Such large overheads may be tolerable in local wired links where capacity is often not an issue, but are excessive for wide area networks and wireless systems where bandwidth is scarce.
The classification algorithm is not defined by the ROHC protocol itself but left to the equipment vendor's implementation.
Several compression profiles are available, including the following: According to RFC 3095, the ROHC scheme has three modes of operation, as follows: Both the compressor and the decompressor start in U-mode.
This mode therefore makes ROHC usable over links where a return path from decompressor to compressor is unavailable or undesirable.
In order to handle potential decompression errors, the compressor sends periodic refreshes of the stream context to the decompressor.
The most important differences are a more intensive usage of the feedback channel, and a stricter logic at both the compressor and the decompressor that prevents loss of context synchronization between compressor and decompressor, except for very high residual bit error rates.
This has the advantage of allowing ROHC to survive many packet losses in its highest compression state, as long as the base frames are not lost.
In First-Order (FO) state, the compressor has detected and stored the static fields (such as IP addresses and port numbers) on both sides of the connection.
In Second-Order (SO) state, the compressor is suppressing all dynamic fields such as RTP sequence numbers, and sending only a logical sequence number and partial checksum to cause the other side to predictively generate and verify the headers of the next expected packet.