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. http://www.videolan.org/
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. http://support.bbc.co.uk/multicast/streams.html
On Thursday 10 March 2005 10:22 pm, Karl Foley wrote:
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.
Thank you, In a few short paragraphs you have answered a lot of questions I had about multicasting, turns out that I shouldn't actually need it for my application (TwonkyVision supports it but I don't think the MP101 needs it) Thanks for the info though, that was really interesting. I would love to see a demo of the Videolan stuff at a ALUG meet (if you have a working and transportable setup)
On Friday 11 March 2005 01:05, Wayne Stallwood wrote:
On Thursday 10 March 2005 10:22 pm, Karl Foley wrote:
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.
(snip)
Thank you,
In a few short paragraphs you have answered a lot of questions I had about multicasting, turns out that I shouldn't actually need it for my application (TwonkyVision supports it but I don't think the MP101 needs it)
Thanks for the info though, that was really interesting. I would love to see a demo of the Videolan stuff at a ALUG meet (if you have a working and transportable setup)
Also, although multicast packets can cross routers they have a time-to-live (hop count) associated with them, so they tend to confine themselves to the local subnet and not propagate through the entire Internet. Multicast is used for a number of things, one being to permit discovery of one machine by another without the need to publish IP addresses. You can always tell who sent a multicast packet, so if a machine announces itself when it joins the network, all the other interested parties will know it's there and respond (or not) accordingly. I had fun writing a Java peer-to-peer distributed processing application using that principle. -- GT
participants (3)
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Graham -
Karl Foley -
Wayne Stallwood