How to synchronize the next generation of IPTV: Explantion of the ETSI standardized version

Text Sample: Kapitel 4.4, SIP-Client: 4.4.1, linphone: The software linphone is an open source SIP UA for every common operating system and smart phone operating systems as well. This UA is not appropriate for the usage in an IMS environment nor an IMS based IPTV systems. The interesting part is the library which is used by linphone and supported by its open source project, because it is a modular library for the RTP and RTCP communication in unicast environments and for the RTP communication in multicast environments. This library is also open source and could be modified for the usage in a multicast RTP environment with unicast feedback. Both, linphone and oRTP are available as ANSI-C source code. The library part is described in detail in the next section. For a test of the modified oRTP library linphone could be used. The reference manual and implementation guidelines could be found at [45]. 4.4.2, UCT IMS Client: The UCT-IMS-Client is an open source IMS-Client with an extension for IPTV (using VLC). It was developed by the University of Capetown. It's main purpose is to show the communication between IMS-Clients and the OpenIMS from Frauenhofer. For a prototyping implementation of IMS based IPTV this client could be used because all SIP signaling is implemented and the software could be extended. An other advantage to VLC and MPlayer, is the exible GTK2[? ] environment for the GUI and the modular structure of the C source code module, as parts of this client. The GUI could be modified by using glade [? ], which saves the GUI as an XML file. This makes it possible for the user to modify the look of the software without compiling its source code. 4.5, NTP Client: In most cases for synchronizing the system clock superuser12 right are required to set the clock. If the final application will use this superuser rights, it could become a security risk and in some cases if the user is not allowed to get these rights it could not even started. This leads to a need of a clock synchronization inside the application which sets a time only used inside the application and all its libraries. For the clock synchronization inside the client application the NTP client implementation created by Larry Doolittle [46] could be used. This stand alone program could be modified to set global variables inside an application and could be run as thread inside that application. This client supports RFC1305[6] for communication and offset calculation. 4.6, Library for mathematical calculations (GSL): As described in section 3.4.2 and section 3.4.3, it is necessary to estimate timestamps and calculate differences between these timestamps with a high precision. The GNU Scientific Library (GSL) provides a couple of functions for interpolation, approximation and regression. This library is open source, which makes it possible to reuse parts of the source code for the calculation part of the MSAS application. The functions gsl_fit_linear() and gsl_fit_linear est() are used to calculate the parameters of the linear function and to estimate the value of the function for a given argument. The coefficients are computed by gsl_fit_linear() using linear regression. This function also returns the variance-covariance matrix, which is estimated by using the scatters from the points around the best fit function. These values could finally used to compute the estimation of the functions value by using gsl_fit_linear est(), which also returns the estimated absolute local error. For a more complex mathematical implementation are all functions described by the GSL homepage [47] and the GSL reference manual [48]. 5, Structure of the Implementation of IDMS for IMS-based IPTV: In the last chapters all theoretical basics were explained, needed to plan the software implementation. This chapter will explain the planing of the IDMS implementation by describing the steps from the modifications of the oRTP library to the Applications needed for profing the concept described in ETSI TS 182 027 [2] and ETSI TS 183 063 [1]. The following description is for the new created functions only. All other functions, if not explained explicitly are described in the reference manual of oRTP (see: [45]). 5.1, Library for sending RTP and RTCP data: For the protocol part of the implementation oRTP is used (see section 4.4.1). This library is able to use RTP and RTCP for unicast sessions and RTP for multicast session. oRTP has to be modified, for handling XR IDMS report blocks and a RTCP only session, which would be necessary for the MSAS application.