Com failure and step climbs.

[Capn Bloggs]

The Australian AIP says thus:
ENR 1.1 - Section 6.2.8 (Page 50 of ENR 1.1)
...
(5) Maintain the last assigned speed and level for a period of 60 minutes following the aircraft’s failure to report its position over a compulsory reporting point (including ADS-C flights), and thereafter adjust speed and altitude in accordance with the filed flight plan;

Note: In OCA, aircraft experiencing communication failure may also initiate strategic lateral offset procedures (SLOP) in
accordance with ENR 2.2 Section 2.2, including an offset of up to 2NM right of track.

(6) Upon exiting OCA, conform to the relevant State procedures and regulations.