 information of a transport block involves the retransmission of all the transport blocks which are linked to it, - in case an ACK / NACK bit is generated by a sub-frame, the coupling generates a bit transmitted in format 1a, in case two ACK / NACK bits are generated by the sub-frame, the coupling generates two bits transmitted in format 1b (Figure 4.14); Transmission instants of data on PDSCH physical channel Sub-frame number Reception instants of ACK/NACK on PUSCH / PUCCH physical channel 0123456789012345 8 ACK/ NACK bits Figure 4.14. Coupling ACK / NACK information Configuration 2 of the time frame Data transfer for downlink. For a color version of the figure, see www.iste.co.uk/perez/volte.zip multiplexing of ACK / NACK information in the PUCCH physical channel: Radio Interface Procedures format 1b is used for transporting 4 bits of information, each bit corresponding to ACK / NACK information generated by a sub-frame, - in case two bits are generated by the sub-frame, the two ACK / NACK corresponding bits are linked by a logical AND (Figure 4.15), the NACK information of a transport block of a sub-frame involves the retransmission of the other transport block of the same sub-frame. Transmission instants of data on PDSCH physical channel Sub-frame number Reception instants of ACK/NACK on PUSCH / PUCCH physical channel >0123456789012345 8 ACK / NACK bits Figure 4.15. Multiplexing ACK / NACK information Configuration 2 of the time frame data transfer for uplink. For a color version of the figure, see www.iste.co.uk/perez/volte.zip 4.2.2.5. TTI bundling function Real-time applications like the voice are sensitive to the packet jitter. The RTP protocol facilitates the correction of the jitter introduced in the network, with a maximum value of 40 ms and packets having a jitter greater than this value are suppressed. The retransmission mechanism of the HARQ function results in an increase of the packet jitter for each retransmission (for example 8 ms in the FDD mode). The HARQ mechanism may be counter-productive in