Re: broadcast address of a network interface
Re: broadcast address of a network interface
- Subject: Re: broadcast address of a network interface
- From: Marshall Eubanks <email@hidden>
- Date: Mon, 9 Feb 2009 12:12:44 -0500
On Feb 9, 2009, at 12:01 PM, Joel Reymont wrote:
On Feb 9, 2009, at 4:47 PM, Jens Alfke wrote:
This is often done using multiple TCP sockets instead of multicast.
I'm working on a walkie-talkie app and broadcasting is _the_
feature. I would just like to say something and have everyone else
hear it, without having to establish multiple socket connections.
Cheap 802.11 access points will broadcast any multicasts, as they do
not "speak" IGMP, and thus
don't know whether or not multicasts are needed by wireless nodes.
That is why there is generally a limit to the
total multicast bandwidth allowed. This is more often a problem going
from the wireline to a wireless subnet -
if there is a 1 Gbps multicast video on the wireline LAN, and it goes
on the wireless LAN, you
have a problem.
Because of this, some wireless AP vendors either don't send multicasts
at all, or don't by default. Even though multicasts sources on the
wireless LAN are less of a problem, they
are sometimes blocked as well. So, you will need to address these
issues somehow.
The particular "push to talk" problem you mention is frequently done
using BiDir PIM now-a-days, at least on wireline networks. See
<http://www.cisco.com/en/US/netsol/ns340/ns394/ns165/ns70/networking_solutions_white_paper09186a00800a3e6c.shtml
>
Granted, there could be just a handful of clients in the vicinity
but what if there are thousands? Unlikely, I know but still...
Also, wouldn't sending just one packet to the multicast address keep
power consumption low?
Note that, because reception feedback is generally not available for
multicasts, in an RF environment it is
generally necessary, or at least a good idea, to use more power per
bit for multicast transmissions.
Regards
Marshall Eubanks
---
http://tinyco.de
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