Why is Delay an Important WebRTC Metric for Contact Centers?

By Allie Mellen on January 23, 2019
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Delay is an important metric that can indicate the audio quality on a call. It can also be used to understand round-trip time, another important and popular WebRTC metric. What is delay, and why should WebRTC-enabled contact centers work to make it as low as possible? Read on to find out.


If you’re interested in learning more about the importance of WebRTC in the call center, check out our white paper: Cloud-based Contact Centers: the WebRTC Story.

What Is Delay?

Delay is a very important computer networking metric that measures the amount of time it takes for a bit of data to move from one endpoint to another. It is typically on the scale of fractions of seconds. It can change based on multiple different factors, including the location of the endpoints, the size of the packet, and the amount of traffic on the network.

What Are The Contributors To Delay?

Delay is most easily understood as the collection of four key components: processing delay, queueing delay, transmission delay, and propagation delay. Processing, queuing and transmission delays are all functions of the nodes in the network. Each node that a packet must transit to reach the endpoint introduces processing, queuing and transmission delay. The more nodes there are between endpoints, the more delay is introduced. In real time communications, common examples of nodes includes proxies, TURN servers, routers and firewalls.

Propagation delay is a function of the media connecting the nodes and endpoints. Here, the driving function is the distance and type of media. Propagation delay for a each media type is expressed as a fraction of the speed of light in a vacuum. For example, fiber optic cable has a lower propagation delay (67%) compared to most copper cables.

  1. Processing Delay is the time associated with a network node analyzing a packet header and determining where the packet must be sent. This depends heavily on the entries in the routing table, the execution of data structures in the node, and the hardware implementation.

  2. Queueing Delay is the time between a packet being placed in a transmit queue and it being sent. This varies depending on the amount of traffic, the type of traffic, and what router queue algorithms are implemented. Different algorithms may adjust delays for system preference, or require the same delay for all traffic.

  3. Transmission Delay is the time needed to push a packet’s data bits into the media. This changes based on the size of the packet and the bandwidth. This does not depend on the distance of the media, as it is solely the time to push a packet’s bits into the meda, not to travel down the media to the receiving endpoint.

  4. Propagation Delay is the time associated with the first bit of the packet traveling from the sending node or endpoint to the receiving node or endpoint. This is often referred to as a delay by distance, and as such is influenced by the distance the bit must travel and the propagation speed.

All four of these components make up the total delay in a network. In a previous blog post, we explained how round-trip time is the combination of these delays from the receiving endpoint and back to the sending endpoint.

 

Why is Delay an Important WebRTC Metric for Contact Centers?

Like RTT, delay can have a profound impact on the user experience. In audio calls, 200 ms of delay is considered the maximum threshold for acceptable call quality. The ITU is more stringent, recommending that delay be kept below 100 ms. In contact centers, ensuring smooth communication is invaluable. Having a high delay can make it difficult for contact center agents to communicate with customers, increasing time to resolution and potential customer frustration. The last thing you need is customers calling in for help and having a hard time getting it just because of technology. Work to monitor delay and keep it as low as possible.

 

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