Best Practice for Video over WLAN - Part 1

By bala posted Dec 05, 2011 03:11 PM

Let us look at some of the challenges involved in deploying Multicast video over WLAN. This will be a multiple part series and in this first part we will look at some of the wired side optimization required. 

Distributing standard and high definition video has long been the promise of Wi-Fi, but the results have been less than satisfactory due to the limitations of slow 802.11 clients, inadequate multicast capabilities, and the lack of control over client behavior. There has been a lot of improvements in terms of technology and understanding some of the generic requirements is key.  

Wired Infrastructure Optimization for Multicast

There are four primary recommendations to consider in the wired network for supporting broadcast-quality video. Reference the User Guide provided by the appropriate wired infrastructure vendor to enable these settings:

1.     Utilize Gigabit Ethernet End-to-End

It is recommended to have Gigabit Ethernet connectivity from the between all components in the path of video delivery. This includes Gigabit to the Video Server, Aruba Controller, and Aruba 802.11n APs.

2.     Enable IGMP

IGMP proxy or IGMP snooping should be used to facilitate video delivery only to those APs with subscribers. 

3.     Configure Quality of Service Traffic Tagging and Prioritization

Traffic tagging and prioritization should be enabled in the wired network to provide Quality of Service (QoS) to the video streams. It is important to enable Layer 3 Video Differentiated Services Code Point (DSCP) tagging and Layer 2 802.1p tagging on the application (server and clients if possible), the controller(see below), and prioritization/QoS on the wired infrastructure for end-to-end QoS guarantees.

4.     Adjust Video Frame Size

It is recommended to set the frame size at the video server low enough to avoid fragmentation, or enable jumbo frames to the largest supported size if possible. It is important to ensure the MTU of the video server is not larger than the maximum frame size on any wired segment. Fragmentation can be verified by monitoring the frame counters on the switch or router interface(s) along the video data path. Fragment loss results in the entire video frame being retransmitted, also increasing over the air bandwidth.


In the next part we will look at some of the optimizations required on the WLAN infrastructure to deliver multicast video on your network.