Couple days ago I made an interesting talk about Video Traffic over Internet. Sales engineer goes to company and he claims that Video traffic can be carried over Internet without any problem. This is of course wrong and to understand why I have to explain some technical concepts. Main take away from this article is PLEASE DO NOT BLINDLY BELIEVE WHAT PEOPLE SAY.
There are many type of video traffic. Broadcast video, real time interactive video, multimedia conferencing and streaming videos are the main type of video traffic which we encounter on the networks. Common characteristics of all these, they are latency, jitter and drop sensitive. Depends on the type sensitivity level might be different but still very high. Let’s do the math and see why it is.
In the Figure-1 calculation is done based on three parameters.
First parameter 1080 refers to 1080 lines of horizontal resolution which are factored by 1920 lines of vertical resolution, resulting 2,073,600 pixels per screen.
Second parameter indicates progressive scan, which means that every line of resolution is refreshed with each frame.
The third parameter 30 refers to the transmission rate of 30 frames per second. When all these information factored together, it results in approximately 1.5Gbps of information.
H.264 can compress this HD video to less than 5Mbps.This is 300:1 compression ratio.
Cisco lab testing has shown even a single HD video packet loss in 10000 can be visually detected by an end user. Compare to VOIP where 1 packet lost in 100 could be concealed from the end user. It can be said that HD video is 100 times more sensitive to packet loss than VOIP.
Since this is not only Quality of Service article and I want to stress the importance of Video traffic over Internet, I want to explain another concept using BGP which is the protocol used on the Internet.
In Figure-2 there are 4 Autonomous Systems. For simplicity I only included 4 ASN and a few devices in the BGP domains. From the AS 100 to AS 400, in this topology you have to pass through AS200 and AS300.
If any on the link on the path for the traffic is congested, flaps or transmission errors are seen, packets are dropped regardless of their importance. Quality of service is enabled to manage fairness; you can punish data traffic and give an importance to video or voice traffic when congestion occurs.
Internet works as best effort from the Quality of Service point of view. Which means data, voice and video all are treated equally if there is congested. There have been many efforts to bring quality of service, first with Diffserv and once it fails with Intserv, all are failed because of commonly layer 8 and above issues. Geoff Huston wrote an article about the issues, you can read from here.
Second argument was, they implemented Video traffic over Internet within the country between two companies which both have PI (Provider Independent) address space and they never see an issue.
As easily can be understood from the Figure-2 , increasing the number of devices and links between the endpoints, more likely congestion can happen, result of this; delay, jitter and packet loss is seen.
If the traffic will pass only between the two autonomous systems like in figure-2 between the border routers of AS200 and AS300, you may not see the problem. But even between them congestion, flapping or transmission error might occur and result of these, delay, jitter and drops are seen.
What can be the alternatives?
You want to protect your voice and video traffic even congestion happens. Underlying transport should be reliable. Also it should understand the overlay policy ( QoS, routing, filtering so on). Quality of service policy is set and service providers understand the marking and treat the traffic based on their importance.
DWDM, POTN, SDH and Dark Fiber all possible options but might be costly. Alternatively MPLS VPN either layer 2 or layer 3 might be a better option from the cost point of view. If more than one provider will involve then Inter-AS MPLS VPN might be a solution. All of them you can give the priority level to your traffic and carry over multiple hop without worrying about many of above issues.
Finally I should mention that Quality of Service is only applicable up to some level. If your links fully congested and software queues also full, all traffic types including voice and video are dropped. In this case, you should definitely plan to increase your bandwidth.