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P2P Latency Diagram

Does P2P CDN Offload Add Latency to Live Video?

José D. Vázquez

Our team works closely with our customers, listening and understanding their needs. We use this to provide solutions that have value to them. One of the questions we hear frequently is whether our network adds latency to live streams. In short, no, and we’ll take this opportunity to explain how we avoid doing so.

Comprehending video streaming

As video content moves through the different processes of a streaming workflow, such as encoding, packaging, or delivery, the latency increases. One of the fears is that integrating our network will result in higher latency. With the industry moving towards low latency this would be a setback. 

Such a concern is understandable, as video using our network may have to travel through more nodes.

A longer route could cause live video to, occasionally, arrive later compared to directly downloading it from the CDN. Even so, playback latency does not increase. And, we found out that introducing P2P delivery with Teltoo actually reduces the overall video startup time (a.k.a. join time).

Playback latency is not altered. This is the result of two factors. The first one being that HLS/DASH live streams are delivered using video segments, each one being several seconds long, and secondly the existence of a buffer in video players.

Both of them are strictly related. When a user starts playback the first segments are always downloaded from the CDN. The video player downloads several segments before displaying video. In general, a video player aims to store around 3 segments at all times. This helps avoid rebuffering and harming the user experience.

Video players usually start by playing the oldest segment, leaving the newest one at the end of the line. Segments that are downloaded as the stream plays will have to wait in the buffer before they are displayed to the user. This last part explains why Teltoo’s network does not add latency. Segments have to wait before being used, normally 2 seconds or more, so it does not matter if they take 50 milliseconds for an extra node hop.

The following diagram shows how the buffer avoids an increase in latency when using Teltoo.

P2P Latency Diagram with Key

Improving startup time

A not so obvious impact of using Teltoo in the delivery chain is that in the most demanding scenarios we are able to reduce the CDN fetch time, and more importantly the so-called metric: video startup or join time. 

A live stream with many users translates to many devices connected to a CDN downloading content. Live video requires video players to constantly ask for new segments, containing the newest generated video. At any point in time, a server may be handling thousands of requests per second, each one consuming a certain amount of bandwidth, CPU and other bare metal resources. 

Therefore, a server or CDN node responding to too many connections simultaneously is vulnerable to not being able to answer on time. Too many requests or insufficient bandwidth will increase the time that is required for each of these requests to finish.

This does not necessarily increase the playback latency for users because, as we previously discussed, the buffer exists to counter these sort of situations. Still, if the user just connected, then the first segments may arrive with an increased CDN response time. This user is then susceptible to playing a video stream with a deteriorated startup time, and an overall higher latency, compared to a less demanding situation. 

Teltoo’s network solves this by reducing the load. Every CDN node has to handle fewer requests when Teltoo is in place, thus reducing the possibility of reaching the point where video startup time is impacted by a worsened CDN response time. 

The many benefits of Teltoo’s network

Delivering a live stream to thousands of users simultaneously can take a toll on performance. Our network is built to secure the reliability of your streams, even in the harshest conditions. We are able to do this without adding any latency to your stream, and at the same time help your CDN’s performance. Using our network and reducing your CDN’s load helps improve the response time of its nodes, therefore achieving better video startup time.

Integrate Teltoo in your current workflow and ensure yourself that you are providing your viewers with the infrastructure necessary to achieve the best experience possible.

About the author

José is part of the Teltoo team, whose software-only decentralized video delivery technology helps live-streaming providers to improve quality and optimize delivery costs.