Calculating Bandwith for Video Calls

25 Oct

A few weeks ago I wrote a blog on determining the bandwidth used by voice calls in Calculating Bandwidth for SIP Trunks.  Now, while voice is an extremely important aspect of SIP communications, the beauty of SIP is that it isn’t limited to strictly voice.  On my various PC and smart phone clients I do voice, presence, instant message, and video.  While communications forms such as instant message and presence do consume some network bandwidth, it’s extremely low and neither is of a real-time nature.   However, video is very real-time in nature and will typically consume far more data than even the most data intensive wide band voice codec.

Video codecs have a number of distinguishing characteristics, but in terms of bandwidth utilization we are concerned with two major factors – resolution and frame rate.  Resolution is expressed by the pixel height and pixel width of the rendered image.  Frame rate is expressed in image frames per second.  Clearly, more pixels sent more often produces the best image.  This, of course, leads to greater bandwidth consumption and possibly less video calls on your network.

It is my experience that the following five video codes are the ones you will most often encounter with video calls – Divx, H.263, H.263+, H.264, and MPEG-4.  Each of these codes offer different resolution and frame rate values that ultimately create different quality experiences and bandwidth requirements.

For DviX codecs you will commonly find the following variations:

Client Setting

Resolution

Frames / sec

Quality

Bandwidth (kbps)

Average (kbps)

Very low bandwidth

160 x 120

2

Very low

10 – 20

15

Low bandwidth

160 x 120

10

Low

60 – 120

80

Medium bandwidth

320 x 240

10

Medium

150 – 300

200

High bandwidth

352 x 288

15

High

400 – 800

600

For H.263, H.263+, H.264, and MPEG-4 it looks like this:

Client Setting

Resolution

Frames / sec

Quality

Bandwidth (kbps)

Very low bandwidth

176 x 144

2

Very low

10

Low bandwidth

176 x 144

10

Low

64

Medium bandwidth

352 x 288

10

Medium

192

High bandwidth

352 x 288

15

High

512

Very high bandwidth

640 x 480

30

Very high

768

At this point you need to determine the number of simultaneous video calls and the quality level of those calls.  Unlike your voice traffic, these numbers might not be as easy to determine.  Video is still a relatively new form of communication and you may not have the empirical knowledge required to do a full analysis.  This means that you will have to take your best guess and be prepared to add or remove bandwidth as users become more comfortable with making and receiving video calls.

However, I will take a stab at a few estimates that may form the basis of your best guess approach.

Expected Video Sessions:

Subscribers

Sessions

10

8

25

12

50

17

75

23

100

27

250

54

500

95

750

134

1000

171

1250

210

Your number may vary quite a bit from these.  The important thing is to do the best job you can in determining the number of sessions.

Next, you need to translate those sessions into bandwidth requirements.  Given the above data I come up with the following video requirements in Mbit/sec.

Sessions

Very Low

Low

Medium

High

Very High

8

0.1

.6

1.6

4.8

6.1

12

0.2

1.0

2.4

7.2

9.2

17

0.3

1.4

3.4

10.2

13.1

23

0.3

1.8

4.6

13.8

17.7

27

0.4

2.2

5.4

16.2

20.7

54

0.8

4.3

10.8

32.4

41.5

95

1.4

7.6

19.0

57.0

73.0

134

2.0

11

27.0

80.0

103.0

171

2.6

14

34.0

103.0

131.0

210

3.2

17

42.0

126.0

161.0

To determine your particular bandwidth needs, I suggest the following:

  • Estimate the total number of SIP video subscribers that will be using each video quality level.
  • From this estimate, determine the number of video sessions using the above table.
  • Using the bandwidth requirements table, determine the bandwidth for each expected codec.  Sum those numbers.
  • Note.  Rather than trying to estimate for each video codec type, pick an average codec and multiply by the expected number of video sessions.

You then need to ensure that your switches, routers, queues, and uplinks are sized to meet the expected video traffic.  Also, make sure that you apply the proper QoS settings to ensure the best video experience possible.

I hope this helps you understand what you need in terms of bandwidth for your video roll-out.  It’s important to realize that video is not going away and the demand for quality, well-behaved video calls will be growing every year.  Do it right and your users will be happy.  Fail to plan and configure your network appropriately and you risk a help desk nightmare.

 

Source: http://andrewjprokop.wordpress.com/2013/10/24/calculating-bandwidth-for-video-calls/?blogsub=confirmed#blog_subscription-2

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