VRPN

Last updated
Virtual-Reality Peripheral Network
Developer(s) ReliaSolve
Written in C++, Python, Java
Type VR Middleware
Website github.com/vrpn/vrpn/wiki

VRPN (Virtual-Reality Peripheral Network) is a device-independent, network-based interface for accessing virtual reality peripherals in VR applications. It was originally designed and implemented by Russell M. Taylor II at the Department of Computer Science of the University of North Carolina at Chapel Hill. VRPN was maintained and supported by Sensics [1] while it was business. It is currently maintained by ReliaSolve and developed in collaboration with a productive community of contributors. It is described more fully at vrpn.net and in VRPN-VRST. [2]

Contents

The purpose of VRPN is to provide a unified interface to input devices, like motion trackers or joystick controllers. It also provides the following:

The VRPN system consists of programming interfaces for both the client application and the hardware drivers and a server application that communicates with the hardware devices. The client interfaces are written in C++ but have been wrapped in C#, Python and Java.

A typical application of VRPN is to encode and send 6DoF motion capture data through the network in real time.

Networking

A VRPN client can establish a connection with a VRPN server (the device providing the data) in two ways: either over TCP (reliable, but less efficient), or over UDP (unreliable, but lower-latency and more efficient). The "unreliable" mode is generally preferred when the latency is critical.

The "unreliable" connection initialization sequence makes use of both the TCP and UDP protocols. It works as follows: [3]

  1. the client opens a TCP socket for listening on an arbitrary port;
  2. the client sends the port number of this socket, along with its own machine name, in a UDP datagram directed to a well known port of the VRPN server (the default is 3883);
  3. the server opens a TCP connection with the client, to the port number communicated at step 2;
  4. if the TCP connection is established, each device tells to the other the supported VRPN version;
  5. if the versions are not compatible, the connection is dropped;
  6. otherwise, each device begins to listen on a new UDP port (different from those used before) and sends the port number to the other device, by using the previously created TCP connection;
  7. from now on, all the data is sent over the two UDP ports opened at step 6.

The advantages of this approach are: fast connection time and fast failure detection during connection.

However, the "unreliable" connection initialization protocol does not honor the strict layering protocol design principle, as the application-level VRPN payload leaks information about lower levels in the network stack, namely the machine names and TCP/UDP port numbers. Because of this design choice, it is impossible to establish a VRPN connection between two devices connected through a NAT: the router would need to translate not only the layer-3 information in the packet headers, but also the references to IP addresses and port numbers inside the VRPN payload.

To deal with this problem, VRPN offers [4] a second "reliable", TCP-only connection initialization mode, which is a standard TCP server-client interaction: the VRPN server listens on a well-known TCP port and the client initiates a connection. In this mode, all the data is sent on the same TCP connection, and no UDP communication is required.

Supported Devices

Trackers (listed alphabetically)

Other devices (listed alphabetically)

References

  1. ↑ Sensics http://sensics.com
  2. ↑ Taylor, Russell (November 15–17, 2001). "VRPN". Proceedings of the ACM symposium on Virtual reality software and technology. pp. 55–61. doi:10.1145/505008.505019. ISBN   9781581134278. S2CID   1487053.
  3. ↑ vrpn: Using vrpn_Connection - Official GitHub Repository, Virtual Reality Peripheral Network, 2018-02-19, retrieved 2018-02-20
  4. ↑ vrpn: Troubleshooting VRPN - Official GitHub Repository, Virtual Reality Peripheral Network, 2018-02-19, retrieved 2018-02-20
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