What is Jitter?
You want smooth streaming when you’re binge-watching your favourite show. You want seamless gaming when you’re online with your friends. You want stress-free browsing when you’re shopping online between tasks. Jitter can cause interruptions to all of these things, causing a lot of frustration.
What is Jitter and how does it affect my connection?
Jitter in the technical sense refers to the variation, inconsistency, or fluctuation in the timing of signals in electronics or data packets in networking. The result of Jitter? You’ll often experience:
- A lag
- Choppy audio
- Interrupted video
- Image distortion.
Network issues can cause data packets to arrive at irregular intervals. These varied delays between received packets can cause problems when the expectation is for them to travel and arrive at evenly distributed times.
Imagine voice packets are being transmitted every 10 milliseconds. You would also expect them to be received at 10ms intervals. If network problems mean that some packets are arriving after 20ms and other after 40ms, or even some packets not arriving at all, the variation and delay in receiving the packets is what we know as Jitter.
How do I reduce Jitter?
Contributing factors that can cause Jitter in a network are:
- Network congestion
- Faulty queuing
- Configuration errors
Mitigating Jitter for a LAN (Local Area Network)
Jitter can be kept to a minimum if a LAN is well planned and well designed. Factors to consider are:
- Ensuring there is enough bandwidth and good physical network connections throughout the network helps reduce potential network Jitter.
- Congestion in a network can be monitored with network health tools to identify areas of poor network design, ensuring that changes can be made to avoid Jitter long term.
- Setting alert thresholds to warn of possible congestion on a link would allow an administrator to tackle the issue before it has a serious impact on end users. If link utilization is 80% or over, this is a good indication that a high level of Jitter exists.
- Buffers can be used to alleviate jitter but they are not a long-term solution. A buffer will collect and delay incoming packets, correct any out-of-sequence errors and will forward them at evenly spaced time intervals. By implementing quality of service (QoS), buffers can be used to manage VoIP traffic or other high-priority packets which when identified are immediately processed and sent out.
- In situations where there is significant jitter, instead of creating delays in the buffer, it may be better to drop packets or create a fixed buffer size. If buffers are full they will be unable to contain all arriving packets.
Mitigating Jitter for a WAN (Wide Area Network)
WAN networks can experience significant jitter, especially when traffic has multiple paths and hops to a destination, or when load balancing through two comparable paths. However, there are several countermeasures that can be adopted to minimize these effects:
- Implement QoS via a service provider as part of a managed service.
- Utilize MPLS circuits. MPLS minimizes the effects of jitter by providing guaranteed QoS.
- Use WAN virtualization – WAN virtualization tackles congestion-based jitter as it occurs by measuring one-way latency across all paths and will migrate data onto another path if it detects significant jitter.
What is an acceptable level of Jitter in a network?
As much as we would love to eliminate Jitter altogether, it’s unlikely that a network will experience zero Jitter. The good news is that even though we can’t eliminate it, we CAN manage it. So with this in mind, if you’re a network administrator, here’s how you can determine an acceptable level of Jitter for your network, and how to keep an eye on particular services that may be more sensitive to Jitter issues.
Jitter and the effects on voice
High quality voice traffic is really important for every network administrator. There are unfortunately many factors that can affect voice quality, and one of the most common metrics to measure it is Jitter and latency.
Voice quality can be affected by network congestion and/or slow internet speeds, resulting in voice packets being received in a different order to how they were sent, or being dropped altogether.
Any Jitter in excess of 40ms can cause severe degradation in the quality of a call. Cisco’s Enterprise QoS Solution Reference Network Design Guide suggests the following guidelines for voice:
- Delay (one-way): 150ms or less
- Jitter: 30ms or less
- Loss: 1% or less
How does Jitter affect Video?
Jitter can have a big impact on gameplay and streaming, hindering user experience quite significantly. A general rule of thumb is to ideally keep jitter for video between 30-50 ms.
For interactive video streams, Jitter should not exceed 30ms. On video streaming platforms (Netflix, NowTV, Amazon Prime, etc) Jitter is better tolerated because video streaming is unidirectional and when using a large buffer more data can be cached. Videoconferencing is more complicated as it utilizes bidirectional streaming. Real-time conferencing and high bitrate video can encounter noticeable issues when jitter is present within a network.
Users will notice the effects of Jitter through frozen or jerky video.
What is the most common cause of Jitter?
The most common cause of Jitter is network congestion at an exit point within a network. This could be via:
- A switch
- A router
- A firewall interface
Most issues will be mitigated by Jitter buffers. However, excessive Jitter will cause these buffers to overflow which results in data packets being lost. On the flip side, if the buffer size is too large it can cause excessive latency on the network. It’s a fine balance!
Managing Jitter on Your Network
Jitter – the variation in data packet arrival times – is an inherent challenge in networking that can severely degrade the quality of real-time applications, resulting in frustrating user experiences like lag, choppy audio or interrupted video.
Whilst eliminating Jitter is nearly impossible, it is entirely manageable for network administrators.
Ultimately, successful management hinges on maintaining a fine balance with Jitter buffers to correct out-of-sequence errors, without introducing latency issues into the mix.
By following industry guidelines, for example keeping Jitter for voice traffic at 30ms or less, network administrators can ensure a reliable and seamless user experience.
