Transport Overview

The Ditto peer-to-peer network architecture supports both direct communication between Small Peers (device-to-device) and communication by way of a Big Peerthat connects and transmits data between Small Peers (device-to-cloud-to-device).

This dual approach provides flexibility — your app remains efficient in any network environment and you control when and what routes through a central server.

Following are the various transports Ditto uses to facilitate peer-to-peer communication across peers:

• Bluetooth Low Energy
• Apple Wireless Direct Link
• Wi-Fi Aware
• Local Area Network

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Transport Connections

Ditto uses as many technologies as possible to communicate with other devices running your app. These modes, such as Bluetooth Low Energy (LE) and Local Area Network (LAN), are called transports.

While many transport methods are set up automatically, others, such as WebSocket, if configured with the Big Peer, require manual configuration. 

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Connections

When an end user launches your app, the first thing they do is observe how quickly it syncs the latest information.

Ditto understands this. When sync begins, it uses all transports aggressively to locate and connect to multiple potential peers concurrently. At the same time, the existing peers notice the newcomer’s arrival. If capacity, they will also establish connections to the new device.

Together these processes ensure that a new peer is integrated into the mesh as quickly as possible.

A mobile phone has a finite battery life; therefore, after the initial burst of activity, Ditto must adapt to become more efficient.

Each additional LAN connection consumes more CPU time but also depletes radio energy. Bluetooth Low Energy (LE) faces particularly stringent constraints — devices can only handle a few concurrent connections, and each connection initiation can take several seconds.

In larger meshes, Ditto must strategically limit the number of interconnections and choose them wisely to optimize efficiency.

At the same time, Ditto must not have too few connections; otherwise, islanding can occur.

Islanding refers to the isolation of different groups of devices within the same network. Put another way, it’s a scenario where different groups of devices, located in the same room, are connected in individual clusters — if there is no connection between those groups, they will not sync data.

Ditto uses the following two techniques to prevent islanding, neither of which requires central coordination:

• Maintaining a reasonably dense mesh to minimize the likelihood of island formation.

• Implementing a random churn, where devices periodically change their connections to different peers.

  This implementation ensures that even if an island forms, it is likely to be transient and only last a few seconds*. *Random churning refers to the process in which devices slowly change which peers they are connected to.

Next, certain optimizations are possible.

For instance, improve the diversity of the mesh. Imagine that two peers are candidates for a Bluetooth LE connection; however, they only have the capacity for one. If you are already connected to one of those peers through a Wi-Fi connection, then the Bluetooth LE connection should be prioritized on the other peer to improve the diversity of the mesh.

Now, let’s consider the same scenario but with the capacity for two Bluetooth Low Energy (LE) connections.

In this case, we would establish connections with both available peers. The Bluetooth connection associated with the Wi-Fi connection will remain inactive for the time being. However, if the Wi-Fi connection is lost in the future, Ditto will seamlessly switch to the pre-established Bluetooth connection without any noticeable disruption for the user.

It might sound complex, but there’s no need to worry. All of these functionalities are integrated into Ditto, and your app will handle them automatically. You simply need to enable your transports, and Ditto will optimize their usage seamlessly.

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Multiplexer

In smaller meshes, Ditto creates multiple connections to the same peer using different transports.

While this approach may seem wasteful, it provides important performance benefits:

• Lower latency during the initial sync process since these transports race to establish a connection, with the first successful connection triggering sync.

• Ensures that large updates sync as quickly as possible by prioritizing the fastest available connection.

  Meanwhile, slower connections like Bluetooth LE, which have limited radio bandwidth, are preserved — remaining idle for peers in urgent need.

  If the fastest connection is lost, whatever the next-best option is ready to take over immediately, reducing or even eliminating the downtown when sync is interrupted.

The seamless switching between transports relies on a Ditto component called the multiplexer.

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Bluetooth Low Energy

Ditto utilizes both traditional Wi-Fi and Bluetooth Low Energy (LE) to maintain a continuous mesh network of Transmission Control Protocol (TCP) connections.

Bluetooth LE technology forms low-powered and high-distance connections between devices, making it highly performant in offline scenarios when replicating small amounts of data. 

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Performance

The following distances, limitations, and capacities are approximations and vary depending on the Bluetooth® firmware installed in the end-user environment.

Bandwidth Capacity	Discoverability Range	Distance Durability
20-kilobyte (KB) maximum per 1-second interval	30- to 60-meter maximum	- For v.4.0, 80-meter maximum

• For v.5.0, 130-meter maximum |

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Limitations

Bluetooth LE performance declines in the following scenarios:

• Physical obstructions, radio signal attenuation, radio frequency congestion, among other environmental challenges.

• Large amounts of binary data such as high-resolution image files or large document objects.

