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Re: broadcast address of a network interface
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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
--- Mac & iPhone




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  • Follow-Ups:
    • Re: broadcast address of a network interface
      • From: Jens Alfke <email@hidden>
    • Re: broadcast address of a network interface
      • From: Joel Reymont <email@hidden>
References: 
 >broadcast address of a network interface (From: Joel Reymont <email@hidden>)
 >Re: broadcast address of a network interface (From: Jens Alfke <email@hidden>)
 >Re: broadcast address of a network interface (From: Joel Reymont <email@hidden>)
 >Re: broadcast address of a network interface (From: Jens Alfke <email@hidden>)
 >Re: broadcast address of a network interface (From: Joel Reymont <email@hidden>)

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