Communications Systems Applications
The DDS standard is unique in the communications industry –it supports many-to-many communications with per-datastream service control. These capabilities allow DDS to adapt to many communications applications, ranging from software defined networking (SDN) to multichannel video to space data links.
Two properties allow this range of application:
- True multi-endpoint session support – most protocols define dataflow between endpoints. TCP, for instance, creates a session between two, and only two, endpoints. The DDS standard instead defines dataflow between publishers and subscribers, and supports multiple publishers and multiple subscribers in a single session. Therefore, DDS can maintain very high-speed communications between sets of remote processes. On a transport that supports it, DDS can also take advantage of multicast.
- Unique per-datastream quality of service (QoS) control – publishers offer, and subscribers request, QoS capabilities. The middleware matches capabilities and establishes session "contracts" that enforce the QoS between endpoints. Each publisher-subscriber pair can thus have different QoS parameters.
As a result, DDS adapts to most any communications challenge. RTI Connext DDS is the fastest and easiest-to-use implementation of DDS.
Connext DDS powers Harmonic video switches, enabling high-performance scalability and future extensibility for the switching network.
Harmonic is the world's largest transmission and video switching equipment vendor. Harmonic video switches deliver worldwide video-on-demand. Harmonic supplies hardware to Comcast, DirectTV, Cox communications, Time-Warner cable and others. If you watch TV using these services, your signal is likely delivered through a switch running RTI software.
A typical stream has hundreds of potential sources. For instance, consider an automated "headend," which is typically just an unmanned box in a neighborhood. The network signals arrive at the headend from a satellite dish. Local station flow may come from cables. Prerecorded content resides on disk. Each channel going to subscribers is assembled into a consistent stream as it is needed.
Video switching is a demanding real-time problem. For example, a nationally-televised football game stream may indicate a coming 28-second gap. The headend switch can choose a 30-second commercial for the local car dealership from the local disk, compress it a bit and drop it into the feed going out to subscribers. All of this must happen fast enough on hundreds of channels to eliminate glitches and ensure a smooth picture.
The video signals do not travel over Connext DDS; Harmonic uses Connect DDS to control the switching itself. Connext DDS reliably conveys programming to the switches and then affects the stream assembly. These switches are huge. To make it all work, Connext DDS handles thousands of clients and millions of messages. These are housed in a rack with many line cards. The communication is over the backplane. Connext DDS delivers the performance and scale required for this application. The architecture will easily expand to handle even larger systems in the future.
Connext DDS helps emergency services connect seamlessly over wireless links. It's fast enough to handle multiple voice and video links.
Exelis (a division of ITT) provides command and control systems for military and civilian agencies, such as fire, police, and emergency response. These systems connect many wireless endpoints – combining voice, video and data communications. The systems must be flexible and reliable.
RTI Connext DDS connects the GUIs used by dispatch to understand the situation and direct resources. It also connects users in the field. Connext DDS allows the system to scale to meet the growing needs of connected multi-agency emergency services.
Connext DDS offers faster, scalable networking for the implementation of SDN.
RTI provides fast backplane communications for telecom equipment in data centers. Several new SDN efforts are implementing equipment control with Connext DDS.
A data center today may include a few hundred switches. Tomorrow's systems may have thousands of switches. Today's systems mostly use OpenFlow to connect switches. OpenFlow runs on top of TCP, a point-to-point protocol. Therefore, all the switches in a data center get updated with an individual message to each switch. This takes time. As the number of switches increase, the total time for updating also increases. During the update, the center is in an inconsistent state which can result in problems, or even data loops.
With reliable multicast, Connext DDS can update hundreds or thousands of switches in one action. It is vastly faster than technologies like OpenFlow. DDS also supports discovery, notification, source content filtering, failover, and more. In tests for one installation, RTI Connext DDS proved capable of supporting thousands of applications and, even more importantly, 50,000 namespaces. Future data centers need this technology.
RTI and Cisco recently submitted an RFP for Software Defined Networking to the OMG standards body. The submission suggests developing a data-centric model and mapping it to both existing technologies and DDS.
NASA uses Connext DDS in space robots and ground stations.
The NASA Ames robotics program was RTI's first customer for Connext DDS (then called NDDS). They used DDS to build an architecture that integrated rover designs for remote exploration of planets such as Mars.
The datalink to the robot must work over millions of miles of space. It takes many seconds or even minutes for signals to reach their destination. Packet loss is routine. It is the polar opposite end of the spectrum from the fast data-center applications mentioned above. Data centers have high bandwidth, low latency and reliable links. Space links are low-bandwidth, high-delay and lossy. However, DDS can adapt to this situation as well, simply by changing QoS settings. Connext DDS is proven over both high-fidelity and disadvantaged links.
NASA recently proved that DDS can work as a space link by testing communications from the International Space Station (ISS) down to a robot running on earth. An operator on the ISS was able to control the robot from space. In reality, of course, the direction would be reversed, with the operator on the ground and the robot in space. Either way, the link works.
NASA Ames recently successfully tested RTI Connext DDS as a datalink from the ISS.
Read more about the NASA Human Exploration Telerobotics program.