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Printable Version: RFC3095.PDF
RFC 3095 Robust Header Compression July 2001
Sections 5.7.6.3-9 describe the currently defined ROHC RTP feedback
options.
5.7.6.3. The CRC option
The CRC option contains an 8-bit CRC computed over the entire
feedback payload, without the packet type and code octet, but
including any CID fields, using the polynomial of section 5.9.1. If
the CID is given with an Add-CID octet, the Add-CID octet immediately
precedes the FEEDBACK-1 or FEEDBACK-2 format. For purposes of
computing the CRC, the CRC fields of all CRC options are zero.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| Opt Type = 1 | Opt Len = 1 |
+---+---+---+---+---+---+---+---+
| CRC |
+---+---+---+---+---+---+---+---+
When receiving feedback information with a CRC option, the compressor
MUST verify the information by computing the CRC and comparing the
result with the CRC carried in the CRC option. If the two are not
identical, the feedback information MUST be ignored.
5.7.6.4. The REJECT option
The REJECT option informs the compressor that the decompressor does
not have sufficient resources to handle the flow.
+---+---+---+---+---+---+---+---+
| Opt Type = 2 | Opt Len = 0 |
+---+---+---+---+---+---+---+---+
When receiving a REJECT option, the compressor stops compressing the
packet stream, and should refrain from attempting to increase the
number of compressed packet streams for some time. Any FEEDBACK
packet carrying a REJECT option MUST also carry a CRC option.
5.7.6.5. The SN-NOT-VALID option
The SN-NOT-VALID option indicates that the SN of the feedback is not
valid. A compressor MUST NOT use the SN of the feedback to find the
corresponding sent header when this option is present.
+---+---+---+---+---+---+---+---+
| Opt Type = 3 | Opt Len = 0 |
+---+---+---+---+---+---+---+---+
Bormann, et al. Standards Track [Page 92]