Hi Rebecca,
I also encountered this default while implementing a bandwidth-based
call admission control method. At the time, I posted related questions
to the list and got good responses. If you search the list archives you
may find the thread.
The short version is that the default 1280 comes from the 64Kbps
bandwidth of a single ISDN b-channel. I believe (and someone should
correct me otherwise) that it is the lowest possible rate that any Q.931
Setup message would contain.
If you're not using routed mode, then the GK would not see any Setup
message, so it probably inserts the default value 1280 in the
%{bandwidth} parameter within the authorization module.
Even in routed mode, in cases where the calling party is not registered
to the GK, but the *called* party is, the first message the GK receives
is the incoming Q.931 Setup. For those instances, the GK inserts the
default 1280 into the %{bandwidth} parameter in the Auth module, rather
than parsing the Setup message for the actual incoming call rate. The
Auth module also ignores the called party's ARQ message bandwidth field.
If the *calling* party is registered to the GK, the GK will insert the
correct value based on the calling party's ARQ.
Since I'm using GnuGK in a videoconferencing application, I hacked the
source to insert 7680 instead, since my most common call rate is
384Kbps. It works in most cases for my CAC method. I manually clean up
the few failed cases once a day or so.
Modding the code to parse the incoming Setup--or the called party's
ARQ--to insert the actual BW into %{bandwidth} is on my "to-do" list.
--
Mike Ockenga
Network Engineer II -- Product Innovations Group
Onvoy, Inc.
> -----Original Message-----
> From: openh323gk-users-bounces@xxxxxxxxxxxxxxxxxxxxx
> [mailto:openh323gk-users-bounces@xxxxxxxxxxxxxxxxxxxxx] On
> Behalf Of rebecca vernon
> Sent: Saturday, December 08, 2007 1:06 AM
> To: GK Forum
> Subject: Why 1280???
>
> Hi all,
>
> I've compiled the gatekeeper from source in the hope of
> adding some kind of dynamic bandwidth control.
>
> My question is, why 1280??? Is this a random number that
> sounded good??? Or is there some reason. Is there a unit to 1280?
>
> Also, am I correct to assume that if I do change this value,
> it won't really have an impact on the actual bandwidth
> PHYSICALLY allocated or used on the network???
>
> It appears (and I could be wrong), that this "allocation" of
> 1280 is more for THEORETICAL control over the number of
> calls/bandwidth used. That is, you state the Total Bandwidth
> in the config file, every time you make a call it takes 1280
> off the total, and when it runs out the gatekeeper denies a
> new call. So if I change this value, it will have an affect on
> the gatekeepers decision on whether to allow a new call, and
> it will change how much bandwidth is left, but it won't
> actually change the PHYSICAL bandwidth used.
> In other words, it's all relative... Am I right???
>
> The whole reason I'm asking is because I want to set the
> values to something relevant. i.e. If codec is G.711, set the
> bandwidth to 87.2 Kbps, etc. So should I set the BW to 87200
> for this case?
> Or convert it to bytes? Do I need to maintain a unit? eg
> Kbps.......I don't know.
>
> Any help???
>
> Thanks heaps,
>
> Bec
>
>
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