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Appendix BProtocol stack and packet formats pThe Protocol Data Unit (PDU) structures for the upstream direction are depicted inFigure B.3. In this channel, ATM Adaptation Layer (AAL5) is used to encapsulateMAC PDUs (Ethernet MAC Frames, IP Datagrams or point-to-point -PPP packets) inATM cells. At the physical layer, these ATM cells are further encapsulated using the(64-byte) slot format (presented in Figure B.2a).In the downstream direction two signalling methods are used: in-band (IB) and out-ofband(OOB).• IB: In the IB signalling method the downstream channel is embedded in thebroadcast channel and is oriented for the EuroModem solution. This method is usedto transmit high data rates. Up to 52 Mbps can be transmitted in one 8-MHzdownstream channel with a 256-Quadataure Amplitude Modulation (QAM). Thetransmission of data packets (MAC PDUs) is based on the DVB specification fordata broadcasting- ETSI EN 301 192 [33], in which Motion Pictures Experts Group(MPEG-2) Transport Stream (TS) frames are used to encapsulate the MAC PDUs.Upstream PDU StructureMAC PDUDataAAL5CPCSPDUDataPADT8SARPDUSAR-PDU48-bytes...SAR-PDU48-bytesATMHPayload ... HPayload5 48 5 48DVB/DAVICUpstream PHYUW4ATM Cell RS GT53 6 164-byte slot...UW4ATM Cell RS GT536 164-byte slotFigure B.3 – Upstream PDU Structure of the DVB/DAVIC protocol.A-viii