Submicrosecond filtering of packet delay variation in video stream over IP metropolitan area network

Broadcasting of digital video signals uses large spectral area. In order to reduce the cost, broadcasters are optimizing their radio network. They build single frequency network (SFN). To maintain efficient quality of service (QoS) to the end user, accurate time synchronization and frequency syntonization is needed between transmitter sites. This function is now fulfilled with local GPS slaved clocks. In order to secure this key service, lower the cost and enable extension in GPS shaded area, an alternate source of synchronization is requested. Version 2 of IEEE 1588 protocol is promising. The application of this protocol on mixed digital voice and data metropolitan area network (MAN) infrastructure for mobile services has already proof reliability in operational backhaul network. The deployment of new services for digital video broadcast (DVB) is demanding for synchronization services that can be implemented on existing dedicated video over IP transmission network. The request is for ppb frequency accuracy and micro second time accuracy transfer. This level shall be maintained with video digitally coded stream on the same media. The variable size of DVB-TS video stream and the buffering scheme inside network switches generates milliseconds packet delay variation (PDV) that destroy the transfer performances of IEEE 1588 dedicated messages. We introduce proper end-user slave clock filtering. This filtering is applied to raw data delay measured in real broadcasting network. The results show a very efficient improvement that exceeds relative frequency accuracy level up to 1.5 times 10^-10 and sub-micro second phase wander. Different stress conditions are tested and the filtering is optimized for minimum slave clock frequency source stability to optimize cost. The results are fitting broadcasting network requirements with some implementation constraint. This alternative synchronization source can secure critical synchronization service.