The I/NAV messages are used in Safety of Life (SoL). The I/NAV message structures are tarnsmitted in E5b (1207.14 MHz) and E1 (1575.42 MHz) frequency bands. In both frequencies the same page layout is used since the service provided on these frequencies is a dual frequency service, using frequency diversity.

Page sequencing is what differs. Pages are swapped between both components in order to allow a fast reception of data by a dual frequency receiver. Nevertheless, the frame is designed to allow receivers to work also with a single frequency.

The I/NAV navigation message is transmitted on both E1 and E5b channels at a rate of 125 bps. The following figure shows the duration of each entity within the message:

I/NAV message structure