AnyDesk

AnyDesk Software GmbH is still quite a young company, having been founded in 2014 by three former TeamViewer employees. In the same year, AnyDesk emerged (Figure 6) as a beta version for Windows XP, 7, 8.x, and 10. The Windows version can also be started with the simple click of a mouse on the .exe file (which is around 1MB in size), making it portable.

Figure 6: Windows session with AnyDesk on Ubuntu. The proprietary protocol transfers data in a flash.

Meanwhile, AnyDesk is also available in stable versions for Linux and BSD. Native versions (for either 32- or 64-bit systems) for Debian, Ubuntu, Fedora, RHEL, Mageia, openSUSE, and SLES, as well as a generic Linux version are on hand for Linux admins. A Mac version and apps for Apple and Android tablets are planned.

Although user-friendliness is definitely a subjective question, the AnyDesk folks are well placed when it comes to the speed and quality of the transferred desktop. They are assisted by a proprietary protocol that transmits the data with DeskRT.

The video codec for graphical user interfaces – specially developed by AnyDesk – compresses the data. The protocol transfers the screen content thanks to a special compression process with up to 60 images per second. At the same time, AnyDesk caches up to 100 screen content captures in a buffer; thus it does not need to resend when need arises.

The developers have integrated AnyDesk into the respective operating system at a low level and optimized it for multi-process architectures. This means the image data reaches the screen after just a few processing steps. The company's servers, shared worldwide, use Erlang/OTP [13], a middleware for building shared, highly available systems, based on the Erlang programming language developed by Ericsson. TLS 1.2 guarantees security, while AnyDesk authenticates the connected subscriber cryptographically.

The software is based on a yearly payment plan. Besides the free version (which provides one workplace with session, sound and video, and data transfer functions), the creators offer a Lite version for $60, and a Pro variant for $180. If you are interested, you can individually negotiate further requirements as part of the Enterprise plan.

NoMachine NX

The terminal server software NX (Figure 7) from Italian software smithy NoMachine is the equivalent of Microsoft's RDP [14] for the Linux world and is particularly suited to connections that only use low bandwidth. NX increases the efficiency of the X11 protocol by compressing the data in the network traffic and creating a cache for data that have already been transferred. Furthermore, the in-house NX protocol reduces the round trips between X client and X server used extensively by X11; these increase the latency of the connection (Figure 8).

Figure 7: NoMachine's NX saves the last connections, facilitating quick access.

Figure 8: If you tinker with the individual options, you can squeeze out even more bandwidth.

NX transfers the data through a SSH tunnel. This relies on the client-server model by which the NX server can forward sessions to VNC servers or via RDP to Windows terminal servers, compressing the data traffic again. The NX client runs on Linux, Windows, OS X, and on other stationary and mobile platforms.

The server and client components of NX have been proprietary since version 4.0. The developers offer a wide spectrum of Enterprise products that admins can test free of charge for 30 days [15]. NoMachine links its licensing model to the number of CPU cores used, along with the respective platform. The chosen distribution also plays a role on Linux. Prices start at around $700 and are uncapped.

X2Go

A popular, free alternative to NX is the terminal server X2Go (Figure 9), which similarly operates under the client-server principle. It is available for Linux, Maemo, and Windows. The client software runs on thin clients, PCs, web browsers, and mobile devices. You can access the sessions over a web client with a Firefox add-on. Like Free NX (no longer in active development), X2Go makes use of the libraries of NoMachine NX version 3, which are still subject to the GPL.

Figure 9: Configuring a session on X2Go, which uses the free NX protocol version 3.0.

Based on this library, the X2Go project has built up a number of extensions, including an alternative graphical interface in the form of PyHoca-GUI. Because X2Go is popular with businesses, too, there is comprehensive documentation and a support forum. The client and alternative GUI are part of the standard repertoire in most distributions. For the server, web plugin, and many other extensions, the admin usually has to integrate the X2Go repository. The project is subject to the GPLv2 and AGPLv3.