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Multicasting?

Posted on 2006-04-28
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Last Modified: 2010-04-17
I need to send identical data to several users in push mode, with these following indicative specifications:
max 5000 users connected by internet
max 4 packets per second
average 6 Kbits per second throughput
 
The only client side (Windows platform) admissible operation is the installation of the client software.
 
Is the use of multicasting realistic or is there the risk that many routers of switches could hamper the operation?
 
If not realistic what is the best way to do that?
 
Thank you in advance.
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Question by:al-pi
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3 Comments
 
LVL 7

Expert Comment

by:wnross
ID: 16562258
Multicasting is a possibility, but not the way you are thinking:

A big pipe at 100Mbps Full duplex is gonna run you $300-$1000/mo
A typical server is lucky to spew out as much as 60Mbps (Thats doing a disk dump)

Now, 5000 users * 4 pkts/s = 20000 pkts/s, at 1520 bytes/packet == 243Mbps
Theoretical Max packets of that connection = 100Mbps / (1520 * 8 bits/ packet) = 8223 pkt/s
Clearly you are talking multiple pipes (or an OC12 - 622Mbps) and a server farm

So your configuration for this is basically
Node A         Node B          Node C
   |                   |                  |
   +--------------+--------------+
                       |||
(at least 3 100Mbps lines or more likely an OC12)
                       |||
                CPE Fiber Demarc
                        |
                  (The 'Net)
                        |
Client1 Client2 ..................................................Client 5000

Ok, how many nodes?
Well if each one is doing processing, you can max out the PCI bus ~ 133Mbps, using Gigabit ethernet you should be
able to blast out about the same.  (Kinda depressing, really).  Better bus architectures *could* let you spew up to 3-400 Mbps, but not using regular (1500byte) packet sizes.  So more servers.
Max load ~243 Mbps, so just an off the cuff figure of 4 servers should handle the load nicely.
You can get away with fewer servers if two of them are not doing any processing:
                Broadcaster
                       |
   +--------------+--------------+ (Multicast source on 224.0.0.1)
   |                   |                  |
Node A         Node B          Node C  (Relays listen on 224.0.0.1 and rebroadcast to TCP connected clients)
   |                   |                  |
   +--------------+--------------+(Regular TCP network)
                       |||

Well, theres your blueprint

Cheers,
-Bill
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Author Comment

by:al-pi
ID: 16563683
Thank you Bill.

You correctly consider all the packets of max size but it is not so in my condition.

Packet dimension is about 190 bytes so 4*190*8 is 6 Kbits/s per client that is about 1/8 of what you calculate.

However, also considering that, I need to understand pros and cons of multicasting solution and if this way is not right the better other one.

Thank you again.
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LVL 7

Accepted Solution

by:
wnross earned 500 total points
ID: 16563982
Larger packet sizes are more efficient at bandwidth, oddly enough, your solution will need to be larger in the case of
smaller packets because the networking components need to do more work.  Its one of the reasons why gigabit
ethernet cards can't practically run at 1000Mbps.

Now multicasting is transmission at ip addresses between 224.x.x.x-239.x.x.x, if you know you're IP Classes, this range is
a Class "D", which meand that the entire address matches a network (Netmask = 255.255.255.255), consequently
the packets cannot route outside a LAN.  (Exception: MBone, but that doesn't help)

Since the multicast packets won't go past your LAN, the only good they can ever do is to help communicate between
computers in your group.

Example Multicast applications
* ntp (Network time protocol) uses Mulitcast for time synchronization in a LAN and TCP to access remote ntp peers
* Ghost can use Multicast to install operating systems to an entire classroom or rack at the same time from a single
   installer machine.
* RealMedia can use Mulitcast to relay live broadcast streams from a single server to a broadcast server farm for load
   balancing

Cheers,
-Bill
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