Exploring DisplayPort: DP Alt Mode, MST, DSC, and Key Advancements in Video Connectivity

DisplayPort has become a leading standard for video connectivity, consistently adapting to meet the rising demands for high-resolution displays, multi-monitor setups, and seamless integration with USB-C.

Developed by the Video Electronics Standards Association (VESA), DisplayPort not only supports high-definition video and audio but also introduces essential features that enhance user experiences, including DisplayPort Alternate Mode (DP Alt Mode), Multi-Stream Transport (MST), and Display Stream Compression (DSC). These are distinct technologies within the DisplayPort ecosystem, each serving unique purposes. These features are particularly beneficial in setups where both high resolutions and multi-monitor configurations are essential.

This article will explore these technologies and how advancements in the DisplayPort standard have significantly improved the modern workspace, delivering higher productivity and enhanced visual experiences.

DisplayPort and USB-C: A Powerful Combination

Integrating DisplayPort video signaling with the USB-C connector creates a powerful solution for modern connectivity needs, making USB-C a true all-in-one port for today’s devices. By supporting “DisplayPort Alternate Mode,” USB-C can seamlessly transmit high-quality video, data, and power through a single cable, significantly reducing clutter and simplifying setups. This combination is especially beneficial in slim, portable devices like laptops, tablets, and cell phones, which rely on streamlined port designs. Additionally, DisplayPort Alt Mode over USB-C enables high-resolution, multi-monitor configurations that maintain the high refresh rates and color fidelity required for creative professional use (like video, photo, or 3D design and editing), all while supporting charging and data transfer. 

With the introduction of DisplayPort 1.2, capabilities such as higher resolutions up to 4K at 60Hz and Multi-Stream Transport (MST) became available, enhancing multi-monitor support and overall video performance. DisplayPort 1.4 further improved upon this by adding support for 8K resolution with Display Stream Compression (DSC) and HDR, allowing for even greater image quality and more efficient bandwidth usage. DisplayPort 2.1, the latest in the series, expands on these capabilities significantly by supporting resolutions up to 16K (with DSC) and higher refresh rates at 8K, as well as improved support for dual-display setups with 8K resolution per screen. This version includes more robust bandwidth handling and improved error correction, ensuring even greater fidelity and performance for demanding multimedia and professional applications. The synergy between DisplayPort and USB-C enhances productivity and provides a cleaner, more efficient workspace.

DisplayPort Alternate Mode (DP Alt Mode)

DP Alt Mode is a protocol that enables DisplayPort video and audio signals to be transmitted over a USB-C connection, allowing devices with USB-C ports to access DisplayPort capabilities without requiring a dedicated DisplayPort connector. This integration reduces the number of ports on modern devices and simplifies connectivity, as USB-C can now carry DisplayPort’s high-bandwidth signals alongside data and power. VESA collaborated with the USB Implementers Forum (USB-IF) to bring this functionality to the USB-C ecosystem, combining DisplayPort’s advanced features with USB-C’s versatility and universal compatibility. One of the key features available through DP Alt Mode is Multi-Stream Transport (MST), which allows multiple monitors to be connected and operated efficiently through a single connection. Additionally, Display Stream Compression (DSC) plays an important role in maximizing video quality and reducing data requirements, enabling high-resolution video transmission, such as 4K and 8K, with minimal impact on bandwidth.

Multi-Stream Transport (MST): Revolutionizing Multi-Monitor Configurations

Multi-Stream Transport (MST), introduced with DisplayPort 1.2, enables a single DisplayPort connection to carry multiple video streams. By using a process called multiplexing, MST combines video signals, which compatible devices like MST hubs or docking stations can then split the video signal into multiple video streams. This technology is particularly useful for users with multi-monitor setups who want to optimize their desktops by bringing everything together with one device, such as a docking station. Another benefit of MST is that it’s a driverless solution, meaning it doesn’t require any additional software installation for it to work. This is because MST operates at a hardware level using DisplayPort standards, so as long as the device and monitors support MST, they can communicate directly. As a result, MST provides a plug-and-play experience, making it straightforward for users to expand their displays across multiple monitors.