In addition, when iOS devices establish a Bluetooth LE connection with Android devices:

• End users can view the connection from their device’s iOS Bluetooth settings.
• When your app is forced to close on the iOS device, the Bluetooth connection to the Android device automatically terminates.

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Peer-to-Peer Wi-Fi

The bandwidth capacity and distance limitation of peer-to-peer Wi-Fi connections depend on the end-user environment, as different devices and platforms support varying Wi-Fi technologies.

The following table provides an overview of the Wi-Fi technologies Ditto supports, organized by platform:

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Apple Wireless Direct Link

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Performance

AWDL-enabled mesh communication between Apple-based peers has significantly higher bandwidth when compared with Bluetooth LE, allowing for low-latency, high-speed data transfers.

Bandwidth Capacity	Discoverability Range	Distance Durability
- 5 GHz frequency range

• 1-Gigabyte maximum per 8-second interval | 30-to 60-meter maximum | 35-meter maximum |

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Limitations

With an average maximum range of 35 meters from point to point, AWDL allows for shorter distances when compared to Bluetooth LE, which can be sustained for distances up to 130 meters.

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Wi-Fi Aware

Wi-Fi Aware technology is a new open standard that you can use to establish a mesh network connection between devices running on the Windows or Android platform. 

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Performance

Wi-Fi Aware, similar to AWDL for the Apple platform, offers significantly higher bandwidth compared to Bluetooth LE, allowing for low latency, high-speed data transfers between Android or Windows devices:

Bandwidth Capacity	Discoverability Range	Distance Durability
- 2.4- to 5-GHz frequency range

• 1 Gigabyte per 8-second interval | 100- to 300-meter maximum | 100- to 300-meter maximum |

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Limitations

Wi-Fi Aware connections have a limited range of shorter distances compared to Bluetooth LE, which can be sustained for distances up to 130 meters. 

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Local Area Network

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Performance

In general, LAN-based connections offer significantly higher bandwidth capacities compared to Bluetooth LE, allowing for low latency, high-speed data transfers:

Bandwidth Capacity	Discoverability Range	Distance Durability
Traditional LANs: 1- to 10-Mbps maximum; higher for fiber-optic LANs	200-meter maximum	200-meter maximum

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Limitations

The following are common conditions that contribute to a decline in LAN performance:

Factor	Description
Network congestion	When there is a high volume of network traffic, in which multiple devices utilize the LAN at the same time, data transfer speeds and response times lag.
Distance to the router or access point	When devices are physically located far away from the router or access point, connections become unreliable or even unavailable altogether.
Network security and privacy	Network infrastructure enabled with various security controls, such as the Client Isolation Mode feature, may directly or indirectly affect performance. (See Security and Privacy: Client Isolation Mode)
iOS direct connections with desktop-based apps	By default, iOS devices require the IP multicast entitlement to establish direct connections with desktop platforms, such as Windows. (See iOS-to-Desktop Connections)

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Optimizations

This section provides an overview of the different optimization strategies you can use to make the most out of your LAN setup.

For instance, improve the overall responsiveness of your LAN connection by minimizing bandwidth consumption and enhancing the reliability of your peer-to-peer LAN connections.

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Optional Discovery Protocol: IP Multicasting

If you want your iOS app to connect to desktop-based apps over LAN, request the multicast entitlement directly from Apple, and then, once received, add the multicast entitlement to your iOS app. For instructions, see the official Apple documentation > Entitlements > com.apple.developer.network.multicast.

Disabled by default, if you want devices located within the same LAN to find and identify each other automatically, manually enable IP multicasting entitlement.

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Security and Privacy: Client Isolation Mode

If network infrastructure is configured with Client Isolation Mode enabled, devices are unable to discover each other and form a LAN connection.

Client Isolation Mode is a network security and privacy feature offered by most Wi-Fi routers and access points that prevents devices on the same Wi-Fi network from communicating directly.

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iOS-to-Desktop Connections

Apple requires iOS device end users to grant permissions before a LAN connection with other devices can be established, such as an iOS device connecting directly with a desktop app running on the Windows operating system.

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WebSockets

Small Peers connect with the Big Peer by way of *WebSocket *connections. Supported on all devices, regardless of model and platform, the WebSocket communication protocol is the most commonly available transport protocol for realtime communication.

A WebSocket* *is a full-duplex communication protocol that enables a long-lived connection between Small Peers and the Big Peer:

• Communication is full-duplex when the client and server can communicate in a bidirectional, back-and-forth manner allowing for low-latency data exchange.

• A connection is considered long-lived when, once established, it remains open for an extended period.

• Referred to as the playground token, Small Peers use this passphrase to authenticate with the Big Peer. Once authenticated, the Big Peer issues a unique JSON Web Token (JWT) to establish and ensure the persistence of the connection between Small Peers and the Big Peer.