[altq 1139] Re: HFSC and overcommiting

[Kenjiro Cho <kjc@csl.sony.co.jp>]

Alireza K Yazdi wrote:
> I use altq to divide a 1.5mbps link between about 10 clients (via hdsl
> leased lines). Our clients have different applications (most of them are
> doing VoIP, some of them are ISPs and one offers both voice and internet
> access) and therefore they rarely go high-traffic at the same time. I need
> to overcommit the bandwidth but altq doesn't allow me. I found a thread
> about overcommiting in the archives and know that in altq 3.0 there's a
> flag to allow overcommiting in CBQ (ALLOW_OVERCOMMIT). But we are using
> HFSC. I couldn't find any similar flag for HFSC. Is there any such flags?

The realtime property of the HFSC algorithm breaks if the bandwidth is
overcommitted since HFSC uses absolute guarantee (rather than
statistical guarantee). 

> If not is there any other way to overcommit bandwidth on an HFSC
> interface?

In HFSC, overcommitting class bandwidth is almost equivalent to
setting a false bandwidth to the interface.
(of course, this breaks the realtime scheduling as well.)

-Kenjiro