SRT

Setting up Main/Backup SRT connection bonding in Callaba Cloud

Oct 11, 2022

As the title says, in this tutorial we’ll show how you can easily set up SRT connection bonding Main/Backup mode to ensure that whatever happens, you stream will continue without any major issues.

What is SRT connection bonding

SRT Main/Backup bonding involves sending video data simultaneously over two (or more) separate paths—one is the main route, and the other is the backup.

The SRT protocol intelligently manages the data flow, constantly monitoring the quality of both paths. If the main path encounters any issues, such as network congestion or packet loss, the system seamlessly switches to the backup path, preventing interruptions in the video stream.

Main/Backup bonding provides a reliable and stable video streaming experience, even in challenging network conditions. Whether it's a temporary glitch in the internet connection or a sudden spike in traffic, SRT Main/Backup bonding ensures that your video stream remains unaffected by quickly switching to backup line if the main one fails.

Why Main/Backup switching is cool

it allows to save bandwidth, because it only uses one active stream at a time
if the main stream stops working for whatever reason, this mechanism switches seamlessly to the backup source and the stream continues
it’s possible to have more than one backup stream: all backup links will stay connected and ready for data transmission, but not activated for actual payload transmission.
backup links are only activated for actual transmission when the main link fails or doesn’t achieve the required throughput

If you want to learn more about how main/backup algorithm works, please refer to official SRT documentation here.

How to set up Main/Backup switching in Callaba

For this tutorial you will need your streaming sources, main one and another one to fall back to, plus a Callaba Cloud instance.

To keep this tutorial short and sweet, we are not going to explain the basics here.
If you’ve never tried Callaba Cloud and this is your first time engaging with a cloud platform, please read our step-by-step manual: How to Launch Callaba on AWS.

Subscribing to Callaba Cloud will take no more than 5 minutes.

Callaba is a streaming service that supports a broad range of video industry standards. We provide simple and convenient video streaming pipeline within a single solution : input source encoding, video processing, output source decoding, live video and audio streaming, video recording, video on demand.

Pro tip :
Make sure you read launching tutorial to the end, so that you know how to stop your instance when your work is finished. This is important to avoid unnecessary charges.

Let’s begin

1. Log into Callaba Cloud Live Streaming dashboard

2. Go to SRT Servers section
Click “Add New”

In the page that opens

Name your server

Port : specify port (in our case 9003)

Scroll down to the Routing Settings

SRT Routing : Public IP

Routing mode : Pull

In our example we’re going to be pulling both of our streams (the main one and the backup one).

Now all we need to do is to specify our sources (Hosts).

Routing Host IP : specify your source IP

Routing SRT Port : specify port

The same way we’ll have to add our backup source.

Click “+ Add SRT Host”

Routing Host IP : specify your backup source IP

Routing SRT Port : specify backup source port

If you have more backup sources, add them the same way

Allow Pulling

This step is required for version 7.3 and above.

In our version 7, we have added Allowed Streams.

"Allowed Streams" is a protective mechanism to ensure that only allowed streams can connect to your instance. No outsiders!

By deafult, each SRT server has two allowed streams - Publisher and Receiver. This means that the SRT server can send (publish) and receive streams.

As we are setting up routing that requires Pulling, we need to add a new allowed stream to tell the SRT server that it's okay to engage in this type of connection. We've allowed it.

Without this explicit permission, Pulling will not work.

Let's do it

Unfold Allowed Streams

Click "Add Stream"

In the new stream that appears, set Role to Puller.

Role : Puller

Click "Save"

Cool. Done. Now Callaba will switch to backup in case if main stream get interrupted.

Pro tip :

To see your incoming / outgoing bitrate you’ll need to set up some kind of a receiver for your stream. A receiver can be a player, a recording process, a restream, for example. Or you can grab the stream any other way.