From: R. Benjamin Kessler (ben@xxxxxxxxxxxxxxxxxxxxx)
Date: Fri Dec 07 2001 - 13:34:17 GMT-3
That's an interesting approach; I hadn't considered NAT as a player in
this...if you could get it to work it would definitely be a kludge.
Personally, I'd try to attack this at the application layer, not network
(more below); but let's look at the NAT scenario first.
The first question would be, can you NAT to a multicast address? (Haven't
tried this one in a lab so I don't know - I can think of more than a few
reasons why it might not work though...)
For giggles, let's say it is possible and we have a network like the
following:
+-----+ +-----+ |---pc1
| web |___| NAT |___|---pc2
| cam | | rtr | |---pc3
+-----+ +-----+ |---pc4
The web cam's IP address is 192.168.1.1/24
The NAT rtr has interfaces on 192.168.1.0/24 and 192.168.2.0/24 networks; .1
is the inside net and .2 is the outside net.
The PC's are all on the .2 net or some other net where the multicast is
routed.
The NAT rtr x-lates the address of 192.168.1.1 to 239.254.254.254
At this point, we have to "trick" the PC's into joining the 239.254.254.254
multicast group so their NICs start processing packets to the MAC address
associated with the multicast group and so the IP stack accepts the
multicast packets.
Of course, all of this _assumes_ that the app is UDP-based, not TCP. At
this point, we have to get the application to listen to the stream of data
for the video; hopefully it is a hard-coded UDP port number not something
that is dynamically established when the app starts. If it is dynamic we
have another issue because how do we synchronize all of the client machines
to have (or at least appear to the web cam source) the same port number...
As you can see, it gets complicated really quickly...thus my initial
question - what are you trying to do. Based-on your response, have a single
camera that gets displayed on multiple workstations which, preferably,
crosses the network as a single stream of data. Sounds like a classic
video-conferencing/video-broadcasting scenario.
There are many options available from free (do a Google search on vic or
MBone) to $$$ (Cisco IP/TV or Real Video Servers). You should be able to
hang an inexpensive camera of an old PC running as the video source.
Hope this helps.
Ben
-----Original Message-----
From: Jim Brown [mailto:Jim.Brown@CaseLogic.com]
Sent: Thursday, December 06, 2001 4:33 PM
To: 'Kirby, Ron'; 'ben@kesslerconsulting.com'; ccielab@groupstudy.com
Subject: RE: Multicast app
Disclaimer:I'm by no means a multicast expert and I'm currently trying to
learn it as we speak.
I may be talking out the wrong end here and this is a very kludge solution,
but why couldn't you NAT the stream at the first hop from the source?
As long as the application is UDP why would it need to know the destination
address was modified to a multicast address after it has left the source
(camera)?
Everything downstream wouldn't care?
-----Original Message-----
From: Kirby, Ron [mailto:Ron.Kirby@getronics.com]
Sent: Thursday, December 06, 2001 3:11 PM
To: 'ben@kesslerconsulting.com'; ccielab@groupstudy.com
Subject: RE: Multicast app
We have a small webcam that unicasts its data. Multiple people within our
company want to attach it to view the area viewed by the webcam. Bandwidth
is an issue, and it seems like this would be a good place to use multicast,
but the webcam doesn't support multicast. While I know this is not the
proper use of this forum, I was hoping someone may know of a tool that would
take unicast data and re-transmit it as multicast.
Thanks for your patience
Ron
-----Original Message-----
From: R. Benjamin Kessler [mailto:bk-lists@kesslerconsulting.com]
Sent: Wednesday, December 05, 2001 4:23 PM
To: Kirby, Ron; ccielab@groupstudy.com
Subject: RE: Multicast app
It's really more complicated than that. What specifically are you trying to
accomplish?
> -----Original Message-----
> From: Kirby, Ron [mailto:Ron.Kirby@getronics.com]
> Sent: Wednesday, December 05, 2001 10:59 AM
> To: 'ccielab@groupstudy.com'
> Subject: Multicast app
>
>
> Does anyone know if there's an app that will take unicast traffic and
> redistribute it as multicast traffic?
>
>
> Thank
> Ron
This archive was generated by hypermail 2.1.4 : Thu Jun 13 2002 - 10:32:40 GMT-3