KitPlus - The TV-Bay Magazine

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MONITORING Paul Robinson UNDERSTANDING THE CAUSE AND EFFECT OF JITTER IN AN OPERATIONAL IP VIDEO NETWORK WHAT ARE THE ADVANTAGES OF MOVING TO AN IP INFRASTRUCTURE? The most commonly cited advantage of deploying IP Video networks in production and other operational applications is the ability to use Commercial Off-The-Shelf (COTS) IT-based infrastructure, which takes advantage of the economies of scale of the IT industry when compared with the relatively small broadcast industry. Additional advantages of reduced cabling cost and weight along with the much greater routing flexibility that offers more flexible production options. These advantages mean that in many parts of the World, trials, proofs of concept and early deployments of IP Video networks are already in place. WHAT ARE THE BIGGEST CHALLENGES WHEN MOVING TO AN IP INFRASTRUCTURE? IP brings both technical and skills challenges. The technical challenges include jitter; latency; the risk of dropped packets and network asymmetry which results in different path delays upstream and downstream. that in most data center applications, lost data can be re-sent – this is not the case with high bitrate Video. The challenge for the network engineer is in understanding video technology and its impact on IT infrastructure. WHAT CAUSES IP PACKET JITTER? In any digital system, Jitter is any deviation from the regular periodicity of the signal. In IP networks jitter variation of the packet arrival interval at a receiver. If the network routers and switches are all configured and operating correctly, the most common cause of jitter is network congestion at router/switch interfaces. The application within a network element will likely require the data to be received in a non-bursty form and as a result, receiving devices adopt a de-jitter buffer, with the application receiving the packets from the output of this buffer rather than directly. Packets flow out of the buffer at a regular rate, smoothing out the variations in the timing of the packets flowing into the buffer. Deploying IP for video production applications is effectively the collision of the two Worlds of video engineering and network engineering. Video engineers are comfortable with the use of SDI, coax., patch panels, black burst and tri-level for timing and above all, monitoring signal quality. The challenge for the video engineer is to understand IT technology and impact of an IT infrastructure on the video. On the other hand, network engineers are familiar and comfortable with, IP Flows, Protocols, Network traffic, Router Configuration and Precision Time Protocol (PTP) and Network Time Protocol (NTP) for timing. The biggest difference however is 50 | KITPLUS - THE TV-BAY MAGAZINE: ISSUE 119 NOVEMBER 2016 Packet jitter is deviation from the periodicity of the packet arrival interval.