QoS Application Classes: Streaming Video, Interactive Video, and Mission-Critical Data

In the last blog, we began discussing the specific applications that are mapped into the various application classes used in a QoS deployment. The 11 application classes are as follows: Routing Voice Interactive Video Streaming Video Mission-Critical Data Call Signalling Transactional Data Network Management Bulk Data Best Effort Scavenger The interactive video class represents two-way real-time video. Cisco’s Unified Video Advantage (CUVA) client and Cisco Unified Personal Communicator (CUPC) both represent video to the desktop solutions that would be mapped to the interactive video class. Cisco’s 7985 series video phone would also be mapped to this application class. Cisco’s telepresence solution has much more stringent requirements than video to the desktop applications and is deserving of its own application class. RFC 4594 details three video classes to differentiate streaming video (broadcast), video to the desktop (multimedia conferencing) and telepresence video (real-time interactive). For more details on telepresence QoS requirements, read the QoS section of the Telepresence 2.0 SRND. Third party videoconferencing solutions (Polycom, Tanberg, Sony, etc.) would be mapped to either the interactive video or real-time interactive video class based on the application requirements. Video to the desktop applications normally have bandwidth requirements in line with the H.263 and H.264 video codecs (384kbps + 20% overhead). The delay and jitter requirements of interactive video are in line with real-time voice, but telepresence has more stringent delay and jitter requirements detailed in the Telepresence 2.0 SRND. Most real-time voice and video traffic are based on the UDP transport layer of the OSI-Rm. UDP based traffic is connectionless; if a packet is lost it will never be retransmitted. The bandwidth, delay, and jitter requirements for both voice and interactive video are as follows: Bandwidth: Dependent upon audio and/or video codec (460kbps for 384kbps H.264 video) Delay: 150ms (one way) Jitter (delay variation): 20ms (jitter should be equal to the sampling rate) Streaming video (broadcast) is one-way video. Broadcast television and pre-recorded distance learning video are two types of streaming video. This type of video is sometimes referred to as on-demand video. Streaming video does not have stringent delay and jitter requirements because the hard drive and memory (DRAM) of the receiving station provides a very large de-jitter (playout) buffer to ensure playback of streaming video is smooth and gapless. www.youtube.com is an example of a streaming video application. To ensure high quality playback, I click the pause button when accessing a youtube video and I wait until the playback bar under the video is red from left to right. The PC is downloading the video packets from Youtube and putting them in the de-jitter buffer (temporary hard drive space). Delay and jitter is not of much concern when you have a large de-jitter buffer and 5 minutes to wait for the de-jitter buffer to fill up. Most streaming video applications are also TCP based which will re-transmit lost packets. The large de-jitter buffer can re-order the packets when they arrive. The next application class is mission-critical data. Mission critical data is normally reserved for one transactional data application that is of higher importance to the company than the other transactional data applications and data application such as instant messaging, telnet, remote desktop, Citrix, and highly interactive groupware applications. Mission critical data applications are usually of a more interactive nature than other important data applications. Most mission critical data applications are TCP based, but the interactive nature of the traffic requires more care than other data traffic. In the net blog, we will continue our conversation of application classes with the signaling class. REFERENCES Cisco Telepresence SRND: http://www.cisco.com/en/US/docs/solutions/Enterprise/Video/TP-Book.html IETF RFCs http://www.ietf.org

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