Video and audio over IP is all the rage and while companies can benefit greatly from deploying all-IP or hybrid-IP/fiber networks, IP infrastructures come with their own set of issues. Jitter and latency are two of the most common problems hindering broadcast quality of audio and video transmissions over IP networks. IT and video engineers who understand the causes can take steps to reduce jitter and improve audio and video quality. 

What is jitter?


Jitter is the variation in packet arrival measured over time. In other words, it is the variation in the packet flow between two end points or two elements, when some packets take longer to travel from one point in the network to another. Jitter results from network congestion, network timing drift, and network route changes. Jitter is more problematic in real-time or time sensitive services like audio and video. Excessive jitter leads to artifacts that degrade the quality of the service. The amount of jitter tolerable on a network is affected by the depth of the “jitter buffer” existing in the network equipment involved in the transmission path. If left unattended buffer overflows, underflows, and missing or late packets can result degrading the quality of the video or audio signals.

How to mitigate jitter and its effects

There are several steps network engineers can take to compensate and control jitter including applying proper quality of service (QoS) settings to protect time sensitive transmission, properly adjusting jitter buffers on endpoint devices as well as intermediary elements, and even addressing the source of the jitter if necessary.

  • QoS: Applying comprehensive QoS methods where time-sensitive services are given priority over secondary services prevents these lower priority services from congesting the network and denying service. This will help reduce the likelihood of missed or discarded packets.
  • Buffering: The more jitter buffer available, the more the network can reduce the effects of jitter. Most endpoint devices and packet-based network devices have jitter buffers to compensate for network jitter. An optimal balance needs to be reached between jitter and latency as excessive buffering adds to latency.
  • Sources of jitter: The most common sources of jitter in IP transmissions are network congestion, poor network synchronization or timing, and lack of route determinism in the network.
    • Network congestion can be addressed by applying proper traffic and bandwidth management techniques like appropriately engineering your network resources or policing bandwidth utilization by lower priority services or traffic
    • Network timing and synchronization needs to be correctly implemented by assuring that the elements in the network in need of timing have their sources traceable to the same source and this source needs to be of high accuracy
    • Route determinism is accomplished by implementing methods such as virtual private networking and virtual transport mechanisms like multi-protocol label switching (MPLS)

Conclusion

Migrating to IP technology brings many benefits but there are considerations on how to “harness” this powerful technology in support of time sensitive content and services. Jitter reduction is one of those considerations. Fortunately, proper network engineering in the areas of traffic and capacity management, and networking timing and synchronization mitigates and creates determinism in packet based networks.

This blog post appears in the July 2017 issue of Wheatstone's Wheat: NewsTV.  Artel's InfinityLink media transport solutions are used with Wheatsone's WheatNet-IP audio networked studios for REMI or live remote production applications.  Learn more about Artel's IP Solutions