The article will provide a reader with information on Cisco’s stream admission and prioritization.The Video Stream is an efficient, highly effective means of communication. It is also very bandwidth-intensive. Not all video content is prioritized the same. Organizations investing in video cannot afford to have network bandwidth consumed without prioritization of business-critical media. With stream admission, network administrators can configure media streams with different priorities based on importance within the organization. The feature can be enabled at the radio level (2.4 and 5 GHz) and at the wireless LAN (WLAN) or Service Set Identifier (SSID) level. It also gives administrators more control to identify specific video streams for preferential QoS treatment.
The configured video stream will have lower priority than voice and higher priority than best-effort traffic. All other multicast traffic will be admitted as best-effort traffic, even though it is marked for QoS for video priority.
Resource Reservation Control
As more and more users begin to use video on Wi-Fi endpoints, the ability to gracefully manage and scale a continuous, high-quality experience for fluctuating groups of users at any given time or location is critical. Resource reservation control (RRC) provides enhanced capabilities to manage admission and policy controls. Admission and policy decisions are performed based upon the radio frequency measurements, traffic statistics measurements, and system configurations. Because the availability of bandwidth is limited in the wireless medium, admission control becomes very important to control access and for the efficient use of the available bandwidth. The resource for which the client needs admission is the medium time, which is the air time packets consume in traveling over the air. RRC provides bandwidth protection for the video client by denying requests that would cause oversubscription. Channel usage is used as a metric to determine the capacity and perform admission control. Figure 3 illustrates how RRC works.
Multicast to Unicast
Native Wi-Fi multicast is not a reliable service. With unicast, acknowledgements (ACKs) help ensure reliability. If no acknowledgement is received, the packet is resent. For multicast there are no ACKs, so the Wi-Fi packet loss rate can be 1 to 2 percent or higher. This unreliability is a problem for streaming video. With multicast-to-unicast conversion, the frames are sent as unicast, allowing the access point to receive ACKs from the clients and to determine when frames need to be retransmitted (in the case of lost or corrupted frames).
By enabling IEEE 802.11n data rates and providing packet error correction, multicast-to-unicast capabilities of Cisco VideoStream enhance the reliability of delivering streaming video over Wi-Fi beyond the best-effort features of traditional wireless networks.
A wireless client application subscribes to an IP Multicast stream by sending an Internet Group Management Protocol (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 and collects metrics and traffic policies for the requested stream.
If the policies allow the requested stream, a response is sent to the wireless client attached to the access point in order to initiate reliable multicast when 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 these criteria are met, a join response is sent to the access point. At this point the access point replicates the multicast frame and converts it to 802.11 unicast frames.