The Bidirectional Communication

The Need for Bidirectional, Connection-Oriented Communication

In the previous sections, you have learned about two of the basic communications services of the SafeTRIP Platform: the broadcasting and messaging services. The two services, taken together, build a bidirectional link: data can be sent from a central point to multiple recipients (broadcast), and messages can be transmitted back by each individual recipient to the central point (messaging).

So what is the need for including an additional bidirectional link in this platform? The main reason lies is the nature of the broadcast and messaging services and the fact that they are not well suited for some applications. Take voice calls, for example. A voice call between two parties (let’s call them A and B) has a number of requirements: it must be established, maintained and terminated; and there must be two continuous, low-latency links, from A to B and from B to A. Now, these requirements are not well met by the combination of broadcast and messaging services. They are not connection-oriented, and do not adapt well to the continuity and low-latency specifications.

The same applies to video streaming from the On-Board Unit to the service centres. While video broadcasting is a natural application of the broadcast services described above, the “return-link” video stream is not suitable to the SMS-like messages carried on E-SSA. Other applications, some of them professionally-oriented, have also tight requirements in terms of latency and throughput that require a point-to-point, connection-based link.

Connection-Oriented Communication in the SafeTRIP Platform

The SafeTRIP Platform solves this problem by including bidirectional communications, or if you prefer: connection-oriented bidirectional communications. This feature is based on the QS-CDMA waveform, also part of the S-MIM standardization process, implemented by the SR40 IP Modem from Indra (see The SafeTRIP OBU Demonstrator).