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Does Link Aggregation work with a single Video Stream?

Posted on 2011-03-02
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Last Modified: 2012-05-11
I have been trying to find the answer to this for days. I cannot find a definitive answer.

We NEED to know if Link Aggregation will help in this scenario or not.
We have a single video monitoring device at one location connecting to a single video device at another location. Because the data stream is video, packet order is much more critical. Does a single network connection, at the actual packet level, have the ability to be "split" across multiple links?
Once a connection is established on one of the links, does ALL of the traffic need to stay on that specific link?
If you need further clarification of what our concern is, please ask and I will reply as soon as possible.
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Question by:dcliebig
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11 Comments
 
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robocat earned 500 total points
ID: 35022359

In general, link aggregation does not increase bandwidth between two individual devices.

E.g. suppose you have a server that uses 2 x 1GBit aggregated links to the network. One single client will always be limited to 1Gbit because the connection from this specific client to the server will always go over the same link.
Only if multple clients connect to the server, will about 50% of the clients use one link and the other 50% the other link, creating an aggregated bandwith of up to 2Gbit.

So in your case, link aggregation will not increase bandwidth because you only have 2 devices.
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by:aleghart
ID: 35022394
That doesn't address the packet issue.  Suppose the LAG is between routing switches.  Each end would negotiate a path to the other through that LAG.  Bandwidth may not be an issue, but differing paths and order of reassembly is in question, if I'm reading the question correctly.

Does the single stream get split across the multiple physical connections?  Is that the question?
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Author Comment

by:dcliebig
ID: 35022551
Yes.....that is the question.  Does as single stream get split across multiple physical connections?  If so, the packets have to be "reassembled" in the proper order to be of value.

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by:aleghart
aleghart earned 1000 total points
ID: 35022603
I came to this question looking for the the same info.

Found this: http://grouper.ieee.org/groups/802/3/hssg/public/apr07/frazier_01_0407.pdf

Page 3 says distribution is packet-by-packet.
Page 7 says reassembly of the packets should be handled in the proper order.

My inference only, and this is not a technical document.  Looks like a presentation.

Summary at the end is true.  Nothing beats a fatter pipe.

But, in my case, I already have gigabit connections.  But if there's a 2x1Gb LAG meant to help the total of network traffic...my video streams must still traverse the LAG.  It wasn't put there just for my streaming.
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by:Don Johnston
Don Johnston earned 500 total points
ID: 35022612
>Does as single stream get split across multiple physical connections?

No.

All the traffic from a single stream will always be sent over the same physical link.
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Expert Comment

by:aleghart
ID: 35022673
That's with a default Layer3 hash, right?  Traffic by IP address?

What if the link is using source and destination port?  And how would one know?  (Checking switch config being an obvious step, if you have access to it?)
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by:Don Johnston
ID: 35022745
>What if the link is using source and destination port?

Wouldn't matter. If it's the same stream, it'll have the same MAC addresses, IP addresses and port numbers.
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Author Comment

by:dcliebig
ID: 35023365
ok....now that I have an general understanding of how LAG works, lets take this one step further:

Instead of the links between switches being Gigabit copper, lets say that they are bridged WIFI.

                            ------WIFIBridge ((((((  ))))))))WIFIBridge------
server----switch                                                                         switch-----client
                           ------WIFIBridge ((((((  ))))))))WIFIBridge------

WIFI bridge has a limitation of 28mb on each link

In theory I think this should work, but I am interested to hear what you guys think.
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by:aleghart
aleghart earned 1000 total points
ID: 35023400
A single stream would still be limited to one link, I'd think.  That stream would negotiate with a unique IP address and port #.  But if you had separate streams, each could possibly use a different connection.

We're back to the fatter pipe issue.  At this point, put in a fatter pipe.  I can't see doing video over WiFi to be usable for much at all.  The latency with each hop, plus slow speed of WiFi would fall apart.
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Expert Comment

by:Don Johnston
ID: 35023429
No difference. The stream would still use a single link.
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by:robocat
ID: 35028477

What's your actual problem ? Do you have video streams exceeding the speed of your (WAN/LAN) links ?
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