> 
> Regards,
> Matthias-Christian
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