Payload Header Suppression (PHS) protocol has been used in communication systems, such as WiMax (IEEE 802.16 specification), to effectively compress packet headers, such as IP/UDP/RTP header in a typical voice over IP call or IP/TCP header of ACK frames. In the case of IP/UDP/RTP header, the suppression typically reduces the packet header from about 40 bytes to 14 bytes (i.e., 62.5%). With PHS, the portion of the payload header repeated in all packets in a session is suppressed (masked) by the sending entity and restored by the receiving entity.
However, PHS, as currently used, is an all-or-nothing technique for suppressing header fields. If a field that is being suppressed changes, then the entire payload header must be restored, unless another PHS session in effect already captures that specific change. If the change persists through subsequent packets, it is possible to establish a new session updating the cache to reflect the new field value, and thus, reestablishing the compression.
However, reverting from a compressed header to an uncompressed header can have a significant impact on jitter and delay with applications, such as Voice-Over-IP (VoIP) sessions in the uplink under Extended Real-Time Polling Service (eRTPS). Since header suppression significantly reduces the bandwidth requirement, reverting to uncompressed headers significantly increases the packet size, and thus, the bandwidth requirement may demand a new bandwidth. Therefore, with current PHS, there exists a strong incentive not to suppress header fields that may have even a small chance of changing during the session.
Other header compression schemes, e.g., Van Jacobson (RFC 1144) and ROHC (RFC 3095), may not be suitable in all applications as they are delta-based, i.e. they code the differences between subsequent packets.
The embodiments of the current invention improve the compression ratio by the conditional suppression of infrequently changing header fields, which increases the robustness of existing PHS.