- RTP/RTCP (Real-time Transport Protocol / Real-time Transport Control Protocol ): For the transmission of Real Time data like the multimedia data
- RTSP (Real Time Streaming Protocol): For the control of the transmission of Real Time data like the multimedia data
- SIP (Session Initiation Protocol): For initiating, modifying, and terminating an interactive user session that involves multimedia data
Moreover LDST has design and implemented various Telematic / Real time services either as research prototypes or as commercial products. Here are some representative services:
- Design and implementation of synchronous teleteaching application for IP (H.323) and ISDN (H.320) for OTE S.A. (Greek PTT)
- Design and implementation of an integrated Open and Distance Learning (ODL) platform which supports synchronous, asynchronous and CSCW learning for the University of Patras, Greece
A typical Telematic Service is Open and Distance Learning (ODL). CTI/LDST has significant experience in desing and implement ODL systems. Open and Distance Learning (ODL) could be regarded as the process of learning with the use of Telematics that is the combination of telecommunication, information and multimedia technology and its services. In such a scenario:
- All the interactions among trainees, trainers and instructional material, which are essential for the instructional process, can be implemented
- The information and the knowledge, which are essential for the instructional process are accessible and readable
- The place, time and the pace of learning are flexible
Open and Distance Learning (ODL) has as target the development and promotion of special methods and techniques for the increase of the quality, the effectiveness and the suppleness of the learning. The Open and Distance Learning (ODL) has two main results
- The educational: The improvement of the existing learning methods and the development of new learning methods.
- The technological: The provision with new distance learning methods with the use of Information and Communication Technologies (ICT)
Open and Distance Learning (ODL) has the following main goals:
- The development of learning environments and methods suitable for the use of information technology to different learning environments
- The improvement of the organization environment, in which these new methods are applied, and the quality and manageability of the multimedia applications and the real time services
- The encouragement achieved is recognizing the quality characteristics obtained through teaching with the use of new ODL technologies and services
- The encouragement of the recognition of the quality characteristics which are gained from learning with the use of new ODL technologies and services
The relation between the services for the integration of an ODL system is shown in following figure:
LDST has contacted research, has designed and implemented various ODL solution both for synchronous, asynchronous and Computer Support Collaborative Work (CSCW) Learning. The following figure shows the interaction among protocols in an ODL system:
The transmission of multimedia data over the network during an asynchronous ODL is controlled by the RTSP (Real Time Streaming Protocol). RTSP is a client-server multimedia presentation control protocol, designed to address the needs for efficient delivery of streamed multimedia over IP networks. The RTSP specification contains a section on the use of RTP with RTSP. RTP is a transport protocol for the delivery of real-time data, including streaming audio and video. RTCP is a part of RTP and helps with lip synchronization and QoS management, among others. The client is adaptive and could change the buffering time and the capacity of its buffer accordingly the condition of the network and the bandwidth requirements of the multimedia stream. With this approach for any participant who want to attend an asynchronous lecture a different "tunnel" of RTP packets is create between the server and the participant's computer. As result the participant can attend the asynchronous lecture with his own pace an asynchronous lecture.
The transmission of the multimedia data during a synchronous ODL can be based on the technique of IP multicasting. IP multicast-based routing facilitates distributed applications to achieve time-critical, "real-time" communications over wide area IP networks, through a lightweight, highly threaded model of communication. The IP multicast routers take the responsibility of distributing and replicating the multicast data stream to their destinations as opposed to individual IP hosts. The IP multicasting topology of IP multicast routers is designed in such a manner that it facilitates "efficient" distribution of packets without congesting any node inappropriately. When a participant wants to join one synchronous lecture (and has the authority to do that) the participant client tries to join the multicasting session. If the participant can not accept multicasting data for various reasons, (for example the router from which the participant accesses the Internet does not support multicasting) the server tries to transmit the multimedia data with the use of UDP (User Datagram Protocol). Finally, if the transmission with the use of UDP is not reliable, the server opens one TCP (Transmission Control Protocol) connection with the participant client and transmits the multimedia data. With this approach, we ensure that all participants, regardless of their network equipment, will have the opportunity to join one session.