Configuring VideoStream – Part 3 – Resource Reservation Control

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Resource Reservation Control

As more and more users begin to utilize video in the workplace on Wi-Fi endpoints, the ability to gracefully manage and scale a continuous, and high-quality experience for fluctuating groups of users at any given time or location is critical.

The controller and access points have a crucial decision making algorithm, that is Resource Reservation
Control (RRC) provides enhanced capabilities to manage admission and policy controls. Admission and policy decisions are made based on the radio resource measurements, statistics measurement of the traffic, and system configurations. The controller initiates RRC requests to the access points for the IGMP join. The accesspoint will process the request for all the parameters listed in this diagram:


 

In the above response all the parameters passed the policy configuration on the controller. The IGMP join request from the client on that access point will be admitted. If the RRC request had a response as shown below, the join request will be investigated and the RRC algorithm will be checked for the policy configuration again. The client will be admitted but as a Best effort client. However, on several attempts of RRC check it will be admitted with a better QoS priority.

RRC is initiated on a client at IGMP join to a stream and can be configured for periodic check. Due to any changes in the wireless characteristic if the RRC metric reply varies considerably the client will be denied to the stream.

RRC provides bandwidth protection for the video client by denying requests that would cause over-subscription. Channel utilization is used as a metric to determine the capacity and perform admission control.


Multicast to Unicast

By enabling 802.11n data rates and providing packet error correction, multicast-to-unicast capabilities of Cisco VideoStream enhance the reliability of delivering streamingvideo over Wi- Fi beyond best-effort features of traditional wireless networks.

A wireless client application subscribes to an IP multicast stream by sending an IGMP join message. With reliable multicast, this request is snooped by the infrastructure, which collects data from the IGMP messages.

 

The system checks the stream subscription and configuration, then collects metrics and traffic policies for the requested stream. If the requested stream is allowed by the policies, a response is sent to the wireless client attached to the access point in order to initiate reliable multicast once the stream arrives.

The system also looks for available bandwidth and configured stream metrics to determine if there is enough airtime to support the new subscription. In addition, the system considers the prevailing load on the radio and the health of the media before making the admission decision. After all the above criteria are met, a join response is sent to the access point. This is when the access point replicates the multicast frame and converts it to 802.11 unicast frames. Finally, a reliable multicast service delivers the video stream as unicast directly to the client.

The Call Admission Control (CAC) configuration stops the oversubscription of the channel and guarantees configured media bandwidth. The CAC configuration will also stop new media users, hence safe-guards the current users from being affected when oversubscribed. The CAC configurations for VideoStream is a key tuning point that balances the voice, video and data users on a wireless media.

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