[maemo-developers] How to setup multicast over wifi, 3G, DVB-H ?

From: Aleksandr Koltsoff czr at iki.fi
Date: Tue Nov 6 13:21:57 EET 2007
Hello Darius (and others),

Darius Jack wrote:
> But what I need to establish is open multicast - broadcasting channel for media (TVersity or another streaming back end servwer).
> In ethernet configuration multicast packets from multicat IP range are copied by a router and sent to each respective IP address assigned by DHCP server running at multicast router .

Multicast in ethernet actually works slightly differently. There is a
mapping from the IP-group addresses ("class d") into specific Ethernet
MACs (which have the broadcast bit set, but not all bits are set to
ones, as in broadcast). Stations on the same segment will then filter
those packets which they deem "useful" (based on programs binding for
multicast IP addresses for reception). Routing multicast IP traffic is
an different issue, as is multicast filtering (both require a working
IGMP setup and multicast routing also requires some higher level
multicast routing protocol like PIM). DHCP is not involved (other than
when used as MADCAP server, which is not common in UNIX/Linux world).
IPv6 changes these things slightly as well.

> Multicast over wifi should be configured as an open stream channel like DVB-H/G3 to provide open listen to, access to any device switched to listen to mode , like fm radio , sat tv or the like.

"Wi-Fi" (802.11a/b/g) works as a transparent "ethernet" service. So in
fact, multicasting IP traffic in a wireless 802.11 environment isn't any
different from multicasting in ethernet. A problem which people often
will run with multicast in wireless is encryption (WEP/WPA/CCMP) and
bad/flakey support of access points to do use correct keys for broadcast
and multicast traffic. A lot of the cheaper APs have serious problems
with proper key usage anyway unless one uses shared key WEP. However, in
your case I think it wouldn't be a problem as you seem to want to run a
"public/open" wireless setup.

> So please let me know how to setup media streamer client's application to ignore IPs in packets streamed by server and have to read selected open channel wifi stream , bufor and read in media streamer application.

Not really sure what you're after here. You might start testing your
setup by running the video lan client (vlc) (for streaming and testing
multicast) first, and when your wireless setup seems to work with normal
Linux boxes over wireless, you'll want to find a media client/player for
the Internet Tablets which is capable of receiving unreliable/multicast
streams and start hacking on that (a topic where other people surely can


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