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Chapter 2Overview of current CATV network pdelay of chunks of audio and video. Bounded transmission delay is vital, since itdictates buffer size within the receiver and transmitter as well as the quality of thetransmission.For instance, for a videoconferencing service, the maximum tolerable (one-way) meanaccess delay for 95% of all video frames transmitted is ≈ 300 ms in order to guarantee agood quality of human interaction [38]. However, voice streams require lower accessdelays. As an example, high quality VoIP frames using a G.711 codec require a delay ofbetween 1-20 ms and controllers for acoustic and electric echo are not needed, [118].This delay can be more flexible for VoIP using codec G.723.1, which can be up to 150ms for a good quality call. Here echo control is required but does not compromise theeffective interaction between the users. If the delays are in the range 200 to 400 ms, theeffectiveness of the interaction is lower but can be still acceptable, [118].2.5 Standards for CATV networksThe development of standards and common protocols is essential to any wide-spreadacceptance of similar technology. Standards are needed for new services so thatdifferent vendors' products can interoperate. Standards will provide economies of scalefor a mass market resulting in lower cost products, because many internal elementswould have the same specifications and could be manufactured in huge quantitiesTo make this vision true, industry groups, including the Digital Audio Visual Council(DAVIC) [129], Digital Video Broadcasting (DVB) [130], EuropeanTelecommunications Standards Institute (ETSI) [132], Institute of Electrical andElectronics Engineering (IEEE 802.14), ATM Forum [5], Multimedia Cable NetworkSystems (MCNS) Holdings [127], and the Society of Cable TelecommunicationsEngineers (SCTE) [134], created specification with the goal of increasinginteroperability between equipment.Alliances between the different groups led one organisation to adopt the other standards.As an example, the SCTE adopted the MCNS specification and the DVB group adoptedDAVIC 1.2, while the IEEE 802.14 decided to work with the ATM Forum for theimplementation of ATM over HFC networks.2-10