However, MST is not compatible with macOS. While macOS does support DisplayPort standards in single-stream (SST) mode, Apple has not enabled MST support at the OS level, which would be necessary to manage multiple independent video streams over a single DisplayPort connection. This restriction means that when macOS is connected to an MST hub or docking station, it can only mirror displays rather than extend them. Without MST support, macOS can only drive additional displays through separate video outputs or through alternate methods like DisplayLink, which requires additional software and uses the CPU to manage external displays.

DisplayPort hubs with MST (Multi-Stream Transport) support provide an efficient way to manage multiple ultra-high-resolution displays, optimizing bandwidth and simplifying multi-monitor setups for high-resolution environments. For those looking to enhance their workspace, Plugable offers innovative solutions tailored to diverse needs. The UD-MSTH2 excels in multi-monitor configurations, the USBC-MSTH2 brings compact versatility, and the USBC-11IN1E stands out as a comprehensive all-in-one option for connectivity and productivity.

Benefits of MST:

1. Simplified Multi-Monitor Setups: MST allows a docking station to connect multiple external monitors to a laptop or desktop through a single USB-C or DisplayPort port. This feature is ideal for users who need to increase screen real estate for productivity—such as programmers, data analysts, designers, or financial professionals.
2. Port Consolidation: Using MST, docking stations can utilize a single port to drive multiple displays, conserving USB-C or DisplayPort ports on the laptop or desktop. This is beneficial when dealing with devices with limited available ports.

Single Cable Solution: MST docking stations can support multiple monitors through a single connection from the computer to the dock, eliminating the need for multiple graphics outputs.

Display Stream Compression (DSC): Maximizing Bandwidth Efficiency

Display Stream Compression (DSC) is a visually lossless compression technology introduced with DisplayPort 1.4 in 2016, designed to address the increasing demand for higher display resolutions without overwhelming available bandwidth. DSC makes it possible to drive higher resolution displays, such as dual 4K or even 8K monitors, through a single DisplayPort or USB-C cable without sacrificing visual quality. Originally developed by VESA to extend the capabilities of DisplayPort connections, DSC maximizes bandwidth efficiency by compressing video data up to a 3:1 ratio, which reduces the amount of data transmitted without noticeable loss of quality. DSC becomes even more valuable when combined with USB-C using DisplayPort Alt Mode because USB-C is designed to carry multiple signals, including video, data, and power. This versatility means that without DSC, the available bandwidth for video might be reduced when USB-C is simultaneously used for other tasks, like data transfer or device charging. By compressing video signals, DSC ensures that high-resolution content can still be transmitted over a USB-C connection, even when the cable is being utilized for multiple purposes. However, not all laptops or GPUs support DSC, meaning that achieving such high resolutions and configurations may require ensuring both the hardware and drivers are compatible with this compression technology.

Benefits of DSC:

1. Optimizing USB-C Bandwidth: USB-C and Thunderbolt connections often carry video, data, and power simultaneously, and DSC helps optimize the limited bandwidth of these connections. By compressing the video signal, DSC allows USB-C ports to continue delivering power and data effectively while providing high-quality video output.
2. More Connected Devices: DSC reduces the bandwidth needed for video, making more bandwidth available for other USB-C-connected devices. This allows docking stations to more easily handle peripherals, Ethernet, and other connections in addition to high-resolution displays.
3. Enhanced Multi-Monitor Capabilities: DSC enables docking stations to handle multiple monitors at high resolutions and refresh rates. For example, using DSC, a laptop can support dual 4K 60Hz monitors or even triple displays through a single docking station without overwhelming the available bandwidth.

Key Features: MST and DSC

• Multi-Stream Transport (MST): MST allows multiple monitors to connect through a single USB-C connection. Using multiplexing, MST splits the signal, enabling configurations like extended desktops and mirrored displays with just one cable. 
• Display Stream Compression (DSC): DSC enables visually lossless compression, pushing higher resolutions (such as dual or triple 4K monitor support) without compromising visual quality or bandwidth on supported systems. DSC, paired with high-bandwidth connections like DisplayPort 1.4, maximizes display performance over USB-C, making it ideal for demanding setups.

The Versatility and Power of DisplayPort Technology

DisplayPort’s continued evolution through standards like MST and DSC meets the demands for high-resolution, multi-display configurations, especially when integrated with USB-C. Whether you’re a gamer, content creator, or professional needing extensive screen real estate, DisplayPort 1.2 and 1.4 and their advanced features empower users to build flexible, high-performance setups with fewer cables and simplified connectivity.