Anyone out there played with this stuff before ?
No, not really. The only opensource media stuff I have played with was VideoLan for multicasting DVD video over a wireless network.
Also in the installation instructions for TwonkyVision it says "Make sure that you have a multicast route set for the server by
issuing a
"route add -net 224.0.0.0 netmask 240.0.0.0 dev eth0"."
Not knowing much about multicast I thought I would pass this through
the
ALUG sanity filter. Is there a specific subnet reserved for multicast
traffic
that I must use (as defined in the above route statement) ? What happens if
my
local subnet is different ?
It's not a subnet, it's a whole new class off addresses. You've probably heard of class A, B and C ip addresses right? Multicast uses class D addresses. Multicast addresses range from 224.0.0.0 right up to 239.255.255.255.
Think of each multicast address as a channel on which servers can send info that can be received by clients tuned to the same channel/multicast address.
It differs from broadcast in that broadcast goes to all hosts (if allowed by the routers) whereas multicast only goes to "tuned in" hosts.
Clients tell their routers they're interested using a protocol called IGMP (Internet Group Messaging Protocol). Network stuff uses it to communicate with all the time. Now it's common to see streaming media using it. The BBC are even transmitting on it experimentally.