Bandwidth Sizing with Multicast Query

Unanswered Question
Nov 8th, 2008


We are building a any to any MPLS network with 70 sites.

Our network will have a central DC with multiple spoke locations.

Using Multicast application server (Omnicast) We want to push 250GB image file from central location to all the spoke locations. File should be transferred within 7hours. For the same we want to know the bandwidth that will be per practical calculation it is coming somewhere near 100Mbps.

Please suggest. Also is there any application level fine tuning required to push the 200GB file in 7Hours.

Attached architecture for reference.


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Mohamed Sobair Sun, 11/09/2008 - 02:08


you will require 10Mbps for each link approximately to push 250 GB to all sites in 7 hours...

As within the MPLS provider, Cisco highly recommends the use of DATA-MDT (SSM) for optimizing multicast traffic & to support such bandwidth, CEs intend recepient of DATA from PEs only joins DATA-MDT Groups assigned by the provider.



deepakbihari Mon, 11/10/2008 - 00:09

Hi Mohamed,

It will be 10Mbps or 100Mbps as when i calculated for a 250GBytes of data to be pushed to a destination in 7hours it gives as close to 90Mbps bandwidth.

Please suggest on ur calculation of 10Mbps link.

Mohamed Sobair Mon, 11/10/2008 - 01:21

Hi fmatrine xyz,

Ok, lets calculate it ...

a link of 10mbps means you can transfer 10M per each second , which means you can transfer 10*60 = 600Mb per minute , which means you can transfer 600*60 = 36000Mb per hour , which means 36Giga bit per each our.

In 7 hours the calculation becomes 36 * 7 = 252 Gb which is almost the required file size to be pushed.



Joseph W. Doherty Mon, 11/10/2008 - 03:52

My math shows a necessary rate of about 79.4 Mbps, just for the data. You'll also need to account for both packet and framing overhead. Without knowing the typical packet's MTU, unable to calculate overhead but if the packet MTU is typical full size Ethernet (1500), you should be able to fit within 100 Mbps assuming you're not also sending other data across the same links concurrently.

I'm unfamilar with Omnicast, but from what I read, it appears to use its own protocol, MFTP, on top of UDP. It also appears it might offer a send rate specification and MTU size to use. Likely you'll want to use the largest MTU supported by your network. As to transmission speed, you'll need to find out whether the application clocks at data rate or physical rate. If the former, setting a data rate for 80 Mbps might be okay. Faster also might be okay if the server's sending interface is set for 100 Mbps.

Something to verify, is whether real multicast is being used. Again, from what I've been reading the application seems to support real multicast, but it might also support a pseudo-multicast, the latter where it sends to multiple receivers concurrently using unicast. Also insure your MPLS vendor accepts true multicast. Some now do but as an extra cost option.

Mohamed Sobair Mon, 11/10/2008 - 23:06


I thought you are talking Gbit, In that case your calculation is correct..!!



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